Repeatable Differences in Integration of Depth Cues across Young Observers

Abstract

Unlike adults, children aged below 12 years did not use multiple depth cues to reduce their uncertainty when judging surface slant (Nardini et al 2010, PNAS 107:39, 17041–17046). This suggests that Bayesian cue integration in the human visual system is not present until late in its development. Here we asked whether individuals at the ‘transitional’ ages of 8 to 12 years show consistent cue integration behaviour across two testing sessions. Identifying observers matched in age who reliably do/do not integrate depth cues would allow us to investigate neuronal mechanisms underlying these individual differences. Thirty observers judged which surface, a 45° standard or a variable comparison, was the most slanted, based on texture alone, disparity alone, or both. The test was repeated, giving a total of 6 (3 conditions x 2 sessions) thresholds per observer. In a principal component analysis (PCA) of distributions of thresholds, the first component (60% of variance) described variation in global ability, while the second (19% of variance) described variation in the balance between single-cue and combined cue thresholds. Thus, children at this age vary in their use of combined depth cues, and do so consistently in measures taken across two sessions. Analyses of correlation and error quantify the stability of observers’ thresholds. Methods for identifying individuals who ‘do’ versus ‘do not’ integrate cues are suggested, based on PCA with elimination of unstable or outlying individuals. These findings provide a basis for investigating neuronal changes underlying development of the ability to integrate visual information to reduce uncertainty.