Infants and toddlers show enlarged visual sensitivity to nonaccidental compared with metric shape changes

Abstract

Some shape changes are more important for object perception than others. We used a habituation paradigm to measure visual sensitivity to a nonaccidental shape change-that is, the transformation of a trapezium into a triangle and vice versa-and a metric shape change-that is, changing the aspect ratio of the shapes. Our data show that an enhanced perceptual sensitivity to nonaccidental changes is already present in infancy and remains stable into toddlerhood. We have thus established an example of how early visual perception deviates from the null hypothesis of representing similarity as a function of physical overlap between shapes, and does so in agreement with more cognitive, categorical demands.

Keywords: development; habituation; looking time; preference; shape perception; shape transformations.

Figure 1.

The stimuli used in the different conditions. The test stimuli are presented side by side (see method section).

Figure 2.

(a) The average looking times towards the test stimuli that differ from the habituation stimulus by a NAP change (full gray) or a metric change (striped), in seconds. (b) The average looking times towards the test stimuli that differ from the habituation stimulus by a NAP change (circles) or a metric change (squares) as a function of age group, in seconds. The whiskers denote standard errors, derived from an ANOVA with nature of the shape change and age group as independent variables.