Signaled Transitions: Effects of Timeout on Post-Reinforcement Pausing
Emily L. Baxter
A Thesis Submitted to the
University of North Carolina Wilmington in Partial Fulfillment
of the Requirements for the Degree of
Master of the Arts
Department of Psychology
University of North Carolina Wilmington
2012
Approved by
Advisory Committee
Raymond C. Pitts
Carole M. VanCamp
Mark Galizio
Christine E. Hughes
Chair
Accepted By
Digitally signed by Ron Vetter
DN: cn=Ron Vetter, o=UNCW,
ou=Computer Science,
email=vetterr@uncw.edu, c=US
Date: 2013.06.12 20:15:27 -04'00'
Ron Vetter
______________________________
Dean, Graduate School
TABLE OF CONTENTS
ABSTRACT ............................................................................................................................ iv
ACKNOWLEDGMENTS ....................................................................................................... v
DEDICATION ........................................................................................................................ vi
LIST OF TABLES ................................................................................................................. vii
LIST OF FIGURES .............................................................................................................. viii
INTRODUCTION ................................................................................................................... 1
Overview ...................................................................................................................... 1
Fixed-Ratio Schedules and the Associated Pause ........................................................ 3
Aversive Functions of FR Schedules ........................................................................... 6
Rich-to-Lean Transitions ............................................................................................. 9
Statement of the Problem ........................................................................................... 22
METHOD .............................................................................................................................. 24
Subjects ...................................................................................................................... 24
Apparatus ................................................................................................................... 25
Preliminary Training .................................................................................................. 25
General Procedure ...................................................................................................... 27
Phase 1 ........................................................................................................... 27
Phase 2 ........................................................................................................... 31
Data Analysis ............................................................................................................. 33
RESULTS .............................................................................................................................. 35
Phase 1 ....................................................................................................................... 35
Phase 2 ....................................................................................................................... 39
ii
DISCUSSION ........................................................................................................................ 50
Phase 1 ....................................................................................................................... 50
Phase 2 ....................................................................................................................... 57
Applied Implications .................................................................................................. 61
Summary .................................................................................................................... 62
REFERENCES ...................................................................................................................... 64
iii
ABSTRACT
Relatively large post-reinforcement pauses (PRP) are observed during transitions from a
rich (e.g., high reinforcer magnitude) environment to a lean (e.g., low reinforcer magnitude)
environment compared to other transition types (i.e., rich-rich; lean-rich; lean-lean). Previous
literature on transitions have used two discriminative stimuli to indicate the upcoming reinforcer
(i.e., large or small).In the Phase 1 of the current study, four pigeons responded on an multiple
FR schedule, in which four discriminative stimuli were used to represent each individual
transition. The magnitudes of the reinforcers were adjusted until there was extended pausing in
the presence of the rich-to-lean transition stimulus compared to the other transitions. The FR and
difference between the small and large reinforcer magnitude were adjusted until each subject had
longer pauses during the rich-to-lean transition than in the other transitions. As the difference
between the small and large reinforcers became more extreme, the PRP in the presence of the
rich-to-lean stimulus increased, while the PRP in the presence of the three other stimuli remained
relatively equal for each pigeon. In Phase 2, timeouts (i.e., blackout or stimulus-termination)
were added after each reinforcer in probe session to determine if the PRP during transitions
would decrease. During blackout timeout, three durations were used: 15, 30, and 60-s. During
stimulus-termination timeout only 30-s timeouts were used. During blackout timeout sessions,
there was no systematic changes in PRP across durations or transitions. The majority of changes
were increases in PRP during timeout sessions. During stimulus-termination timeouts, however,
decreases in PRP were observed across all transitions and subjects. The current study replicated
the patterns of pausing seen in previous research using four stimuli for each transition and
stimulus-termination decreased PRP during rich-to-lean transitions more reliably than did
blackout timeout.
iv
ACKNOWLEDGEMENTS
First and foremost I would like to thank my mentor through this process, Dr. Christine
Hughes. Over the last 2.5 years, her guidance has helped me become a better student, writer, and
researcher. My confidence as a person and an academic has soared because of her and I am
forever grateful.
I would like to thank all the faculty of the UNCW behavior analysis program, particularly
the members of my thesis committee, Dr. Ray Pitts, Dr. Mark Galizio, and Dr. Carole Van
Camp. They have been so helpful and insightful during my research process here. I have learned
so much from them. I am entering the world of behavior analysis with confidence, knowing that I
have learned from the best.
I would like to thank all the members of the PPH lab. Without everyone’s hard work
daily in the lab my project would not have been completed. I would especially like to thank
Kelsey Knight and Cassee Stem who have taken a large role in past and future analysis of my
pigeons’ rich-to-lean transitions. I am grateful for the open ears and arms of Shelley Murawsky,
Marcelle Medina, and Ashley Aikman, who have listened to and supported me while I have been
completing the final steps of my thesis.
Many thanks are due to my behavior analysis cohorts: Rachel Eure, Whitney Luffman,
Amanda Rickard, Tracy Taylor, and Kristin Yonkers. We went through the trenches together and
I am so thankful for their support over the last 2.5 years.
Finally, I would like to thank those responsible for raising me to be the person I am
today; my mom and dad, Deborah Unangst and Bruce Baxter; my step-dad, Louis Schum; and
my brother and sister, Matthew and Talitha Baxter. I would not be where I am today without
your love and support. Thank you.
v
DEDICATION
I would like to dedicate this thesis to my late step-brother, Joshua D. Bridenbaker. He
inspired me and was the spark for my interest in behavior analysis. I am forever grateful for the
impact he has had on my life.
vi
LIST OF TABLES
Table
Page
1. The Discriminative Stimulus of Each Transition Type for Each Subject ...................... 29
2. Description of Different Conditions as Categorized by the Magnitude of
the Lean and Rich Reinforcer Presentations in Terms of How Many Seconds
Reinforcer is Presented .................................................................................................. 30
3. Number of Sessions for Each Timeout Duration Subjects Experienced During Blackout
Timeout Sessions ........................................................................................................... 32
4. Number of Timeout Sessions Each Subject Experienced During
Stimulus-Termination Timeout Sessions ....................................................................... 34
vii
LIST OF FIGURES
Figure
Page
1. Post-Reinforcement Pauses During Each Transition Across Reinforcer
Magnitudes for Each Subject ......................................................................................... 36
2. Run Rate During Each Transition Across Reinforcer Magnitudes for Each Subject .... 38
3. Average Proportion of Baseline and Absolute Change From Baseline of PostReinforcement Pauses During Blackout Timeout Sessions ........................................... 40
4. Average Proportion of Baseline and Absolute Change from Baseline
of Run Rates During Blackout Timeout Sessions.......................................................... 42
5. Average Proportion of Baseline and Absolute Change from Baseline of PostReinforcement Pauses During Stimulus-Termination Timeout Sessions ...................... 44
6. Average Proportion of Baseline and Absolute Change from Baseline of
Run Rates During Stimulus-Termination Timeout Sessions ......................................... 46
7. Post-Reinforcement Pauses During Each Timeout Condition for Each Subject ........... 47
8. Run Rate During Each Timeout Condition for Each Subject ........................................ 49
viii
INTRODUCTION
There are many ways in which behavior can be controlled. Operant contingencies that
control behavior include positive and negative reinforcement, and positive and negative
punishment. The control of behavior through positive reinforcement is generally viewed as
ethical and socially valid in increasing behavior in individuals. Sidman (1989) stated that
although it is preferable to change behavior using positive reinforcement, aversive control
(coercion) is a natural part of behavior change in our society. The use of aversive control,
negative reinforcement or punishment, is commonly thought of as maladaptive, because it may
cause fear and anxiety in the individual that experiences it.
Perone (2003) discussed how viewing aversive control as maladaptive, might not always
be valid. He defined an aversive stimulus in terms of both negative reinforcement and
punishment. With respect to negative reinforcement, a stimulus is considered aversive if the
contingent removal or postponement of the stimulus increases the behavior that removed or
postponed it. With respect to positive punishment, a stimulus is considered aversive if the
contingent presentation of it decreases the behavior that produced it. Aversive control, however,
should not always be considered maladaptive. An example of an adaptive behavior change in the
presence of an aversive stimulus can be observed when a psychology student has failed her
previous introduction to psychology test. In order to avoid another failing grade, the student will
increase her studying. In order to avoid the aversive stimulus of another failing grade, the
behavior of studying increases. Another example of when aversive control is adaptive is when it
begins to thunder and lightning while a person is on a walk. The person will move indoors in
order to remove this aversive stimulus. If they stay outside they are increasing the likelihood that
they will be harmed by the inclement weather. Perone also cited an example in which the lack of
aversive control is detrimental. When a frog is put into hot water, it will immediately jump out,
responding to the stimulus of the hot water. When the frog is placed into cold water, however,
and the temperature is slowly increased, the frog will boil to death because the frog is not able to
discriminate the aversive situation.
It is important to note that a single stimulus can be considered aversive or nonaversive
depending on how it affects behavior. The context in which the stimulus is presented can often
determine its effect on the individual’s behavior. For example, attention from others is something
that is commonly thought of as a positive stimulus. In a situation in which a person has said or
done something embarrassing, however, the attention of others could be considered an aversive
stimulus. If after a person has made a comment at which others laughed in a negative manner,
that person will be less likely to emit that type of behavior in the future. This example shows
how a stimulus, such as laughing, can be considered aversive or nonaversive depending on the
context in which it was received.
Further, Perone (2003) discussed how there are also aversive effects produced by the use
of positive reinforcement. When an individual receives reinforcement contingent on a particular
behavior, there might be a time when the reinforcer is no longer available (i.e., the behavior is
put on extinction). The deleterious effects of removing the opportunity to receive a reinforcer for
a behavior might be considered aversive. For example, a teacher might praise a student for
raising her hand and giving the correct answer in class. The teacher may not always call on that
particular student, and in that situation no praise is received for hand raising. The transition from
receiving praise to not receiving praise could be aversive, because a reinforcer was given
previously for the same behavior. Additionally, there often is a time period immediately after a
reinforcer is received in which the opportunity to respond for the reinforcer again may not be
2
available. In the previous example, it is only fair for a teacher to call on several students during a
class session. Once a student has been called on and has received praise for hand raising, there is
a certain period of time that will pass before the teacher will call on that student. This period of
time may be aversive to a student because the opportunity to respond, and in turn receive a
reinforcer, is not available. That is, the behavior of hand raising is undergoing extinction, and
eventually, the student might not continue to raise his or her hand. The aversive qualities of
positive reinforcement can be better understood by studying reinforcement schedules and the
pattern of behavior that these schedules occasion. Specifically, fixed-ratio (FR) schedules will be
discussed in greater detail.
Fixed-Ratio Schedules and the Associated Pause
Fixed-ratio schedules consist of a response requirement that is held constant and a
reinforcer that is received upon completing the response requirement (Crossman, Elliot, Phelps,
1987; Ferster&Skinner,1957). For example, on an FR 50, a subject makes 50 responses before
receiving the reinforcer. Once the reinforcer has been received, the response count starts over,
and an additional 50 responses are required. This pattern of 50 responses followed by a
reinforcer continues until the session is complete. Fixed-ratio schedules produce a reliable
pattern of behavior that, when viewed on a cumulative record creates a stair-case pattern. The
staircase pattern signifies that once responding begins for the upcoming ratio, there is typically a
continuous run of responses until the reinforcer is received. Once the reinforcer is received, there
is a generally a pause, in which no responses occur, before the subject begins responding. This
pause has been called pre-ratio pause (PreRP), or the post-reinforcement pause (PRP), depending
on the context in which the pause occurs.
3
Crossman (1968) conducted a study to investigate how the ratio in FR schedules affected
pausing in two White Carneau pigeons. The first phase consisted of a multiple FR 10 FR 100
schedule of food presentation. A multiple schedule consists of two or more components and a
different discriminative stimulus is associated with each component. In this study, the FR 10
component was associated with a green key light, and the FR 100 component was associated
with a red key light. Upon the completion of each ratio requirement, the pigeons received 3-s
access to grain. Crossman found that the PreRP before the FR 10 was shorter than the PreRP
before the FR 100. In this context the pause would be considered a PreRP, because it was not
controlled by the amount of work just completed (i.e., the FR), but rather was controlled by the
upcoming work/FR. The longer pause might indicate that the upcoming large ratio was aversive
to the pigeon, and therefore the pigeon did not initiate responding as quickly as before a small
ratio. In the next part of the experiment, the subjects experienced a chained FR 10 FR 100
schedule. Similar to a multiple schedule, a chained schedule consists of two or more components
and a different discriminative stimulus is associated with each component; however, in a chained
schedule, all components must be completed before the primary reinforcer is presented. Once the
first component is completed, the only signal that the next component is in effect is a change in
the discriminative stimulus. The change in the discriminative stimulus can be considered a
conditioned reinforcer. There was a change in the relative reinforcer rate from the multiple
schedule to the chained schedule. The reinforcer magnitude after each FR had changed from
being equal during the multiple schedule, to only a conditioned reinforcer after the FR 10 and a
3-s presentation of food after the FR 100. In the chained schedule, the pauses were shorter before
the FR 100 than before the FR 10. This suggests that ratio size is not the only factor that is
responsible for pausing, but the delay to the reinforcer affects the PreRP duration. That is, the
4
PreRP might have been longer before the FR 10 in the chained schedule, because the first
component was more delayed from the primary reinforcer and there was only a conditioned
reinforcer presented contingent on completion of the FR 10 unlike completion of the FR 100. It
might be less aversive to begin responding on a large ratio when the signaled delay to
reinforcement in the large ratio component is shorter than the delay to reinforcement in the small
ratio component.
In a follow-up study, Crossman (1971) studied PRPs in both multiple and mixed FR
schedules. A mixed schedule is similar to a multiple schedule in that it consists of two or more
components. Unlike a multiple schedule, the components are not signaled by different
discriminative stimuli; that is, a single stimulus is used for all components. The pause during a
mixed schedule is considered a PRP because the pause is controlled by the previously
experienced ratio. In this study, both the multiple and mixed schedules consisted of two FR
components. The small ratio remained the same (FR10), whereas the large ratio was adjusted
across conditions. In the multiple schedule, similar to the previous study, the pauses were shorter
before the FR 10, and longer before the larger FR (15, 25, or 55), and in the component with the
large FR, the PRP increased as the FR increased. Once the large ratio was increased to FR 25,
there was no longer an overlap between the PRPs of the small and large ratios. As the difference
between the small and large ratio increased, so did the PRP before the large ratio. This suggests
that the context in which the large ratio occurs determines how aversive it is to the subject. The
transition from an FR 10 to an FR 15 is not as aversive as the transition from an FR 10 to an FR
55, as evidenced by the longer PRP in the latter. The results of the mixed schedule were similar
to those in the multiple schedule; however, the large ratio had to be an FR 40 before there was no
overlap in the PRPs between the small and large ratios. Therefore, the difference between the
5
small and large ratios was larger in the mixed schedule when there was no signal of the
upcoming ratio. Because there was no signal for the upcoming ratio, the pigeons could not
discriminate between the differences in the ratios to the extent that they were able to in the
multiple schedule. The previously experienced ratio is the only part of the component that could
have been controlling the pigeons’ PRP in the mixed schedule.
Aversive Functions of Fixed-Ratio Schedules
There is evidence to support that the pause during fixed-ratio responding during could be
induced by the aversive nature of the time immediately following reinforcement. There are other
observable behaviors that occur following reinforcement during FR schedules such as escape and
aggression. Azrin (1961) found that pigeons will respond in order to escape from an FR schedule
by responding on a timeout operandum in order to self-impose timeout (extinction). Although
timeout is typically thought of as punishing, Azrin suggested that in a condition in which a
subject could put itself into a period of timeout during FR responding, timeout would be
considered reinforcing. Pigeons were used as subjects in this study. For each pigeon the FR
requirement was raised from 65 to 200 across sessions. During a 60-min session, pigeons’ key
pecking was reinforced according to an FR schedule that remained constant within a session; the
reinforcer magnitude (i.e., food) remained constant. There was a separate timeout key that was
continuously available to the subject on which it could respond at any time. When there was a
response on the timeout key, there was a decrease in the intensity of the transillumination on
both the FR and timeout keys. The lights did not turn off, but the change in intensity signaled
that there were no programmed consequences for responding on the FR key. At any point, the
subject could respond a second time on the timeout key. The transillumination would return to its
normal intensity, and responses on the FR key once again were reinforced. Azrin found that as
6
the FR increased, time spent in timeout increased. In addition, the pigeons tended to escape
almost exclusively during the latter part of the PRP. Self-imposed timeout almost never occurred
immediately after a reinforcer was received. This might indicate that there are specific times
during the PRP that are particularly aversive. Additionally, the longer the pigeon is in a PRP
before it responds on the timeout key, and the longer the pigeon self-imposes timeout, the more
aversive the upcoming ratio is considered.
Thompson (1964) conducted a systematic replication of Azrin’s (1961) study, in which
he studied the aversiveness of increasing FR schedules and the reinforcing properties of selfimposed timeout, or escape, in lever pressing in rats. There were a few adjustments made to the
procedure. In Azrin’s study, FR requirements were only observed in ascending order. Thompson
examined if the effect of increasing the FR was reversible by first increasing the FR requirement,
and then decreasing it. Thompson also wanted to evaluate if responding on a timeout lever was
maintained by escape from the current FR. In all sessions, a timeout lever was available
concurrently with the FR lever. Three responses on the timeout lever initiated a 30-s timeout.
Timeout was signaled either by a change of the discriminative stimulus from light to dark, or
dark to light depending on the condition. During timeout there were no programmed
consequences for responding on either lever. Time spent in timeout and the frequency of timeout
responses were measured. In one experiment, the FR was increased in increments of 25 across
sessions, starting at FR 25, until there was a dramatic increase in the PRP duration. Once a
subject reached their peak FR requirement, the ratio was then decreased in increments of 25
responses across sessions, until an FR 25 was reached. The frequency of responding on the
timeout lever increased as the FR increased and then decreased as the FR decreased. This
7
suggests that the greater the FR was, the more aversive it may have been to the subject, as
evidenced by the increased number of responses on the timeout lever.
An additional experiment in Thompson’s (1964) study was conducted in order to see if
escape from the food lever was reinforcing responding on the timeout lever. First, the FR
requirement was increased in increments of 25 responses over each session until a breaking point
was reached and the subject no longer responded. Once this FR was reached, it was held
constant, and response requirements on the timeout lever increased from an FR 1 to an FR 3 and
continued to increase across sessions until responding on the timeout lever was extinguished.
Once the FR requirement for the timeout key had reached a certain size, the typical pattern of a
run of responses and a PRP occurred. This is further evidence that FR schedules have aversive
functions, because lengthy PRP durations occurred during responding for both timeout and
water.
Another behavior that occurs during FR responding is aggression toward other subjects
(e.g., Gentry, 1968; Knutson, 1970). Gentry demonstrated that pigeons were more likely to
attack a target pigeon when they were responding on an FR 50 schedule than in an extinction
condition. There were two types of subjects: the experimental pigeons whose key pecking was
reinforced on an FR 50, and the target pigeons, which were stationed in the back of the chamber
enclosed in an apparatus that measured the frequency of attacks. This study used an ABAB
design. Condition A was a no reinforcement component for responding, in which the food key
was inoperative. This provided a baseline for how often the pigeon attacked when there was no
response requirement or reinforcement provided. Condition B was an FR 50 schedule. Gentry
found that virtually no attacks were made during the no-reinforcement condition, but attacks
were frequently made in the FR 50. One subject emitted up to 2000 attack responses in a single
8
session. The range of attacks across subjects during the FR 50 was about 200-2000. Another
piece of evidence of the aversive qualities of FR schedules is that most of the attacks occurred
during the PRP. The subjects were more aggressive when they had to work to receive a
reinforcer (FR 50), than when they did not receive a reinforcer at all.
The studies by Crossman (1968, 1971), Azrin (1961), Thompson (1964), and Gentry
(1968) demonstrate that particular aspects of an FR schedule can function aversively, such as the
time immediately after a reinforcer is received. The time period in which extended pausing is
most likely can be considered a transition from one schedule to the next schedule. The duration
of the PRP during the transition from one schedule to the next schedule can be an especially
effective measure of the aversiveness of any type of transition. The aversiveness of the
transitions can further be manipulated by the arranging different contingencies between which
the subject is transitioning.
Rich-to-Lean Transitions
Transitions are ubiquitous and should be considered a part of all contingencies and
behaviors. Transitions are present in each change in reinforcement or workload from one
contingency to the next, not just during FR schedules. Behavior can be affected in different ways
depending on the context in which a transition occurs. In certain transitions, the change in the
contingency may be a loss of reinforcement. In other transitions the change in the contingency
may be a gain of reinforcement. It is important to know how they function in different
circumstances. For example, when a behavior therapist is working with a client, it is helpful to
know what activities are more preferred versus less preferred. If the therapist is trying to make a
smooth transition from one activity to the next, it would not be beneficial to transition from an
activity that is highly reinforcing with a low work load, to an activity that is much less
9
reinforcing with a heavy work load. This is a very specific example, but as previously stated
transitions are present in every type of contingency. Transitions from stimuli signaling one
activity to stimuli signaling the next activity, depending on the change in the contingency, can be
considered aversive. The analysis of the aversive function of transitions in contingencies will be
given further consideration.
Transitions from one FR schedule to another FR schedule are one way to assess the
aversive functions of these schedules. The aversive qualities of FR schedules can be observed
during transitions from situations that are “rich” to situations that are “lean,” relative to each
other. For example, in a rich condition a subject might receive more reinforcers, have a lighter
work load, or a mix of both. In a lean condition, a subject might receive fewer reinforcers, have a
heavier work load, or a mix of both. In situations in which both rich and lean environments are
available, there are four types of transitions: rich to rich, rich to lean, lean to rich, and lean to
lean. A reinforcer or work load may be valued at an “x” amount, but that value can change
depending on what reinforcer or workload is presented before or after. This is observed during
transitions as the establishing operations are in constant flux. For example, a small reinforcer is
potentially worth less when preceded by a large reinforcer, than when it is preceded by a small
reinforcer.
Perone and Courtney (1992) used an animal model to study the effects of rich-to-lean
transitions on behavior. The study was conducted in order to determine what was functionally
controlling pausing during transitions. The authors hoped to elucidate the controlling variables of
the pause; that is whether the pause between transitions was controlled by the past reinforcer
(PRP) or the upcoming reinforcer (PreRP). The authors hypothesized that pausing during
transitions might be a function of both the previously experienced ratio and the signaled
10
upcoming ratio, depending on the context of the condition (mixed or multiple schedule). They
used both mixed and multiple schedules to compare the patterns of pausing across the four
transitions types. In the mixed schedule, there was a single stimulus during all transitions (e.g.,
white). In the multiple schedule, there was one stimulus that indicated whether the upcoming
reinforcer magnitude was small (e.g., red) and another stimulus that indicated whether the
upcoming reinforcer was large (e.g., green). Perone and Courtney hypothesized that in a mixed
schedule, the pause would be controlled only by the previous reinforcer and not the upcoming
reinforcer; in a multiple schedule the pause would be controlled by both the previous reinforcer
and the signaled upcoming reinforcer.
In Perone and Courtney’s (1992) study, four male White Carneau pigeons were the
subjects. All four pigeons were studied in sessions using a mixed schedule, and two of these
pigeons were also studied using a multiple schedule. For both schedules, the pigeons’ key
pecking was maintained by an FR 80 schedule, and the reinforcers used were either a small or a
large magnitude of grain. Presentation of the components (small and large) varied throughout the
session such that there were the four transitions described above. There were 41 reinforcers
presented in a quasi-random order, such that each type of transition occurred 10 times in each
session. Within a session no more than four large or four small reinforcers were presented in
succession. In half of the sessions, the first reinforcer received was large and in the other half of
the sessions the first reinforcer was small. Therefore, the first reinforcer (e.g., small) received in
each session was presented 21 times and the other reinforcer (e.g., large) was presented 20 times.
In the mixed schedule, the small reinforcer ranged from 0.5 s to 4 s; the large reinforcer ranged
from 5.25 s to 20 s. In the multiple schedule, the small reinforcer ranged from 0.5 s to 4 s; the
large reinforcer ranged from 4.5 s to 20 s. The houselight remained lit during sessions.
11
In Phase 1, the small and large reinforcer magnitudes were changed across conditions in
both the mixed and multiple schedules. In the first condition of both schedules, the magnitude of
the reinforcer in both components was equal. Changes to the conditions were made when
pausing across each of the four transitions was stable for 10 sessions, or after a maximum of 50
sessions, and there could be no increasing or decreasing trends. Across the previous 10 sessions,
the differences between the mean of the first 5 medians and the mean of the last 5 medians had to
be within 10%of the grand mean, or within 1s. When criteria were met to move on to the next
sequence, the small reinforcer duration was decreased by half and the large reinforcer duration
was increased by half. In Phase 2, only two of the birds were studied, both under mixed and
multiple schedules. The difference between Phase 1 and Phase 2 was that instead of adjusting
both the large and the small reinforcers, the experimenters adjusted only the magnitude of the
large reinforcer. The small reinforcer remained at 4 s during Phase 2, while the large reinforcer
magnitudes were 4-s, 12-s, and 20-s access to grain.
Perone and Courtney (1992) found that during the mixed schedule, PRPs were longer
after a large reinforcer was received than after a small reinforcer was received. There was no
interaction between the past reinforcer and the upcoming reinforcer in respect to pause length.
The PRP increased as a function of the difference between the small and the large reinforcer
durations. The results from the multiple-schedule condition suggested that there was an
interaction between the past and upcoming reinforcers such that when the past reinforcer was
large and the signaled upcoming reinforcer was small, there was a longer PRP than in any of the
other transition types. Similar to in the mixed schedule, the PRP increased as a function of the
difference between the small and the large reinforcers. The interaction between the past and the
upcoming reinforcers became more evident as the difference between the small and large
12
reinforcers became more extreme. Across the two pigeons, the average difference in PRP
duration between a rich-to-lean transition and any of the other three types of transitions was 25 s.
When the upcoming reinforcer was large, pause duration was as short as 0.18 s regardless of
whether the previous reinforcer was small or large.
The results from sessions in which multiple schedules were used made it evident that
pausing was controlled by both the past and the upcoming reinforcers. The lengthy pause
following a rich to lean transition suggests an aversive quality to that particular type of transition.
This study led to several follow-up studies in which various ways of determining the
aversiveness of rich-to-lean transitions have been investigated.
Wade-Galuska, Perone, and Wirth (2004) investigated how force requirements on
responding could influence the PRP. The study was arranged similarly to Perone and Courtney’s
(1992) study of rich to lean transitions. The difference was that instead of adjusting the reinforcer
magnitudes, the experimenters adjusted the force requirement. Four male Sprague-Dawley rats
were used in this experiment. Lever pressing was maintained by a multiple schedule of food
delivery in which a different lever (left/right) was used in each component of the multiple
schedule. Pressing on either lever was reinforced with a food pellet, according to an FR 30
schedule. During baseline, both levers had a force requirement of 0.25 N in order for lever
presses to be counted as responses. Across phases, the force requirement for one of the levers
remained at 0.25 N, while the force requirement for the other lever increased in four increments;
0.40 N, 0.55 N, 0.70 N, and 0.85 N. Similar to Perone and Courtney’s study, there were 41
components presented in a semi-random order in each session. The sequence of the components
allowed for each of the four transitions of force requirements to occur 10 times: low force to low
13
force (rich to rich), high force to high force (lean to lean), low force to high force (rich to lean),
and high force to low force (lean to rich).
In general, Wade-Galuska et al. (2004) found that pausing was the longest when the
upcoming force requirement was high, which is comparable to the lean reinforcer magnitude.
The harder the upcoming workload, the less favorable it was and the pause increased. The
longest PRP occurred before a high-force requirement that followed a low-force requirement
(rich to lean). Run rates also were analyzed in this study. Generally, run rates were the lowest in
the low to high force requirement transition (rich to lean). These results are consistent with the
findings in the Perone and Courtney (1992) study. The long PRP and low run rate during the
rich-to-lean transition suggests that this type of transition is aversive. In addition, this study
supported Perone and Courtney’s account of how both the previous and upcoming ratios affect
the PRP.
The study of rich-to-lean transition in reinforcement schedules has been studied with
other reinforcers, such as drugs. Galuska, Wade-Galuska, Woods, and Winger (2007) studied
self-administration of cocaine in rhesus monkeys using the methods of Perone and Courtney
(1992). They were interested in i.v. self-administration of cocaine. Most of the previous accounts
of self-administration claimed that pausing on FR schedules is maintained by the previous dose
received (e.g., Skjoldager et al., 1991; Winger and Woods, 2001). Galuska et al. studied lever
pressing maintained on a multiple schedule. Both the dose size of cocaine and the FR varied
across conditions. When the small and large drug doses used for self-administration were 0.003
mg/kg and 0.03 mg/kg, respectively, the FRs used were 10, 30, 50, 70, 90, 150, and 210. When
the small and large drug doses used for self-administration were 0.0056 mg/kg and 0.056 mg/kg,
respectively, the FRs used in each condition were 30, 90, 150, and 210. Each condition lasted 20
14
sessions. The large and small doses were arranged quasi-randomly so that each transition was
experienced either 25 times (smaller dose condition) or 12 times (larger dose condition). The
four types of transitions in this study were large dose to small dose (rich to lean), small dose to
large dose (lean to rich), large dose to large dose (rich to rich), and small dose to small dose (lean
to lean). Once the monkeys completed the FR, the center key light turned green and the cocaine
infusion began. Once the infusion was complete, a 2-s timeout started in which the green light
turned off. Every response made during this timeout started the timer over again. The pause
timer started once the 2-s timeout was over.
In general, the PRP was the longest after a large dose was received and the upcoming
dose was small. This effect was more pronounced the higher the FR requirement. Galuska et al.
(2007) did not find any major differences in the rich to lean pause duration between the two dose
size conditions (0.003 mg/kg and 0.03 mg/kg versus 0.0056 mg/kg and 0.056 mg/kg). The run
rates were the highest in the transition from a small dose to a large dose (lean to rich), and lowest
in the transition from a large dose to a small dose (rich to lean). These results are in line with
those of Perone and Courtney (1992). Transitioning from a favorable condition to an unfavorable
condition disrupted responding in the form of longer pausing before a run of responding began,
and a lower rate of responding during the run of responding.
Applied Implications
The aversive functions of rich-to-lean transitions also have been studied in humans. It is
beneficial to study the effects of transitions in all populations, but it is particularly helpful for
populations that might display more challenging behaviors. Certain individuals with
developmental disabilities might self-injure, aggress, or display other types of destructive
behaviors. Studying these individuals in the context of rich-to-lean transition contingencies
15
would be helpful in identifying when these behaviors occur most frequently. This could lead to
adjustments in the environment that would decrease the probability of these behaviors occurring.
Bejarano, Williams, and Perone (2003) used similar techniques as in the previous studies
(Perone & Courtney, 1992; Wade-Galuska et al., 2005; Galuska et al., 2007) to investigate richto-lean transitions in humans. Their participant was a man with mild mental retardation. The
apparatus used to study his responding was a touch screen computer that had a dispenser by its
side that provided reinforcers. The reinforcers consisted of either a quarter (large reinforcer) or a
penny (small reinforcer). Responding was maintained on a multiple schedule using a match-tosample procedure. In both components, an observing response to a single object on the screen
was required initially. Once the observing response was made, the object disappeared and a 0.25s feedback tone occurred. Two objects then appeared on the screen, and if the comparison that
matched the sample was selected, the participant received one coin (either a quarter or a penny)
from the dispenser. The rich component, which consisted of an FR 10 schedule and a quarter as a
reinforcer, had black greater- or less-than signs as the stimuli for the match-to-sample task and a
red background. The lean component, which consisted of an FR 60 and a penny as a reinforcer,
had a black sideways “U” shapes as stimuli for the match-to-sample task and a yellow
background. Therefore, the rich component consisted of a lower response effort and a larger
reinforcer, and the lean component consisted of a higher response effort and a smaller reinforcer.
There was no difference in the difficulty of matching between the rich and lean components.
Berajano et al. (2003) found results similar to those in the animal literature. The PRP was
the longest when there was a transition from the rich-to-lean component. Berajano et al. also
plotted the pause durations in 1-s bins. This showed frequency distributions of each pause time
for each type of transition. The longest bin was 19-s, and during the rich-to-lean transition, the
16
highest proportion of PRPs were in this bin. Berajano et al. illustrated that the effects seen in the
basic research are also relevant in applied research with humans. When a subject has just
experienced a rich environment and transitions to a lean environment, the PRP will be at its
longest. This might be an indication that the rich-to-lean transition functions more aversively
compared to the other types of transitions.
Williams, Saunders, and Perone (2011) extended the applied research with individuals
with mild intellectual disabilities. The study consisted of three experiments. The first experiment
was similar to the previously discussed study. That is, both the magnitude of the reinforcer and
the work requirement were different in the rich and lean conditions. This was done in order to
create ideal conditions to observe the effect of the previous reinforcer and upcoming work
requirement on the PRP. The rich and lean components were presented according to a multiple
schedule. The stimuli for both the rich and lean components were displayed at the same time,
however, only one of the schedules was active. In this experiment they were able to replicate the
results of Perone and Courtney (1992); that is the longest PRP occurred during the rich-to-lean
transition. The second experiment was an attempt to replicate the results from Perone and
Courtney ’s Experiment 2 in which mixed and multiple schedules were used. During a mixed
schedule pausing would be under control of the previous reinforcer regardless of the upcoming
ratio and during a multiple schedule pausing would be under control of both the previous
reinforcer and the upcoming ratio. The results were consistent with Perone and Courtney’s
findings. In the mixed schedule, pausing was extended following a rich component, regardless of
the upcoming component. In the multiple schedule, there was an interaction between the past
reinforcer and workload and upcoming reinforcer and workload. When the past ratio was rich
and the signaled upcoming ratio was lean, pausing was the longest. In the third experiment, the
17
sensitivity to changes in the ratio and the reinforcement in the rich and lean components were
examined. In some of the sessions the FRs were different while the reinforcers were the same,
the FRs were the same while the reinforcers were different, or both were different from each
other creating a double discrepancy in the rich and lean components. It was found that sensitivity
to reinforcers or ratio varied depending on the individual.
The study of the PRP during rich-to-lean transitions has been the focus in the animal and
human literature. There are additional studies, however, that focus on other behaviors that may
increase or decrease during rich-to-lean transitions.
Additional Evidence of the Aversive Function of Rich-to-Lean Transitions
A situation is considered aversive, if a subject engages in behavior to escape from and/or
avoid it (Azrin, 1961; Thompson, 1964). Therefore, if rich-to-lean transitions are aversive, it
would be expected that individuals would engage in an escape response to avoid the transition in
place. Perone (2003) reported a study that illustrated this point by showing that pigeons’ escape
responses increased during rich-to-lean transitions. The general method was similar to that of
Perone and Courtney (1992); however, an escape key was available during 5 out of 10
presentations of each type of transition during a session. The pigeons’ key pecking was
reinforced according to a multiple schedule of food presentation. There were six conditions in
which the FR was held constant (FR 20, FR40, FR60, FR80, FR 100, FR 120). During half of the
transitions, a side key was lit simultaneously with the center food keys, and the pigeon could
respond on it in order to turn off the food key light and the house light. During transitions in
which the escape key was available and the pigeon initiated responding on the center key first
(i.e., made a single peck on the FR key), the escape key was turned off. If the pigeon pecked the
escape key first, however, the center key light and house light were turned off and the escape key
18
dimmed until the pigeon pecked the escape key a second time. Once the pigeon pecked the
escape key a second time, the center key light and house light turned on, the escape key light
turned off, and the pigeon had to finish the FR currently in place. As the FR increased across
sessions, pausing and number of escape responses in the rich to lean component increased. This
suggests that it was aversive for the pigeon to respond after a large reinforcer had been received
when the upcoming signaled reinforcer was small. Responding in order to terminate the escape
period, however, might suggest that the aversiveness of the rich-to-lean transition decreases over
time. The pigeon did not completely avoid the current FR, but only postponed its completion by
responding to escape. As the duration since the last reinforcer received increased, the
aversiveness of responding for the smaller reinforcer decreased and the pigeon responded to
terminate the escape contingency.
Holtyn (2010) supported the claim that escape responses indicate that the rich-to-lean
transitions have aversive functions. It was unclear in Perone (2003) whether the escape response
was maintained by escape from the FR schedule in place or escape from the stimulus indicating
the upcoming reinforcer; that is, a stimulus change. In order to determine what was functionally
maintaining escape responses, Holtyn conducted an experiment in which a response on the
escape key changed the schedule in place from a multiple schedule to a mixed schedule.
Therefore, the FR schedule remained in effect and responses on the response key satisfied the FR
requirement. Thus, responding on the escape key presumably would be maintained by the escape
of the stimulus that indicated the upcoming reinforcer. During preliminary training, four White
Carneau pigeons’ key pecking was maintained by an FR 100 schedule with two alternating
components consisting of a small (1 s) or large (7 s) reinforcer. The training phase consisted of
sessions in which the schedule in place alternated daily between a mixed schedule (center key
19
light transilluminated by white) one day and a multiple schedule (center key light
transilluminated by one of two colors depending on the upcoming reinforcer) the other day.
In the experimental conditions, a multiple schedule was initially in place in which
reinforcers were received by responding on the center key. In half of the components, the left key
light, called the stimulus-termination key (i.e., escape key) was transilluminated by the same
color as the center key. If the initial response was to the stimulus-termination key, the stimulus
on the center key changed to white, and the termination key turned off. Once the pigeon
completed the FR requirement, the mixed schedule would change back into the multiple
schedule. If the initial response was made to the center key, the stimulus for the upcoming
reinforcer remained, the termination key turned off, and the pigeon was required to complete the
FR. There was no condition in which responding on the termination key allowed the subject to
escape the FR in place. Responding on the termination key would only change the multiple
schedule into a mixed schedule. The FR requirement was adjusted across conditions, ranging
from 20 to 200. Each condition lasted at least 20 sessions.
In general, Holtyn (2010) found that the pause duration was the longest in the rich-to-lean
transition, and the pause during the rich-to-lean transitions increased as the FR requirement
increased during experimental conditions. The number of responses on the stimulus-termination
key also increased as a function of increasing the FR requirement. Though it was variable across
pigeons, generally the number of responses on the termination key was highest when the
upcoming reinforcer was lean regardless of the previous reinforcer. The proportion of time spent
in the mixed schedule was variable across birds as well. The pigeons spent the most time in the
mixed schedule when the stimulus indicated an upcoming lean reinforcer. The FR requirement
did not appear to affect the proportion of time spent in the mixed schedule. It was demonstrated
20
in this study that the stimulus indicating the lean upcoming reinforcer has an aversive function
regardless of the past reinforcer, as evidenced by the responses made to escape the stimulus that
represented the upcoming lean reinforcer.
Long (2005) also studied the aversive function of the lean stimulus, in the context of richto-lean transitions. An observing response was used in this study, in order to determine if
pigeons would respond to change the schedule in place from a mixed schedule to a multiple
schedule. Four White Carneau pigeons were trained using the same procedures that were used in
Perone and Courtney (1992). During training, a multiple schedule was in effect on the center
key, in which one color indicated an upcoming small reinforcer and a different color indicated an
upcoming large reinforcer. In a different phase of training, pigeons were trained to make
observing responses by pecking one of the two side keys. During the experimental conditions, a
mixed schedule with an FR 100 was in place on the center key; in one component the reinforcer
was small (1 s) and in the other component, the reinforcer was large (6 s or 7 s). Across phases,
the left and/or right key also would be lit on half of the trials. A peck to that key, an observing
response, changed the mixed schedule on the center key to a multiple schedule. The stimulus
signaling the upcoming reinforcer was presented and the pigeon was required to finish the
current FR under the multiple schedule. Once the FR was completed, the mixed schedule
stimulus would turn back on. Depending on the condition, an observing response on one of the
side keys produced the rich or lean stimulus, only the rich stimulus, only the lean stimulus, or
neither stimulus. These observing conditions were counterbalanced across the two side keys.
Long (2005) calculated the probability of responding on the observing key as a function
of the observing conditions; that is, whether a response on the observing key turned on the either
the rich or lean stimulus, only the rich stimulus, or only the lean stimulus. Responding was
21
maintained on the observing key when the observing response produced the rich or lean stimulus
or when the observing response produced the rich stimulus only. Responding was not maintained
on the observing key when the observing response produced only the lean stimulus. Long
suggested that the stimulus that signals an upcoming rich reinforcer is a conditioned reinforcer;
its production maintained responding on the observing response key in any condition in which
the rich stimulus was produced. The results also suggest that the stimulus signaling an upcoming
lean reinforcer is neither a conditioned reinforcer nor a conditioned punisher. It is not a
conditioned reinforcer because the production of the upcoming lean stimulus did not maintain
observing. It is not a conditioned punisher because the presence of the upcoming lean stimulus
did not punish responses on the observing key that produced either the upcoming rich or lean
stimulus.
Long (2005) might have made an incorrect assumption when she stated that the stimulus
associated with the lean upcoming reinforcer was not a conditioned punisher. An issue that needs
to be considered with respect to the aversive function of the lean stimulus is that in the Perone
and Courtney (1992) procedure, the stimulus that indicates an upcoming lean reinforcer
represents two different types of transitions (rich to lean and lean to lean). This makes it difficult
to tease apart its function as a punisher. In contrasting the two types of transitions involved, the
transition from a rich to a lean reinforcer is different than the transition from a lean to a lean
reinforcer. Holtyn (2010) demonstrated that escape responding was maintained by termination of
the lean stimulus, but it is not clear if responding is maintained due to the aversive function of
the stimulus or the aversive function of the transition itself.
Statement of the Problem
22
In the previous literature published on rich-to-lean transitions (Perone and Courtney,
1992; Wade et al., 2004, 2007; Berajano et al., 2003; Perone, 2003; Holtyn, 2010; Long, 2005)
the transitions in all of the studies have been signaled by only two stimuli: the stimulus that
signals whether the upcoming reinforcer was small or large. Much emphasis has been placed on
the role of the stimulus that indicates an upcoming lean reinforcer (Holtyn, 2010; Long, 2005). It
might be more beneficial, however, to focus on the aversive function of individual transitions. It
is not possible to do this by observing transitions in which only the upcoming rich or lean
reinforcers are indicated by discriminative stimuli. If each transition was indicated by an
individual signal, then each transition could be assessed separately and the PRP for each
transition could be compared to the PRP of other transitions.
There is applied importance in studying the effects of rich-to-lean transitions (Berajano,
Williams, & Perone, 2003; Williams, Saunders, & Perone, 2011). All individuals can have
trouble transition from one activity to the next, but for individuals with developmental
disabilities the negative effects of transitions can include aggression, self-injurious behaviors,
and escape (Sainato, Strain, Lefebvre, & Rapp, 1987; Waters, Lerman, & Hovanetz, 2009).
These aversive effects of transitioning could be thought of as being functionally the same as the
extended PRP seen in the animal literature during rich-to-lean transitions. If this statement is
true, it would be beneficial to study a way that could decrease the aversiveness of the transition
as evidenced by a decrease in the length of the PRP between transitions.
Mazur and Hyslop (1982) studied the effects of adding a timeout following reinforcement
on the PRP. Pigeons responded on an FR 50, 100, or 150. During a session, half of the ratios
began with a 30-s timeout. During timeout, the house light remained on, but the key on which the
pigeons responded was turned off for 30 s. Once the time out was complete, the key was lit
23
again, and the FR was completed. The PRP following a timeout was less than when there was no
timeout between ratios. Therefore, it was proposed that adding a timeout between each of the
transitions would decrease the PRP, particularly during the rich-to-lean transition, possibly
decreasing the aversive function of each transition type.
Phase 1.In Phase 1, small and large reinforcer magnitudes were manipulated in order to
observe a difference in PRP during each type of transition. This phase established the transitions
of large to large (rich to rich), large to small (rich to lean), small to large (lean to rich), and small
to small (lean to lean).
Phase 2.Once control of each transition was established, two timeout conditions (i.e.,
blackout and stimulus-termination) were conducted to examine if adding a timeout in between
transitions would decrease PRP.
The current study helps to answer the following two experimental questions: (1) Will
stimulus control form for each transitions if four discriminative stimuli are used to signal each of
the four transition types using a multiple schedule. (2) Will adding a timeout between each
transition decrease the PRP between each transition type, therefore decreasing the aversive
function of the transitions?
Method
Subjects
The subjects were four Racing Homer pigeons (Pigeons 190, 192, 8381,and 10312 were
born in 2007, 2008, 2006, and 2008, respectively).Two pigeons (Pigeons 190 and 8381) had
previous experience responding on random interval (RI) schedules and received acute
administration of d-amphetamine more than 1 year before the current experiment. Two pigeons
were experimentally naïve (Pigeons 192 and 10312). Pigeons 192, 8381, and 10312 were
24
maintained at 85% free feeding weight, and Pigeon 190 was maintained at 80% free feeding
weight. Subjects received Milo grain during experimental sessions and, if necessary, were fed a
supplementary amount of Purina Pigeon Checkers after experimental sessions to maintain their
specified weight. Fresh water and grit were provided at all times while the pigeons were in the
colony room cages. The colony is located in a temperature and humidity regulated room on a
12:12 hr light/dark time schedule, starting at 7 a.m.
Apparatus
Experimental sessions were conducted in four identical sound-attenuating Med
Associates, Inc. modular operant chambers, ENV-007, with exhaust fans that ran throughout all
sessions. To further block extraneous noise, white-noise was played on multiple speakers within
the running room. The dimensions of the inside of the operant chambers were 30.5 cm L x 24.1
cm W x 29.2 cm H. On the front wall there are three response keys, each 2.5 cm in diameter. All
response keys were equidistant from each other (6.6 cm from each center), with the middle key
in the center of the wall. Each key was 21.5 cm above the floor of the operant chamber. In this
experiment, only the center key was used, and it was transilluminated by white, green, or red. A
fourth color light was required for this experiment. To accomplish this both the green and red
light were transilluminted at the same time to in order to produce an orange color light. The force
required for a key peck to register ranged from .18-0.38 N across boxes. When enough force was
applied there was a single audible click of a relay within the chamber. There was a light (1.5 cm
in diameter), on the center of the back wall 2.5 cm from the top that provided general
illumination. The reinforcer of milo grain was delivered with a hopper that was accessed through
a 6.5 cm x 5.5 cm opening centered on the front wall, 12.8 cm below the center key.
Preliminary Training.
25
Pigeons 190 and 8381 did not require preliminary training as they already key pecked.
Pigeons 192 and 10312 were both experimentally naïve and therefore required initial training.
First, Pigeons 192 and 10312 were placed in the chamber with the houselight on for 30-min
sessions over 5 days to habituate them to being in an enclosed chamber. Then hopper training
was necessary in order to teach them to eat from the hopper. During the initial sessions of hopper
training the houselight remained on, and the hopper light was on while the hopper was raised.
The food hopper was initially raised, and milo was available to the pigeons. Using a remote from
outside of the chamber, the experimenter quickly dropped the hopper and then raised it once
again. This oriented the pigeon to the hopper and allowed habituation to the noise the hopper
makes. There was a maximum of 50 hopper presentations, or until the pigeon was eating from
the hopper reliably, within each training session. Initially, each pigeon was required to eat
continuously from the hopper for 10 s without pulling its head out. Once the pigeon ate
continuously for 10 s, the hopper was dropped and immediately raised. This pattern repeated, but
the requirement decreased by 1 s, until the pigeons continuously ate from the hopper. Once the
pigeon completed this initial hopper training, the process repeated once again, except that the
houselight was off while the hopper was raised with the hopper light on. Next, key pecking was
shaped by differentially reinforcing closer and closer approximations of the target behavior of
key pecking. The center light was transilluminated white during the shaping sessions. The house
light was on, but the side keys were dark. Each presentation of milo lasted 4 s. This process took
about five sessions for each pigeon.
Once all of the pigeons were hopper trained and key pecking, the next step was to train
all pigeons to peck the center key when it is tranilluminated white, green, red, and orange. Over
the course of 12 days, daily sessions were held in which a single color (white, green, red, or
26
orange) was transilluminated on the center key, the houselight was on, and pecking was
reinforced on a fixed-ratio (FR) 1 schedule, until 50 reinforcers were received. A 4-s presentation
of the reinforcer was provided. A single key light color was experienced for 2 days in a row. The
pattern of the key lights during training was red, white, orange, and green. Once the pigeons
reliably pecked to all color stimuli on the center key, the process repeated one more time.
General Procedure
The general procedures of this experiment were based on that of Perone and Courtney
(1992). Experimental sessions were held 7 days a week at approximately the same of time of
day. In each session, there was a sequence of 40 transitions and 41 reinforcers received. There
were 40 sequences available, and the order in which they were presented daily was chosen semirandomly using a random sequence generator. Half of the sequences included one extra large
reinforcer, and the other half of the sequences included one extra small reinforcer (i.e., the one
delivered at the start of the session). Each transition type (lean to lean, lean to rich, rich to lean,
and rich to rich) was presented 10 times within a session. Each transition type was signaled by its
own colored discriminative stimulus (four total discriminative stimuli). In a session, no more
than four small or large reinforcers could be received consecutively. In the beginning of each
session, the only light illuminated was the houselight for 3 s, and then a response-independent
presentation of a small or large reinforcer occurred. Following the initial presentation, the first
discriminative stimulus turned on.
Phase 1.A multiple schedule was in place in which the FR remained the same for each
component and the reinforcer magnitude was identical (4 s/4 s), but the key light changed color
indicating the four components. Because there was no difference in the reinforcer amount in,
there were no transitions from small to small, small to large, large to small, or large to large. In
27
this phase, milo was presented for 4 s after the completion of each ratio. There was no intercomponent interval. The FR requirement gradually raised from FR 1 to FR 50 (Pigeons 190, 192,
10312) or FR 80 (Pigeon 8381) over the course of 17-20 sessions
This process determined if each of the pigeons paused more or less in the presence of a
particular stimulus. The hierarchy of the PRP for the key light colors determined what stimulus
would be used for each type of transition for each pigeon. To control for color bias, the stimulus
that produced the longest PRP when reinforcers were equal was used as the small to large (lean
to rich) discriminative stimulus when the magnitudes changed. Likewise, the stimulus that
produced the shortest PRP was used as the large to small (rich to lean) discriminative stimulus
when the magnitudes changed. The second longest PRP stimulus was the large to large (rich to
rich) transition, and the third longest PRP stimulus was designated to the small to small (lean to
lean) transition. Table 1 provides the discriminative stimuli for each transition type for each
subject.
The reinforcer magnitudes were adjusted until the ideal conditions for pausing were in
place (i.e., the PRP during the rich-to-lean transition was the longest compared to the other
transitions). Once a pigeon demonstrated extended pausing during the rich-to-lean transitions,
the small and large reinforcers were no longer adjusted. The conditions were labeled with the
small reinforcer on the left and the large reinforcer on the right. All four pigeons experienced the
1.25 s/ 4.25 s condition. Three of the pigeons (Pigeons 192, 8381, 10312) experienced the 1.25 s/
6.25 s condition. One pigeon (Pigeon 8381) experienced the 1.25 s/ 8.25 s condition. The 0.25 s
was added into each of the times in order to both allow for the hopper to come up and the pigeon
to move to the hopper. In the conditions that follow, the small magnitude remained at 1.25 s,
while the large magnitude increased by 2 s for each manipulation. Table 2 provides the number
28
Table 1
The Discriminative Stimulus of Each Transition Type for Each Subject
Pigeon
Lean to Rich
Rich to Lean
Rich to Rich
Lean to Lean
190
Green
White
Red
Orange
192
Green
White
Orange
Red
8381
Red
White
Orange
Green
10312
Green
Red
Orange
White
Note: Discriminative stimulus colorbased on the initial PRP length in the presence of each
stimulus. There was a reversal of longest to shortest and its associated stimulus for experimental
conditions (i.e., the stimulus that occasioned the longest PRP became the lean-to-rich stimulus
and the stimulus that occasion the shortest PRP became the rich-to-lean stimulus).
29
Table 2
Description of Different Conditions as Categorized by the Magnitudes of the Lean and Rich
Reinforcer Presentations in Terms of How Many Seconds Reinforcer is Presented
Pigeon
Small Magnitude
Large Magnitude
Sessions
190
4s
4s
50
1.25 s
4.25
223
4s
4s
50
1.25 s
4.25 s
55
1.25 s
6.25 s
170
4s
4s
58
1.25 s
4.25 s
60
1.25 s
6.25 s
140
1.25 s
8.25 s
27
4s
4s
50
1.25 s
4.25 s
55
1.25 s
6.25 s
144
192
8381
10312
30
of sessions for each of the conditions the pigeons experienced during Phase 1. Additional
manipulations to the FR were required for Pigeons 8381 (FR 150), 10312 (FR 40), and 190 (FR
35). For Pigeons 190 and 10312, a decrease in FR was required as the subjects were not
completing sessions. For Pigeon 8381 an increase in FR was required as the subject did not have
extended pausing during the rich-to-lean transition with smaller FR. The magnitudes of the
reinforcers were adjusted in order to observe the ideal conditions for extended pausing in the
rich-to-lean component for each pigeon. The stability criterion to move on to the next condition
was that all four pause duration measures lacked increasing or decreasing trends and were stable
over the last 10 sessions. The stability criterion to move on to Phase 2 was a clear distinction in
pause duration between the rich-to-lean transition and the other three transition types. That is, the
PRP during the rich-to-lean transition should have been be 20 s greater than the PRP during the
other three transitions, as demonstrated in the Perone and Courtney (1992) study.
Phase 2. The same schedule as in Phase 1 was in effect during this phase, however, a
timeout was added following each reinforcer during probe sessions. These probe session
occurred based on stability; that is there was no increasing or decreasing trend in PRPs for each
transition. Two types of timeouts were examined; blackout and stimulus termination timeouts.
Blackout timeouts consisted of a blackout in the chamber following each reinforcer. Three
timeout durations (15 s, 30 s, and 60 s) were tested in a quasi-random order. All four pigeons
were included in this condition. There was a 1.5-hr time limit during the probe sessions. Table 3
lists the number of timeout sessions at each timeout duration each pigeon experienced during
blackout timeout.
Once all of the blackout timeout sessions were completed, stimulus-termination timeout
sessions began. Pigeon 8381 was not included in this condition due to the instability of his
31
Table 3
Number of Sessions for Each Timeout Duration Subjects Experienced During Blackout Timeout
Sessions
Pigeon
15 s
30 s
60 s
Total
190
4
3
2
9
192
3
6
2
11
8381
2
1
1
4
10312
2
5
2
9
32
baseline sessions. Stimulus-termination timeout sessions consisted of stimulus-termination (i.e.,
center keylight remained off, houselight turned on) following each reinforcer. One timeout
duration was used during this condition (30 s). The 30-s timeout was chosen as that was the
condition in which the most decreases were seen in PRP during the blackout timeout sessions.
There was a 1.5-hr time limit during the probe sessions. Table 4 lists the number of timeout
sessions for each pigeon during stimulus-termination timeout.
Data Analysis
Data from each session was recorded using MedPC behavioral software. In Phase 1, the number
of responses, PRP duration between transitions, and time per ratio was recorded. The PRP and
run rate of each transition type were of primary interest. Recording of responses and time was
done in 0.01 s intervals. For each session, the median PRP duration and run rate was analyzed for
each transition type. The median of the median PRP for each transition over the last 10 days was
analyzed in Microsoft Excel daily in order to compare the transition types. In Phase 2, the
number of responses, PRP duration following the timeout, and time per ratio was recorded. The
PRP and run rate of each transition were still of primary interest. Each timeout condition (i.e.,
each duration during blackout timeout sessions; stimulus-termination sessions) was analyzed
separately within subjects. Proportion of baseline of PRP (run rate) was analyzed by dividing the
mean of the timeout sessions for every transition by the mean of baseline sessions (sessions
immediately before the timeout session) for every transition. Absolute change of PRP (run rate)
was analyzed by subtracting the mean of baseline sessions from the mean of timeout sessions.
33
Table 4
Number of Timeout Sessions Each Subject Experienced During Stimulus-Termination Timeout
Sessions
Pigeon
30 s
190
2
192
5
10312
3
34
Results
Phase 1
Figure 1 shows the median (inter-quartile range) PRP (s) for each pigeon when the
upcoming reinforcer was small (white circles) and when the upcoming reinforcer was large
(black circles) as a function of the past reinforcer. The size of the reinforcers (s) is indicated on
the x-axis; the small reinforcer amount is on the left and the large reinforcer amount is on the
right. Therefore, each transition type is represented on each individual graph (rich-rich, rich-lean,
lean-rich, lean-lean). Every condition that the pigeons experienced is represented across graphs
(i.e., 4 s /4 s, 1.25 s /4.25 s, 1.25 s /6.25 s, 1.25 s /8.25 s). Figure 1 shows that during the 4 s /4 s
condition (left column) for three of the four pigeons (Pigeon 190, 8381, and 10312), the PRP in
the presence of all stimuli was relatively equal. The median PRP (s) in the presence of each of
the stimuli for Pigeon 8381, 10312, and 190 was 6.1, 5.03, 8.15 s, respectively. The median PRP
in the presence of the green stimulus that represented the future lean-to-rich transition for Pigeon
192 was slightly elevated relative to the PRP in the presence of the other stimuli. The average
PRP (s) of the other three transition stimuli was 8.0 s; whereas, the PRP (s) in the presence of the
rich-to-lean stimulus was 12.2 s.
In general, as the difference between the small and large reinforcers became more
extreme, the PRP in the presence of the rich-to-lean stimulus increased, while the PRP in the
presence of the three other stimuli remained relatively equal for each pigeon. For Pigeon 8381,
there was relatively no change in PRP for any of the transitions in the 1.25 s/ 4.25 s condition. In
the 1.25 s/ 6.25 s condition, the PRP in the presence of the rich-to-lean stimulus (19.95 s) was 10
s longer than that of the PRP in the presence of the lean-to-lean stimulus (9.4 s). In the 1.25 s/
8.25 s condition, the PRP in the presence of both the rich-to-lean and lean-to-lean stimuli
35
Figure 1
Post-Reinforcement Pauses During Each Transition Across Reinforcer Magnitudes for Each
Subject
45
8381
30
15
0
4.00
75
4.00
1.25
4.25
1.25
6.25
4.00
1.25
4.25
1.25
6.25
4.00
1.25
4.25
1.25
6.25
1.25
8.25
10312
50
Pause (s)
25
0
4.00
30
192
20
10
0
4.00
80
60
190
Upcoming Small
Upcoming Large
40
20
0
4.00
4.00
1.25
4.25
Past Reinforcer (s)
Figure 1.Median (IQR) post-reinforcement pause (s) for the last 10 days of each condition for each of the
four pigeons. Past reinforcer is labeled on the x-axis, and the upcoming reinforcers are indicated by the
white circles (small) and black circles (large). Note the different scales on the y-axis.
36
decreased. The PRP in the presence of the rich-to-lean stimulus (17.6 s), however, remained 10 s
longer than that of the PRP in the presence of the lean-to-lean stimulus (7.7 s).
For Pigeon 10312, the PRP in the presence of the rich-to-lean stimulus (21.7 s) was 10 s
longer than that of the PRP in the presence of the lean-to-lean stimulus (11.6 s) in the 1.25 s/4.25
s condition. In the 1.25 s/6.25 s condition, the PRP in the presence of the rich-to-lean stimulus
(23.5 s) was 15 s longer than that of the PRP in the presence of the lean-to-lean stimulus (8.3 s).
For Pigeon 192, the PRP in the presence of the rich-to-lean stimulus (18.9 s) was 14.6 s longer
than that of the PRP in the presence of the lean-to-lean stimulus (4.3 s) during the 1.25 s/4.25 s
condition. The PRP in the presence of the rich-to-lean stimulus (20.6 s) was 18.7 s longer than
that of the PRP in the presence of the lean-to-lean transition (1.9 s). For Pigeon 190, the PRP in
the presence of the rich-to-lean stimulus (48.8 s) was 42 s longer than that of the PRP in the
presence of the lean-to-lean stimulus (6.8 s) in the 1.25 s/4.25 s condition.
Figure 2 shows the median run rates (responses/min) during the subsequent ratio of each
transition type over the last 10 stable days of each condition for each pigeon. The data are
graphed in the same way as in Figure 1. During the 4 s/4 s condition, the run rates were relatively
equal in the presence of each stimulus. The average run rate for Pigeons 8381, 10312, 192, and
190 was 216, 215.5, 125.5, and 242.2 responses/min, respectively. For Pigeon 8381, there was
relatively no change in run rate for any of the transitions in the 1.25 s/ 4.25 s condition. In the
1.25 s/ 6.25 s condition, the run rate in the presence of the rich-to-lean stimulus (179) was 43
responses/min slower than that of the run rate in the presence of the lean-to-lean stimulus (222).
In the 1.25 s/ 8.25 s condition, the run rates in the presence of all four stimuli decreased;
however, the run rate in the presence of the rich-to-lean stimulus (141) remained the lowest and
37
Figure 2
Run Rates During Each Transition Across Reinforcer Magnitudes for Each Subject
400
300
200
100
8381
0
4.0
4.0
1.25
4.25
1.25
6.25
4.00
1.25
4.25
1.25
6.25
4.00
1.25
4.25
1.25
6.25
1.25
8.25
Median Run Rates (responses/min)
300
200
100
10312
0
4.00
200
100
192
0
4.00
300
Upcoming Small
Upcoming Large
200
100
190
0
4.00
4.00
1.25
4.25
Past Reinforcer (s)
Figure 2. Median (IQR) run rates (responses/minute). Shown are the last 10 days of each condition for
each of the four pigeons. Past reinforcer is labeled on the x-axis, and the upcoming reinforcers are
indicated by the white circles (small) and black circles (large). Note the different scales on the y-axis.
38
was 48 response/min slower than that of the run rate in the presence of the lean-to-lean stimulus
(141).
For Pigeon 10312, the run rates in the presence of all stimuli remained relatively equal
within and across conditions. The average run rates in the 4 s/4 s, 1.25 s/4.25 s, and 1.25 s/6.25 s
conditions were 215, 221, and 221 responses/min, respectively. For Pigeon 192, the run rate in
the presence of the rich-to-lean (102) and the lean-to-lean (100) stimuli were on average 13
responses/min slower than the lean-to-rich (118) and rich-to-rich (113) stimuli in the 1.25 s/4.25
s condition. In the 1.25 s/6.25 s condition, the run rate in the presence of the rich-to-lean stimulus
(151) was 18 responses/min slower than that of the run rate in the presence of the lean-to-lean
stimulus (169). For Pigeon 190, the run rate in the presence of the rich-to-lean stimulus (134)
was 50 responses/min slower than that of the run rate in the presence of the lean-to-lean stimulus
(184) in the 1.25 s/4.25 s condition.
It should be noted in the first column in Figures 1 and 2 each symbol is not representative
of the actual transition it symbolizes. Changes to discriminative stimuli were made
simultaneously to the start of the reinforcer magnitude adjustments.
Phase 2
Blackout Timeout. Figure 3 shows the average proportion of baseline (left column) and
absolute change from baseline (right column) of the average PRP during each transition (R =
Rich; L= Lean) when 15-s (black bars), 30-s (light-gray bars), and 60-s (dark-gray bars) timeouts
occurred. For the proportion of baseline graphs, a dashed line at 1 represents no change from
baseline. For the absolute change graphs, a dashed line at 0 represents no change from baseline.
If a bar is above the dashed line, the PRP increased during these conditions; if a bar is below the
dashed line, the PRP decreased during these conditions. The average absolute changes from
39
Figure 3
Average Proportion of Baseline and Absolute Change from Baseline of Post-Reinforcement
Pause During Blackout Timeout for Each Subject
20
6
8381
10
4
0
2
-10
0
Absolute Change from Baseline (s)
6
20
10312
Proportion of Baseline
4
2
0
6
192
4
10
0
-10
50
40
30
20
10
2
0
-10
0
6
190
15 s
30 s
60 s
200
150
4
100
50
2
0
-50
0
RL
LR
RR
RL
LL
LR
RR
LL
Transition
Figure 3. Average proportion of baseline (left column) and average absolute change from baseline (right
column) of PRP (s) during blackout timeout. Shown are each transition (R = Richreinforcer and L = Lean
reinforcer) on the x-axis for each pigeon across timeout durations. The dashed line represents baseline.
Note the different scales on the y-axis on right column graphs.
40
baseline data are included with the proportion because although the proportion of baseline may
appear to be large, the change in absolute pause in some cases may only be a couple seconds. For
example, if a change in proportion is 0.5, the absolute change could either be 50 s (100 s during
baseline) or 2 s (4 s during baseline). It is also beneficial to have the visual aid of average
absolute change as it gives a more complete picture of how PRP was affected by timeout.
There was no systematic effect of increasing timeout duration within or across pigeons.
The majority of changes in PRP compared to baseline were increases. There were only 14
decreases in PRP relative to baseline out of 48 opportunities (between pigeons and timeout
durations). Pigeon 8381 is the only subject in which the proportion of baseline decreased during
all three timeout in the rich-to-lean transition. The PRP decreased to 0.88, 0.79, and 0.42 of
baseline for the 15, 30, and 60-s timeouts, respectively. For Pigeon 10312, PRP decreased to
0.84 of baseline during the 30-s timeout. For Pigeon 192, PRP decreased to 0.79 and 0.96 of
baseline during the 15 and 30-s timeouts, respectively. The decrease during the 30-s timeout,
however, was only 0.54 s. For Pigeon 190, PRP decreased to 0.72 of baseline during the 30-s
timeout. There in one notable decrease in PRP during the lean-to-lean transition. For Pigeon
8381, PRP decreased to 0.52 of baseline, a 7.9-s decrease, during the 30-s timeout.
Figure 4 shows the average proportion of baseline (left column) and absolute change
from baseline (right column) for run rate (responses/min). The graphs are arranged identical to
those in Figure 3. The majority of changes in run rate compared to baseline were decreases.
There were only 14 increases in run rate relative to baseline, out of 48 opportunities (between
pigeons and timeout durations). The largest decreases in proportion of baseline were observed
during the rich-to-lean transition. In the 15-s timeout, run rate decreased to 0.69, 0.73, and 0.73
of baseline, for Pigeons 8381, 10312, and 192, respectively. In the 30-s timeout, run rate
41
Figure 4
Average Proportion of Baseline and Absolute Change from Baseline of Run Rates During
Blackout Timeout for Each Subject
1.5
75
8381
0
1.0
-75
0.5
-150
0.0
50
1.5
Change from Baseline (responses/min)
10312
Proportion of Baseline
1.0
0.5
0.0
1.5
192
1.0
0.5
0
-50
30
0
-30
-60
0.0
1.5
190
30
0
1.0
-30
-60
0.5
15 s
30 s
60 s
-90
-120
0.0
RL
LR
RR
RL
LL
LR
RR
LL
Transition
Figure 4. Average proportion of baseline (left column) and average absolute change from baseline (right
column) of run rate (responses/min) during blackout timeout. Shown are each transition (R =
Richreinforcer and L = Lean reinforcer) on the x-axis for each pigeon across timeout durations. The
dashed line represents baseline. Note the different scales on the y-axis on right column graphs.
42
decreased to 0.36, 0.93, 0.59, and 0.16 of baseline for Pigeons 8381, 10312, 192, and 190,
respectively. Although there was a large difference in the proportion of change between Pigeon
8381 (0.36) and Pigeon 192 (0.59), the absolute changes from baseline were relatively equal; the
decreases were 74.8 and 64.5 responses/min, respectively. In the 60-s timeout, run rate decreased
to 0.6, 0.85, and 0.9 of baseline for Pigeons 8381, 10312, and 192, respectively. For Pigeon
8381, there were also large decreases in run rate in the lean-to-lean transition during the 15 and
60-s timeouts. In the 15-s timeout, run rate decreased to 0.41 of baseline. In the 60-s timeout, run
rate decreased to 0.29 of baseline.
Stimulus-Termination Timeout. Figure 5 shows the average proportion of baseline of
PRP (top graph) and absolute change (bottom graph) for PRP when a 30-s timeout occurred after
each reinforcer during which time only the key light was turned off. The graph is arranged
similar to Figure 3. The vertical bars now, however, represent the following individual subjects;
Pigeon 10312 (black bars), 192 (light-gray bars), and 190 (dark-gray bars). Pigeon 8381 was
excluded from this part of the study due to instability of daily PRP durations in each transition.
Overall, the PRP during timeout sessions decreased across all pigeons and transition
types. There is one exception during the lean-to-rich transition for Pigeon 192, in which the PRP
remained at baseline. Decreases were most notable during the rich-to-lean and the rich-to-rich
transitions. For Pigeons 10312, 192, and 190, PRP decreased to 0.71, 0.98, and 0.68 of baseline,
respectively, during the rich-to-lean transition. Although the proportion of change for Pigeon 190
was 0.68, it was only a 1.7-s decrease. During the rich-to-rich transition, the PRP decreased to
0.41, 0.39, and 0.16 of baseline, for Pigeons 10312, 192, and 190, respectively. The decreases for
Pigeons 10312 and 192, however, were only 2.75 and 0.85 s, respectively.
43
Figure 5
Average Proportion of Baseline and Absolute Change from Baseline of Post-Reinforcement
Pause during Stimulus-Termination Timeout for Each Subject
1.2
Proportion of Baseline
30-s TO
1.0
0.8
0.6
0.4
0.2
0.0
Change from Baseline (s)
5
0
-5
-10
-15
-20
Pigeon 10312
Pigeon 192
Pigeon 190
-25
RL
LR
RR
LL
Transition
Figure 5. Change in proportion (top graph) and the median absolute change from baseline (bottom graph)
in PRP (s) during the second timeout condition. Shown are each transition (R = Rich reinforcer and L =
Lean reinforcer) on the x-axis for each pigeon. The dashed line represents baseline.
44
Figure 6 shows the average proportion of baseline (top graph) and absolute change
(bottom graph) in run rate. The graphs are set up identical to that of Figure 5, except the y-axis
for the bottom graph now represents responses/min. Overall, there are no systematic effects of
timeout on run rate across transition types and the proportions of change remained relatively
close to 1. There were effects of timeout, however, seen within subjects.
The run rates for Pigeon 10312 remained relatively close to baseline across all transitions.
The run rates only slightly decreased to 0.98, 0.98, 0.96, and 0.99 of baseline during the rich-tolean, lean-to-rich, rich-to-rich, and lean-to-lean transitions, respectively. The run rates for Pigeon
192 increased during all transitions. The run rates increased to 1.05, 1.15, 1.3, and 1.1 of baseline
during the rich-to-lean, lean-to-rich, rich-to-rich, and lean-to-lean transitions, respectively. The
second largest increase across subjects was observed during the rich-to-rich transition for Pigeon
192. The run rate increased by 47.4 responses/min. For Pigeon 190, run rate increased to 1.55 of
baseline during the rich-to-lean transition, a 59 response/min increase. This was the largest
increase in run rate across all subjects and transitions.
Figure 7 shows the median (inter-quartile range) PRP (s) for each pigeon when the
upcoming reinforcer was small (white circles) and when the upcoming reinforcer was large
(black circles) as a function of the past reinforcer. The size of the reinforcers (s) is indicated on
the x-axis; the small reinforce amount is on the left and the large reinforce amount is on the right.
Therefore, similar to Figure 1, each transition type is represented on each individual graph (richrich, rich-lean, lean-rich, lean-lean). For all pigeons, the first column represents the last 10 days
of baseline before any timeout was introduced into sessions. The second, third, forth, and fifth
columns represent the median PRPs for 15-s blackout timeout, 30-s blackout timeout, 60-s
blackout timeout, and 30-s stimulus termination timeout, respectively.
45
Figure 6
Average Proportion of Baseline and Absolute Change from Baseline of Run Rates During
Stimulus-Termination Timeout for Each Subject
1.8
30-s TO
Proportion of Baseline
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Change from Baseline (responses/min)
0.0
80
Pigeon 10312
Pigeon 192
Pigeon 190
60
40
20
0
-20
RL
LR
RR
LL
Transition
Figure 6. Change in proportion (top graph) and the median absolute change from baseline
(bottom graph) in run rate (responses/min) during the second timeout condition. Shown are each
transition (R = Rich reinforcer and L = Lean reinforcer) on the x-axis for each pigeon. The
dashed line represents baseline.
46
Figure 7
Post-Reinforcement Pauses During Each Timeout Condition for Each Subject
300
225
Baseline
Stimulus Termination
30 s
Blackout 15 s Blackout 30 s Blackout 60 s
20
190
15
150
10
75
5
0
0
1.25
4.25
1.25
4.25
1.25
4.25
1.25
4.25
1.25
4.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
8.25
1.25
1.25
8.25
1.25
75
10312
50
Pause (s)
25
0
1.25
20 192
10
0
1.25
30 8381
20
10
0
1.25
8.25
Past Reinforcer (s)
8.25
Upcoming Small
Upcoming Large
Figure 7. Median (IQR) post-reinforcement pause (seconds). Shown are the medians of the last 10 days of
baseline and median of all sessions for each timeout condition for each of the four pigeons. Past reinforcer
is labeled on the x-axis, and the upcoming reinforcers are indicated by the white circles (small) and black
circles (large). Note the different scales on the y-axis.
47
Compared to baseline, there is no orderly change for the rich-to-lean transition across
timeout durations during blackout timeout condition for all pigeons. During the stimulus
termination timeout condition, however, the PRP during the rich-to-lean transition decreased for
all pigeons. For Pigeons 190, 10312, and 192 PRP across the rich-to-rich, lean-to-lean and leanto-rich transition remained in the same range across all timeout conditions.
For Pigeon 190, the median PRP during the rich-to-lean transitions, compared to
baseline, increased by 100 s and 200 s during the blackout 15-s timeout and blackout 60-s
timeout, respectively. Compared to baseline, the PRP for all transitions during the blackout 30-s
timeout condition remained in the same range as baseline. During the stimulus termination
timeout condition, the rich-to-lean PRP decreased by 40 s. For Pigeon 10312, all PRPs remained
relatively in the same range. The exceptions are the blackout 30-s timeout and the stimulus
termination timeout conditions, in which PRP during the rich-to-lean transition decreased by 35 s
and 42 s, respectively. For Pigeon 192, the median rich-to-lean PRP during the blackout 30-s
timeout and stimulus termination timeout conditions decreased by 10 s and 9 s, respectively. The
median rich-to-lean PRP during the blackout 60-s timeout, however, increased by 50 s. For
Pigeon 8381, the median PRP of the rich-to-lean transition remained in the same range, with the
exception of the 60-s blackout timeout. In the 60-s blackout timeout the PRP decreased by 7 s.
Figure 8 shows the median run rates (responses/min) for each transition type. For all
pigeons, the first column represents the last 10 days of baseline before any timeout was
introduced into sessions. The second, third, forth, and fifth columns represent the median PRPs
for 15-s blackout timeout, 30-s blackout timeout, 60-s blackout timeout, and 30-s stimulus
termination timeout, respectively. In general, there was no difference or orderly change in run
rate during the rich-to-lean transition compared to baseline.
48
Figure 8
Run Rates During Each Timeout Condition for Each Subject
Baseline
Stimulus Termination
30 s
Blackout 15 s Blackout 30 s Blackout 60 s
225
150
75
0
190
Run rate (responses per minute)
1.25
4.25
1.25
4.25
1.25
4.25
1.25
4.25
1.25
4.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
1.25
6.25
8.25
1.25
1.25
8.25
1.25
300
200
100
10312
0
1.25
225
150
75
192
0
1.25
300
200
100
0
8381
1.25
8.25
Past Reinforcer (s)
8.25
Upcoming Small
Upcoming Large
Figure 8. Median (IQR) run rates (responses/minute). Shown are the medians of the last 10 days of
baseline and median of all sessions for each timeout condition for each of the four pigeons. Past reinforcer
is labeled on the x-axis, and the upcoming reinforcers are indicated by the white circles (small) and black
circles (large). Note the different scales on the y-axis.
49
For Pigeon 190, the median run rate during the rich-to-lean transition remained in the
same range across all timeout conditions, with the exception of the 30-s blackout timout in which
it decreased by 130 responses/min compared to baseline. For Pigeon 192, run rate during the 15s and 30-s blackout timeout decreased compared to baseline by 50 responses/min. For Pigeon
8381, run rate decreased during the 15-s, 30-s, and 60-s timeout durations in the blackout timeout
condition by 56, 100, and 59 responses/min, respectively.
Discussion
Phase 1
The purpose of Phase 1 was to systematically replicate Perone and Courtney’s (1992)
study that focused on PRPs during different types of transitions (i.e., rich-to-lean, lean-to-rich,
lean-to-lean, and rich-to-rich), particularly the extended pausing that was observed during the
rich-to-lean transition. Additional studies also have replicated Perone and Courtney, using
different subject types, reinforcers, and work requirements (Bejarano et al., 2003; Wade-Galuska
et al., 2004;Long, 2005; Galuska et al., 2007; Holtyn, 2010; Williams et al., 2011). The previous
studies have only used two discriminative stimuli to signal the upcoming component (e.g.
reinforcer magnitude, work load). The actual transition, therefore, was not explicitly signaled. In
order to assess individual differences in the aversiveness of each transition, as defined by the
PRP, the current study used four unique stimuli to signal the current transition.
For all four pigeons, relatively longer pausing (15-40 s) were observed when the signaled
upcoming reinforcer was small compared to when the signaled upcoming reinforcer was large.
There was an interaction between the past and upcoming reinforcers such that when the past
reinforcer was large and the signaled upcoming reinforcer was small, there was a longer PRP
than in any of the other transitions. This response pattern is similar to what was found using
50
only two stimuli for the upcoming reinforcer in Perone and Courtney (1992) and related
literature.
Manipulations to FR and reinforcer size were made in order to observe extended pausing
in the rich-to-lean transition. It should be noted that across both types of manipulations, changes
in the PRP during the other three types of transitions (lean-to-rich, rich-to-rich, lean-to-lean)
were relatively small. The FR requirement was adjusted for Pigeons 8381, 10312, and 190. In
order to observe the extended pauses during the rich-to-lean transition the FR ranged from a 35
(Pigeon 190) to 150 (Pigeon 8381). Previous literature points out that as FR increases, typically
PRP increases (Crossman, 1971; Galuska et al., 2007; Thompson, 1964). For Pigeon 8381, PRP
increased as the FR increased. Initially, PRP was relatively equal across transition types during
FR manipulations. Once the FR was adjusted from 100 to 150, however, the PRP during the richto-lean transition exceeded the PRPs of the other three transitions. For Pigeons 10312 and 190,
PRP decreased as FR decreased. Initially, the PRPs (particularly during the rich-to-lean
transition) were so lengthy that the session time limit would occur before all 40 transitions were
completed. In this case, decreases to the ratio stopped once each subject was completing every
session. The relation between FR and PRP in the current study is that PRP decreased as FR
increased across pigeons. Pigeon 8381 had the largest FR, but the shortest PRPs, particularly
during the rich-to-lean transition. Pigeons 10312 and 190 had the two smallest FRs, but the
longest PRPs, particularly during the rich-to-lean transition.
The reinforcer amount also was also adjusted until extended pausing during the rich-tolean transitions was observed. Manipulations to reinforcer size were also done in previous richto-lean literature (Perone and Courtney, 1992; Bejarano et al., 2003; Williams et al., 2011). In
these studies, as the difference between the two reinforcer amounts increased, the PRP increased.
51
With the exception of Pigeon 8381, PRP increased as the difference between the small and large
reinforcers increased.
Even though Pigeon 8381 required the largest FR and largest difference between the
small and large reinforcers, this subject’s pauses were still shorter compared to the other three
pigeons. In fact, pauses during the rich-to-lean transition for Pigeon 8381 were shorter when
there was a 7-s difference than when there was a 5-s difference between the reinforcers.
Additional increases in FR were not made, because the subject would not complete sessions
when the FR was greater. Additional increases in the difference between the reinforcers were not
made as it is unclear if grain would still available in the hopper following more than 8.25 s of
consumption. Even though Pigeon 190 required the smallest FR and smallest difference between
small and large reinforcers, this subject’s pauses were the longest compared to the other three
pigeons. It might be important to note that these two subjects are the two that were in previous
experiments in which their key pecking was reinforced according to an RI schedule. Thus, the
experimental history of the subjects did not appear to influence the relations between FR and
reinforcer amount and pausing.
It was necessary to manipulate the FR and reinforcer amounts until extended pausing was
seen in the rich-to-lean transition because an important aspect of this study was to see if using
four stimuli could occasion extended pausing as was observed in Perone and Courtney (1992)
using only two stimuli. If the manipulations had not been made, it would not have appeared that
using four stimuli had the same effect on pausing. Similar manipulations to FR size and
reinforcer amount were made across subjects in previous subjects in order to see extended
pausing during the rich-to-lean transition (Bejarano et al., 2003; Galuska et al., 2007; Perone and
Courtney, 1992; Williams et al., 2011).
52
In the current study, three out of the four pigeons’ (Pigeons 8381, 192, 190) run rates
(responses/min) differed between transitions and across conditions. Of the three pigeons whose
run rates were different, there was a main effect of the upcoming reinforcer; that is, when the
upcoming reinforcer was small, run rates were slower than when the upcoming reinforcer was
large. For Pigeons 8381 and 190, an interaction between the past and upcoming reinforcers was
observed in the condition with the largest discrepancy between the large and small reinforcers.
That is, when the previous reinforcer was large and the upcoming reinforcer was small, the run
rate was slower than in the other three transitions. For Pigeon 10312, there were no systematic
differences in run rates between transition types and across conditions. The pattern of run rate
observed in Perone and Courtney (1992) differed slightly than those observed in the current
study. In the Perone and Courtney study, run rates did not differ greatly between transitions and
across conditions. A possible explanation for the difference in run rates could be that in the
current study the transition that was in place remained signaled throughout the entire FR, and
there was a constant “reminder” while responding in the presence of the transition stimuli. When
the rich-to-lean transition was signaled, the discriminative stimulus might have been occasioning
longer pauses throughout responding, and therefore decreased the overall run rate.
One purpose of the current study was to see if using a unique stimulus for each transition
would produce a change in the sensitivity to the rich-to-lean transition compared to Perone and
Courtney’s (1992) study (i.e., pauses would be longer or shorter during the rich-to-lean
transition). Regardless of the upcoming reinforcer, the when the past reinforcer was small PRP
tended to be longer in duration in both studies. The longest PRP observed in both studies was
during the rich-to-lean transition. In Perone and Courtney, the PRP during the rich-to-lean
transition for Pigeons 3280, 3611, and 5112 ranged between 30.17 s and 36.5 s. In the current
53
study, the PRP for all pigeons ranged between 20.6 s and 48.7 s. The current study has a larger
range and the highest PRP during the rich-to-lean transition. The ranges overlap, however, and
both data sets are variable when compared across subjects. Comparing the proportion of the richto-lean transition over the lean-to-lean transition is another analysis that helps compare using two
stimuli versus four stimuli. In Perone and Courtney, the proportion of change between the richto-lean and lean-to-lean transition for two of the three subjects is 2.68 and 5.6. The proportion of
change for the third subject is 177.4, though the PRP during the rich-to-lean transition is only
30.2 s. In the current study, the proportions of change for Pigeons 10312, 192, 190, and 8381 are
3.7, 17.2, 12.3, and 11, respectively. Overall, with the exception of the outlier in Perone and
Courtney, the proportion of change in the current study is higher than that of Perone and
Courtney. The larger proportion of change observed in the current study suggests that using four
unique stimuli for each transition increases the sensitivity to the rich-to-lean transition, versus
using only two stimuli to indicate the upcoming reinforcer.
The extended pause and decreased run rate during the rich-to-lean transition might be
explained by contrast effects. Contrast effects occur when one component of a multiple schedule
is preceded or precedes another component with a differing schedule of reinforcement (Nevin
and Shettleworth, 1966). Positive contrast is observed when transitioning from a lean reinforcer
to a rich reinforcer. The PRP was slightly shorter and the run rate (in three out of the four
pigeons) was higher in the lean-to-rich transition than in the rich-to-rich transition. Even though
overall reinforcement was higher in a rich-to-rich transition, the contrast between the lean and
the rich reinforcer occasioned an increase in responding in the presence of the rich-to-lean
transition stimulus. Negative contrast is observed when transitioning from a rich reinforcer to a
lean reinforcer. Even though overall reinforcement was less during the lean-to-lean transition
54
than during the rich-to-lean transition, the contrast between the rich and the lean reinforcer
occasioned a greater decrease in responding in the presence of the rich-to-lean transition
stimulus. Contrast effects on PRP and run rate became more pronounced in the current study
during the rich-to-lean transition as the difference between the reinforcers increased.
There was an interaction between the previous reinforcer and upcoming reinforcer, such
that when the previous reinforcer was large and the upcoming reinforcer was small the PRP was
longer than it was in the other three transitions. This suggests that there was joint control by the
previous and upcoming reinforcer of the PRP. If just the previous reinforcer or the upcoming
reinforcer controlled pausing, it would be expected that the PRP during the rich-to-rich and richto-lean transitions or rich-to-lean and lean-to-lean transitions would be similar. The PRP during a
rich-to-lean transition, however, was longer than the PRP during the other three transition types.
Perone and Courtney (1992) focused on the joint control by the previously experienced
reinforcer and the signaled upcoming reinforcer. Joint control of the previous and upcoming
reinforcer was conceptualized differently in the current study, as the upcoming reinforcer was
not the only reinforcer that was signaled. By using four individual stimuli for the transitions,
each combination of previous and upcoming reinforcer pairs was signaled. It is difficult in the
current study, therefore, to determine if the PRP was under joint control of the previous and
upcoming reinforcer or if the stimuli signaling the transition were controlling the pauses. There
is a possibility that the two stimuli, for example, that signal the rich-to-lean and lean-to-lean
transition functioned in the same way. That is, they signaled an upcoming lean reinforcer, and
the previously experienced reinforcer has joint control in differentiating the PRP between the
two stimuli.
55
Future directions: Phase 1. Although the longest PRP was seen in the presence of the
rich-to-lean transition stimulus, it is still unclear whether the stimulus itself was controlling the
pause, or if the joint control of the previously experienced reinforcer and the upcoming
reinforcer was controlling the pause. A procedure to test for stimulus control of the transition
stimulus should be conducted in order to observe what is controlling the pause. A procedure that
could test for stimulus control would be to present the rich-to-lean stimulus during an
incompatible transition. For example, during a lean-to-rich transition, in which the PRP is
usually short, the rich-to-lean stimulus could be substituted for the lean-to-rich stimulus. In a
typical session, this presentation would be impossible because a rich-to-lean stimulus would only
be presented following a rich reinforcer. If extended pausing is observed, this would be evidence
that the specific stimulus does have control over the pause that is seen during the rich-to-lean
transition.
Although the proportion of change in the current study was greater than the proportion of
change in Perone and Courtney, it did not demonstrate that using four stimuli necessarily
occasions longer pauses than using only two stimuli. There should be a direct comparison, using
the same pigeons, of the PRP using only two stimuli to signal whether the upcoming reinforcer is
large or small. Once this replication is done, then the PRPs during the rich-to-lean transition can
be compared across studies. The following comparisons between the two studies would be
needed: the differences between the PRP during the rich-to-lean transition in each study and the
difference between the PRP of the rich-to-lean transition and the other three transitions in each
study. It might be predicted that shorter pauses, particularly during the rich-to-lean transition
would be observed using only two stimuli. Using only two stimuli requires “remembering” what
was previously experienced, and there is no “reminder” (i.e., individual transition stimulus) of
56
the current transition. The joint control by the previous and upcoming reinforcer of the PRP
would not be as strong as it was in the current study.
Phase 2
The purpose of Phase 2 was to decrease the PRP during the rich-to-lean transition. Mazur
and Hyslop (1982) successfully decreased the PRP during FR responding by adding a 30-s
timeout following half of the reinforcers received in a session. In the current study, two timeout
conditions were arranged. The first timeout condition consisted of a blackout timeout with
durations of 15, 30, and 60 s; whereas the second timeout condition consisted of the key light
turning off for 30 s. During blackout and stimulus-termination timeout sessions, the timeouts
were added following each reinforcer. It was hypothesized that the addition of a timeout between
transitions would decrease the PRP during all transition types. If there was joint control by the
previous and upcoming reinforcer, a timeout would degrade the control of the previous
reinforcer, shifting the control to the upcoming reinforcer. Therefore, pauses in the rich-to-lean
transition would be similar to those in the lean-to-lean transition, as the lean upcoming reinforcer
would be controlling the pause.
The results from the blackout timeout within and between pigeons were variable across
transition types and timeout durations. Overall, the addition of the timeouts increased the PRP
and decreased the run rate across all transition types compared to baseline for three of the four
pigeons (10312, 192, and 190). Pigeon 8381 is the only subject in which there was a decrease in
the average PRP with all timeout durations during the rich-to-lean transition. The stimulustermination timeout procedure was conducted with three of the four pigeons (10312, 192, and
190). For all three subjects the stimulus-termination timeout procedure decreased the average
57
PRP during the rich-to-lean transition. Run rates varied across pigeons, but overall remained
relatively close to baseline.
An explanation for the decreases seen in both timeout conditions might be that perhaps
after many sessions the PRP was controlled in part by how much time had passed since the
previous reinforcer was received and not solely by the illumination of the key light after the
reinforcer. For example, if a pigeon on average paused for 20 s following a reinforcer, and the
timeout was 15 s, the measured PRP would have been only 5 s. In this example, temporal control
is not being considered as a mechanism that degraded the control of the previous reinforcer, but
instead as a sort of “counting” mechanism. During the blackout timeout, each timeout (15, 30,
and 60 s) decreased the PRP during the rich-to-lean transition for Pigeon 8381. The explanation
of temporal control could apply to this subject, as his pauses during the rich-to-lean transition
were already relatively low. With the addition of a timeout, the PRP during the rich-to-lean
transition would have decreased even more if the timeout was included as part of his pausing
time.
The different effects on PRP observed across pigeons during the blackout timeout suggest
that this type of timeout did not degrade the control of the previous reinforcer. If the timeout had
degraded the control by the past reinforcer, thus breaking the joint control by the past and
upcoming reinforcers, it would be expected that the PRP would have decreased across all
conditions. Decreases in the PRP might not have been observed across all pigeons during the
rich-to-lean transition due to the effect of the long history the subjects had with the stimuli.
Though the timeout put temporal distance between the previously experienced reinforcer and the
upcoming reinforcer, the discriminative stimulus for the transition was still present. These data
suggest that the stimuli came to function as discriminative stimuli for the actual transition;
58
therefore, timeout would not degrade the control of the past reinforcer. Perhaps if the timeouts
occurred daily, not just during occasional probe sessions, the strength of the control by each
transition stimulus would decrease.
Might the decreases in PRP seen during the blackout timeouts be explained by contrast
effects? When the pigeon was in timeout, there was no opportunity for reinforcement. A
transition from a timeout to a key-light signaling a rich-to-lean transition was an overall increase
in reinforcement rate, even though previously the rich-to-lean stimulus had occasioned an
extended PRP. Sadowsky (1973) showed that when pigeons were responding on a signaled
variable-interval schedule, response rates increased following a black-out timeout period. In the
current study, however, the majority of changes in PRP were increases and in run rate were
decreases across all transitions. Consequently, though there were some decreases seen in PRP
and increases in run rate, it is not likely that these changes were solely due to contrast between
the transitions and blackout timeout.
During the stimulus-termination timeout, the rich-to-lean transition PRP decreased and
run rate increased more reliably than during the blackout sessions. Two previously discussed
explanations could apply to the decreases in PRP seen across all birds during the stimulustermination timeout. First, stimulus-termination timeout might have degraded the control of the
previous reinforcer. The history with the individual transition stimuli, however, is the same as
that of the blackout timeout; so why would the blackout not have also degraded the control of the
previous reinforcer? Second, contrast effects could explain the decreases in PRP and increases in
run rate during the stimulus-termination. It is difficult, however, to say that contrast effects were
only present in the stimulus-termination timeout. After all, there was also contrast between the
59
blacked-out chamber and a transition stimulus that signaled the opportunity for reinforcement
was once again available.
Why was there such a discrepancy in the number of decreases seen in PRP a between
blackout and stimulus termination? An interpretation of the inconsistency in decreases during the
blackout timeouts is that stimulus termination was not as much of a disruptor as blackout was
during timeout. Baseline sessions began with the house light on and the keylight off, which is
identical to how timeouts were presented during stimulus-termination timeout sessions. A
chamber blackout was not something that was common in a session, therefore the distraction
provided by blackouts following each reinforcer may have increased PRP and decreased run rate.
Galuska and Yadon (2011) studied how prefeeding affected the PRP during rich-to-lean
transitions. They found that pre-feeding increased the PRP during the rich-to-lean transition. If a
blackout was a disruptor similar to prefeeding that would explain why the PRP increased during
the black-out timeout sessions. There is another interpretation of blackout as a disruptor that
should be considered. During baseline sessions, the only time that a blackout in the chamber
would occur was once the session was complete. Per anecdotal observation, the pigeons would
turn away from the keys and towards the door at the end of sessions in preparation to leave the
chamber. If this behavior occurred during the blackout timeout sessions, it would explain why
the PRP increased overall during these sessions.
Future Directions: Phase 2. Similar to Phase 1, Phase 2 should be replicated using only
two stimuli to signal the upcoming reinforcer. This replication should be done in order to
determine if using a timeout during transitions can break the joint control of the previous and
upcoming reinforcer when only the upcoming reinforcer is explicitly signaled. Stimulustermination timeout sessions should be run in order to compare the difference between using two
60
stimuli versus four stimuli. It might be expected that if joint control by the previous and
upcoming reinforcer is more easily broken using only two stimuli, the PRP during timeout would
be shorter than what was observed when four stimuli were used. This replication would not be
done with blackout timeouts, as there were few decreases in PRP observed during the current
study.
Another direction is to present each timeout type over consecutive days in order to see
what happens to the PRP all transitions when timeout is no longer just a probe. One prediction
might be that after many sessions timeout would no longer degrade the control of the previous
reinforcer. Joint control by the previous and upcoming reinforcer would form once again. PRP,
therefore, would increase over time to the duration that was observed during baseline sessions of
the current study.
Applied Implications
Transitions, particularly those going from a highly preferred activity to a less preferred
activity, can be difficult for all people. More challenging behaviors during these transitions can
be seen in the developmentally delayed populations. During rich-to-lean transitions behaviors
such as aggression, self-injury, and general disruptive behavior can occur which threaten harm to
the individual and to others (Tustin, 1995; Waters et al., 2007; Wilder, Chen, Atwell, Pritchard,
Weinstein, 2006). Studies have been conducted looking for ways in which these problem
behaviors during transitions could be reduced. Waters et al. used visual schedules to attempt to
reduce problem behaviors. Visual schedules were pictures that were presented to the subject that
represented the current activity and the upcoming activity. Once the current activity was
complete, the subject would put the picture of the current activity into a bag, and then bring the
picture of the upcoming activity to the designated activity area. They found that providing the
61
pictures preceding transitions helped to decrease aggressive and disruptive behaviors, but only
when used in conjunction with differential reinforcement of other behavior (DRO) and
extinction. Another method to decrease problem behaviors during transitions was to use a
warning prior to the transition (Tustin, 1995; Wilder et al., 2006). The results varied, as
sometimes behaviors decreased with a warning of the upcoming transition, while other times
behaviors increased with a warning of the upcoming transition. Overall, there has not been a
method that consistently decreases problem behaviors during rich-to-lean transitions in the
applied field.
In the current study, the “problem” behavior of pigeons (i.e., extended pausing) during
rich-to-lean transitions was reduced using a stimulus-termination timeout. A similar behavior
that might be seen in an applied setting is noncompliance or deviance (e.g., engaging in
behaviors that are incompatible to a behavior that has been requested; not engaging in a behavior
that has been requested). These behaviors are similar to PRP in the current study, as all are
measures of latency to start responding to a requested task. An important next step would be to
conduct a similar study with human subjects who display these behaviors during transitions.
Using a stimulus-termination timeout during transitions in an applied setting might include a
period in which the preferred activity is not being engaged before transitioning to the nonpreferred activity. For example, if a subject is watching television and it is time to set the table
before dinner, the television would first be turned off for a specified amount of time before the
request to set the table was made. In general, using timeouts during rich-to-lean transitions
should be studied to determine whether it would be a useful tool for decreasing problem
behaviors.
Summary
62
During signaled rich-to-lean transition, for animal subjects and humans alike, aberrant
behaviors can occur. The behavior of interest in the current study was the PRP. Adding a
blackout timeout between each transition did not reliably decrease the PRP during the rich-tolean transition. Adding a stimulus-termination between each transition, however, did decrease
the PRP during the rich-to-lean transition. Moving forward it will be important to translate this
research into the applied setting. If the right type of transitional timeout in the applied setting
can be studied, dangerous and disruptive behaviors could be decreased and prevent harm to
individuals.
63
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