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Visual Size Perception and Haptic Calibration during Development

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Title: Visual Size Perception and Haptic Calibration during Development
Language: English
Authors: Gori, Monica, Giuliana, Luana, Sandini, Giulio, Burr, David
Source: Developmental Science. Nov 2012 15(6):854-862.
Availability: Wiley-Blackwell. 350 Main Street, Malden, MA 02148. Tel: 800-835-6770; Tel: 781-388-8598; Fax: 781-388-8232; e-mail: cs-journals@wiley.com; Web site: http://www.wiley.com/WileyCDA/
Peer Reviewed: Y
Page Count: 9
Publication Date: 2012
Document Type: Journal Articles
Reports - Research
Descriptors: Visual Perception, Tactual Perception, Children, Adolescents, Adults, Geographic Location, Accuracy, Individual Development, Foreign Countries
Geographic Terms: Italy
DOI: 10.1111/j.1467-7687.2012.2012.01183.x
ISSN: 1363-755X
Abstract: It is still unclear how the visual system perceives accurately the size of objects at different distances. One suggestion, dating back to Berkeley's famous essay, is that vision is calibrated by touch. If so, we may expect different mechanisms involved for near, reachable distances and far, unreachable distances. To study how the haptic system calibrates vision we measured size constancy in children (from 6 to 16 years of age) and adults, at various distances. At all ages, accuracy of the visual size perception changes with distance, and is almost veridical inside the haptic workspace, in agreement with the idea that the haptic system acts to calibrate visual size perception. Outside this space, systematic errors occurred, which varied with age. Adults tended to overestimate visual size of distant objects (over-compensation for distance), while children younger than 14 underestimated their size (under-compensation). At 16 years of age there seemed to be a transition point, with veridical perception of distant objects. When young subjects were allowed to touch the object inside the haptic workspace, the visual biases disappeared, while older subjects showed multisensory integration. All results are consistent with the idea that the haptic system can be used to calibrate visual size perception during development, more effectively within than outside the haptic workspace, and that the calibration mechanisms are different in children than in adults. (Contains 4 figures.)
Abstractor: As Provided
Number of References: 47
Entry Date: 2013
Accession Number: EJ988489
Database: ERIC
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  Value: <anid>AN0082891384;5g501nov.12;2019May28.13:40;v2.2.500</anid> <title id="AN0082891384-1">Visual size perception and haptic calibration during development. </title> <p>It is still unclear how the visual system perceives accurately the size of objects at different distances. One suggestion, dating back to Berkeley's famous essay, is that vision is calibrated by touch. If so, we may expect different mechanisms involved for near, reachable distances and far, unreachable distances. To study how the haptic system calibrates vision we measured size constancy in children (from 6 to 16 years of age) and adults, at various distances. At all ages, accuracy of the visual size perception changes with distance, and is almost veridical inside the haptic workspace, in agreement with the idea that the haptic system acts to calibrate visual size perception. Outside this space, systematic errors occurred, which varied with age. Adults tended to overestimate visual size of distant objects (over‐compensation for distance), while children younger than 14 underestimated their size (under‐compensation). At 16 years of age there seemed to be a transition point, with veridical perception of distant objects. When young subjects were allowed to touch the object inside the haptic workspace, the visual biases disappeared, while older subjects showed multisensory integration. All results are consistent with the idea that the haptic system can be used to calibrate visual size perception during development, more effectively within than outside the haptic workspace, and that the calibration mechanisms are different in children than in adults.</p> <p>It is still unclear how the visual system perceives accurately the size of objects at different distances. One suggestion, dating back to Berkeley's famous essay, is that vision is calibrated by touch. If so, we may expect different mechanisms involved for near, reachable distances and far, unreachable distances. To study how the haptic system calibrates vision we measured size constancy in children (from 6 to 16 years of age) and adults, at various distances.</p> <p>Graph</p> <hd id="AN0082891384-2">Introduction</hd> <p>When we observe an object, the size of the retinal image varies with object distance. That the apparent size of objects remains constant despite the changes in the retinal image size with distance is called 'size constancy'. The acquisition of this invariance is fundamental for correct interaction with the world, but many studies show that its development is long and definitely not simple. Infants of 4–6 months and newborns seem to have some degree of size constancy ([<reflink idref="bib11" id="ref1">11</reflink>]; [<reflink idref="bib24" id="ref2">24</reflink>]; [<reflink idref="bib35" id="ref3">35</reflink>]; [<reflink idref="bib40" id="ref4">40</reflink>]), but perceptual biases for size estimation have been observed also late in development ([<reflink idref="bib23" id="ref5">23</reflink>], [<reflink idref="bib25" id="ref6">25</reflink>]; [<reflink idref="bib33" id="ref7">33</reflink>]; [<reflink idref="bib47" id="ref8">47</reflink>]) and persists into adulthood (e.g. [<reflink idref="bib9" id="ref9">9</reflink>]; [<reflink idref="bib21" id="ref10">21</reflink>]; [<reflink idref="bib26" id="ref11">26</reflink>]).</p> <p>Interestingly, the biases in size perception seem to vary with distance, being greater when the object is positioned farther away. Some studies suggest that perception is almost veridical at short distances, even for 4–5‐year‐olds ([<reflink idref="bib42" id="ref12">42</reflink>]), while for longer distances misperceptions occur at this young age ([<reflink idref="bib23" id="ref13">23</reflink>]) and even in adults. Interestingly, two opposite trends have been observed for children and adults. Children younger than 4–5 years of age underestimate the size of objects positioned beyond 3 meters ([<reflink idref="bib23" id="ref14">23</reflink>]), and those beyond 15 meters up to 9 years of age ([<reflink idref="bib5" id="ref15">5</reflink>]; [<reflink idref="bib25" id="ref16">25</reflink>]; [<reflink idref="bib26" id="ref17">26</reflink>]). Adults, on the other hand, tend to overestimate the dimension of distant objects, at least under some circumstances ([<reflink idref="bib9" id="ref18">9</reflink>]; [<reflink idref="bib14" id="ref19">14</reflink>]; [<reflink idref="bib17" id="ref20">17</reflink>]; [<reflink idref="bib21" id="ref21">21</reflink>]; [<reflink idref="bib26" id="ref22">26</reflink>]).</p> <p>Size perception, and perception of the world in general, depends on interactions of all sensory modalities. Communication between the senses could be important for the acquisition of some perceptual concepts. Along these lines we have recently shown that the haptic system plays a fundamental role in the development of visual size perception ([<reflink idref="bib8" id="ref23">8</reflink>]; [<reflink idref="bib19" id="ref24">19</reflink>]; [<reflink idref="bib20" id="ref25">20</reflink>]; [<reflink idref="bib22" id="ref26">22</reflink>]). In children younger than 8 years, haptic information dominates vision in size judgments, even though haptic judgments are less precise ([<reflink idref="bib19" id="ref27">19</reflink>]). However, for orientation evaluations, vision dominates touch. We have interpreted these results to imply that in young children, touch calibrates visual size perception, and that vision calibrates haptic orientation perception. Interestingly, the modality that dominates depends on the situation; neither seems to act as the 'gold standard'. Given the overwhelming body of evidence for optimal integration in adults, that children do not integrate in an optimal manner was not expected, and suggests that multisensory interaction in infants is fundamentally different from that in adults. How could it differ?</p> <p>Most recent work on multisensory interactions has concentrated on sensory <emph>fusion</emph>. There is now a clear consensus that fusion of cross‐sensory information in adults usually depends on the relative <emph>reliability</emph> of the various signals: when in conflict – either for natural or experimentally induced reasons – the resulting perception is given by the weighted average of the signals, with weights proportional to relative reliability. It is simple to demonstrate that this combination rule optimizes performance (e.g. [<reflink idref="bib31" id="ref28">31</reflink>]) and it has been verified experimentally in many laboratories for many sensory modalities ([<reflink idref="bib1" id="ref29">1</reflink>]; [<reflink idref="bib15" id="ref30">15</reflink>]; [<reflink idref="bib16" id="ref31">16</reflink>]; [<reflink idref="bib28" id="ref32">28</reflink>]; [<reflink idref="bib30" id="ref33">30</reflink>]; [<reflink idref="bib32" id="ref34">32</reflink>]; [<reflink idref="bib41" id="ref35">41</reflink>]). And the idea makes good intuitive sense: if the goal is increased reliability the more reliable signals should receive more weight. It is less clear which sensory signals should govern cross‐sensory calibration. [<reflink idref="bib16" id="ref36">16</reflink>] suggested – with evidence – that reliability should also determine calibration, but the theoretical reasoning behind this argument is less clear. Reliability is a measure of <emph>precision</emph>, the variability of repeated measures of an object. It is not a measure of how close the estimates are to physical reality: that is termed <emph>accuracy</emph>. A reliable but inaccurate signal would be of little value in calibrating another system. Calibration involves correction of systematic biases, and for that one would want the most accurate signal: even if it happens to be the less precise. Although accuracy is far harder than precision to measure experimentally, we can speculate on which system has access to accurate information. For example, as Bishop George [<reflink idref="bib3" id="ref37">3</reflink>] correctly observed, vision has no direct access to attributes such as distance, solidarity or 'bigness'. These can be acquired visually only after they have been associated with touch (proposition 45): in other words 'touch educates vision', perhaps better expressed as 'touch <emph>calibrates</emph> vision'. Calibration is probably necessary at all ages, but during the early years of life, when children effectively 'learning to see', calibration may be expected to be more important. It is during these years that limbs are growing rapidly, eye‐length and eye‐separation are increasing, all necessitating constant recalibration between sight and touch. Indeed, many studies suggest that the first eight years in humans corresponds to the critical period of plasticity in humans for many attributes, such as binocular vision ([<reflink idref="bib2" id="ref38">2</reflink>]), acquiring accent‐free language ([<reflink idref="bib12" id="ref39">12</reflink>]) and motor skills ([<reflink idref="bib18" id="ref40">18</reflink>]; [<reflink idref="bib36" id="ref41">36</reflink>]; [<reflink idref="bib37" id="ref42">37</reflink>]; [<reflink idref="bib43" id="ref43">43</reflink>]).</p> <p>Before 8 years of age, calibration may be more important than integration. The advantages of fusing sensory information are probably more than offset by those of keeping the evolving system calibrated: and using one system to calibrate another precludes fusion of the two. So if we accept Berkeley's ideas that vision must be calibrated by touch, that may explain why size discrimination thresholds are dominated by touch, even though touch is less precise than vision. But why are orientation thresholds dominated by vision? Perhaps Berkeley was not quite right, and touch does not always calibrate vision, but the more accurate, as discussed above, sense for a particular task is the calibrator. And orientation perception that is coded directly by primary visual cortex ([<reflink idref="bib29" id="ref44">29</reflink>]), and calculated from touch only indirectly, via complex coordinate transforms can be calibrated by vision, explaining visual dominance in childhood.</p> <p>Strong evidence in support of the idea of cross‐sensory calibration during development has been recently provided by studies in children with sensory and motor disabilities. If the idea of calibration is correct, then early deficits in one sense should impact on the function of other senses that rely on it for calibration. Specifically, haptic impairment should lead to poor visual discrimination of size and visual impairment to poor haptic discrimination of orientation. We have tested and verified both these predictions showing that children born without sight have impaired haptic orientation discrimination compared with controls, but as good or better size discrimination ([<reflink idref="bib20" id="ref45">20</reflink>]) and that children with haptic disabilities show impaired visual size discrimination and similar visual orientation discrimination compared with controls ([<reflink idref="bib22" id="ref46">22</reflink>]).</p> <p>In order to better investigate the role of the haptic system on the development of visual perceptual attributes, we study here the role of the haptic cues on the development of visual perception of size constancy. One way to test the hypothesis of haptic calibration of visual size perception is to observe whether visual accuracy changes inside and outside the haptic workspace – within and outside arm's reach. If the haptic system is used to calibrate vision, it should be most effective inside the haptic workspace (especially for older children), with reduced or no efficiency outside it. Therefore, in the first experiment we tested the development of size constancy for different distances. In children between 6 and 16 years of age, and in adults, we measured visual size perception of objects positioned at different distances from the observer (inside and outside the haptic workspace) using a methodology that reveals small biases (of the order of a few mms). Our results are consistent with our cross‐sensory calibration hypothesis. Small perceptual biases are present within the haptic workspace and disappear with age while larger biases outside this space persist into adulthood.</p> <p>In the second experiment we studied the role of haptic feedback of visual size perception. The results show that the visual bias within the haptic workspace in children is reduced or even eliminated when they are allowed to touch the object (showing a haptic dominance, in agreement with our previous work; [<reflink idref="bib19" id="ref47">19</reflink>]). This result is in agreement with the idea that the use of one modality to calibrate the other in children precludes the increment in precision that adults obtain by integrating the unisensory cues (see [<reflink idref="bib15" id="ref48">15</reflink>]). On the other hand it allows the child to correct the accuracy of his final percept by curtailing the intrinsic uncertainties and biases in the visual system.</p> <hd id="AN0082891384-3">Materials and methods</hd> <p>The stimuli used for this study were plastic spheres of about 5 cm in diameter, produced by a 3D printer. The spheres were positioned on a plane patterned with a black grid on a white background (Figure 1A). Subjects observed the scene from a fixed height (11 cm above the plane), with chin resting on a chin rest fixed at the level of the plane. Thirty‐seven children from 6 to 16 years of age and 13 adults (seven males and six females, average age 29.3 ± 0.6) participated in the study. The test was presented in the form of a game. As with the adults, children were presented with two successive stimuli on each trial, and asked to judge which was the taller (guessing if unsure). Positioning of the spheres lasted about 2 seconds, so each trial took around 4 seconds. Subjects were well trained on the task before data collection and before the beginning of the test the researcher ensured that the child was confident with the concept of size. To explain the size task, young children were shown a very small and a very large block and were asked which was larger. They voiced their responses, which the experimenter recorded on a laptop computer.</p> <p>Graph: 1 A. Setup for the first experiment task. The child observes a sequence of two balls and reports which seemed larger. The standard ball was always presented at 60 cm from the observer and had a fixed diameter of 50 mm. The comparison was presented at one of four possible distances (42.5, 60, 85 and 120 cm), and had variable diameter (see method section). B. Image with the four distances from the observer at which the comparison ball could be presented.</p> <p>In the first experiment two stimuli were shown successively, the standard stimulus with a fixed diameter of 50 mm (randomly presented first or second) positioned 60 cm from the observer, and a comparison sphere (varying in diameter from 38 to 62 mm in steps of 1 mm) positioned at one of four randomly chosen distances (42.5 cm, 60 cm, 85 cm and 120 cm: see Figure 1B). The size of the comparison sphere varied depending on the subject's response, following the QUEST algorithm ([<reflink idref="bib44" id="ref49">44</reflink>]), plus a random offset drawn from a Gaussian distribution. This procedure ensured that the psychometric function was well sampled at the best point for estimating both the PSE and slope of the functions, as well as giving observers a few 'easy' trials from time to time. Also, as the Gaussian offset was centered at zero, it ensured that equal responses related to stimuli bigger and smaller than the standard. The proportion of trials where the probe was judged larger was computed for each probe height and fit by cumulative Gaussians, yielding PSE (point of subjective equality, given by the mean) and threshold (standard deviation) estimates from the mean and standard deviation of the best‐fitting function, respectively. Standard errors for the PSE and threshold estimates were obtained by bootstrapping ([<reflink idref="bib13" id="ref50">13</reflink>]). The bias was computed as the difference between the standard dimension (50 mm) and the estimated PSE. A positive bias indicated size overestimation while a negative bias indicated underestimation. One hundred trials were collected for each experimental condition (with a total of 400 trials in total for the four distances).</p> <p>Adult subjects were recruited from the local university, while children were recruited from elementary, intermediate and high schools in Prato (PO, Italy). In the first experiment, both adults and children were tested for 2–3 hours (the test was longer in children because they had many breaks between and within sessions). This experiment was performed by nine 6‐year‐olds, ten 8‐year‐olds, nine 10‐year‐olds, five 14‐year‐olds, four 16‐year‐olds and thirteen adults.</p> <p>To investigate more directly the role of haptic calibration on vision, in the second experiment we introduced a haptic cue. The procedure for the visual task was identical to that used in the previous experiment except that the comparison sphere was positioned at only 42.5 cm distance. Also in this case positioning of the spheres lasted about 2 seconds, so each trial took around 4 seconds. In the haptic condition, subjects were presented a sequence of spheres in the hand (occluded from vision) and were asked to report which sphere appeared larger (by using only haptic information). In the bimodal condition subjects were allowed to observe and touch (in the same visual location while observing it) the comparison and the standard sphere (presented in random order) and to report which of the two was the larger. Given the visual bias, a natural conflict was present between the visual and the haptic modality and any other artificial conflict was inserted between modalities. Nine 6‐year‐olds, nine 8‐year‐olds, eight 10‐year‐olds, four 14‐year‐olds and four 16‐year‐olds who performed the first experiment also performed this experiment. One hundred trials for condition were collected (a total of 200 trials per child). The duration of this test was about 1 hour. Also in this case the proportion of trials where the probe was judged bigger was computed for each probe height and fitted by cumulative Gaussians, yielding PSE (point of subjective equality, given by the mean) and threshold (standard deviation) estimates from the mean and standard deviation of the best‐fitting function, respectively. Both unimodal and bimodal visual‐haptic thresholds and PSEs were compared with the prediction of the Bayesian optimal‐integration model.</p> <hd id="AN0082891384-4">Maximum likelihood model</hd> <p>The MLE calculation (described in [<reflink idref="bib1" id="ref51">1</reflink>]; and [<reflink idref="bib15" id="ref52">15</reflink>]) assumes that the optimal bimodal estimate of PSE () is given by the weighted sum of the independent haptic and visual estimates (<emph>Ŝ</emph><subs><emph>V</emph></subs> and <emph>Ŝ</emph><subs><emph>H</emph></subs>).</p> <p>1</p> <p>Graph</p> <p>Where weights <emph>w</emph><subs><emph>V</emph></subs>and<emph>w</emph><subs><emph>H</emph></subs>sum to unity and are inversely proportional to the variance (σ<sups>2</sups>) of the underlying noise distribution, assessed from the standard deviation σ of the Gaussian fit of the psychometric functions for visual and haptic judgments:</p> <p>2</p> <p>Graph</p> <p>The MLE prediction for the visuo‐haptic threshold () is given by:</p> <p>3</p> <p>Graph</p> <p>where <emph>σ</emph><subs><emph>V</emph></subs> and <emph>σ</emph><subs><emph>H</emph></subs> are the visual and haptic unimodal thresholds. The improvement is greatest () when <emph>σ</emph><subs><emph>V</emph></subs> = <emph>σ</emph><subs><emph>H</emph></subs>.</p> <hd id="AN0082891384-5">Results</hd> <p>Figure 2A shows how size constancy varies with distance for the six different age groups, plotting both individual and mean group data. The pattern of results clearly changes with age. For the younger children, aged 14 and below, size was overestimated at the near distance, and systematically underestimated at greater distances. However, for adults the bias was in the opposite direction, an overestimation at great distances, veridical for near. Interestingly, the intermediate age group – the 16‐year‐olds – showed veridical size estimations for both near and far objects. This seems to be a consistent pattern of all subjects, rather than an artifact of averaging. Figure 2B plots the mean data from the six age groups on the same graph, to allow more immediate comparison.</p> <p>Graph: 2 A. Error in perceived size as a function of comparison ball position (42.5, 60, 85, 120). Individual data are plotted with different symbols for each age (<reflink idref="bib6" id="ref53">6</reflink>, 8, 10, 14, 16 years old and adults). The solid line represents the average of the group. In all cases, two asterisks represent a significance level of less than.01 and one asterisk a significance level of less than.05 in one‐tailed one‐sample t‐tests. B. Average perceived size as a function of comparison positions for different ages. 6‐year‐olds (N = 9) are reported in light blue, 8‐year‐olds (N = 10) in dark blue, 10‐year‐olds (N = 9) in green, 14‐year‐olds (N = 5) in orange, 16‐year‐olds (N = 4) in gray and adults (N = 13) in red. The adult data were taken from our previous study ([<reflink idref="bib21" id="ref54">21</reflink>]).</p> <p>Two clear patterns are apparent: children younger than 14 overestimate sizes at great distances, while adults underestimate in this range; and at short distances, inside the haptic workspace, children overestimate size while adults are veridical. Planned one‐tailed paired <emph>t</emph>‐tests show that the overestimation within the haptic workspace is significant at either the.05 or the.01 level (see asterisks in Figure 2A and caption) for the 14‐year‐old and younger children but, not for the 16‐year‐old children or for the adults. Outside the haptic workspace (85 and 120 cm) the bias was significantly present for all groups except the 16‐year‐olds. The bias seems quite stable up to 14 years of age, and then begins to change. Planned one‐tailed one‐sample <emph>t</emph>‐tests show that the underestimation is significant in the 85 cm and 120 cm distances for the 6‐, 8‐, 10‐, and 14‐year‐old children (see asterisks in Figure 2A and caption) but not for the 16‐year‐old children (<emph>p </emph>> .05). Adults, on the other hand, show a significant overestimation for both distances (<emph>p </emph>< .01).</p> <p>Figure 3A plots the same results as a function of age for the different distances. At 120 cm, children up to 14 years systematically underestimated size by 2–3 mm; the direction of the bias then inverts, passing through veridicality at 16 years. Figures 3B and 3C show how the precision of size judgments (given by the slope of the psychometric functions) changes with age, inside (Figure 3B) and outside (Figure 3C) the haptic workspace. In general the precision improves slightly (but not significantly) with age, particularly for distances inside the haptic workspace. Interestingly, in adults inside the haptic workspace (where the visual bias is not present) thresholds seem to be better than the younger group (also if not significantly), whereas outside it (where the visual bias is present and strongest in adults in comparison with the younger group) the thresholds seems to be similar or even worse than the younger group (also if not significantly).</p> <p>Graph: 3 A. Error in perceived object size as a function of age for different comparison positions: 42.5 in light blue, 60 in dark blue, 85 in green and 120 in red. B. Precision thresholds as a function of age inside (on the left) the haptic workspace. Color code as for Figure 3A. C. Precision thresholds as a function of age outside the haptic workspace (on the right). Color code as for Figure 3A.</p> <p>We next measured the influence of touch on vision by performing size comparisons with stimuli that subjects can observe and also touch. An evident sign of sensory calibration in the youngest children would be the dominance of one sense over the other (precluding multisensory integration). In this visual haptic size task, the presence of haptic dominance could reflect a process of cross‐sensory calibration that would be functional in the bimodal condition, annulling the visual bias present within the haptic workspace. In this experiment the comparison ball was presented only at a distance of 42.5 cm. The graph on the left of Figure 4 represents the average results for children between 6 and 10 years of age (average 8 years) while the graph on the right shows the average results for children between 13 and 16 years of age (average 15 years). The green bars show the average visual bias (Figure 4A) and precision thresholds (Figure 4B) at 42.5 cm, inside the haptic workspace (the same data as reported in Figures 2 and 3 for those children who performed this task). The blue bars in Figure 4A and B show the results for haptic judgments without vision (see the materials and methods section for more information). The orange bars show the bimodal bias and thresholds when the subjects were requested to observe and simultaneously touch the ball. The light gray bars are the predictions for bias (Figure 4A) and thresholds (Figure 4B) given by the 'Bayesian', maximum likelihood model (calculated respectively with equations 1 and 3; [<reflink idref="bib1" id="ref55">1</reflink>]; [<reflink idref="bib15" id="ref56">15</reflink>]). For the younger group (children less than 10 years of age Figure 4A), the bias in the bimodal condition vanishes almost completely, reflecting total haptic dominance. Indeed, the bimodal bias was not significantly different from the haptic condition (two‐tailed paired‐sample <emph>t</emph>‐tests <emph>p </emph>> .05) as observed by [<reflink idref="bib19" id="ref57">19</reflink>] and is significantly less than the Bayesian prediction (one tailed paired‐sample <emph>t</emph>‐tests <emph>p </emph>< .01). On the contrary, in the older group the prediction of the Bayesian model is in agreement with the bimodal data (two‐tailed paired‐sample <emph>t</emph>‐tests <emph>p </emph>> .05), supporting multisensory integration at this age.</p> <p>Graph: 4 A. Error in perceived size for the 6–10‐year‐old children (N = 26, average 8 years) and for the 14–16‐year‐old children (N = 8, average 15 years), at 42.5 cm. The visual condition (V) is shown in green, the haptic condition (H) in blue, the bimodal condition (BIM) in orange and the Bayesian prediction (PRED) in gray. B. Average precision thresholds for the 6–10‐year‐old children (N = 26, average 8 years) and for the 14–16‐year‐old children (N = 8, average 15 years). Color code as for Figure 4A. Two asterisks represent a significance level of less than.01 and one asterisk a significance level of less than.05 in two‐tailed paired‐sample t‐tests or in one‐tailed paired‐sample t‐tests. C. Precision thresholds as a function of distance for the haptic, bimodal condition and Bayesian prediction. Color code as for Figure 4A.</p> <p>The improvement in thresholds (Figure 4B) also seem to follow the same trend: for the 8‐year‐old group, bimodal thresholds were not significantly different with respect to the haptic condition (two‐tailed paired‐sample <emph>t</emph>‐tests <emph>p </emph>> .05) and significantly higher than the Bayesian prediction (one‐tailed paired‐sample <emph>t</emph>‐tests <emph>p </emph>< .05); while for the 15‐year‐old group it is not significantly different from the Bayesian prediction (two‐tailed paired‐sample <emph>t</emph>‐tests <emph>p </emph>> .05).</p> <p>The lack of multisensory integration and the clear unisensory dominance can also be observed in Figure 4C, which reports thresholds for all age groups. Bimodal thresholds remain clearly higher than the predictions – and very close to the haptic thresholds – until about 14–16 years of age. At this age the bimodal precision thresholds decrease below the haptic thresholds, as predicted by the Bayesian model (equation 3). The reduction in thresholds is considered to be strong evidence for multisensory integration.</p> <hd id="AN0082891384-6">Discussion</hd> <p>The evidence from these two experiments suggests that the sense of touch can have a fundamental role in the acquisition of visual size constancy during development. The first task highlights three principal results. The first is that the effectiveness of object constancy changes as a function of distance from the observer, far more accurate inside than outside the haptic workspace at all the ages tested. This result supports the idea that the haptic system can be involved in the development of visual size perception. This result is also in agreement with a recent study showing that children with haptic disabilities have impaired visual size discrimination, but similar visual orientation discrimination compared with controls ([<reflink idref="bib22" id="ref58">22</reflink>]). In the range where the haptic modality can operate effectively, visual perception is far less biased, especially in older children and adults; outside this range it is biased both in children and in adults. Previous studies reported that nearly accurate size perception, at distances closer than 1 m, can be mediated by ocular convergence (e.g. [<reflink idref="bib34" id="ref59">34</reflink>]). On the other hand, since our data show strong biases for distances of 0.85 and 1.2 m and since this bias is not present for the older children's group, we can exclude that for this kind of task the reduction of the biases can be mediated only by ocular convergence. Further, given the importance of this visual cue for size and distance perception ([<reflink idref="bib34" id="ref60">34</reflink>]), we could speculate that the haptic system might act on visual size perception also through calibration of ocular convergence.</p> <p>The second interesting point is that the visual bias outside the haptic workspace occurs in the opposite direction for children and adults. Children underestimate size outside the haptic workspace, increasing with distance up to an underestimation of about 4 mm at 120 cm. This result is in agreement with previous studies where larger distances were tested ([<reflink idref="bib5" id="ref61">5</reflink>]; [<reflink idref="bib9" id="ref62">9</reflink>]; [<reflink idref="bib23" id="ref63">23</reflink>], [<reflink idref="bib24" id="ref64">24</reflink>], [<reflink idref="bib25" id="ref65">25</reflink>]). During development, there is a clear shift from perceptual underestimation to overestimation outside the haptic workspace. Interestingly, the visual bias disappears completely at 16 years of age, when object size is perceived correctly at all tested distances. This seems to be a real effect, occurring for all the subjects tested, rather than an artifact of averaging. In adults, the bias in size perception outside the haptic workspace reappears, in the opposite direction, as a clear size overestimation. This result is in agreement with previous studies showing that overestimation often occurs in adults when they estimate the size of objects positioned at far distances ([<reflink idref="bib9" id="ref66">9</reflink>]; [<reflink idref="bib14" id="ref67">14</reflink>]; [<reflink idref="bib17" id="ref68">17</reflink>]; [<reflink idref="bib26" id="ref69">26</reflink>]). Why the bias is in the opposite direction in adults compared to children is not clear: further studies are necessary to investigate this point. One possible explanation of these results, recently proposed by [<reflink idref="bib23" id="ref70">23</reflink>], [<reflink idref="bib24" id="ref71">24</reflink>], [<reflink idref="bib25" id="ref72">25</reflink>], is that it could derive from a cognitive mechanism (metacognitive theory) that adults use to compensate the perceptual deficit of underestimation. He suggests that both adults and children have the same tendency to underestimate the size of distant objects, but that young children are not able to adopt the same cognitive compensation strategy used by older children and adults.</p> <p>The third result is that our technique allows us to measure the presence of small visual biases for short distances (inside the haptic workspace at 42 cm) up until 14 years of age. This is in contrast to previous studies ([<reflink idref="bib42" id="ref73">42</reflink>]) in which the technique used did not allow detection of such small misperceptions.</p> <p>The second experiment shows how the haptic system could be used to calibrate vision. In children, the visual bias inside the haptic workspace disappeared when they were allowed to touch the stimuli. We interpret this as the correction of an internal conflict between the (naturally) visually biased signals and the unbiased haptic signals, leading to a similar results as that found in our previous work [<reflink idref="bib19" id="ref74">19</reflink>] in which was deliberately introduced an artificial bias into the stimuli. Under these conditions, the haptic dominance 'corrects' the visual bias, improving accuracy estimation of object size. It is not clear why we find such a long developmental trend in the development of size constancy and of visual haptic integration under these conditions, about 14–16 years, compared with 8–10 years for development of visual haptic optimal sensory integration in our previous experiment ([<reflink idref="bib19" id="ref75">19</reflink>]). One possible explanation is that in that previous study the objects were always presented at the same distance, so there was no need to exercise size constancy for visual haptic integration. The current experiment requires a comparison between two different distances, a more complex task that does require size constancy. It is reasonable to think that this sort of more complex function requires more time to stabilize than a simple calibration for distance at arm's length, even if both require cross‐sensory calibration.</p> <p>Recent evidence has previously suggested that the haptic system could be used to calibrate vision for size estimation because it has access to more direct and intrinsically accurate information for this specific task ([<reflink idref="bib8" id="ref76">8</reflink>]). Unisensory dominance could indeed be important to maintain a calibrated system, even if it undergoes continual changes with the developing body. Using one system to calibrate the other precludes fusion of the two modalities, and therefore does not result in the improvement in precision that has been demonstrated in adults. However, in children the advantages of fusing sensory information are probably more than offset by those of keeping the evolving system calibrated.</p> <p>The evidence for calibration between senses is steadily accumulating, for many modalities, including vision and audition (e.g. [<reflink idref="bib38" id="ref77">38</reflink>], [<reflink idref="bib39" id="ref78">39</reflink>]; [<reflink idref="bib45" id="ref79">45</reflink>]), vision and vestibular input (e.g. [<reflink idref="bib46" id="ref80">46</reflink>]) and visual‐motor coordination (e.g. [<reflink idref="bib6" id="ref81">6</reflink>]; [<reflink idref="bib7" id="ref82">7</reflink>]; [<reflink idref="bib10" id="ref83">10</reflink>]). Cross‐comparison between senses is clearly a good strategy to establish and to maintain calibration, as each sense has access to different sources of information, differently affected by noise and distortions. As mentioned in the Introduction, while both theory and experiment suggest that signal reliability should govern sensory fusion, it is less clear what to expect for cross‐calibration. Reliability is a measure of constancy, or <emph>precision</emph>, that does not necessarily correspond to accuracy (closeness to physical reality), which is what is needed for calibration and error‐correction. Few studies have attempted to establish the underlying principles of cross‐sensory calibration. [<reflink idref="bib16" id="ref84">16</reflink>] reported that calibration of visual and auditory space was determined by reliability (like sensory fusion), but this may have been a specific case, where precision and accuracy happen to be correlated, and not true in general. In a more recent study, [<reflink idref="bib46" id="ref85">46</reflink>] showed that a mismatch between visual and vestibular signals will cause each to recalibrate towards the other, but the amount of recalibration does not depend on reliability; rather, it follows a fixed ratio rule independent of reliability. As previous studies in their laboratory ([<reflink idref="bib27" id="ref86">27</reflink>]) have shown that integration of visual and vestibular signals are governed by reliability, this is clear evidence that calibration and fusion can follow different rules. Young children do not fuse visual and haptic signals, but one or the other dominates: haptic signals for size and vision for orientation ([<reflink idref="bib19" id="ref87">19</reflink>]). This dominance is not in the direction predicted by reliability as, under the experimental conditions of that study, visual size judgments were more reliable than haptic size judgments, and both were similar for orientation. Reliability – which is a measure of repeatability or precision – is not in general a good criterion for calibration, as it is possible to be reliably wrong. What is needed for calibration is accuracy. Although hard to prove objectively, it makes sense that haptic information may be more accurate than vision for size judgments, as the visual estimate can only be made indirectly, by multiplying retinal size by perceived distance (itself an indirect measure), while visual orientation is encoded in the primary visual cortex.</p> <p>A growing body of evidence suggests that development of multisensory integration is the result of a complex exchange of signals from the various senses (e.g. [<reflink idref="bib4" id="ref88">4</reflink>]). The calibration that we hypothesize during the development is a long‐term process that requires many years (at least three years as suggested by results in children with acquired disability), and cannot be manipulated experimentally. Its effect can be observed studying it indirectly in children with sensory‐motor disabilities ([<reflink idref="bib20" id="ref89">20</reflink>]; [<reflink idref="bib22" id="ref90">22</reflink>]) or testing sensory perception in conditions in which a sensory system cannot operate ([<reflink idref="bib21" id="ref91">21</reflink>]). We believe that studying cross‐sensory processes during childhood could be a key strategy both to understanding the developing brain and to applying this knowledge for the development of new rehabilitation programs for children with sensory disabilities. The absence of communication between modalities, as we have seen, could have direct implications in children with sensory deficits (e.g. see [<reflink idref="bib20" id="ref92">20</reflink>]; [<reflink idref="bib22" id="ref93">22</reflink>]) in which perceptual damage could be caused by the absence of cross‐sensory calibration between modalities. These concepts still require further investigation to understand whether this cross‐sensory calibration is present, and to understand which neural mechanisms are in action, but the predictions are clear, and to date very consistent.</p> <hd id="AN0082891384-7">Acknowledgements</hd> <p>We thank Alessandra Sciutti for her valuable comments on the manuscript, and all the children for their willing participation in this research.</p> <ref id="AN0082891384-8"> <title> References </title> <blist> <bibl id="bib1" idref="ref29" type="bt">1</bibl> <bibtext> Alais, D., & Burr, D. (2004). The ventriloquist effect results from near‐optimal bimodal integration. Current Biology, 14 (3), 257 – 262.</bibtext> </blist> <blist> <bibl id="bib2" idref="ref38" type="bt">2</bibl> <bibtext> Banks, M.S., Aslin, R.N., & Letson, R.D. (1975). Sensitive period for the development of human binocular vision. 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  Data: Visual Size Perception and Haptic Calibration during Development
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  Data: <searchLink fieldCode="AR" term="%22Gori%2C+Monica%22">Gori, Monica</searchLink><br /><searchLink fieldCode="AR" term="%22Giuliana%2C+Luana%22">Giuliana, Luana</searchLink><br /><searchLink fieldCode="AR" term="%22Sandini%2C+Giulio%22">Sandini, Giulio</searchLink><br /><searchLink fieldCode="AR" term="%22Burr%2C+David%22">Burr, David</searchLink>
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  Data: <searchLink fieldCode="SO" term="%22Developmental+Science%22"><i>Developmental Science</i></searchLink>. Nov 2012 15(6):854-862.
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  Data: Wiley-Blackwell. 350 Main Street, Malden, MA 02148. Tel: 800-835-6770; Tel: 781-388-8598; Fax: 781-388-8232; e-mail: cs-journals@wiley.com; Web site: http://www.wiley.com/WileyCDA/
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  Data: <searchLink fieldCode="DE" term="%22Visual+Perception%22">Visual Perception</searchLink><br /><searchLink fieldCode="DE" term="%22Tactual+Perception%22">Tactual Perception</searchLink><br /><searchLink fieldCode="DE" term="%22Children%22">Children</searchLink><br /><searchLink fieldCode="DE" term="%22Adolescents%22">Adolescents</searchLink><br /><searchLink fieldCode="DE" term="%22Adults%22">Adults</searchLink><br /><searchLink fieldCode="DE" term="%22Geographic+Location%22">Geographic Location</searchLink><br /><searchLink fieldCode="DE" term="%22Accuracy%22">Accuracy</searchLink><br /><searchLink fieldCode="DE" term="%22Individual+Development%22">Individual Development</searchLink><br /><searchLink fieldCode="DE" term="%22Foreign+Countries%22">Foreign Countries</searchLink>
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  Data: 10.1111/j.1467-7687.2012.2012.01183.x
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  Data: It is still unclear how the visual system perceives accurately the size of objects at different distances. One suggestion, dating back to Berkeley's famous essay, is that vision is calibrated by touch. If so, we may expect different mechanisms involved for near, reachable distances and far, unreachable distances. To study how the haptic system calibrates vision we measured size constancy in children (from 6 to 16 years of age) and adults, at various distances. At all ages, accuracy of the visual size perception changes with distance, and is almost veridical inside the haptic workspace, in agreement with the idea that the haptic system acts to calibrate visual size perception. Outside this space, systematic errors occurred, which varied with age. Adults tended to overestimate visual size of distant objects (over-compensation for distance), while children younger than 14 underestimated their size (under-compensation). At 16 years of age there seemed to be a transition point, with veridical perception of distant objects. When young subjects were allowed to touch the object inside the haptic workspace, the visual biases disappeared, while older subjects showed multisensory integration. All results are consistent with the idea that the haptic system can be used to calibrate visual size perception during development, more effectively within than outside the haptic workspace, and that the calibration mechanisms are different in children than in adults. (Contains 4 figures.)
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– Name: DateEntry
  Label: Entry Date
  Group: Date
  Data: 2013
– Name: AN
  Label: Accession Number
  Group: ID
  Data: EJ988489
PLink https://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=eric&AN=EJ988489
RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1111/j.1467-7687.2012.2012.01183.x
    Languages:
      – Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 9
        StartPage: 854
    Subjects:
      – SubjectFull: Visual Perception
        Type: general
      – SubjectFull: Tactual Perception
        Type: general
      – SubjectFull: Children
        Type: general
      – SubjectFull: Adolescents
        Type: general
      – SubjectFull: Adults
        Type: general
      – SubjectFull: Geographic Location
        Type: general
      – SubjectFull: Accuracy
        Type: general
      – SubjectFull: Individual Development
        Type: general
      – SubjectFull: Foreign Countries
        Type: general
      – SubjectFull: Italy
        Type: general
    Titles:
      – TitleFull: Visual Size Perception and Haptic Calibration during Development
        Type: main
  BibRelationships:
    HasContributorRelationships:
      – PersonEntity:
          Name:
            NameFull: Gori, Monica
      – PersonEntity:
          Name:
            NameFull: Giuliana, Luana
      – PersonEntity:
          Name:
            NameFull: Sandini, Giulio
      – PersonEntity:
          Name:
            NameFull: Burr, David
    IsPartOfRelationships:
      – BibEntity:
          Dates:
            – D: 01
              M: 11
              Type: published
              Y: 2012
          Identifiers:
            – Type: issn-print
              Value: 1363-755X
          Numbering:
            – Type: volume
              Value: 15
            – Type: issue
              Value: 6
          Titles:
            – TitleFull: Developmental Science
              Type: main
ResultId 1