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Estimation of Reach inPeripersonal and ExtrapersonalSpace: A Developmental ViewCarl Gabbard a , Alberto Cordova a & Diala Ammar aa Department of Health and Kinesiology , Texas A&MUniversityPublished online: 05 Dec 2007.

To cite this article: Carl Gabbard , Alberto Cordova & Diala Ammar (2007)Estimation of Reach in Peripersonal and Extrapersonal Space: A Developmental View,Developmental Neuropsychology, 32:3, 749-756, DOI: 10.1080/87565640701539451

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Estimation of Reach in Peripersonaland Extrapersonal Space:A Developmental View

Carl Gabbard, Alberto Cordova, and Diala AmmarDepartment of Health and Kinesiology

Texas A&M University

This study explored the developmental nature of action processing via estimation ofreach in peripersonal and extrapersonal space. Children 5 to 11 years of age andadults were tested for estimates of reach to targets presented randomly at sevenmidline locations. Target distances were scaled to the individual based on absolutemaximum reach. While there was no difference between age groups for total error, asignificant distinction emerged in reference to space. With children, significantlymore error was exhibited in extrapersonal space; no difference was found with adults.The groups did not differ in peripersonal space; however, adults were substantiallymore accurate with extrapersonal targets. Furthermore, children displayed a greatertendency to overestimate. In essence, these data reveal a body-scaling problem inchildren in estimating reach in extrapersonal space. Future work should focus on pos-sible developmental differences in use of visual information and state of confidence.

For a reaching task, one of the initial steps is to derive a perceptual estimate of theobject’s distance and location relative to the body. Is the object close enough toreach while seated, or do I need to stand up to contact the object? From a Gibsonianview (1979), the detection of the affordance for a particular mode of reaching en-tails perceiving whether the reach action will fit in the existing layout of the envi-ronment. Arguably, this estimate forms the initial cognitive basis of action pro-cessing. Although research with children in the context of estimating reach as usedhere is limited, there are indications that children, like adults, exhibit the tendencyto overestimate their ability (children: McKenzie, Skouteris, Day, Yonas, & Hart-man, 1993; Schwebel & Plumert, 1999; adults: Fischer, 2000; Gabbard, Ammar, &Rodrigues, 2005a; Robinovitch, 1998; Rochat & Wraga, 1997). For example,

DEVELOPMENTAL NEUROPSYCHOLOGY, 32(3), 749–756Copyright © 2007, Lawrence Erlbaum Associates, Inc.

Correspondence should be addressed to Carl Gabbard, TAMU 4243, College Station, TX 77843-4243. E-mail: c-gabbard@tamu.edu

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Rochat (1995) asked 3- to 5-year-olds to judge (“yes” or “no”) whether they couldtouch an apple presented at varying distances at midline. Results suggested thatfrom 3 years of age, children’s “general” perceived reachability resembled that ofadults. These children exhibited body scaling in reference to arm length, and aswith most adult studies, revealed a tendency to overestimate their reachability. Al-though studies of reachability have been conducted with infants (e.g., Rochat,Goubet, & Senders, 1999), obviously the inherent limitation is the problem withdetermining the level of cognitive processing; studies of this nature typically ob-serve gestures (forward lean and gaze) or actual contact with the object. We alsowish to note that none of the studies described differentiated reachability in regardto peripersonal (within reach) and extrapersonal space (beyond actual reach).

Here, with the intent of improving our understanding of action processing, weexamined the ability of children to estimate reachability for objects placed inperipersonal and extrapersonal space; a task that requires effective use of visual in-formation and subsequent body-scaling. For a wider glimpse of the developmentalnature of this ability, these data were compared to a sample of adults.

METHOD

Participants

The sample consisted of 71 children representing ages: 6 (n = 25), 8 (n = 24), and10 (n = 22) years, and a group of adults (n = 29); all strong right-handers. Themean ages for each group were 6.5, 8.6, 10.7 (range of 5 to 11 years), and 21.0years, respectively. For children, hand preference assessment was behaviorally ad-ministered (i.e., manual performance rather than by questionnaire) with the fouritems of the Lateral Preference Inventory (LPI; Coren, 1993): draw, throw, useeraser, remove top card from deck. For adults, the standard LPI questionnaire wasused. Only those participants that used the right hand consistently with all fourtasks participated in the remainder of the study.

Apparatus

Actual maximum reach (used as the comparison) and imaged reach targets wereprojected via an overhead system linked to a PC programmed with Visual Basic.The table was constructed on a sliding bracket frame, allowing it be moved backand forward for adjustment to the participant. Participants sat in an adjustable er-gonomics chair fixed to the floor, aligned with the midline of the table and pro-jected image midline, and adjusted to a fixed height of 44 cm from the top of theseat pan to the floor. Table surface height was 74 cm, which allowed each adult tosit comfortably with his or her feet flat on the floor. Table and chair height were

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adopted from Carello, Grosofsky, Reichel, Soloan, & Turvey (1989) and Heft(1993). For children and short adults, an adjustable foot-stool was used to createthe same general leg position. To aid in establishing actual (absolute) reach limita-tions for a 1-df action (described in the next section), a commercial seatbelt systemwas modified and secured to the back of the chair. The room was darkened with theexception of light from the computer monitor and white visual images. The fixa-tion point was projected onto a rectangular box (with a 45° angle surface) placed atmidline approximately 15 cm from most distal target.

Procedure

Participants were initially told that they would be asked to make judgments relativeto whether a target (projected image) was within reach using their right hand. Afterbeing systematically positioned in the chair, actual reach was determined; maxi-mum extension of middle finger to push forward a penny using a 1-df reach(Carello et al., 1989). A 1-df reach involved a comfortable effort of the hand, fore-arm, and upper arm acting as a single functional skeletal unit. Based on maximumreach, seven imagery targets (2 cm diameter-penny size) were randomly pro-grammed with “4” representing actual reach complemented with three imagessites above and three below touching at the rims. Peripersonal space included tar-gets 1–4, while extrapersonal space represented targets 5–7. In essence, actualreach was “scaled” to individual arm lengths, therefore allowing acceptablecomparison.

Estimation of reachability was determined via the use of motor (kinesthetic)imagery. Participants were asked to kinesthetically “feel” themselves executingthe movement (“feel your arm extending…”); therefore being more sensitive tothe biomechanical constraints of the task (Johnson, Corballis, & Gazzaniga 2001;Sirigu & Duhamel, 2001; Stevens, 2005). In order to facilitate the “focus” of im-aged hand use, the right hand was placed on the table edge at the midline, and theleft (non-use) limb placed in the participant’s lap, resting on the upper thigh. Datacollection began with a 5 sec “Ready!” signal—followed immediately by a centralfixation point lasting 3 sec, at the end of which the participant heard a tone. The tar-get appeared immediately thereafter and lasted 500 msec ending in another tone.The participant was instructed to respond immediately with a “Yes” or “No” in ref-erence to whether the stimulus was reachable or not. The cycle continued for theduration of the block of trials. Stimulus presentation was given in random orderwith participants receiving three trials at each of the seven sites. A second experi-menter served to motivate and ascertain that the instructions and constraints (e.g.,central fixation, motor imagery, 1-df movement) were not violated; in such a situa-tion, the trial was repeated. Although the imagery technique has been found to beeffective with adults (Gabbard, Ammar, & Lee, 2006; Gabbard et al., 2005a,2005b), prior to this study pilot-testing was conducted to determine methodology

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appropriate for the youngest children (5- and 6-year-olds). In addition, each partic-ipant was trained in the use of motor imagery and allowed practice trials (typically3–5) prior to data collection. During initial practice trials a few children were elim-inated (their data) due to immaturity in understanding task instructions or by virtueof answering “yes” with all trials.

RESULTS

In reference to percent error for total trials, chi-square analyses indicated no statis-tical distinction between groups (ps > .05); error values (%) for 6-, 8-, 10-year-olds, and adults were 16, 18, 15, and 14, respectively. However, when view-ing error in reference to peripersonal and extrapersonal space, differences emerged(Figure 1). Although the three child groups produced similar responses in peri-personal and extrapersonal space (ps > .05), within each group significantly moreerror was displayed in extrapersonal space (ps < .05). This outcome was not dis-played by adults; that is, responses in peripersonal and extrapersonal space weresimilar; 14% and 15% error, respectively. Furthermore, there was no difference inerror in peripersonal space between children and adults; the closest value was be-tween the 10-year-olds and adults, p = .09. In regard to extrapersonal space, adultswere significantly more accurate than each of the younger groups, ps < .05.

These general profiles were also evident in view of the distribution of erroracross targets (Figure 2). As a general observation, each group displayed less accu-racy in extrapersonal compared to peripersonal space. Perhaps it is not surprising

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FIGURE 1 Mean error for peripersonal and extrapersonal targets.

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that most error occurred at and just beyond the critical boundary (target 4) forreach in this setup. For children as a whole, it was around targets 4, 5, and 6,whereas with adults it was targets 4 and 5. These results suggest that the threeyounger groups (children) revealed a greater tendency to overestimate reacha-bility, especially in extrapersonal space. In regard to the general direction of error(mean bias), a 4 × 7 (Age × Target Location) ANOVA revealed a significant maineffect of Age, F(3,82) = 4.48, p < .01, and as expected, Target, F(6,82) = 52.16, p <.01; there was no interaction, p > .05. Concerning the key effect, Age, the childgroups displayed a slight tendency to overestimate, (+0.30 cm, +0.37 cm, +0.29cm), whereas the adults tended to underestimate (–0.13 cm). Given that these re-sults are arguably of marginal significance, it is recommended that they be viewedtogether with the distribution data (Figure 2).

DISCUSSION

The intent of this experiment was to gain developmental insight into action pro-cessing displayed by children and adults via making reachability estimates of tar-gets displayed in peripersonal and extrapersonal space. Our results indicated thatthere was no difference between age groups in total error. However, when compar-ing responses in peripersonal and extrapersonal space, distinctions emerged. Foradults, error values for responses in peripersonal and extrapersonal space weresimilar. On the other hand, each of the child groups exhibited considerably moreerror in extrapersonal compared to peripersonal space. Between group results

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FIGURE 2 Distribution of error across targets.

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indicated no differences in peripersonal space; however, children were signifi-cantly less accurate in extrapersonal space. As a general profile, children displayedthe tendency to overestimate reachability, especially in extrapersonal space. In es-sence, these results suggest that children were having more difficulty with estima-tions of reachability outside their peripersonal space; that is, in extrapersonalspace.

In regard to the claim in the literature of the general tendency to overestimate bychildren and adults, our results found this to be more supportive for children. As ageneral observation of all age groups, more error occurred in extrapersonal com-pared to peripersonal space. However, children as a whole displayed an error rangeextending from targets 4 to 6, whereas error for the older group was narrowed totargets 4 and 5 (Figure 2). In essence, both groups had more difficulty in extra-personal space—significantly more so for children. Mean bias results supportedthe general observation that children were more likely to overestimate than adults.For adults at least, it seems reasonable to assume that part of this outcome may be areflection of experience in peripersonal workspace with more difficulty when esti-mating distance (scaling the body) at the absolute boundary and beyond (seeCarello et al., 1989, and Mark et al., 1997, discussions of critical boundaries forreaching). However, the difference between groups in extrapersonal space sug-gests that perceptual (e.g., visual perception, spatial awareness) and psychologicalfactors (level of confidence), as well as experience may be involved.

Although quite speculative based on our data, perhaps there is a developmentaldifference in the perceptual system of children compared to adults that is relevantto the task used here. With our task, participants were asked to derive an estimateof the object’s distance relative to the body and via motor imagery map the coordi-nates for a body-scaling response. Studies with adults demonstrate that actions ofthis nature (reaching) are most effective when using an egocentric frame of refer-ence as opposed to depending on allocentric information alone (Bradshaw, Watt,Elliot, & Riddell, 2004; Goodale & Humphrey, 1998; Stevens, 2005). This obser-vation begs the question and need for further study considering the developmentalstatus of the visual pathways in children compared to adults. Current reports aresomewhat conflicting—for example, one notes that children rely on both visualpathways during perceptual and visuomotor activities; therefore suggesting thatthese pathways ‘are not’ functionally segregated (Hanisch, Konczak, & Dohle,2001). On the other hand, another study concluded that the systems are relativelymature and segregated by 7 years of age (Rival, Olivier, Ceyte, & Bard, 2004).Their data suggested that children use mainly egocentric object representationswhen performing motor tasks and allocentric cues when making only perceptualjudgments. With both studies, illusion paradigms were used.

Although we did not measure level of confidence per se, previous work allowsfor some speculation. In earlier papers with adults (Gabbard et al., 2005a, 2005b),we argued that proficiency in perceived reach is based in large part on one’s

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perceived ability and perceived task demands. Both of these factors provide a basisfor confidence in action processing. Given the nature of the present study, wewould add to these factors—developmental status. In the results here, children fre-quently (significantly more than adults) overestimated their ability with distal(extrapersonal) targets by responding “yes” when in fact the object was out ofreach. As noted in the introduction, overestimation in judging reach at midline is infact a common observation among children and adults.

Based on these findings, the following preliminary conclusions warrant men-tion. First, it appears that estimates of reachability in peripersonal space areadult-like as early as 5 years of age. However, these data also lead to the suggestionthat the ability to map visual information from extrapersonal space for estimates ofreach, emerge sometime between early adolescence (> 11 years) and early adult-hood.

ACKNOWLEDGMENT

The research was supported by the Research Consortium (American Alliance forHealth, Physical Education, Recreation, and Dance) awarded to Carl Gabbard.

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