divided attention trying to do two things at the same time
Some dual tasks cause no interference.
Example
Walk and chew gum
Some dual tasks cause interference.
Example
Drive and talk on cell phone.
Question
What kinds of tasks can be done concurrently without interference?

Demo Task A = Rotate right arm clockwise.
Task B = Rotate left arm counterclockwise
A & B  no interference
Demo Task A = Rotate right arm clockwise.
Task B = Rotate right leg counterclockwise
A & B  interference
Typical Divided Attention Experiment
3 conditions: A only
B only dual-task (A and B at the same time) dual task interference occurs if
Performance on A is better during A-only condition than during dual-task.
or Performance on B is better during B-only condition than in dual-task.

Laws prohibiting cell phone use while driving (as of 2013)
For experienced drivers, hands-free phone banned in 0 states.
Handheld phones banned in 10 states (but not Florida).
Texting while driving is banned in 41 states, including Florida.
In Florida, texting is “secondary offense”
(Source - Insurance Institute for Highway Safety) www.iihs.org/laws/cellphonelaws.aspx

Left blank

Driver Distraction
Common belief: Driving is unaffected by driver’s use of hands-free phone
Typical explanation. The two tasks are very dissimilar.
driving car  visual, spatial, manual talking on hands-free phone  oral, verbal, auditory
Laws conform to this belief.
Use of handheld phones prohibited in many states.
Use of hands-free phones allowed in every state (as of 2011).
Does this make sense? Or do hands-free phones also cause interference?

Driver Distraction experiments
Task
Ss drive in simulators
Ss must avoid cars, pedestrians.
Typical Measures
Braking time
Number of collisions
Common Conditions driving while talking on handheld phone driving while talking on hands-free phone driving while talking to passenger driving while reading text driving while composing text driving intoxicated

Experiment: Effect of hands-free phone
Ss drove in simulator. During dense traffic, car in front stopped unexpectedly.
Sample result no distraction
Brake Time (ms)
933 talking on hands-free phone 1112
Conclusion
Interference is attentional – not just manual.
(Strayer et al., 2003)

Experiment: Hands-free phone vs. Intoxication
Ss drove in simulator. Car in front suddenly stopped.
One result: intoxicated (BAC 0.08%) hands-free phone
Brake time (ms)
779
849
(Strayer et al., 2011)

Experiment: Is hands-free phone worse than talking to passenger?
“… Passengers tend to adjust their conversation based on driving difficulty; often helping the driver to navigate and identify hazards on the roadway and pausing the conversations during difficult sections of the drive. By contrast, this real-time adjustment based upon traffic demands is not possible with cell phone conversations.”
Strayer and Drews (2006, p. 130)
Experiment
S drove in simulator; was asked to exit the highway at rest stop “about 8 miles away”
S listened to friend tell story
Result: driving alone
Drivers who Missed the Exit
4% passenger conversation hands-free cell phone conversation
12%
50%
(Drews et al., 2008)

Other findings from driver distraction studies:
Most Ss overestimate their ability to drive while using a hands-free phone.
Hands-free phone as bad as handheld phone
Four 1-minute videos (bottom of webpage) www.psych.utah.edu/lab/appliedcognition/news.html
Strayer and his colleagues (2001, 2003, 2006, 2009)

Bottleneck Experiments
Driving and talking are hard tasks.
Can interference occur if tasks are dissimilar and easy?
Procedure
Task 1 S
1
Hear high or low tone
RT
1
R
1 say “high” or “low”
Task 2 S
2
See “A” or “B”
RT
2
R
2 press left or right key

Ss practiced task 1 alone, task 2 alone, and dual task.
Practice trial data were excluded from final analysis.
Results:
Task 2 alone
Task 2 in dual task
RT
2
~ 500 ms
~ 700 ms
Conclusion
Even two easy, dissimilar tasks can yield massive dual-task interference.
(Pashler, 1984; Welford, 1941)

Why does Task 2 take so long? That is, in which stage does interference arise?
Perception
Perceive high tone
Perceive “A”
Response Selection
Since tone is high, say “high”
Since letter is A, press left key
Response Production
Say “high”
Press left key.
Hypothesis: The mind can perform only one “response selection” at a time.

Two findings showing bottleneck during Response Selection
Manipulation
-----------------
Task 2 Perception made harder
(e.g., “A” appeared blurry)
Effect on RT
1
Effect on RT
2
----------------------------------none none
Task 2 Response-Selection made harder none
(e.g., if “A” then press B key) increased lag
(Pashler, 1984)
RT
1 wait
RT
2

Bottleneck Practice Questions
Predict the effect of each manipulation on RT
1 and RT
2
Manipulation
Harder P
1
Harder P
2
RT
1 increase none increase Harder RS
1
Harder RS
2
Harder RP
1
Harder RP
2 none increase none
RT
2 increase none increase increase none increase lag
RT
1 wait
RT
2

Another Prediction: Increasing lag by 1 ms should shorten RT
2 by 1 ms (up to a point) lag
50 wait
150
RT
2
= 600 lag
100 wait
100
RT
2
= 550

Another Bottleneck Experiment
Same Basic Procedure
Task 1 S
1
Hear high or low tone
RT
1
Task 2 S
2
See “A” or “B”
RT
2
Lag between S
1 and S
2 varied from 50 to 900 ms
R
1 say “high” or “low”
R
2 press left or right key
(continued)

Prediction of bottleneck theory
RT
2
Slope = -1
Lag between S
1 and S
2
Actual data
RT
2
(Pashler, 1984)
Lag between S
1 and S
2

What dual-tasks can be done without interference?
Distinction choice-RT task Perception Response Selection Response Production
Examples Tasks used in bottleneck studies simple-RT task Perception Response Production
Examples hit key as soon as light appears catch ruler dropped between your fingers
Two choice tasks  interference
Two simple tasks  no interference
One simple, one choice  no interference

Summary of Bottleneck Studies
Many easy tasks require “response selection.”
If people try to do two such tasks concurrently, one task must wait (bottleneck).
The bottleneck occurs if both tasks need “response selection”

Task Switching
If we cannot do two things at once, can we at least switch back and forth?
Yes, but switch is costly task 1 alone -------------------------task 2 alone --------------------------
Switch without cost
1 --------
2 ---------
---------
---------
---------
--------
Switch with cost
1 ---------
2 ---------
---------
---------
Data show that switch cost is high.
---------
--------

Experiment
Ss shown two category names (e.g., Insect, Vegetable)
Ss immediately say 4 examples of each category as quickly as possible
Ss told in advance that responses should be: blocked or
A ant
A gnat
A A moth fly
B B bean corn
B pea
B yam alternating A B A B A B A B ant bean gnat corn moth pea fly yam
Result
Alternating is almost twice as slow!
Conclusion
Switching is costly.

demo
Reversed Normal

Mental Rotation demo
Indicate whether F is mirror-reversed or normal

Mental Rotation
Letter Rotation Experiment
Indicate whether letter can be rotated so that it looks normal.
no yes
IV = amount of rotation 135 ° 30 °

Results
800
RT(ms)
500
0 rotation (degrees)
180
Interpretation Ss “mentally rotated” object at constant rate

Demo: For each pair, indicate whether two images depict same object.
yes yes no

More examples yes yes no

3D mental rotation experiment
Ss saw pairs of images depicting 3D objects.
For each pair, Ss indicated whether two images depict same object or different objects.
When images depicted the same object, it was rotated.
within the plane or in depth
(continued)

Results
Interpretation
Object is mentally rotated
(Shepard & Meltzer, 1971)

Demo –digit span forward
7
8
9
10
5
6
3
4
11
12
8 7 2
6 1 9 4
3 7 8 6 9
6 9 4 5 2 8
4 2 6 9 8 5 7
8 1 6 3 7 2 4 9
6 2 5 7 3 4 9 8 1
9 3 8 2 4 7 1 5 3 6
5 8 1 4 7 9 3 2 6 1 7
6 9 5 1 7 2 8 5 3 7 2 4

Demo –digit span backward
6
7
8
2
3
4
5
7
6
3
5
7
9
5
5
8
1
8
3
3
9
9
9
4
5
4
7
8
1
2
8
3
3
6
1
3 4
6
7
8
9 2

Span Task
S hears 3 – 10 items (digits or words), typically at a rate of item per second
Immediately afterwards, S tries to repeats items aloud in same order
DV = span = number of items S can report in the correct order
Digit span task used on many IQ tests.
(e.g., Baddeley, 2003; Cowan, 2005)

How do people perform the span task? rehearsal loop
Mental mechanism that is used to rehearse verbal info (silently or aloud)
Examples
Rehearsing a phone number until you have a chance to jot it down
Rehearsing someone’s name so you’ll remember it later.
Mental arithmetic
23 x 15
= (20 x 15) + (3 x 15)
= 300 + 45
= 345

Does span increase if items rhyme?
rope dark hand moon soft fear edge rake bake make lake take cake fake book love trap wait bird head wall who blue view do coup you true

Word Span Experiment
Each list included 7 words.
Two kinds of lists: rhyme and non-rhyme
Results rhyme span < non-rhyme span
This is the phonological similarity effect
Effect occurs even if rhyming words are spelled very differently crew, who, moo, through
Thus, when using rehearsal loop, information is stored as sound , not image .
(e.g., Baddeley, 1986)

How many items can you hold in your rehearsal loop?
7 ± 2 ?
Demo
6 words on each list sum hate wit bond yield twice association opportunity representative organization considerable immediately

Another Word Span Experiment
Ss perform word span task
Each list included 6 words.
Two kinds of lists: short words (1 syllable each) and long words (5 syllables each)
Results long-word span < short-word span
This is the word length effect
Conclusion span = amount of info that can be said in about 2 s
The magic number 7 is wrong
(Baddeley et al., 1975)

If magic number is wrong, why does digit span equal about 7?
Observation
IQ tests reveal that English kids had greater digit span than Welsh kids
Experiment
Welsh-English bilinguals tested in both languages
Results: English digit span > Welsh digit span
Why? English digit words are shorter than Welsh digit words
(Ellis & Hennelly, 1980)

Prediction
If digit span = 2 sec, then digit span should vary by language so that digit span = number of digits that can be said in 2 s
Arabic Digits
1. wahed
2. ithnan
3. thalatha
4. arba
5. khamse
6. sitta
7. seba
8. thamanya
9. tesa
10. ashara
Cantonese Digits
1. yat
2. yih
3. saam
4. sei
5. ngh
6. luhk
7. chat
8. baat
9. gau
10. sahp

Cross-Language Digit Span Experiment
E measured how fast Ss could read digits in their native language
E measured Ss’ digit span in their native language
Results
Language syllables per digit
Arabic 2.3
Spanish
English
1.6
1.2 words read in 2 s digit span
5.4
5.8
7.0
7.6
6.4
7.2
Thus, digit span = number of digits that can be said in about 2 seconds.
Conclusion
Magic number 7 is merely an artifact of the English language.
(Naveh-Benjamin & Ayres, 1986; see also Stigler, Lee, & Stevenson, 1986)

Sign Language
In ASL, some words take longer to sign
Long signs include PIANO, BICYCLE, CROSS
Short signs include TYPEWRITER, MILK, CHURCH
Word span is shorter if signs are long.
(Wilson & Emmorey, 1998)

Sometimes, we need to “work with” or “hold information” that is visual
Questions
How many windows are on the front of your house?
If you’re traveling south, and you must turn east, do you turn left or right?

Demo
1 7 7 6 1 4 9 2 1 9 4 1
1 7 7 6 1 4 9 2 1 9 4 1 chunking increases span by reducing number of items

visuospatial scratchpad
Used for temporary storage and manipulation of spatial and visual information
Examples
Visualizing the campus layout in order to give someone directions.
If you’re traveling south, and you must turn east, do you turn left or right?

Sample Task
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16

Are visual-spatial scratchpad and rehearsal loop truly different mechanisms?
Experiment
Dual-task
Results
Both verbal  hard
Both visual  hard
One of each  easier
(Baddeley & Hitch, 1974; Brooks Cocchini et al., 2002; Fougnie & Marois, 2006)

Demo
Verbal Task
As the woman chased her poodle , her poodle chased a cat
Spatial Task
Spatial Response
Verbal Response
(Brooks, 1968) point to “yes” or “no” say “yes” or “no”

What is meant by analog?
Example
On hard drive, similar images have dissimilar representations (digital)
12:59:59 and 1:00:00 look similar on analog clock (but not on digital clock)

Implications of mental rotation studies…
1. Mental imagery can be studied objectively and quantitatively
(without relying on introspection).
2. Linear RT growth suggests that images are mentally rotated.

demo
How many left turns as you drive from
● to
▲
?
… right turns?

Subtraction method has untenable assumptions.
1. Stages are non-overlapping.
For example, RP might begin before RS complete.
2. Stage durations are independent.
Duration of RP might depend on duration of RS.
Still, in some cases, subtraction method has utility.

Demo
How fast does sensory info (e.g., ankle twist) move from ankle to brain?
Compare ankle and shoulder: E taps S’s ankle or shoulder; S raises finger
Since d = r t
 d r = ------
 t
1.5 m
= -------=
0.01 s
150 m/s

Fact from textbook
Impulse along myelinated axon can move as fast as 120 m/s = 260 mph

Demo – semantic similarity
Same task as before.
sky nail nurse box light noise shirt grass cat dog pig horse goat sheep cow hen

Some details from study by Naveh-Benjamin and Ayres (1986)
Language
English
Spanish
Arabic
Syllables
Per Digit
1.1
1.5
2.5
Digit
Span
7.3
6.5
5.5
Reading Aloud rate
(in digits / 2 sec)
8.0
6.2
5.2

Mental Rotation Experiment
Ss first became familiar with several irregular polygons.
On each trial, Ss saw one of the polygons or its mirror image.
Task It is the same or mirror-reversed?
(continued)

Alternative version: stimuli = irregular polygons
( rotation

(
What about 3-D mental rotation?

Visual tasks and verbal tasks are controlled by different mechanisms.
Evidence dual-task studies
Both verbal  very hard
Both visual  very hard
One of each  easier
KF (motorcycle accident) visual storage okay, verbal storage imparied
(Baddeley & Hitch, 1974; Brooks Cocchini et al., 2002; Fougnie & Marois, 2006)

latent bottleneck (Lien et al., 2006)
RT
2
0 200 400 600 800
S
1
- S
2
Lag

Why exactly does this dual-task interference occur?
Traditional Explanation
Resources are limited, so progress on at least one task is slowed.
Task 1 alone
Task 2 alone |
|------------------------------|
-----------------------------|
500
Dual-Task
Task 1 |------------------------------|
Task 2 | --------------------------------------------|
700
(continued)

Bottleneck Theory
During certain stage in completion of Task 2, progress completely stops.
Task 1 alone |------------------------------|
Task 2 alone |------------------------------|
500
Dual-Task
Task 1 |------------------------------|
Task 2 |------- wait -----------------------|
700
In other words, at some point, Task 2 must wait for Task 1.

Experiment
Ss saw between 1 6 “study letters” at rate of one per s
Then Ss saw target letter.
Ss hit yes or no key, depending on whether target was a study letter.
For target-absent trials, task included :
Perceive Target
Mentally scan study letters, one at a time
Select response (“no”)
Produce response
Results: Each additional study letter increased RT by 38 ms
Conclusion : Ss “mentally scanned” letters at rate of one per 38 ms
(For complicated reasons, this interpretation is no longer popular.)
(Sternberg, 1966)

Bottleneck finding conflicts with traditional view of dual-task interference: limited resource theory tasks can be done concurrently and without interference if demand < supply.
(e.g., Kahneman, 1973; Pashler, 1984; Welford, 1941)

Everyone knows what attention is.
(James, 1890)
A formal definition of the term “attention” is not presently available…
(Pashler & Johnston, 1998)

Demo
Even two easy tasks can cause dual-task interference
Easy: Pat head and stomach
Harder: Pat head, rub stomach
Easy: R hand CW, R foot CW.
Harder: R hand CW, R foot CCW.

Sample Experiment
Ss shadowed 10 words presented to one ear.
At same time, S tried to remember 10 other items simultaneously.
1) seen as pictures
2) seen as words
3) heard as words (in other ear)
Then Ss tried to recall the 10 non-shadowed items.
Results
(3) was hardest; (1) was easiest.
Conclusion
Task similarity increases dual task interference.
(Allport, Antonis, & Reynolds, 1972)

Statistic
In 2009, cell phone use was a factor in 995 driving fatalities in US (NHTSA).

3 possible locations of bottleneck
Perception Bottleneck
| ------ P
1
------| ------------- RS
1
---------| -- RP
1
-| lag | --wait-| ------ P
2
------| ------------- RS
2
---------| -- RP
2
-|
Response-Selection Bottleneck
| ------ P
1
------| ------------- RS
1
---------| -- RP
1
-| lag | ------ P
2
------| ------ wait ------| ------------- RS
2
---------| -- RP
2
-|
Response-Production Bottleneck
| ------ P
1
------| -------------- RS
1
---------| ------ RP
1
----| lag | ------ P
2
------| ------------- RS
2
---------| -- wait-| ------ RP
2
------|

Bottleneck Experiment 1
Ss did two choice-RT tasks described in previous study (see/press & hear/say).
E varied difficulty of P
2
Hypothesis
Bottleneck during Perception
Bottleneck in Response Selection
Predicted Effect on RT
2 increase no change
Results
Conclusion
(Pashler, 1984) no change no bottleneck during Perception

Bottleneck Experiment 2
Ss performed the two choice-RT tasks described in previous study.
E varied difficulty of RS
2
Hypothesis
Bottleneck during Response Selection
Bottleneck during Response Production
Effect on RT
2 increase no change
Results increased
Conclusion Bottleneck does not occur during Response Production
(Pashler, 1984)

Practice Questions
Assume bottleneck in Perception stage. Indicate effect on RT
1 and RT
2
Manipulation RT
1 increase
RT
2 increase Slightly harder P
1
Slightly harder P
2
---increase
Slightly harder RS
1
Slightly harder RS
2 increase
----
---increase
Perception Bottleneck
| ------ P
1
------| ------------- RS
1
---------| -- RP
1
-| lag | --wait-| ------ P
2
------| ------------- RS
2
---------| -- RP
2
-|

Assume bottleneck in Response Production stage.
Indicate effect on RT
1 and RT
2
Manipulation RT
1 increase Slightly harder P
1
Slightly harder RS
1
Slightly harder RS
2
Slightly harder RP
1 increase
---increase
RT
2 increase increase
---increase
Response-Production Bottleneck
| ------ P
1
------| -------------- RS
1
---------| ------ RP
1
----| lag | ------ P
2
------| ------------- RS
2
---------| -- wait-| ------ RP
2
------|

An analogy showing why initial slope of -1 supports bottleneck
Suppose two customers visit ATM and each requires exactly 1 minute
ATM can handle only 1 customer at a time, so bottleneck occurs
RT
2 equals the time Customer 2 is at the ATM
Lag between their arrival
0:15
0:30
0:45
1:00
1:15
1:30
Customer 2 time at ATM (including wait)
1:45
1:30
1:15
1:00
1:00
1:00
Thus, adding 15 s to lag simply adds 15 s to RT
2 unless Customer 1 has already left

A diagram showing why initial slope of -1 supports bottleneck
S
1
R
Task 1 |-----------------------------------|
1
S
2
Task 2 |….lag….|- - - - -wait - - - - -|---------------------------------- |
R
2
S
2
|………lag………. |- -wait - |---------------------------------- |
R
2
Remember: RT
2
= time between S
1 and R
2
So, add 1 ms to lag  shorten wait by 1 ms  reduce RT
2 by 1 ms

Actual Data:
RT
2
(ms)
(Pashler, 1984)
Lag (ms)

Optional: Results of last two studies inconsistent with P or RS bottleneck
Perception Bottleneck
| ------ P
1
------| ------------- RS
1
---------| -- RP
1
-| lag | --wait-| ------ P
2
------| ------------- RS
2
---------| -- RP
2
-|
Response-Selection Bottleneck
| ------ P
1
------| ------------- RS
1
---------| -- RP
1
-| lag | ------ P
2
------| ------ wait ------| ------------- RS
2
---------| -- RP
2
-|
Response-Production Bottleneck
| ------ P
1
------| -------------- RS
1
---------| ------ RP
1
----| lag | ------ P
2
------| ------------- RS
2
---------| -- wait-| ------ RP
2
------|

Illustration of CEO
Dual-task X
Dual-task Y hear/say one passage & read/type another hear/type one passage & read/say another
Which dual-task creates more dual-task interference? Y
For both tasks in X, stimulus = response
For both tasks in Y, stimulus
 response
Example
Hear “iz”, say “iz”
Hear “iz”, type “is”
Thus , both tasks in Y require a more difficult “response selection”
(Shaffer, 1975)

Results
4
Data are linear.
RT(s) intercept = 1 s slope = 1 s / 60 °
1
0 rotation (degrees)
Every additional 60 ° of stimulus rotation increased RT by 1 s
180
Interpretation Ss “mentally rotated” mental image at rate of 60° per sec
Claim Mental rotation data are observable measure of “mental imagery”
(Shepard & Meltzer, 1971)

Demo rectangle trapezoid parallelogram

Demo pentagram pentagram within pentagon hexagram

Mental Imagery
Many people believe that they can form mental image of familiar object.
Experiment
Ss were asked question about simple shape
Example
Does this include a rectangle?”
Two Conditions Performance
Answer question while looking at shape. Perfect
See shape. Form mental image. Answer question. Poor
Conclusion
People overestimate their ability to form mental image
(Reisberg, 1993)

However, “mental imagery” does appear to have a visual component.
Experiment
Ss told to “think about” a cat OR “form mental image” of a cat
While they did that, Ss were asked:
Does the cat have a head?
or
Does the cat have claws?
Results
Thinkers
Imagers
Question Answered More Quickly
----------------------------------------------claws head
(Kosslyn, 1976)