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Research Article

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Nicolas Poirel,1 Manuel Vidal,2 Arlette Pineau,1 Céline Lanoë,1 Gaëlle Leroux,1 Amélie Lubin,1 Marie-Renée Turbelin,1 Alain Berthoz,2 and Olivier Houdé1,3

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Evidence of Different Developmental Trajectories for Length Estimation According to Egocentric and Allocentric Viewpoints in Children and Adults

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UMR 6232, Ci-NAPS, CNRS, CEA, University of Caen & University of Paris Descartes, Sorbonne, France, 2 UMR 7152, LPPA, CNRS, Collège de France, France, 3Institut Universitaire de France, France Abstract. This study investigated the influence of egocentric and allocentric viewpoints on a comparison task of length estimation in children and adults. A total of 100 participants ranging in age from 5 years to adulthood were presented with virtual scenes representing a park landscape with two paths, one straight and one serpentine. Scenes were presented either from an egocentric or allocentric viewpoint. Results showed that when the two paths had the same length, participants always overestimated the length of the straight line for allocentric trials, whereas a development from a systematic overestimation in children to an underestimation of the straight line length in adults was found for egocentric trials. We discuss these findings in terms of the influences of both bias-inhibition processes and school acquisitions. Keywords: cognitive development, visuospatial processing, length estimation, egocentrism, allocentrism

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Piaget, Inhelder, and Szeminska (1960) reported that up to the age of 7, children judge a straight line and a sinuous Q2 one equal in length when the end points are even. This underscores the fact that young children erroneously rely only upon visual topological intuitions when they estimate Q3 lengths. Poincare´ (1999) and later Piaget (1984) and Piaget et al. (1960) stated that the perception of the external world is essentially based on spatial intuition during childhood: young children never try to introduce any sort of objective measure of length. With age, they learn to compare lengths at school through the introduction of numbers and objective values. Consequently, young children’s intuition strategies lead to erroneous judgment. When presented with a straight line and a sinuous one having exactly the same length, perceptual intuitions bias their judgment, and children compulsorily interpret the straight line longer because the end is far away compared to the end of the sinuous one (Figure 1). Both developmental psychology and neuroimaging studies have suggested the necessity of executive control ability in order to resist this perceptual bias (Bjorklund & Harnishfeger, 1990; Dempster & Brainerd, 1995; Houde´, 2000; Experimental Psychology 2010 DOI: 10.1027/1618-3169/a000079

Houde´ & Guichart, 2001; Leroux et al., 2006). In particular, a right frontal executive network, which develops with age, is strongly involved in inhibiting the aforementioned perceptual bias of length, as demonstrated in a number of comparisons (Houde´ et al., 2009; Leroux et al., 2009). It is worth noting that the perceptual biases of childhood are not fully overcome in adults (Diamond & Kirkham, 2005; Leroux et al., 2009) and that length estimation remains a difficult visuospatial task for adults (see Mossio, Vidal, & Berthoz, 2008; Sun, Campos, Chan, Young, & Ellard, 2004). Different sources of visual information are used during visuospatial cognition (Nadel & Hardt, 2004). They are traditionally classified into two main categories: Allocentric and egocentric frames of reference (Berthoz, 2002, 2006; Committeri et al., 2004; Ishikawa & Montello, 2006; Poirel, Zago, Petit, & Mellet, 2010). From the allocentric perspective (a map-like also called ‘‘survey’’ perspective, Figure 1), the localization of an object does not depend on the location of the subject. Instead, its localization is specified in relation to the whole space or to the other objects present in the environment. This view, which is presented in two dimensions, does  2010 Hogrefe Publishing

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N. Poirel et al.: Length Estimation and Egocentric/Allocentric Viewpoints

Figure 1. Top: Examples of allocentric and egocentric viewpoint stimuli used in the experiment. Bottom: Mean type of error according to age and viewpoint. ns = nonsignificant. *p < .05 (inter-participants comparisons: Fisher’s protected least significant different tests, intra-participants tests: one tailed t tests).

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not depend on the location of the subject and provides direct access to the global configuration of a scene. By contrast, in the egocentric perspective the localization of an object is defined relative to the location of the subject in a three-dimensional scene. The egocentric perspective (also called ‘‘route’’ perspective) constitutes what is likely the first basic reference for human beings (Acredolo, 1978; Piaget & Inhelder, 1967). Interestingly, when a static scene is presented, major visual cognition processing differentiates allocentric and egocentric viewpoints. In contrast to the allocentric viewpoint, the egocentric one depends upon the use of various perceptual cues that allow the brain to reconstruct the depth dimension of the scene (see Parker, Cumming, Johnston, & Hurlbert, 1995). Because motion parallax is missing in an egocentric static visual scene, human beings must take into account several perceptual cues to estimate depth and distances, such as an object’s geometry, ratio estimation, shading, and texture gradient (see Rogers & Graham, 1979). Recent findings indicate that young children are sensitive to the pictorial depth cues present in a two-dimensional static image. As early as 4 months of age, children are able to infer the three 2010 Hogrefe Publishing

dimensional structure of a visual scene (Shuwairi, 2009; Q4 85 86 Shuwairi, Albert, & Johnson, 2007). 87 Parallel developmental trajectories were suggested 88 regarding allocentric and egocentric viewpoints (Burgess, 89 2006, Nardini, Burgess, Beckenridge, & Atkinson, 2006). 90 To our knowledge, developmental change during the length 91 estimation task for these two different viewpoints has never 92 been investigated. It should be noted that, when compared to 93 the egocentric viewpoint, the allocentric viewpoint presents 94 a greater opportunity for perceptual bias, due to its inherent 95 convergence and vanishing point characteristics (Figure 1). 96 Consequently, due to the development of inhibitory control 97 with age (Bjorklund & Harnishfeger, 1990; Davidson, 98 Amso, Anderson, & Diamond, 2006; Dempster & Brainerd, 99 1995; Diamond, Barnett, Thomas, & Munro, 2007; Houde´, 100 2000), we hypothesized that the overestimation of straight 101 line length would diminish more slowly with age for the 102 allocentric view than for the egocentric view. In this study, 103 we used a length comparison task to observe the develop104 ment with age of the overestimated length bias according 105 to egocentric and allocentric viewpoints. Experimental Psychology 2010

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N. Poirel et al.: Length Estimation and Egocentric/Allocentric Viewpoints

Methods

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Participants

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A total of 100 participants were tested, including 20 in each of the following age group (M: mean, SD: standard deviation): 5-year-olds (M = 5 years, SD = ± 3.5 months, 10 boys), 8-year-olds (M = 8 years, SD = ± 4.4 months, 9 boys), 10-year-olds (M = 10 years, SD = ± 3.9 months, 10 boys), 12-year-olds (M = 12 years, SD = ± 4 months, 12 boys), and adults (M = 29 years, SD = ± 4 years, 10 males). All participants spoke French as their native language and all parents gave consent for their child’s participation in the study.

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Apparatus

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Stimulus presentation and data acquisition were controlled through the use of a laptop computer connected to a 17 in. screen. Color figures were presented at a resolution of 1,024 · 768 pixels. Viewing distance was maintained at 50 cm with a chin piece. Stimuli were delivered using E-prime software applications (Psychology Software Tools Inc.).

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Stimuli

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The stimuli were designed using the professional 3D Studio Max software (Autodesk Inc.) and consisted of virtual scenes representing a park landscape with two paths; one straight and one serpentine (Figure 1). The two paths had either equal length (10 m each), or the straight line path was 20% longer or 20% shorter than the serpentine path. These last items (20% longer or shorter) were used as distractor trials. Two stimuli were designed for each length variation: One with the straight line path on the left and a second with the straight line path on the right. Each scene was presented from both allocentric and egocentric viewpoints. Each viewpoint was elaborated from the same initial scene. Allocentric viewpoint stimuli were identical for each age group (3D Studio Max parameters: horizontal field of view of 125, central top view at a height of 10 m above the ground), whereas the egocentric viewpoint was adapted to the body height of each participant (3D Studio Max parameters: horizontal field of view of 60, side view, height ranging from 1.05 to 1.75 m by steps of 10 cm).

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Design and Procedure

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Participants were presented with virtual park scenes during an individual session in a quiet room. They were told they were going to play a game in which a doll had to choose between two paths to take for a walk. Participants were asked to indicate if the doll would cover the same length or not the same length between the two paths. When the participant judged that the two paths had different lengths, they were instructed to point out with their right or left finger the

longer path (i.e., either the straight or serpentine line), and they answered ‘‘the same’’ when they judged that the two paths were equal. Each response was entered by the experimenter with a three button response box (i.e., straight line longer, same, and serpentine line longer). An example of allocentric and egocentric stimuli was presented at the onset of the testing session to ensure that participants understood the task. An experimental session consisted of a randomized presentation of eight trials in which the straight line and serpentine line represented the same length (four allocentric and four egocentric viewpoints), and 16 distractor trials (eight allocentric and eight egocentric viewpoint trials in which the straight line was either longer or shorter than the serpentine path). Analyses were based on eight trials in which the straight line and the serpentine were equal in length, to measure the judgment variations according to age and viewpoints concerning this physical equality. A measure of the type of response (i.e., tendency to either overestimate or underestimate the straight line path) was calculated for each participant, by assigning for each of the four egocentric tests and four allocentric tests the values of 0.25, 0, or 0.25 for underestimation, correct response, and overestimation of the straight line length, respectively. The score for each condition was then totaled, with values falling within the range of 1 (systematic underestimation) and 1 (systematic overestimation). Note that a score near 0 signified that the participant made nearly the same number of over- and underestimations. The data were subsequently analyzed in a two-factor repeated measures analysis of variance with inter-participants factor of age (5-, 8-, 10-, 12-year-olds, or adults) and intra-participants factor of viewpoint (egocentric or allocentric).

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Results

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188 As intended, the task was difficult and thus the error rate was 189 very important in all age groups (percentage of erroneous 190 responses for the test trials in which the straight line and ser191 pentine line represent equal length: mean ± standard devia192 tion, 98.8 ± .8%, 81.3 ± 5%, 70.6 ± 5%, 70 ± 5%, and 193 65 ± 6% for the 5-, 8-, 10-, 12-year-olds and adults, 194 respectively). 195 Analysis revealed an Age · Viewpoint interaction, F(4, 196 94) = 15.80, p < .0001, power = 1) indicating that when par197 ticipants responded erroneously, participants always overesti198 mated the length of the straight line for allocentric tests trials, with a decrease of this visual bias with age (Figure 1, left). On Q5 199 200 the other hand, development from a systematic overestima201 tion of the straight line length to an underestimation of the 202 straight line length in adults was found for egocentric tests tri203 als (Figure 1, right). Post hoc analyses confirmed these signif204 icant developments and indicated a stabilization of the 205 perceptual bias from 12 years of age for both allocentric 206 and egocentric viewpoints (see Figure 1). 207 Additional qualitative analyses were performed regarding 208 the development with age of the proportion of overestimation 209 versus underestimation of the straight line length. Results  2010 Hogrefe Publishing

N. Poirel et al.: Length Estimation and Egocentric/Allocentric Viewpoints

were similar to those presented above: Five-year-old children always overestimated the length of the straight line, whichever the viewpoint. Regarding the allocentric viewpoint, within-groups comparisons revealed that at all ages, participants overestimated the length of the straight line (8-yearolds: v2(1, N = 20) = 38, p < .0001; 10-year-olds: v2(1, N = 20) = 38, p < .0001; 12-year-olds: v2(1, N = 20) = 22, p = .0012; adults: v2(1, N = 20) = 26, p < .0001). Finally, concerning the egocentric viewpoint, the results indicated comparable proportions of overestimation and underestimation of the line length for the 8-year-olds, v2(1, N = 20) = 1.2, p = .87). Regarding the 10-, 12-year-olds and adults, the results showed a higher proportion of underestimation of the straight line length (10-year-olds: v2(1, N = 20) = 20, p = .0025, 12-year-olds: v2(1, N = 20) = 34, p < .0001; adults: v2(1, N = 20) = 32, p < .0001).

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Discussion

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The current study examined the developmental changes during length estimation task according to egocentric and allocentric viewpoints. Virtual scenes representing a park landscape with two paths, one serpentine and one straight line, were used. Scenes were presented in either a two-dimensional allocentric viewpoint or a three-dimensional egocentric viewpoint. We found that when the two paths had the same length, the type of error varied according to age and viewpoint. In agreement with our hypothesis, allocentric viewpoint situations systematically lead to a spontaneous overestimation of the straight line length; this error decreased with age. Interestingly, a different pattern of development was evident for the egocentric viewpoint, from a systematic overestimation of the straight line length in young children to an underestimation of the straight line length in adults. The results in the group of 5-year-old children were not surprising. As is generally reported (Piaget, 1984), they systematically base their judgments on salient spatial cues and instinctively used topological intuitions. Thus, if the end of one path is far away compared to the end of the other path, it is compulsorily longer for them, whichever the viewpoint. From 8 years of age onward, the present results indicate that the type of errors made varies according to allocentric and egocentric viewpoints. When visual scenes were presented from an allocentric viewpoint, results revealed a progressive decrease of the overestimation of the straight line length with age. In agreement with previous work, the results reinforce the hypothesis of an increasing capacity to inhibit the perceptual bias with age (Houde´, 2000; Houde´ & Guichart, 2001; Schirlin & Houde´, 2007) in the view of continuity between children and adults (Diamond & Kirkham, 2005). The results also highlight the fact that adults never fully outgrow the cognitive and perceptual biases of infancy and early childhood: The overestimation of the straight line length, extremely active in children, does not completely disappear even in adulthood (Leroux et al., 2006, 2009). Why was this pattern of results not evidenced for the egocentric viewpoint? Results indicated that before 8 years of age children tend to overestimate the line length, and after

this age they tend to underestimate the line length. It should be kept in mind that the score found for 8-year-old children did not signify that they correctly estimated the length of the straight line (these children made 81.3 ± 5% errors). It simply indicates that 8-year-old children made approximately the same number of over- and underestimations of the length during the task. In agreement with our hypothesis, the threedimensional egocentric perspective reduced the perceptual bias that must be inhibited between the straight line and the sinuous one. Consequently, and contrary to the results found for the allocentric viewpoint, the systematic overestimation of the straight line length was no longer observed from 8 years of age onward. What is the explanation for the surprising and unattended result of a development from a systematic overestimation of straight line length to an underestimation of straight line length from 8 years of age? We hypothesize that the results found at this pivotal age reflect a shift in visuospatial perception due to both visual experience and school teaching programs. Indeed, 8-year-old French children are in the second year of elementary school. During this school year, an advanced acquisition of geometry and spatial concepts is included in the French school program (such as threedimensional cube construction and locations in a layout and in space). This could lead to a visuospatial shift in thinking at this age, which would compete with the instinctively topological intuitions described above. It is thus possible that school learning such as geometrical concepts and distances and measures, including metric space concepts, could strongly influence their judgment. In particular, 8-year-olds have learned the well-known heuristic that ‘‘between two points A and B, the straight line is always the shortest path from A to B’’. This could lead the children to conclude that the straight line is shorter. This potential ‘‘overinhibition’’ of the line length is surely maximized by the fact that the perceptual difference between the two paths was diminished in an egocentric viewpoint. It could also explain why this hypothesis is not applicable when a two-dimensional allocentric perspective is presented. In conclusion, the present findings reinforce the view that visual cognition is affected by bias-inhibition processes, and suggest that other factors such as school knowledge seem to have a potential influence on visuospatial judgments. In line with this assumption, it is also possible that the growing influence of new technologies, such as video games in which virtual scenes are usually presented from both egocentric and allocentric viewpoints, may have an impact on the development of visuospatial cognition (Subrahmanyam, Kraut, Greenfield, & Gross, 2000). Detailed investigation of this issue is an important challenge for developmental psychology, pedagogy, and cognitive neurosciences.

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Experimental Psychology 2010

Received March 31, 2010 Revision received May 14, 2010 Accepted May 14, 2010

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Universite´ Paris Descartes Sorbonne 46 rue Saint Jacques 75005 Paris France E-mail [email protected]

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