Footprints Sticking Out of the Sand. Part 2: Children's Bayesian Priors for Shape and Lighting Direction

Abstract

The shading information in images that depict surfaces of 3D objects cannot be perceived correctly unless the direction of the illuminating light source is known, and, in the absence of this knowledge, perception in adults is consistent with a light-from-above Bayesian prior assumption. In order to investigate if children make use of a similar assumption, 171 children between the ages of 4.6 and 10.8 years were tested using 20 images containing shading information, where the shape depicted in each image can be perceived as either convex or concave. Each child's Bayesian prior probability that light comes from above was estimated, and (assuming that decision-noise is approximately the same in all children) regression analyses revealed a significant increase in this prior probability of 0.034-0.035 per year, and predict a neutral prior (ie 0.5) at 1.6 years for naturalistic picture stimuli and 3.6 years for abstract symbol stimuli. Additionally, each child's prior probability for perceiving shapes as being convex/concave was estimated, and was found to be close to a neutral value of 0.5 for all ages. Together, these results indicate that children have a neutral prior for shape convexity, and that their prior probability for lighting direction gradually shifts towards an adult-like prior value as they grow older. Finally, the status of these one-dimensional priors is discussed in relation to marginal distributions of high-dimensional priors implicit in the statistical structure of the physical word.

The light-from-above prior is intact in autistic children

“…Our findings are in contrast to other research reporting developmental increases in responses consistent with light-from-above prior (Stone, 2011, Stone and Pascalis, 2010, Thomas et al, 2010), although the evidence is not clear-cut. Thomas et al (2010) found an overall effect of age on children’s interpretation of ambiguous stimuli, so that trials answered assuming light from above increased across childhood.…”

The perception of shape from shading in a new light

“…The results reported here provide further evidence that the perception of shape from shading, like other aspects of visual perception (Purves, Wojtach & Lotto, 2011), arises from interactions with the natural world rather than internal biases that give rise to illusory perception (Stone, 2011; Stone & Pascalis, 2010). Importantly the demonstration here does not depend on a complex analysis of psychophysical data, but rather a simple shape-from-shading drawing and a candle would do, allowing even Rittenhouse (1786) to experience this himself.…”

“…Contrary to those who theorized that the overhead bias is hard-wired and innate (Ramachandran, 1988; Hoffman, 1998), Stone found that the overhead Bayesian prior requires developmental experience (Stone, 2011). A recent study demonstrated that the assumption that light comes from above has a lesser role than lighting cues in the perception of shape from shading (Morgenstern, Murray & Harris, 2011).…”

“…Although most recent investigators have accepted the “light is overhead” bias as a strong rule used by the human visual system (Thomas, Nardini & Mareschal, 2010; Gerardin, Kourtzi & Mamassian, 2010; Dobbins & Grossmann, 2010), a number of studies have taken a Bayesian modelling approach to demonstrate how other information is incorporated with such a prior to modify the ultimate perception in favour of the most likely outcome (Stone, Kerrigan & Porrill, 2009; Stone, 2011; Adams, 2007; Adams, 2008; Adams, Graf & Ernst, 2004). Contrary to those who theorized that the overhead bias is hard-wired and innate (Ramachandran, 1988; Hoffman, 1998), Stone found that the overhead Bayesian prior requires developmental experience (Stone, 2011).…”

The effects of grouping on speed discrimination thresholds in adults, typically developing children, and children with autism

“…There may also be agerelated changes in the effects of grouping on speed discrimination. Although children make use of prior information from an early age (Sciutti, Burr, Saracco, Sandini, & Gori, 2014;Thomas, Nardini, & Mareschal, 2010), the weighting assigned to these priors may change as the child develops (Stone, 2011;. Furthermore, it has been suggested that the extent of global processing increases with age (Dukette & Stiles, 1996;Harrison & Stiles, 2009;Kramer, Ellenberg, Leonard, & Share, 1996;Poirel, Mellet, Houdé, & Pineau, 2008;Tada & Stiles, 1996;Vinter, Puspitawati, & Witt, 2010; but see also Enns & Girgus, 1985).…”