Child Development, November/December 2008, Volume 79, Number 6, Pages 1869 – 1890
Postural and Object-Oriented Experiences Advance Early Reaching,
Object Exploration, and Means – End Behavior
Michele A. Lobo and James C. Galloway
The University of Delaware
The effects of 3 weeks of social (control), postural, or object-oriented experiences on 9- to 21-week-old infants’ (N 5
42) reaching, exploration, and means – end behaviors were assessed. Coders recorded object contacts, mouthing,
fingering, attention, and affect from video. Postural and object-oriented experiences advanced reaching, haptic
exploration of objects, and developing means – end behavior compared to social experience. Object-oriented
experience best-advanced means – end behavior. The results suggest that the development of novel behaviors is
dependent on multiple subsystems and can be similarly advanced by addressing a variety of these subsystems.
They also suggest that past experiences with active object exploration can facilitate early information processing
and the development of early knowledge.
Early experiences shape the development of many
skills in infancy, such as early stepping (Vereijken &
Thelen, 1997; Zelazo, Zelazo, Cohen, & Zelazo, 1993),
reaching (Lobo, Galloway, & Savelsbergh, 2004), object exploration (Needham, Barrett, & Peterman,
2002), and crawling (Adolph, Vereijken, & Denny,
1998). The goal of this project was to assess the effects
of advanced parent – infant experiences on the future
development of three behaviors proposed to be
developmentally related: (a) reaching, (b) object
exploration, and (c) means – end behavior. We predicted that altering parent – infant interactions when
infants were 2 – 3 months of age and not yet reaching
would propel infants onto different developmental
trajectories in the months after the prescribed experiences ended. In the current study, parents provided
just 3 weeks of advanced postural or object-oriented
experiences. We assessed the effects of these experiences on future reaching, object exploration, and
means – end behavior across a 12-week period.
The onset of the ability to reach at about 4 months
of age is a milestone that alters daily life for infants
and their parents (E. J. Gibson, 1988; Thelen et al.,
This study was conducted as the doctoral thesis for M.A.L. and
was funded by dissertation fellowships through The University of
Delaware. We thank the families who generously agreed to
participate in this study, our wonderful undergraduate research
assistants, especially Rachel Farley, Rebecca Silver, Lindsey Moore,
Morgan Randles, and Lauren Emerson, for hours of coding
assistance and the members of the thesis committee, Nancy
Getchell, Slobodon Jaric, and Mark Stanton, for their invaluable
input throughout the project.
Correspondence concerning this article should be addressed to
Michele A. Lobo, Motor Behavior Laboratory, Department of
Physical Therapy, 329 McKinly Lab Building, The University of
Delaware, Newark, DE 19716. Electronic mail may be sent to
malobo@udel.edu.
1993; von Hofsten, 1991). Prior to the onset of reaching, infants in the United States spend most of their
time supine on their backs engaging in face-to-face
social interactions (Davis, Moon, Sachs, & Ottolini,
1998; Fogel, Messinger, Dickson, & Hsu, 1999; Mildred, Beard, Dallwitz, & Unwin, 1995). If parents
introduce objects to their infants in these months, they
typically present them to infants out of reach for
visual inspection (Eppler, 1995; Fogel, 1997; Fogel
et al., 1999). Parents occasionally place objects in
infants’ hands or mouths; however, the grasping
ability required for sustained oral or manual object
exploration does not emerge until after the onset of
reaching (Konczak & Dichgans, 1997; Rochat, 1989).
Infants move their arms often in the period before they
begin to reach with and without the presence of objects
or people. It is through these spontaneous movements
that infants explore the biomechanics of their bodies
and the forces acting upon them and gain the motor
control required for later object interaction (Bhat,
Heathcock, & Galloway, 2005; Thelen, 1990; von Hofsten, 1993). In effect, the period before the onset of
reaching could be termed a primarily ‘‘supine, spontaneous, and social period.’’
After reaching emerges, infants’ and parents’ daily
activities change. Infants move their arms with more
control, which allows for more purposeful interaction
with objects (Bhat et al., 2005; Thelen et al., 1993). The
onset of reaching also coincides with the time when
infants typically begin to assume more varied postural orientations, rolling prone and supine, being
# 2008, University of Delaware
Journal Compilation # 2008, Society for Research in Child Development, Inc.
All rights reserved. 0009-3920/2008/7906-0023
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Lobo and Galloway
placed vertical and in semireclined sitting more often,
and sitting with assistance (Fogel et al., 1999; Snow,
1989). Better postural control coupled with reaching
and grasping ability allows infants to independently
explore objects in new ways for sustained periods
through mouthing and touching (Adolph, Eppler,
Marin, & Wechsler-Clearfield, 2000; J. J. Gibson,
1979). Furthermore, the onset of reaching changes
the parent – infant – object dynamic. As parents
observe their infants’ emerging ability to interact with
objects, they begin to present repeated, daily opportunities for their infants to haptically interact with
objects (Fogel, 1997; Fogel et al., 1999; Reed & Bril,
1996). Compared to the prereaching period, the
period following the onset of reaching could be
termed a primarily ‘‘postures, purpose, and play
period.’’
In our previous work, we showed that advanced
general movement experiences and object-oriented
experiences advanced infants’ abilities to reach for
objects (Heathcock, Lobo, & Galloway, 2008; Lobo
et al., 2004). Below we detail why we chose to expand
on these results by assessing the effects of advanced
postural and object-oriented experiences on not only
reaching but also on later object exploration and
means – end behavior.
The Role of Postural Experiences in the
Ontogeny of Reaching
The first objective of this project was to test whether
advancing the development of postural stability
would advance the onset of reaching. Postural stability involves the ability to dynamically maintain the
position of the body, or the center of mass, within
one’s stability limits (Shumway-Cook & Woollacott,
1995). The role of parents in promoting the development of postural stability in early infancy has been
documented in several cross-cultural (Bril & Sabatier,
1986; Hopkins & Westra, 1988, 1989, 1990) as well
as prospective (Davis et al., 1998; Hadders-Algra,
Brogren, & Forssberg, 1996) studies. Young infants
lack the mobility to independently transition between
positions, thus the variety of positions and postural
challenges they experience is largely a function of
how parents handle them. Therefore, the emergence
of postural stability is dependent not only upon the
evolving abilities of infants but also upon parents’
responses to these abilities.
Postural stability has been proposed as a requirement for reaching (Bertenthal & von Hofsten, 1998;
Hopkins & Ronnqvist, 2002; Rochat & Goubet,
1995; Savelsbergh & van der Kamp, 1993). Developmentally, postural advancements accompanied
improvements in reaching (Fallang, Saugstad, &
Hadders-Algra, 2000; Fontaine & le Bonniec, 1988;
Rochat, 1992; Spencer & Thelen, 2000). Reaching also
improved in real time when external postural stability was provided (Amiel-Tison, 1985; Grenier,
1981; Rochat & Goubet, 1995). If postural stability
facilitates reaching, then advancing the development of postural stability should advance the emergence of reaching (Bertenthal & von Hofsten, 1998;
Hopkins & Ronnqvist, 2002; Rochat & Goubet, 1995).
Being placed more often in postures, such as sitting
and standing, has been shown to directly advance
the emergence and control of these postures (Bril &
Sabatier, 1986; Hopkins & Westra, 1988, 1989, 1990;
Zelazo et al., 1993). This is the first study to attempt
to assess the effects of advanced postural stability on
another unpracticed behavior (reaching). The postural experiences prescribed in this project were
non-object-oriented experiences aimed at advancing
postural stability across a variety of positions. We
hypothesized that infants who received enhanced
postural experience would have advanced reaching
emergence and ability compared to control infants.
The Role of Object-Oriented Experiences in
the Ontogeny of Reaching
The second objective of this project was to test
whether providing earlier than typical object experience would advance reaching. Parents play an important role in helping their infants learn to reach around
4 – 5 months of age by presenting them with objects to
reach for and scaffolding their early reaching attempts (Fogel, 1997; Fogel et al., 1999; Reed & Bril,
1996). Young infants cannot independently seek out
objects; thus, they rely on parents to present them
with opportunities to interact with objects. Therefore,
as with postural stability, the emergence of reaching
is dependent on the evolving abilities of infants as
well as parents’ responses to these evolving abilities
(Bakeman, Adamson, Konner, & Barr, 1990; Bruner,
1972; Landry & Chapieski, 1988).
Experience moving and interacting with objects
has been proposed to be an important factor in the
emergence of reaching (Bhat & Galloway, 2006; Fogel
et al., 1999; Thelen et al., 1993). Specifically, reaching
was advanced after 2 weeks of daily, object-oriented
movement experiences provided 1 – 2 months prior
to typical reach onset (Lobo et al., 2004). If experience
haptically interacting with objects facilitates reaching, then advancing parent – infant interactions to
incorporate objects earlier should again advance the
emergence of reaching (Fogel, 1997; Fogel et al., 1999;
Lobo et al., 2004; Reed & Bril, 1996). Here, we
Experiences Advance Early Behaviors
assessed the effects on reaching behavior across
a longer time span. The object-oriented experiences
prescribed in this project were aimed at advancing
infants’ reaching ability and haptic experience with
objects in supine. We hypothesized that infants who
received enhanced object experience would have
advanced reaching emergence and ability compared
to control infants.
The Role of Reaching Experience in the
Ontogeny of Object Exploration
The third objective of this project was to test for
a developmental connection between reaching and
object exploration. That is, would infants in groups
who reached early due to the effects of enhanced
postural or object-oriented experiences also display
advanced object exploration? Infants learn to extract
information about the affordances and properties of
objects through active object interaction (Campos
et al., 2000; E. J. Gibson, 1988; J. J. Gibson, 1979). Not
surprisingly, the emergences of reaching and object
exploration are important milestones linked with
abilities across multiple domains, including cognitive, social, and language (Bremner, 2000; E. J. Gibson,
1988, 2000; Needham, 2000; Piaget, 1952, 1954). The
onset of reaching is rapidly followed by the ability
to grasp objects for sustained periods (Wimmers,
Savelsbergh, Beek, & Hopkins, 1998; Wimmers,
Savelsbergh, van der Kamp, & Hartelman, 1998). This
grasping ability coupled with increased opportunities
to explore objects presented by parents may be
important in transitioning infants into more frequent,
purposeful, exploratory object interactions.
Although experience actively exploring objects
has been viewed as necessary for infants to learn about
the actions they can perform on objects (Bourgeois,
Khawar, Neal, & Lockman, 2005; Case-Smith, Bigsby,
& Clutter, 1998; Needham, Cantlon, & Holley, 2006), for
infants less than 6 months of age, we know of only one
study assessing reaching and exploration behaviors in
combination (Needham et al., 2002). In that study,
nonreaching infants given experience interacting with
objects using sticky mittens with Velcro later showed
greater object engagement and haptic exploration of
objects. If experience actively exploring objects facilitates early knowledge about how to examine objects,
then advancing the onset of reaching should advance
object exploration behavior. This project aimed to
determine the effect of advanced reach onset on the
ontogeny of object exploration. We hypothesized that
infants in groups expected to reach earlier (postural
and object experience) would show more haptic exploration of objects earlier compared to control infants.
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The Role of Object Experience in the Ontogeny
of Means – End Behavior
The final objective of this project was to test for
a connection between reaching, object exploration,
and means – end behavior. That is, would infants who
had been reaching and exploring objects longer also
display advanced means – end behavior? By acting on
objects, infants learn information about the match
between their actions and external events (E. J. Gibson,
2000). For instance, by exploring a jack-in-the-box,
infants learn that cranking the handle results in the
sight and sounds of a toy. Such active interaction with
objects has been proposed to be the vehicle by which
infants gain knowledge about more complex action –
environment relationships such as means – end relationships (Bremner, 2000; E. J. Gibson & Pick, 2000;
Piaget, 1952, 1954; von Helmholtz, 1962). Means – end
behavior involves acting on one object as the means to
affect another object (Munakata, Bauer, Stackhouse,
Landgraf, & Huddleston, 2002). Most means – end
studies test infants older than 6 months of age with the
general consensus that means – end behavior is present by 8 months of age (Funk, 2002; Lewis, Alessandri,
& Sullivan, 1990; Munakata et al., 2002).
Several studies have investigated the emergence of
means – end knowledge (Funk, 2002; Gowen, Goldman, Johnson-Martin, & Hussey, 1989; Menard, 2005).
Visual attention paradigms have suggested that infants may possess means – end knowledge before
they can demonstrate means – end behavior (Hofstadter & Reznick, 1996; Sommerville & Woodward,
2005b). It remains unclear how to reconcile the
discrepancies between the behavioral and visual
studies. One account for the discrepancies is the
means – end deficit account, which claims that young
infants may possess means – end knowledge but
cannot demonstrate it because they cannot perform
the tasks typically used to measure means – end
behavior (Shinskey & Munakata, 2001).
To study the early emergence of means – end
behavior, we designed a task in which the means
were in line with infants’ skills and the end was
meaningful to young infants. The requirements of
the means – end tasks used in other studies are too
difficult for infants younger than 6 months of age
(Hood, 2001; Menard, 2005). For example, infants
younger than 6 months are not able to grasp and pull
a towel or to grasp and lift an enclosure while reaching for and grasping an object behind the enclosure
with the opposite hand (Bojczyk & Corbetta, 2004;
Corbetta, Thelen, & Johnson, 2000; Fagard, 2000).
Similar to studies with older infants, our means – end
task required that infants coordinate their existing
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Lobo and Galloway
behaviors to perform in an unfamiliar task, acting on
one object to affect another while demonstrating
intention via interest in the ‘‘end’’ object (Munakata
et al., 2002; Willatts, 1999). However, our task required
motor, perceptual, and affect regulation abilities that
young infants possess. If experience acting on objects
facilitates the learning of means – end relationships,
then advancing the onset of reaching and object
exploration should advance emerging means – end
behavior. We hypothesized that infants who had the
longest duration of active object exploration, those
who received object-oriented experiences prior to the
onset of reaching, would show the most advanced
means – end behavior.
Method
Participants
Healthy, full-term infants entered the study when
they were 8 – 11 weeks of age and not yet reaching.
Before Visit 1, 42 infants were randomly assigned to the
social experience (control) group (age at Visit 1: M 5 61
days, SD 5 5 days, range 5 54 – 77 days), the postural
movement experience group (age at Visit 1: M 5 62
days, SD 5 5 days, range 5 57 – 79 days), or the objectoriented movement experience group (age at Visit 1:
M 5 61 days, SD 5 5 days, range 5 55 – 74 days).
Infants among groups were matched for gender.
Each group contained 7 boys and 7 girls. We located
families with infants through local birth announcements. Parents provided informed consent. All infants
were from two-parent families. Two infants were
African Americans, and the remaining infants were
Caucasians.
Fourteen additional infants were excluded from the
sample. Nine were excluded because of advanced
reaching at Visit 1 evidenced by more than 10 object
contacts during the reaching task. Excluding these
infants was important because one objective of this
study was to determine the effect of advanced experiences on the initial emergence and subsequent development of reaching. The remaining 5 infants were
excluded because of parents’ inability to provide home
experience for more than 60% of the days during the
3-week prescribed home experience period. We requested that parents provide the experiences daily yet
emphasized that missing occasional days would be an
acceptable reality. Parents reported in journals how
much experience was provided daily and were
unaware of the 60% criterion. Please see the Results
section for specifics on parental reports of provision of
experiences. Participants received certificates of par-
ticipation and DVD recordings of their infants’ first
and fifth visits as gifts upon completion of the study.
Procedure
The same experimenter visited families in their
homes for six visits over a period of 12 weeks. Visits 1,
3, 4, 5, and 6 were separated by 3 weeks. Visits 1, 2, and
3 were separated by 1.5 weeks. We documented each
session using two synchronized video recordings to
provide right- and left-side views of infants for
coding. A splitter was used to place both views on
one screen, and a vertical interval time code generator
was used to superimpose the hour, minute, second,
and frame on the image.
Parents provided enhanced experiences daily only
between Visits 1 and 3. Thus, parents were asked to
provide the experiences for a total of 3 weeks when
infants were between 2 and 3 months old. At each
visit, we assessed infants’ ratings on the Alberta
Infant Motor Scale (AIMS) and performance in three
tasks: (a) use of arm movements to reach, (b) use of
arm movements to explore objects, and (c) use of arm
movements to explore a means – end task.
Rating on the AIMS
At each visit, we observed infants’ general motor
development and rated them using the AIMS (Piper &
Darrah, 1994; Piper, Pinnell, Darrah, Maguire, &
Byrne, 1992). AIMS scores were used to ensure that
the three groups were not different in their motor
development at the initiation of the study and as an
independent measure of whether the activities provided to the postural experience group actually
resulted in advanced postural development. The
AIMS is a valid and reliable developmental assessment tool that compares infants’ motor performance
to that of a normative sample to provide percentile
rankings reflecting general motor development. It
consists of observation of infants’ weight bearing,
posture, and antigravity movement in supine, prone,
sitting with support, and standing with support.
Task 1: Using Arm Movements to Reach
At each visit, infants were provided opportunities to
reach for an object while lying supine and sitting
upright in a custom seat (Figure 1). In the seat, infants
had their trunks secured but had freedom of movement of their arms. In each position, an object was held
stationary in midline at the infant’s chest level for six
30-s trials. The object distance was determined at the
Experiences Advance Early Behaviors
1873
Figure 1. Task 1: One infant positioned supine (A) and vertically in the seat (B) for the assessment of the use of arm movements to reach.
beginning of each session by extending the infant’s
arm into midline, noting the location of the infant’s
wrist, and presenting the object in this location. Trials
began when infants were in a positive behavioral state
and visually attending to the object (Prechtl, 1974).
Task 2: Using Arm Movements to Explore Objects
At each visit, infants were provided opportunities
to use arm and hand movements to haptically explore
objects while sitting upright in our seat. Infants could
not reliably grasp objects for prolonged periods at the
start of the study. Thus, objects were attached to
infants’ wrists using Velcro bands (Figure 2). The
experimental design for this task was based on Ruff
(1984). Three pairs of objects varying in weight,
texture, or sound-making ability were presented to
infants for exploration. One object in each pair served
as the familiarization object, and the other object
served as the novel object. Infants had 60 s to explore
each familiarization object and 45 s to explore each
novel object. These times kept the familiarization
period longer and novelty period shorter similar to
Ruff. But the total presentation time for each pair
(familiarization period plus novelty period) was
shorter to increase the likelihood that the very young
infants in this study could complete the
entire paradigm. For the purposes of this article, we
focus on global exploration of the objects by grouping
the data.
At each visit, the familiarization and novelty trials
were immediately preceded by the experimenter
attaching the object to the wristband, raising the hand
and object into the infant’s view, and then releasing
the hand at the start of the trial. There was no contact
between the experimenter and infant during trials.
Successive objects were attached to alternating hands.
The initial hand of attachment was the right for half of
the infants in each group and left for the others.
Within infants, the initial hand of attachment was
altered at each visit.
Task 3: Using Arm Movements to Explore a
Means – End Task
At each visit, infants were provided opportunities
to use arm movements to explore a means – end relationship while sitting upright in our seat (Figure 3).
The means – end task began with a 30-s pre-means –
end period followed by two means – end periods.
During the pre-means – end period, a toy was placed
to the left of the infant at a distance of 1 m (see C in
Figure 3). The toy was within view but out of reach of
the infant and was inactive. This period allowed us to
Figure 2. Task 2: One infant positioned in the seat for the assessment of the use of arm movements to explore objects.
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Lobo and Galloway
attached to the seat (‘‘nonactivations’’; see B in
Figure 3). The light allowed coding of nonactivations
and was out of the infant’s view.
A certain level of activity was required for infants
to demonstrate means – end behavior. Therefore, in
the early visits, we discontinued the assessment if
infants produced five or less total activations of the
switches within the first 2 min of the first means – end
period. When an infant met this criterion, the entire
assessment was completed for that visit and all
subsequent visits.
Prescribed Home Experiences
Figure 3. Task 3: One infant positioned in the seat for the assessment of the use of arm movements to explore a means – end task.
Note. Note the two lever switches in the infant’s reach (A), the small
light secured to the chair (B; out of the infant’s view), and the
musical spinning bug toy (C; out of reach, in view for the infant).
test for changes in visual attention to the toy when it
was not active or under infants’ control.
The assessment continued with two means – end
periods, one 4-min period followed by a second 3- to
4-min period. The length of the second period was
dependent on the behavioral state of the infant
(Prechtl, 1974). During both periods, the toy remained
in its position and two lever switches were presented
to infants within reach, one laterally to the right and
one to the left (see A in Figure 3). To test infants’
knowledge of the means – end relationship, switch –
toy control was altered so one switch activated the toy
during the first means – end period and the other
switch activated the toy during the second means –
end period. The position of the switch activating the
toy during the first means – end period was counterbalanced among subjects in each group.
The lever switches were activated immediately
when infants reached to displace them in any direction. One switch activated the toy (‘‘toy activations’’),
which resulted in colorful plastic bugs spinning in
circles to music. The other switch activated a light
Parents in each group were asked to perform the
home experiences for 15 min daily throughout the
first 3 weeks of the study (Visit 1 to Visit 3) in
addition to their typical daily activities. After Visit
3, parents were informed that they did not need to
continue performing the home experiences for the
purposes of this project. Although this amount of
experience seems minimal, we have seen large
changes in behavior as a result of prescribed experiences of similar durations (Lobo et al., 2004). It is
likely that these changes result from carryover of
the prescribed activities into daily parent – child
interactions.
Parents were taught to provide the experiences
via demonstrations from the experimenter at Visit 1
along with illustrated instruction manuals kept by
parents. At Visit 2, parents were asked to perform
an independent demonstration of the experiences
with their infants for the experimenter and to
discuss any questions or concerns regarding the
experiences. Parents tracked the frequency and
duration of their performance of the experiences
in daily journals.
Social experience. Parents in the social experience
group were asked to position their infants in supine
while encouraging face-to-face, non-object-oriented
interaction for 15 min. This served as a control for the
increased social interaction and associated general
movement that infants in the postural and object
experience groups would receive.
Postural experience. Parents in the postural experience group were asked to perform non-objectoriented activities to improve postural stability and
midline hand movement ability for 15 min. Specifically, the activities involved parents assisting infants
to push up in prone, to pull up supine to sitting, to
maintain their heads and upper trunks upright when
their lower body was moved different directions in
supported sitting and standing, and to move their
hands to midline for clapping play.
Experiences Advance Early Behaviors
Object-oriented experience. Parents in the objectoriented experience group were asked to teach their
infants to reach for midline objects and to encourage
haptic exploration of objects. To teach reaching,
parents spent 5 min for each hand showing the infant
his or her hand, showing an object at midline, moving
the hand to the object, and then allowing the infant
opportunities to perform this actively. To encourage
haptic exploration of objects, parents spent 5 min
assisting infants to feel objects varying in characteristics such as shape, size, texture, and hardness with
their hands and mouths.
Data Analysis
Arm movement task coders were blind to group
assignment. AIMS coding was performed by a pediatric physical therapist. Coding reliability was assessed based on a comparison of agreements and
disagreements from each visit. For each variable,
the number of behaviors coders agreed and disagreed on was determined and percentage of reliability was calculated using the equation: [agreed/
(agreed + disagreed)] 100. This is a strict measure
of reliability (Angulo-Kinzler & Horn, 2001; Harris
& Lahey, 1978; Lobo et al., 2004). Individuals were
qualified for coding once they achieved and maintained inter- and intrarater reliabilities greater
than 90%.
Variables for Rating on the AIMS
Changes in AIMS ratings across the span of the
home experience (Visit 1 to Visit 3) and across the span
of the study (Visit 1 to Visit 6) were analyzed in total
and for the supine, prone, sitting, and standing
subscales.
Variables for Task 1: Using Arm Movements to Reach
The variables for this assessment were analyzed
in total with secondary analyses for the supine and
vertical positions because previous research suggested that early vertical reaching abilities are
more advanced than supine (Carvalho, Tudella, &
Savelsbergh, 2007; Savelsbergh & van der Kamp,
1994).
Numbers of infants reaching. An infant was categorized as reaching if he or she contacted the object
more than five times in 3 min of supine or vertical
object interaction. These criteria are based on our past
reaching studies (Lobo et al., 2004) with infants
demonstrating that infants who have learned to reach
perform this action repeatedly and reliably across all
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sessions after the onset of reaching with high numbers
of object contacts.
Numbers and durations of object contacts. Object
contact occurred when any surface of the hand contacted the object. Right- and left-limb variables were
summed, such that, for example, one bilateral contact
was counted as two contacts. Duration of each contact
was coded using the time code on the video.
Numbers of infants reaching bilaterally and percent
bilateral contact time. Bilateral midline reaching is
typically observed after the onset of unilateral midline reaching (van Hof, van der Kamp, & Savelsbergh,
2002). We analyzed bilateral contact data because
manipulating an object with two hands versus one
allows infants to use actions not possible with just one
hand to gather more information about objects’ properties (Ballesteros, Manga, & Reales, 1997; Provine &
Westerman, 1979). A bilateral contact was recorded
any time right- and left-handed object contacts overlapped. An infant was recorded as reaching bilaterally if this occurred more than 10 times total or more
than 5 times in supine or vertical. The total time of
overlap between right- and left-handed contacts was
extracted from the data and analyzed to determine the
percentage of time infants were interacting with the
object using both hands.
Variables for Task 2: Using Arm Movements to
Explore Objects
The percent time fingering or mouthing the exploration objects was coded and calculated. ‘‘Fingering’’
occurred when the opposite hand contacted the
attached object. ‘‘Mouthing’’ occurred when the
mouth or lips contacted the attached object. The time
spent fingering or mouthing was totaled and then
converted to a percentage of the total possible exploration time or the sum of the trial times (three 60-s
trials and three 45-s trials for a total of 315 s).
Variables for Task 3: Using Arm Movements to Explore
a Means – End Task
Our means – end task was similar to the one used
by Munakata et al. (2002) in that infants acted on
a switch to inflict consequences on another, more
distant object in the environment that did not appear
physically linked to the switch. We modeled Willatts’s
(1999) use of multiple variables, including behavior
with the means object and visual fixation on the end
object, to assess for intentional means – end behavior.
Means – end behavior in this paradigm was defined
based on four criteria involving the three variables
that follow.
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Lobo and Galloway
1. Number of toy activations and nonactivations.
Coders recorded toy and nonactivations noting
the time superimposed on the video. These data
provided (a) the total number of switch activations (toy activations plus nonactivations), (b) the
number of toy activations, and (c) the number of
nonactivations for each means – end period.
2. Percent of toy activations and nonactivations accompanied by visual attention to the toy. Coders
determined whether infants visually attended
to the toy within 5 s of each switch activation.
Visual attention to the toy was not coded more
than 5 s from an activation because each event of
toy activity only lasted 5 s. These data were
compiled to determine the percentage of toy
activations and nonactivations accompanied by
visual attention to the toy in each period.
3. Percent time with positive or negative/neutral affect.
Each 5-s interval of each means – end period
was coded using A System for Identifying Affect
Expressions by Holistic Judgments (AFFEX),
a general scale of affect for infants and children
(Izard, Dougherty, & Hembree, 1989). Infants’
affect on this scale could be coded as interest,
happy, sad, angry, fearful, or neutral. No periods
of fearful affect were observed, so affect was
grouped into positive (interest or happy) or
negative (sad or angry)/neutral. These data were
compiled to determine the percent of time in each
period during which infants demonstrated positive or negative/neutral affect.
Means – end behavior during one means – end period.
The means – end task challenged young infants to
coordinate their visual attention and arm movements
to explore the relationship between switch activations
and distant toy activity while maintaining a positive
affect. An infant was recorded as having demonstrated means – end behavior in a period if he or she
met four criteria incorporating the three aforementioned variables: (a) infants must first actively reach to
explore, so infants were required to have an average
of greater than two total activations per minute
during the period; (b) infants should then match their
actions to the desired toy activity, so it was required
that greater than two thirds of the total activations be
toy activations during the period (E. J. Gibson, 1997);
(c) positive affect accompanies periods of learning, so
it was required that infants demonstrate positive
affect greater than two thirds of the total time during
the period (Lewis et al., 1990; Lewis, Hitchcock, &
Sullivan, 2004); and (d) as a suggestion of whether
infants were able to link their actions with the toy
activity, infants were required to look at the toy within
5 s of greater than one half of the toy activations
(Willatts, 1999). To demonstrate that the criteria
captured behavior that was unique to toy activations,
the same criteria were also applied to non-activations.
Means – end behavior during both means – end periods.
To allow for a period of exploration after the change
in the switch – toy activation relationship between
periods, only the final 2 min of the second means –
end period were analyzed in cases where means – end
behavior occurred in the first means – end period of the
visit. We analyzed toy activations as well as nonactivations to ensure that the criteria captured behavior
unique to activations resulting in toy activation. The
four means – end criteria remained the same.
Secondary Variables Related to Means – End Behavior
(Task 3)
Anticipated differences in means – end behavior
among groups could potentially be attributed to
differential development among groups. That is,
groups may not have been able to achieve the four
individual means – end behavior criteria in a similar
manner due to differential motor, perceptual, or affect
regulation abilities. We tracked the following secondary variables to determine whether any means – end
behavior differences among groups were due to more
general differences in the motor, perceptual, or affective requirements of the means – end task.
1. Numbers of infants completing the entire assessment. Differences in means – end behavior could
have been due to differential motor ability to
activate the switches. This may have resulted in
group differences in the numbers of infants
completing the entire means – end assessment.
The numbers of infants completing the entire
means – end performance assessment were
recorded for each visit.
2. Ability to turn to visually attend to the toy location.
Differences in means – end behavior could have
been due to differential motor ability to rotate
one’s head to attend to the location of the toy.
The ability to turn to visually attend to the toy
included any instance of head rotation to attend
to the toy during the means – end assessment or
to the toy’s anticipated location during the
reaching and exploration assessments. The
numbers of infants demonstrating the motor
ability to turn to visually attend to the toy
location were recorded for each visit.
3. Visual attention to the toy or switches. Differences
in means – end behavior could have been due to
differential visual – perceptual performance or
Experiences Advance Early Behaviors
object interest during the means – end task. This
may have resulted in group differences in visual
attention to the switch and toy (means and end)
and in the coordination of toy activations with
attention to the toy. The data on visual attention
to the toy or switches describe infants’ looking
behavior throughout the entire assessment, providing a broader picture of looking behavior
than solely analyzing attention to the toy at
times of switch activations. The durations infants looked at the toy during the 30-s premeans – end period and at the toy or switches
during the means – end periods at each visit
were coded, summed, and converted to a percentage of the total period time.
Statistical Analyses
Kruskall – Wallace (KW) analysis of variance
(ANOVA) was performed for most between-group
comparisons. If the resultant a was .05, KW post hoc
tests by ranks were performed. Fisher’s exact test was
performed for planned between-group comparisons
of nominal variables. For within-group comparisons
of secondary means – end performance variables,
Friedman’s ANOVAwas performed because the same
participants contributed to the data being compared.
In all statistical analyses, a .05 represents significant
results. When multiple results are presented within
the same set of parentheses, the first p value in a set
represents the three-way result and the following p
values represent the results of comparisons between
pairs of groups.
1877
appear different from control infants (Lobo et al., 2004).
This percentage was not significantly different among
groups (social experience: M 5 87.5, SD 5 11.5%;
postural experience: M 5 88.1, SD 5 5.9%; object
experience: M 5 78.2, SD 5 10.5%).
Rating on the AIMS
AIMS ratings were not significantly different
among the three groups at Visit 1, suggesting that
infants began the study with similar levels of general
motor development. Changes in AIMS ratings suggested that the postural experiences effectively
advanced motor development by advancing postural stability. This was particularly the case for
prone skills after the 3-week home experience period
compared to both other groups and at the end of the
study compared to the social experience group. The
change in total AIMS rating from Visit 1 to Visit 6 was
different among the groups and was significantly
greater for postural experience infants than for social
experience infants, v2(2, N 5 42) 5 6.27, ps 5 .04, .02,
respectively. The change in prone subscale rating
from Visit 1 to Visit 3 was different among groups
and was significantly greater for the postural experience infants than for infants in the social experience
and object experience groups, v2(2, N 5 42) 5 7.18,
ps 5 .03, .02, .03, respectively. The change in prone
subscale rating from Visit 1 to Visit 6 continued to be
different among groups with a greater change for
postural experience infants compared to social experience infants, v2(2, N 5 42) 5 7.72, ps 5 .02, .01,
respectively.
Task 1: Using Arm Movements to Reach
Results
There were no differences among groups in terms of
age, days between visits, or amount of home experience. Infants in each group received a similar number
of days of home experience (social experience: M 5
18.0, SD 5 2.7; postural experience: M 5 19.1, SD 5 1.7;
object experience: M 5 16.9, SD 5 2.1) and a similar
number of total minutes of home experience (social
experience: M 5 304.1, SD 5 146.6; postural experience: M 5 263.2, SD 5 64.9; object experience: M 5
252.5, SD 5 41.2). As mentioned, provision of home
experience was sufficient for inclusion in the study if it
occurred on more than 60% of the days between Visit 1
and Visit 3 according to journal reports from parents.
We chose this criterion based on pilot data from our
previous intervention studies in which infants who
received experiences less than 50% of the time did not
Number of Infants Reaching
A greater number of postural and object experience infants reached earlier than social experience
infants (Table 1). More object experience infants
reached than did social experience infants at Visits
3 and 4 (ps 5 .02, .01, respectively). More postural
experience infants reached than did social experience infants at Visit 3 (p 5 .03). When separating the
data from the supine and vertical positions, these
group differences were more evident in the vertical
position earlier for both the postural and the object
experience groups (Visit 2: ps 5 .08, .006, respectively; Visit 3: ps 5 .03, .01, respectively; Visit 4: p 5
.02 for object experience) than in the supine position
(Visit 3: p 5 .02 for object experience; Visit 4: p 5 .05
for postural experience; Visit 5: p 5 .002 for object
experience). The total number of infants reaching in
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Lobo and Galloway
Table 1
Total Numbers of Infants Reaching Unilaterally and Bilaterally Across
Visits for the SE, PE, and OE Groups
Visit number
Group
1
2
3
Numbers of infants reaching unilaterally
SE
0
2
3
PE
0
4
9a
OE
0
5
10a
Numbers of infants reaching bilaterally
SE
0
0
0
PE
0
1
3
OE
0
0
2
4
5
6
6
9
13a
10
12
13
13
14
14
0
4a
4a
5
11a
13a
12
11
13
Note. SE 5 social experience; PE 5 postural experience; OE 5 object
experience.
a
Signifies a difference from the SE group, p .05.
each group was greater in the vertical position than
the supine position for each group from Visits 2
through 6.
Number and Duration of Object Contacts
Postural and object experience infants contacted
the object more frequently at Visits 3 – 5 compared to
social experience infants (Figure 4a). There were
differences among groups for average number of
contacts at Visits 3, 4, and 5, Visit 3: v2(2, N 5 42) 5
8.30, p 5 .02; Visit 4: v2(2, N 5 42) 5 8.32, p 5 .02; Visit
5: v2(2, N 5 42) 5 8.39, p 5 .02. Object experience
infants contacted the object more frequently than did
social experience infants at Visits 3, 4, and 5 (ps 5 .003,
.004, and .01, respectively). Postural experience infants contacted the object more frequently than did
social experience infants at Visit 4 (p 5 .03). When
separating the data from the supine and vertical
positions, these group differences were more evident
in the supine position earlier, Visit 2: v2(2, N 5 42) 5
7.58, p 5 .02; Visit 3: v2(2, N 5 42) 5 10.15, p 5 .01; Visit
5: v2(2, N 5 42) 5 13.34, p 5 .001, than in the vertical
position, Visit 4: v2(2, N 5 42) 5 9.84, p 5 .01. Yet, the
average number of contacts in each group was greater
in the vertical position for every group from Visits 2
through 6.
Postural and object experience infants contacted
the object for longer durations at Visits 2 – 4 compared
to social experience infants (Figure 4b). There were
differences among groups for duration per contact at
Visits 2, 3, 4, and 6, Visit 2: v2(2, N 5 370) 5 23.47, p 5
.000; Visit 3: v2(2, N 5 777) 5 21.99, p 5 .000; Visit 4:
v2(2, N 5 1169) 5 20.58, p 5 .000; Visit 6: v2(2, N 5
3042) 5 13.54, p 5 .001. Object experience infants
contacted the object longer than did social experience
infants at Visits 2 and 4 (ps 5 .002, .000, respectively).
Object experience infants contacted the object longer
than did postural experience infants at Visits 4 and 6
(ps 5 .05, .001, respectively). Postural experience
infants contacted the object longer than did social
experience infants at Visits 2, 3, and 4 (ps 5 .000, .002,
.001, respectively). Postural experience infants contacted the object longer than did object experience
infants at Visits 2 and 3 (ps 5 .01, .000, respectively).
Social experience infants contacted the object longer
than did the postural experience infants at Visit 6 (p 5
.002). When separating the data from the supine and
vertical positions, these group differences were more
evident earlier in the vertical position, Visit 2: v2(2,
N 5 27) 5 31.93, p 5 .000; Visit 3: v2(2, N 5 467) 5
15.81, p 5 .000; Visit 4: v2(2, N 5 906) 5 18.27, p 5 .000,
than in the supine position, Visit 3: v2(2, N 5 467) 5
15.81, p 5 .000. The average duration of contact in
each group was similar in both positions for every
group for the early visits but was longer in supine for
the final visit.
Number of Infants Reaching Bilaterally and Percent
Bilateral Contact Time
A greater number of postural and object experience infants reached bilaterally earlier than social
experience infants (Table 1). More postural and
object experience infants had bilateral object contacts
than did social experience infants at Visits 4 and 5
(Visit 4: ps 5 .05, .05, respectively; Visit 5: ps 5 .03,
.002, respectively). When separating the data from
the supine and vertical positions, these group differences were more evident in the vertical position
earlier for both the postural and object experience
groups (Visit 4: ps 5 .04, .006, respectively; Visit 5: p 5
.02 for object experience) than in the supine position
(Visit 5: p 5 .05 for both groups). The total number of
infants reaching bilaterally in each group was
greater in the vertical position for every group from
Visits 2 through 6.
Postural and object experience infants spent
more time bilaterally contacting the object at Visits
4 and 5 (Figure 4c). There were differences among
groups at Visits 4 and 5 in terms of the percent time
infants were bilaterally contacting the object, Visit
4: v2(2, N 5 42) 5 10.24, p 5 .01; Visit 5: v2(2, N 5
42) 5 7.64, p 5 .02. Both postural and object
experience infants spent more time bilaterally contacting the object than did social experience infants
at these visits (Visit 4: ps 5 .04, .001, respectively;
Visit 5: ps 5 .05, .002, respectively). When separating the data from the supine and vertical positions,
Experiences Advance Early Behaviors
1879
Figure 4. (a) Mean numbers of object contacts across visits for each group. (b) Mean durations per contact across visits for each group. (c)
Mean percent times infants spent bilaterally contacting the object across visits for each group. (d) Mean percent times infants fingered or
mouthed the exploration objects.
Note. Error bars reflect standard error of the mean.
a
Signifies a difference from the social experience group. bSignifies a difference from the postural experience group. cSignifies a difference
from the object experience group.
*Signifies a difference from the social experience group, p .05.
these group differences were more evident in the
vertical position earlier, Visit 4: v2(2, N 5 42) 5 9.60, p
5 .01; Visit 5: v2(2, N 5 42) 5 6.08, p 5 .05, than in the
supine position, Visit 5: v2(2, N 5 42) 5 8.97, p 5 .01.
The average percent time spent bilaterally contacting
the object in each group was greater in the vertical
position for every group from Visits 2 through 6.
exploring across the study, but at Visit 5, the postural
and object experience groups spent more time fingering and mouthing the exploration objects than did the
social experience group, v2(2, N 5 42) 5 8.20, ps 5 .02,
.01, .04, respectively. By the end of the study, infants in
all groups were fingering and mouthing the exploration objects similarly.
Task 2: Using Arm Movements to Explore Objects
Task 3: Using Arm Movements to Explore a
Means – End Task
Postural and object experience infants spent more
time haptically exploring objects at Visit 5 than did
social experience infants (Figure 4d). Infants in all
groups increased the time they spent haptically
First, we report how each group performed during
both means – end periods of a visit as well as the total
number of periods in which infants displayed
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means – end behavior. We then report results from the
secondary means – end variables.
Means – End Behavior During Both Means – End Periods
of a Visit
Object experience infants demonstrated the best
means – end behavior as evidenced by means – end
behavior during both means – end periods of a visit.
Table 2 shows the numbers of infants in each group
demonstrating means – end behavior during both
periods of the visit.
At Visit 6, more infants in the object experience
group demonstrated means – end behavior during
both periods of the visit than did infants in the social
and postural experience groups (p 5 .049 for both
comparisons). The object experience group also had
the greatest total number of infants showing means –
end behavior during both periods of a visit compared
to the social experience group (p 5 .02). This means –
end behavior was unique to toy activations. No infants
in any group ever met the means – end behavior criteria
for nonactivations during both periods of a visit.
Number of Periods With Means – End Behavior
Satisfying the means – end behavior criteria during
just one means – end period of a visit does not
demonstrate true means – end behavior. However, it
does demonstrate emerging means – end behavior
because this ability must be present in order for
infants to show means – end behavior in both periods.
Both the object and postural experience groups displayed more individual periods of means – end
behavior than the social experience group. Specifically, the object and postural experience groups had
greater numbers of total periods of means – end
performance than the social experience group, v2(2,
N 5 42) 5 6.31, ps 5 .04, .02, .04, respectively. Object
experience infants had 24 and postural experience
Table 2
Numbers of Infants Demonstrating Means – End Behavior During Both
Means – End Periods of a Visit Across Visits and in Total for the SE, PE,
and OE Groups
Group
SE
PE
OE
Visit 1
Visit 2
Visit 3
Visit 4
Visit 5
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
Visit 6
0
0
4a,b
Total
0
1
5a
Note. SE 5 social experience; PE 5 postural experience; OE 5 object
experience.
a
Signifies a difference from the SE group, p .05. bSignifies
a difference from the PE group, p .05.
infants had 21 periods of means – end behavior,
whereas social experience infants had only 12 periods
across all visits.
The total numbers of periods where infants met
these criteria for nonactivations were significantly
lower for all groups (social experience, 1 period;
postural experience, 2 periods; object experience, 0 periods) than were the number of periods where infants
met these criteria for toy activations, social experience:
v2(1, N 5 28) 5 11.63, p 5 .001; postural experience:
v2(1, N 5 28) 5 16.82, p 5 .000; object experience: v2(1,
N 5 28) 5 20.96, p 5 .000, and were not different among
groups. This suggests that the performance criteria
captured behaviors unique to exploration of the
switch – toy means – end relationship.
Results for Secondary Variables Related to Means – End
Behavior
This means – end task required the coordination of
motor, perceptual, and affective aspects of behavior.
Results from secondary measures help to rule out
whether the means – end behavior results simply
reflect group differences in these requirements. Ruling out these general differences would provide
further support that means – end behavior differences
resulted from varying abilities of the infants in each
group to coordinate these abilities to perform a
challenging task.
Motor requirements for the means – end task. Group
differences in means – end behavior were not explained by differences in motor ability. Infants in each
group developed the motor requirements for the
means – end performance task similarly. Motor requirements for the task involved the ability to (a)
activate the switches using arm movement and (b)
turn to the side to view the toy using head movement.
1. Switch activation: Each group activated the
switches enough to have similar opportunities
to display means – end behavior. Specifically,
there were no significant differences among
groups in the number of infants meeting the
switch activation criterion more than five switch
activations in the first 2 min of the first means –
end period) and subsequently completing the
entire assessment at each visit. At least two thirds
of infants in each group completed the entire
assessment by Visit 3, and all infants did so by
Visit 6.
In addition, each group activated the switches
a similar number of times at each visit. Specifically,
there were no significant differences among groups
Experiences Advance Early Behaviors
for the number of toy activations or nonactivations
except at Visit 4. Postural and object experience
infants had more toy activations and nonactivations
at Visit 4 than did social experience infants, toy
activations: v2(1, N 5 28) 5 7.45, ps 5 .02, .01, .05,
respectively; nonactivations: v2(1, N 5 28) 5 8.86, ps 5
.01, .01, .02, respectively.
2. Head turning to visually attend to the toy: Each
group had the ability to turn their head to the
side where the toy was located at each visit.
There were no significant differences among
groups in the numbers of infants who turned
their heads toward the toy location. The majority of infants in each group demonstrated this
ability at Visit 1, and all infants in each group
demonstrated this ability by Visit 3.
Perceptual requirements for the means – end
task. Group differences in means – end behavior were
not due to general differences in visual – perceptual
ability, although there were some differences among
groups. That is, infants in each group developed the
perceptual requirements for the means – end task
similarly. These requirements were the ability to
visually attend to (a) the toy during the pre-means –
end period and (b) the toy or switches during the
means – end periods.
Each group increased its visual attention to the toy
during the pre-means – end period across visits. Each
group had similar ability and interest to maintain
attention to the toy during the pre-means – end period
at each visit except at Visit 6. At Visit 6, the groups
were different with object experience infants attending more to the toy than infants in the postural
experience group, v2(2, N 5 42) 5 5.79, ps 5 .05, .02,
respectively.
Each group increased its visual attention to the toy
and switches during the means – end periods across
visits. Each group had similar ability and interest to
maintain attention to the toy or switches during the
means – end periods at each visit except at Visit 6. At
Visit 6, the groups were different and the object
experience group spent more time looking at the toy
than did the social and postural experience groups,
v2(2, N 5 42) 5 7.70, ps 5 .02, .01, .04, respectively.
It was expected that once infants understood the
switch – toy relationship, they would spend increased
time looking at the toy, a focal point of the means – end
behavior (Willatts, 1999). Therefore, we wanted to
analyze not only how much each group attended to
the toy compared to the other groups but also how
much time within each group involved looking at the
toy versus the switches at each visit. The social and
1881
postural experience groups spent more time looking
at the switches than the toy at every visit (Figure 5a),
Visit 2: social experience v2(1, N 5 14) 5 10.00, p 5
.002, postural experience v2(1, N 5 14) 5 9.31, p 5 .002;
Visit 3: social experience v2(1, N 5 14) 5 6.23, p 5 .01,
postural experience v2(1, N 5 14) 5 9.31, p 5 .002; Visit 4:
social experience v2(1, N 5 14) 5 13.00, p 5 .000,
postural experience v2(1, N 5 14) 5 14.00, p 5 .000;
Visit 5: social experience and postural experience v2(1,
N 5 14) 5 14.00, p 5 .000; Visit 6: social experience
v2(1, N 5 14) 5 10.29, p 5 .001, postural experience
v2(1, N 5 14) 5 14.00, p 5 .000. Infants in the object
experience group showed this same pattern of looking until Visit 6, the visit where they demonstrated the
greatest means – end performance, when they visually attended to the switches and the toy the same
amount of time, v2(1, N 5 14) 5 10.29, p 5 .001 for
Visits 1 – 5.
Affect requirement for the means – end task. Group
differences in means – end behavior were not explained by general differences in ability to regulate
affect across visits. Each group met the means – end
behavior affect requirement of maintaining a positive
affect more than two thirds of the time in a period for
the final three to four visits. Each group increased the
time it maintained a positive affect across visits, and
the duration of positive affect was not different
among groups at each visit. Each group demonstrated
more positive than negative/neutral affect from Visits
4 to 6 (Figure 5b), Visit 4: social experience, postural
experience, and object experience v2(1, N 5 14) 5 7.14,
p 5 .008; Visit 5: social experience v2(1, N 5 14) 5 4.57,
p 5 .03, postural experience and object experience
v2(1, N 5 14) 5 10.29, p 5 .001; Visit 6: social
experience and postural experience v2(1, N 5 14) 5
10.29, p 5 .001, object experience v2(1, N 5 14) 5 14.00,
p 5 .000.
Motor – perceptual coupling requirement for the
means – end task. Group differences in means – end
behavior were explained, in part, by differences in
motor – perceptual coupling abilities. Specifically,
groups differed in their ability to meet the motor –
perceptual coupling requirement of accompanying
toy activations with visual attention to the toy.
The postural and object experience groups
demonstrated selective motor – perceptual coupling
behavior earlier than the social experience group.
Groups did not differ in the percentage of toy activations accompanied by attention to the toy at each visit.
However, true means – end behavior requires that
infants do not simply randomly attend to the toy with
any switch activation but rather that they selectively
attend to the toy more often with toy activations
than with nonactivations. We term this selective
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Lobo and Galloway
Figure 5. (a) Mean percent times each group attended to the toy or switches during the means – end periods across visits. (b) Mean percent
times each group demonstrated positive or negative/neutral affect during the means – end periods across visits. (c) Mean percentages of toy
activations and nonactivations for each group accompanied by attention to the toy during the means – end periods across visits.
Note. In Figure 5(a), note that the groups looked more at the switches except at Visit 6 when the object experience group looked similar
amounts at the toy and switches. In Figure 5(b), note that each group increased positive affect and decreased negative/neutral affect over time
without differences among groups. In Figure 5(c), note that the postural and object experience groups showed earlier selectivity of their
motor – perceptual coupling than did the social experience group, attending to the toy more with toy activations than with nonactivations.
Error bars reflect standard error of the mean.
*p .05.
Experiences Advance Early Behaviors
motor – perceptual coupling. Indeed, group differences
in this selective coupling emerged with greater attention to the toy with toy activations for postural
experience infants by Visit 3 (Figure 5c), Visit 3: v2(1,
N 5 14) 5 7.00, p 5 .01; Visits 4 and 5: v2(1, N 5 14) 5
8.33, p 5 .004; Visit 6: v2(1, N 5 14) 5 14.00, p 5 .000,
for object experience infants by Visit 4, Visit 4:
v2(1, N 5 14) 5 8.33, p 5 .004; Visit 5: v2(1, N 5 14) 5
9.308, p 5 .002; Visit 6: v2(1, N 5 14) 5 14.00, p 5 .00,
and for social experience infants by Visit 5, Visit 5:
v2(1, N 5 14) 5 10.00, p 5 .002; Visit 6: v2(1, N 5 14) 5
7.14, p 5 .008. In effect, the postural and object
experience groups attended more often to the toy
selectively with toy activations earlier than did the
social experience group. This suggests that they had an
earlier association between their actions on the
switches and the activity of the toy.
Discussion
Summary of the Results
Postural and object experience infants had
advanced reaching, exploration, and developing
means – end behavior compared to social experience
infants (Figure 6). Most of the group differences were
observed after the 3-week prescribed home experience period ended at Visit 3. Differential ability to
reach for and contact objects was the only change
observed during the 3-week home experience period.
Differences in reaching ability continued, and differences in object exploration and means – end behavior
emerged weeks to months after the home experience
period ended. Therefore, infants who had similar
1883
abilities at the first visit embarked on different developmental trajectories even after their prescribed
home experience period ended. Specifically, postural
and object experience infants had more frequent
object contacts at Visits 2 – 5, longer contact durations
at Visits 2 – 4, more bilateral contact time at Visits 4
and 5, more haptic object exploration at Visit 5, and
greater numbers of periods of developing means –
end behavior primarily at Visits 5 and 6 compared to
social experience infants. The object experience group
had the greatest number of infants demonstrating
means – end behavior in both periods at Visit 6.
Task 1: Postural and Object Experience Infants Had
Advanced Reaching Emergence and Ability
Postural and object experience infants had earlier
onsets for reaching and advanced reaching ability
compared to social experience infants. The differences
in reaching ability among the three groups suggest
that the emergence of reaching is dependent on
multiple interacting subsystems and can be similarly
advanced by experiences that affect a variety of these
subsystems (Bertenthal & von Hofsten, 1998; Hopkins
& Ronnqvist, 2002; Thelen, 1990; Thelen et al., 1993;
von Hofsten, 1993). This supports and extends our
previous work showing that the emergence of reaching can also be advanced via experiences to increase
arm flapping (Lobo et al., 2004).
This study is the first to demonstrate that reaching
emergence can be advanced by the provision of
advanced postural experiences. This builds on previous work showing that experience being placed in
different postures, such as sitting or standing, can
Figure 6. Effects of postural and object-oriented experiences on reaching, exploration, and means – end behavior represented by effect size, r.
Note. A value of zero indicates no difference in behavior from the social experience group.
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Lobo and Galloway
directly advance infants’ abilities to maintain these
postures (Bril & Sabatier, 1986; Hopkins & Westra,
1988, 1989, 1990; Zelazo et al., 1993). This work was
unique, however, in that the goal of the experiences
was to directly advance postural stability, whereas
our focus was whether this would then advance the
unpracticed behavior of reaching.
To understand how postural experiences led to the
emergence of reaching, we must consider factors both
internal and external to the infants. Parents of postural experience infants were asked to provide infants
with opportunities to improve their postural stability
by placing and moving them in a variety of postures.
This occurred during the supine, spontaneous, and
social period when infants spend much of their time
supine (Davis et al., 1998; Mildred et al., 1995). Ratings
on the AIMS suggest that postural experience advanced
infants’ postural stability across postures. Postural experience infants likely had improved head and trunk
strength and control for visual exploration and reaching, more appropriate muscle responses to maintain
balance, and increased perceptual – motor experiences
in a variety of positions (Bril & Sabatier, 1986; Thelen &
Spencer, 1998; Wijnroks & van Veldhoven, 2003;
Witherington et al., 2002). In addition, we suspect that
as parents observed their infants’ abilities to maintain
different postures and to begin to reach for objects,
they likely switched their parent – infant – object interactions to ‘‘postures, purpose, and play’’ earlier
than typically reported (Fogel, 1997; Fogel et al., 1999;
Reed & Bril, 1996). This switch was likely influenced
by the effects of the postural experiences but was not
assigned as part of the prescribed experiences. As
a result, postural experience infants likely had early,
increased opportunities to improve their postural
stability across positions and to interact with objects
throughout each day (Bertenthal & von Hofsten, 1998;
Eppler, 1995). It is likely that such changes within
infants combined with changes in parent handling
and interaction to advance reaching ability in infants
provided with postural experiences.
To understand how object-oriented experiences led
to the emergence of reaching, we must again consider
factors both internal and external to the infants.
Parents of object experience infants were asked to
provide their infants with opportunities and assistance to reach for and explore objects (Fogel, 1997;
Fogel et al., 1999; Lobo et al., 2004). This occurred
during the supine, spontaneous, and social period
when parents primarily interact with infants face-toface with little active object exploration (Fogel et al.,
1999). Object experience infants likely had improved
movement control in a midline task space, motivation
to reach for objects presented, and knowledge that
objects presented within reach afford haptic exploration. In addition, as parents observed their infants’
abilities to reach for, grasp, and mouth objects, they
likely switched their parent – infant – object interactions to ‘‘purpose and play’’ earlier than typical
(Fogel, 1997; Fogel et al., 1999; Reed & Bril, 1996).
Consequently, object experience infants likely had
increased opportunities to interact with objects on
a daily basis even outside of the prescribed home
experience periods (Bakeman et al., 1990; Bruner,
1972). The home experience for these infants was
provided in supine, and these infants did not advance
in their postural stability according to AIMS ratings as
did postural experience infants. In fact, their changes
in total and subscale AIMS scores were not different
from social experience infants. This suggests that
parents of object experience infants did not provide
infants the same advanced opportunities to improve
their postural stability across positions as did parents
of postural experience infants.
Social experience infants did not have advanced
reaching ability. By Visit 6, however, their reaching
abilities were similar to infants in the two advanced
experience groups. The experiences parents of these
infants provided involved face-to-face interactions in
supine, the type of interaction most common during
the supine, spontaneous, and social period (Davis
et al., 1998; Fogel et al., 1999; Mildred et al., 1995).
Therefore, it was expected that reaching development
in these infants would mirror typical development. In
fact, social experience infants began reaching at an
average of 18.25 6 1.81 weeks of age, which is within
the 4- to 5-month-old period typically reported
(Thelen et al., 1993; von Hofsten, 1991). Consequently,
social experience infants likely did not transition to
postures, purpose, and play and have increased
opportunities to interact with objects on a daily basis
until after their onset of reaching at Visit 5 (Eppler,
1995; Fogel, 1997; von Hofsten, 1997).
More infants were able to contact the object more
frequently with one hand as well as bilaterally earlier
and throughout the study in the vertical position
compared to supine. The average duration per contact
was not different between the vertical and supine
positions throughout the study but was greater in the
supine position by the end of the study. These data
support the proposal that it is easier for young infants
to initiate reaches but more difficult to sustain contact
with objects in a vertical position (Carvalho et al.,
2007; Savelsbergh & van der Kamp, 1994). In supine,
infants may find it more challenging to initiate
reaches but easier to sustain contacts with objects
due to the effects of gravity on the arm’s biomechanics. When the hand is farther away from the center of
Experiences Advance Early Behaviors
mass, infants must produce more muscle force to
overcome gravitational force. This is the case when
reaches are initiated in supine with the hands resting
laterally on the floor and in trying to sustain contacts
in vertical with the hands held in front of the trunk.
In this study, two distinct experiences advanced
reaching ability. These results support the idea that
even the earliest behaviors emerge as the result of
a dynamic process involving the coordination of
multiple interacting subsystems encompassing task,
environmental, and organismic factors (Bertenthal &
von Hofsten, 1998; Corbetta & Bojczyk, 2002; Hopkins
& Ronnqvist, 2002; Joh & Adolph, 2006; Lee, Liu, &
Newell, 2006; Thelen, 1990; Thelen et al., 1993; von
Hofsten, 1993). Acceleration of the development of
one or more of these subsystems can advance the
ontogeny of early object interaction behavior (Lobo
et al., 2004). For this study, we suspect that advancing
parent – infant – object interactions, head and trunk
control, postural stability, and/or perceptual – motor
experiences across positions may have advanced
reaching development.
Task 2: Postural and Object Experience Infants Had
Advanced Haptic Exploration of Objects
Postural and object experience infants demonstrated advanced haptic exploration of objects compared to social experience infants. These results
suggest that haptic exploration of objects is dependent on infants’ past experiences, the emergence of
reaching, as well as ongoing daily parent – infant –
object interactions (Berthier, Rosenstein, & Barto,
2005; Bourgeois et al., 2005; J. J. Gibson, 1962, 1966;
Millar, 2005; Needham, 2000; Needham et al., 2002).
This is the first study presenting empirical evidence
for a link between the onset of reaching and later
haptic object exploration across developmental time.
It is important to note that increased haptic exploration of objects did not occur until the weeks after reach
onset in all groups. These results are particularly
interesting given that at the start of the study, infants
already demonstrated the ability to bring their hands
to their mouths for mouthing and to one another for
fingering of the objects attached to their wrists (Rochat, 1989).
What might young infants learn from haptic exploration of objects? First, information processing via
haptic exploration provides infants with knowledge
about properties of objects, such as hardness, texture,
and shape, which cannot be accurately detected by
vision alone (Ballesteros et al., 1997; Carello, Grosofsky,
Reichel, Solomon, & Turvey, 1989; Case-Smith et al.,
1998; Turvey, 1996). This knowledge base allows older
1885
infants to discriminate and categorize objects of
varying characteristics (Booth, 2006; Bourgeois et al.,
2005; Ellis & Oakes, 2006; Palmer, 1989; Ruff, 1984).
Yet, infants have weeks to months of experience
haptically exploring objects before this discrimination
ability emerges (Case-Smith et al., 1998; Rochat, 1989).
Besides knowledge about physical properties of objects, what could infants be learning from these early
exploration experiences?
Even before infants are able to discriminate physical properties of objects, it has been proposed that
they are able to learn what actions those objects afford
(E. J. Gibson, 2000). The fact that infants did not use
their available movements to explore the Velcroed
objects until after the onset of reaching suggests that
haptic exploration of objects may in itself be a global
affordance that young infants must learn (Bourgeois
et al., 2005; J. J. Gibson, 1962, 1966; Millar, 2005;
Needham, 2000; Needham et al., 2002). Infants at each
visit were shown the exploration objects before trials
began, but they disregarded the objects at early visits
before they were consistently reaching. For instance,
most infants spent less than 10% of the time exploring
objects haptically across the first few visits, whereas at
the final visit, most infants spent about 40% of the
time exploring objects haptically (Figure 4d). Object
exploration in this paradigm did not require grasping
as objects were Velcroed to infants’ wrists. It was as if
prereaching infants did not yet realize that they could
use their existing arm movements to haptically
explore objects. We propose that as young infants
begin to reach for, grasp, and transport objects, they
learn to match these new action abilities to objects to
learn that objects of certain sizes and shapes afford
mouthing and fingering (Case-Smith et al., 1998; E. J.
Gibson, 2000; Millar, 2005). Then, via early, frequent,
active haptic exploration of a range of objects, infants
learn more about how to adapt and refine their actions
to more specifically match the various properties of
objects (Adolph et al., 2000; Ballesteros et al., 1997;
Bourgeois et al., 2005; Needham et al., 2006). For
instance, infants may later learn that in addition to
mouthing and fingering, objects such as rattles and
spoons afford sound production and food transport.
In effect, learning that some objects can be explored
haptically may be the first step in the process of
gaining object knowledge required for future object
categorization and discrimination.
Task 3: Object and Postural Experience Infants Had
Advanced Means – End Behavior
Object experience infants had the most sophisticated means – end behavior, evidenced by means – end
1886
Lobo and Galloway
behavior during both periods of a visit. Postural experience infants had better developing means – end
behavior than social experience infants, evidenced
by a greater number of periods of means – end behavior. These results suggest that the developmental
origins of means – end behavior may lie in the ongoing motor, perceptual, and cognitive experiences
associated with early reaching and object exploration
(Bremner, 2000; E. J. Gibson & Pick, 2000; Menard,
2005; Piaget, 1952, 1954; von Helmholtz, 1962). These
results highlight the critical role action performance
on objects plays in the development of means – end
behavior and expand the view that early knowledge
development relies primarily on perceptual and cognitive changes (Baillargeon, 1987; Johnson, Slemmer,
& Amso, 2004).
Our results suggest that means – end behavior
emerges after infants are able to coordinate their
motor, perceptual, and affect regulation abilities.
Specifically, there were no differences in the individual motor, perceptual, or affect regulation abilities
among groups that can fully account for the results.
This supports Willatts’s (1999) idea that intentional
means – end behavior involves the coordination of
multiple variables. In our task, infants had to display
a greater frequency of toy activations in coordination
with looking to the toy while maintaining a positive
affect (Lewis et al., 1990; Munakata et al., 2002; Willatts, 1999). Infants’ abilities to coordinate these emerging abilities across domains to perform in a novel task
are a hallmark of means – end behavior.
Our results support the idea that means – end
knowledge is gained in part via active exploration of
objects (Bremner, 2000; Piaget, 1952). E. J. Gibson
(1997) suggested that infants learn by first performing
exploratory activity, then observing the consequences
of this activity, and finally selecting from the activities
explored. She viewed trial-and-error experience as
essential to learning. This type of activity is exactly
what infants were required to do to explore the
means – end relationship within our paradigm. To
learn, infants were required to explore the switches
via reaching, observe that movement of one switch
resulted in distant toy activity, and then repeatedly
select the behavior that resulted in that toy activity by
activating that switch more frequently than the other.
Our results provide the first empirical support for
the idea that the emergence of means – end behavior is
in part dependent on the amount of previous object
exploration. Object experience infants had increased
opportunities to explore objects from Visit 1, and they
demonstrated the most sophisticated means – end
behavior. Postural experience infants began reaching
and likely had increased opportunities to explore
objects from Visit 3 and had more advanced developing means – end behavior than social experience infants. Social experience infants began reaching and
likely had increased opportunities to explore objects
late in the study from Visit 5 and had the poorest
means – end behavior.
The results of this study provide important data on
the developmental origins of the means – end behavior so often observed in older infants (Bojczyk &
Corbetta, 2004; Goubet, Rochat, Maire-Leblond, &
Poss, 2006; Munakata et al., 2002). Using a means –
end task such as the one presented here that calls on
infants to coordinate abilities they already possess
to demonstrate that means – end knowledge may
help avoid the performance competency issue encountered by other behavioral means – end studies
(Bremner, 2000; Matthews, Ellis, & Nelson, 1996).
Means – end paradigms such as ours that capitalize
on infants’ existing behaviors may help researchers
avoid the challenge of comparing violation of expectancy paradigms with behavioral paradigms (Bremner,
2000; Hood, 2001; Munakata et al., 2002; Shinskey,
Bogartz, & Poirier, 2000; Sommerville & Woodward,
2005). Future studies can build upon these results to
tests for developmental connections between early associative learning and memory paradigms such as Rovee
and Rovee’s (1969) mobile paradigm and later assessments of object exploration and means – end behavior.
Implications for Developmental Theory and Intervention
The developmental relationships among the three
behaviors investigated in this study and the ways the
prescribed experiences affected these behaviors support theories of development proposing actions as the
foundation for perceptual and cognitive development
(Bremner, 2000; E. J. Gibson, 2000; J. J. Gibson, 1979;
Piaget, 1952; von Helmholtz, 1962). Our results also
have implications for intervention for infants with
developmental delay. First, the results support the
premise that early intervention can advance the
emergence of a behavior (Heathcock et al., 2008; Lobo
et al., 2004; Ulrich, Ulrich, Angulo-Kinzler, & Yun,
2001; van Beek, Hopkins, Hoeksma, & Samsom, 1994).
Postural and object experiences provided to infants
with special needs may be able to advance reaching
(Heathcock et al., 2008), just as experience walking
supported on a treadmill can advance the emergence
of walking in infants with Down syndrome (Ulrich
et al., 2001). Although therapeutic interventions often
begin in early infancy and frequently rely on techniques attempting to advance postural stability or object
interaction, we are not aware of any prospective
studies directly relating such controlled movement
Experiences Advance Early Behaviors
interventions to advanced behavioral outcomes in
infants less than 6 months of age. Second, providing
early experiences for one skill may advance development of a range of motor, perceptual, and cognitive
abilities (Hack & Taylor, 2000; van Beek et al., 1994).
Perhaps similar advancements across developmental
domains could be achieved by advancing other early
behaviors. For instance, language development may
be advanced via experiences to advance early object
banging or gesturing (Iverson & Fagan, 2004; Iverson
& Goldin-Meadow, 2005) or later problem-solving
ability could be advanced via experiences to broaden
the ranges of exploratory behaviors young infants
perform on various objects (Caruso, 1993). Although
most therapists would agree that skill attainment
generally advances development across domains,
there is little empirical support for this idea in early
infancy (Needham, 2000).
In summary, the behavior of infants in this study
provides empirical support that (a) the development
of novel behaviors is dependent on multiple subsystems and can be similarly advanced by addressing
a variety of these subsystems (Bertenthal & von
Hofsten, 1998; Hopkins & Ronnqvist, 2002; Thelen,
1990; von Hofsten, 1993); (b) reaching ability can be
indirectly advanced via activities to improve postural
stability; (c) parent – infant interactions play a critical
role in early development and can be altered to
advance development (Bakeman et al., 1990; Bruner,
1972; Cintas, 1995; Landry & Chapieski, 1988); (d)
reaching, object exploration, and means – end behavior are developmentally related behaviors that can all
be advanced via experiences aimed at advancing
reaching; and (e) past experiences with active object
exploration can facilitate early information processing and the development of early knowledge
(Ballesteros et al., 1997; Bremner, 2000; E. J. Gibson &
Pick, 2000; Needham, 2000).
References
Adolph, K. E., Eppler, M. A., Marin, L., Weise, I. B., &
Wechsler-Clearfield, M. (2000). Exploration in the service
of prospective control. Infant Behavior & Development, 23,
441 – 460.
Adolph, K. E., Vereijken, B., & Denny, M. A. (1998).
Learning to crawl. Child Development, 69, 1299 – 1312.
Amiel-Tison, C. (1985). Pediatric contribution to the present knowledge on the neurobehavioral status of infants
at birth. In J. M. R. Fox (Ed.), Neonatal cognition: Beyond
the blooming buzzing confusion (pp. 365 – 380). Hillsdale,
NJ: Erlbaum.
Angulo-Kinzler, R. M., & Horn, C. L. (2001). Selection
and memory of a lower limb motor-perceptual task in
1887
3-month-old infants. Infant Behavior & Development, 24,
239 – 257.
Baillargeon, R. (1987). Object permanence in 3½- and 4½month-old infants. Developmental Psychology, 23, 655 – 664.
Bakeman, R., Adamson, L. B., Konner, M., & Barr, R. G.
(1990). Kung infancy: The social context of object exploration. Child Development, 61, 794 – 809.
Ballesteros, S., Manga, D., & Reales, J. M. (1997). Haptic
discrimination of bilateral symmetry in 2-dimensional
and 3-dimensional unfamiliar displays. Perception &
Psychophysics, 59, 37 – 50.
Bertenthal, B., & von Hofsten, C. (1998). Eye, head and
trunk control: The foundation for manual development.
Neuroscience and Biobehavioral Reviews, 22, 515 – 520.
Berthier, N. E., Rosenstein, M. T., & Barto, A. G. (2005).
Approximate optimal control as a model for motor
learning. Psychological Review, 112, 329 – 346.
Bhat, A. N., & Galloway, J. C. (2006). Toy-oriented changes
during early arm movements: Hand kinematics. Infant
Behavior & Development, 29, 358 – 372.
Bhat, A., Heathcock, J., & Galloway, J. C. (2005). Toyoriented changes in hand and joint kinematics during
the emergence of purposeful reaching. Infant Behavior &
Development, 28, 445 – 464.
Bojczyk, K. E., & Corbetta, D. (2004). Object retrieval in the
1st year of life: Learning effects of task exposure and box
transparency. Developmental Psychology, 40, 54 – 66.
Booth, A. E. (2006). Object function and categorization in
infancy: Two mechanisms of facilitation. Infancy, 10,
145 – 169.
Bourgeois, K. S., Khawar, A. W., Neal, S. A., & Lockman,
J. J. (2005). Infant manual exploration of objects, surfaces,
and their interrelations. Infancy, 8, 233 – 252.
Bremner, J. G. (2000). Developmental relationships
between perception and action in infancy. Infant Behavior
& Development, 23, 567 – 582.
Bril, B., & Sabatier C. (1986). The cultural context of motor
development: Postural manipulations in the daily life of
Bambara babies (Mali). International Journal of Behavioral
Development, 9, 439 – 453.
Bruner, J. (1972). The nature and uses of immaturity.
American Psychologist, 27, 687 – 708.
Campos, J. J., Anderson, D. I., Barbu-Roth, M. A., Hubbard,
E. M., Hertenstein, M. J., & Witherington, D. (2000).
Travel broadens the mind. Infancy, 1, 149 – 219.
Carello, C., Grosofsky, A., Reichel, F. D., Solomon, H. Y., &
Turvey, M. T. (1989). Visually perceiving what is reachable. Ecological Psychology, 1, 27 – 54.
Caruso, D. A. (1993). Dimensions of quality in infants‘
exploratory behavior: Relationships to problem-solving
ability. Infant Behavior & Development, 16, 441 – 454.
Carvalho, R. P., Tudella, E., & Savelsbergh, G. J. P. (2007).
Spatio-temporal parameters in infant’s reaching movements are influenced by body orientation. Infant Behavior
& Development, 30, 26 – 35.
Case-Smith, J., Bigsby, R., & Clutter, J. (1998). Perceptualmotor coupling in the development of grasp. American
Journal of Occupational Therapy, 52, 102 – 110.
1888
Lobo and Galloway
Cintas, H. (1995). Cross-cultural similarities and differences in development and the impact of parental expectations on motor behavior. Pediatric Physical Therapy, 7,
103 – 111.
Corbetta, D., & Bojczyk, K. E. (2002). Infants return to twohanded reaching when they are learning to walk. Journal
of Motor Behavior, 34, 83 – 95.
Corbetta, D., Thelen, E., & Johnson, K. (2000). Motor
constraints on the development of perception-action
matching in infant reaching. Infant Behavior & Development,
23, 351 – 374.
Davis, B. E., Moon, R. Y., Sachs, H. C., & Ottolini, M. C.
(1998). Effects of sleep position on infant motor development. Pediatrics, 102, 1135 – 1140.
Ellis, A. E., & Oakes, L. M. (2006). Infants flexibly use
different dimensions to categorize objects. Developmental
Psychology, 42, 1000 – 1011.
Eppler, M. A. (1995). Development of manipulatory skills
and the deployment of attention. Infant Behavior &
Development, 18, 391 – 405.
Fagard, J. (2000). Linked proximal and distal changes in
the reaching behavior of 5- to 12-month-old human
infants grasping objects of different sizes. Infant Behavior
& Development, 23, 317 – 329.
Fallang, B., Saugstad, O. D., & Hadders-Algra, M. (2000).
Goal directed reaching and postural control in supine
position in healthy infants. Behavioural Brain Research,
115, 9 – 18.
Fogel, A. (1997). Information, creativity, and culture. In
C. D.-R. P. Zukow-Goldring (Ed.), Evolving explanations
of development. Washington, DC: American Psychological
Association.
Fogel, A., Messinger, D. S., Dickson, K. L., & Hsu, H.
(1999). Posture and gaze in early mother-infant communication: Synchronization of developmental trajectories.
Developmental Science, 2, 325 – 332.
Fontaine, R., & le Bonniec, G. P. (1988). Postural evolution
and integration of the prehensile gesture in children
aged 4 to 10 months. British Journal of Developmental
Psychology, 6, 223 – 233.
Funk, M. S. (2002). Problem solving skills in young yellowcrowned parakeets (cyanoramphus auriceps). Animal
Cognition, 5, 167 – 176.
Gibson, E. J. (1988). Exploratory behavior in the development of perceiving, acting, and the acquiring of knowledge. Annual Review of Psychology, 39, 1 – 41.
Gibson, E. J. (1997). An ecological psychologist’s prolegomena for perceptual development: A functional
approach. In C. Dent-Read & P. Zukow-Goldring
(Eds.), Evolving explanations of development (pp. 23 – 54).
Washington, DC: American Psychological Association.
Gibson, E. J. (2000). Perceptual learning in development:
Some basic concepts. Ecological Psychology, 12, 295 – 302.
Gibson, E. J., & Pick, A. D. (2000). An ecological approach to
perceptual learning and development. Oxford, UK: Oxford
University Press.
Gibson, J. J. (1962). Observations on active touch. Psychological Review, 69, 477 – 491.
Gibson, J. J. (1966). The senses considered as perceptual
systems. Boston: Houghton Mifflin.
Gibson, J. J. (1979). The ecological approach to visual perception. Boston: Houghton Mifflin.
Goubet, N., Rochat, P., Maire-Leblond, C., & Poss, S.
(2006). Learning from others in 9-18-month-old infants.
Infant and Child Development, 15, 161 – 177.
Gowen, J. W., Goldman, B. D., Johnson-Martin, N., &
Hussey, B. (1989). Object play and exploration of handicapped and nonhandicapped infants. Journal of Applied
Developmental Psychology, 10, 53 – 72.
Grenier, A. (1981). Liberated-motricity by holding the head
during the 1st weeks of life. Archives Francaises De
Pediatrie, 38, 557 – 561.
Hack, M., & Taylor, H. G. (2000). Perinatal brain injury in
preterm infants and later neurobehavioral function.
Journal of the American Medical Association, 284, 1973 –
1974.
Hadders-Algra, M., Brogren, E., & Forssberg, H. (1996).
Ontogeny of postural adjustments during sitting in
infancy: Variation, selection and modulation. Journal of
Physiology, 493, 273 – 288.
Harris, F. C., & Lahey, B. B. (1978). A method for
combining occurrence and nonoccurrence interobserver
agreement scores. Journal of Applied Behavioral Analysis,
11, 523 – 527.
Heathcock, J. C., Lobo, M. A., & Galloway, J. C. (2008).
Movement training advances the emergence of reaching
in infants born preterm at , 33 weeks gestational age.
Physical Therapy, 88(3), 1 – 13.
Hofstadter, M., & Reznick, J. S. (1996). Response modality
affects human infant delayed-response performance.
Child Development, 67, 646 – 658.
Hood, B. (2001). Guest editorial—When do infants know
about objects? Perception, 30, 1281 – 1284.
Hopkins, B., & Ronnqvist, L. (2002). Facilitating postural
control: Effects on the reaching behavior of 6-month-old
infants. Developmental Psychobiology, 40, 168 – 182.
Hopkins, B., & Westra, T. (1988). Maternal handling and
motor development: An intracultural study. Genetic,
Social, and General Psychology Monographs, 114, 379 – 408.
Hopkins, B., & Westra, T. (1989). Maternal expectations
of their infants’ development: Some cultural differences.
Developmental Medicine and Child Neurology, 31, 384 – 390.
Hopkins, B., & Westra, T. (1990). Motor development,
maternal expectations, and the role of handling. Infant
Behavior and Development, 13, 117 – 122.
Iverson, J. M., & Fagan, M. K. (2004). Infant vocal-motor
coordination: Precursor to the gesture-speech system?
Child Development, 75, 1053 – 1066.
Iverson, J. M., & Goldin-Meadow, S. (2005). Gesture paves
the way for language development. Psychological Science,
16, 367 – 371.
Izard, C. E., Dougherty, L. M., & Hembree, E. A. (1989). A
System for Identifying Affect Expressions by Holistic Judgments (AFFEX). Newark: University of Delaware.
Joh, A. S., & Adolph, K. E. (2006). Learning from falling.
Child Development, 77, 89 – 102.
Experiences Advance Early Behaviors
Johnson, S. P., Slemmer, J. A., & Amso, D. (2004). Where
infants look determines how they see: Eye movements
and object perception performance in 3-month-olds.
Infancy, 6, 185 – 201.
Konczak, J., & Dichgans, J. (1997). The development
toward stereotypic arm kinematics during reaching in
the first 3 years of life. Experimental Brain Research, 117,
346 – 354.
Landry, S. H., & Chapieski, M. L. (1988). Visual attention
during toy exploration in preterm infants: Effects of
medical risk and maternal interactions. Infant Behavior &
Development, 11, 187 – 204.
Lee, M., Liu, Y., & Newell, K. M. (2006). Longitudinal
expressions of infant’s prehension as a function of object
properties. Infant Behavior & Development, 29, 481 – 493.
Lewis, M., Alessandri, S. M., & Sullivan, M. W. (1990).
Violation of expectancy, loss of control, and anger
expressions in young infants. Developmental Psychology,
26, 745 – 751.
Lewis, M., Hitchcock, D. F. A., & Sullivan, M. W. (2004).
Physiological and emotional reactivity to learning and
frustration. Infancy, 6, 121 – 143.
Lobo, M. A., Galloway, J. C., & Savelsbergh, G. J. P. (2004).
General and task-related experiences affect early object
interaction. Child Development, 75, 1268 – 1281.
Matthews, A., Ellis, A. E., & Nelson, C. A. (1996). Development of preterm and full-term infant ability on AB,
recall memory, transparent barrier detour, and meansend tasks. Child Development, 67, 2658 – 2676.
Menard, K. R. (2005). Means-end search for hidden objects by
6.5-month-old infants: Examination of an experiential limitation hypothesis. Doctoral thesis, Univerisity of Waterloo.
Mildred, J., Beard, K., Dallwitz, A., & Unwin, J. (1995). Play
position is influenced by knowledge of SIDS sleep
position recommendations. Journal of Pediatric Child
Health, 31, 499 – 502.
Millar, S. (2005). Network models for haptic perception.
Infant Behavior & Development, 28, 250 – 265.
Munakata, Y., Bauer, D., Stackhouse, T., Landgraf, L., &
Huddleston, J. (2002). Rich interpretation vs. deflationary accounts in cognitive development: The case of
means-end skills in 7-month-old infants. Cognition, 83,
B43 – B53.
Needham, A. (2000). Improvements in object exploration
skills may facilitate the development of object segregation
in early infancy. Journal of Cognition and Development, 1,
131 – 156.
Needham, A., Barrett, T., & Peterman, K. (2002). A pickme-up for infants‘ exploratory skills: Early simulated
experiences reaching for objects using ’sticky mittens‘
enhances young infants’ object exploration skills. Infant
Behavior & Development, 25, 279 – 295.
Needham, A., Cantlon, J. F., & Holley, S. M. O. (2006).
Infants‘ use of category knowledge and object attributes
when segregating objects at 8.5 months of age. Cognitive
Psychology, 53, 345 – 360.
Palmer, C. F. (1989). The discriminating nature of infants
exploratory actions. Developmental Psychology, 25, 885 – 893.
1889
Piaget, J. (1952). The origins of intelligence in children. New
York: Norton.
Piaget, J. (1954). The construction of reality in the child. New
York: Basic Books.
Piper, M. C., & Darrah, J. (1994). Motor assessment of the
developing infant. Philadelphia: W.B. Saunders.
Piper, M. C., Pinnell, L. E., Darrah, J., Maguire, T., & Byrne,
P. J. (1992). Construction and validation of the Alberta
Infant Motor Scale (AIMS). Canadian Journal of Public
Health, 83(2), 46 – 50.
Prechtl, H. F. R. (1974). The behavioral states of the
newborn infant (a review). Brain Research, 76, 185 – 212.
Provine, R. R., & Westerman, J. A. (1979). Crossing the
midline: Limits of early eye-hand behavior. Child
Development, 50, 437 – 441.
Reed, E. S., & Bril, B. (1996). The primacy of action in
development. In M. T. Turvey (Ed.), Dexterity and its
development (pp. 431 – 451). Mahwah, NJ: Erlbaum.
Rochat, P. (1989). Object manipulation and exploration in
2-month-old to 5-month- old infants. Developmental
Psychology, 25, 871 – 884.
Rochat, P. (1992). Self-sitting and reaching in 5- to 8month-old infants: The impact of posture and its
development on early eye-hand coordination. Journal
of Motor Behavior, 24, 210 – 220.
Rochat, P., & Goubet, N. (1995). Development of sitting
and reaching in 5- to 6-month-old infants. Infant Behavior
& Development, 18, 53 – 68.
Rovee, C. K., & Rovee, D. T. (1969). Conjugate reinforcement of infant exploratory behavior. Journal of Experimental Child Psychology, 8, 33 – 39.
Ruff, H. A. (1984). Infants’ manipulative exploration of
objects: Effects of age and object characteristics. Developmental Psychology, 20, 9 – 20.
Savelsbergh, G. J. P., & van der Kamp, J. (1993). The coordination of infant’s reaching, grasping, catching and
posture: A natural physical approach. Advances in Psychology, 97, 289 – 317.
Savelsbergh, G. J. P., & van der Kamp, J. (1994). The effect
of body orientation to gravity on early infant reaching.
Journal of Experimental Child Psychology, 58, 510 – 528.
Shinskey, J. L., Bogartz, R. S., & Poirier, C. R. (2000). The
effects of graded occlusion on manual search and visual
attention in 5- to 8- month old infants. Infancy, 1, 323 –
346.
Shinskey, J. L., & Munakata, Y. (2001). Detecting transparent barriers: Clear evidence against the means-end
deficit account of search failures. Infancy, 2, 395 – 404.
Shumway-Cook, A., & Woollacott, M. H. (1995). Motor
control: Theory and practical applications. Philadelphia:
Williams & Wilkins.
Snow, C. W. (1989). Infant development. Upper Saddle River,
NJ: Prentice Hall.
Sommerville, J. A., & Woodward, A. L. (2005a). Infants’
sensitivity to the causal features of means-end support
sequences in action and perception. Infancy, 8, 119 – 145.
Sommerville, J. A., & Woodward, A. L. (2005b). Pulling out
the intentional structure of action of action: The relation
1890
Lobo and Galloway
between action processing and action production
infancy. Cognition, 95, 1 – 30.
Spencer, J. P., & Thelen, E. (2000). Spatially specific changes
in infants‘ muscle coactivity as they learn to reach.
Infancy, 1, 275 – 302.
Thelen, E. (1990). Coupling perception and action in the
development of skill: A dynamic approach. In H. Bloch
& B. I Berthenthal (Eds.), Sensory-motor organizations and
development in infancy and early childhood. Boston: Kluwer
Academic.
Thelen, E., Corbetta, D., Kamm, K., Spencer, J. P.,
Schneider, K., & Zernicke, R. F. (1993). The transition
to reaching: Mapping intention and intrinsic dynamics.
Child Development, 64, 1058 – 1098.
Thelen, E., & Spencer, J. P. (1998). Postural control during
reaching in young infants: A dynamic systems approach.
Neuroscience and Biobehavioral Reviews, 22, 507 – 514.
Turvey, M. T. (1996). Dynamic touch. American Psychologist,
51, 1134 – 1152.
Ulrich, D. A., Ulrich, B. D., Angulo-Kinzler, R. M., & Yun, J.
(2001). Treadmill training of infants with Down syndrome: Evidence-based developmental outcomes. Pediatrics, 108, U42 – U48.
van Beek, Y., Hopkins, B., Hoeksma, J. B., & Samsom, J. F.
(1994). Prematurity, posture and the development of
looking behavior during early communication. Journal of
Child Psychology and Psychiatry and Allied Disciplines, 35,
1093 – 1107.
van Hof, P., van der Kamp, J., & Savelsbergh, G. J. P. (2002).
The relation of unimanual and bimanual reaching to
crossing the midline. Child Development, 73, 1353 – 1362.
Vereijken, B., & Thelen, E. (1997). Training infant treadmill
stepping: The role of individual pattern stability. Developmental Psychobiology, 30, 89 – 102.
von Helmholtz, H. (1962). Handbook of physiological optics
(Rev. ed.). New York: Optical Society of America.
von Hofsten, C. (1991). Structuring of early reaching
movements: A longitudinal study. Journal of Motor
Behavior, 23, 280 – 292.
von Hofsten, C. (1993). Prospective control: A basic aspect of action development. Human Development, 36,
253 – 270.
von Hofsten, C. (1997). On the early development of predictive abilities. In C. Dent-Read & P. Zukow-Goldring
(Eds.), Evolving explanations of development (pp. 163 – 194).
Washington, DC: American Psychological Association.
Wijnroks, L., & van Veldhoven, N. (2003). Individual differences in postural control and cognitive development
in preterm infants. Infant Behavior & Development, 26,
14 – 26.
Willatts, P. (1999). Development of means-end behavior in
young infants: Pulling a support to retrieve a distant
object. Developmental Psychology, 35, 651 – 667.
Wimmers, R. H., Savelsbergh, G. J. P., Beek, P. J., &
Hopkins, B. (1998). Evidence for a phase transition in
the early development of prehension. Developmental
Psychobiology, 32, 235 – 248.
Wimmers, R. H., Savelsbergh, G. J. P., van der Kamp, J., &
Hartelman, P. (1998). A developmental transition in
prehension modeled as a cusp catastrophe. Developmental Psychobiology, 32, 23 – 35.
Witherington, D. C., von Hofsten, C., Rosander, K.,
Robinette, A., Woollacott, M. H., & Bertenthal, B. I.
(2002). The development of anticipatory postural adjustments in infancy. Infancy, 3, 495 – 517.
Zelazo, N. A., Zelazo, P. R., Cohen, K. M., & Zelazo, P. D.
(1993). Specificity of practice effects on elementary neuromotor patterns. Developmental Psychology, 29, 686 – 691.