Abstract
The human visual system is well equipped to inform us about whether an image depicts a possible viewpoint of a structurally coherent 3-D object. Adult observers can readily classify simple 2-D line drawings as depicting “possible” or “impossible” 3-D objects. Our previous work demonstrated that 4-month-olds showed a strong novelty preference (i.e., significantly longer looking times) for impossible relative to possible object displays (Shuwairi et al., 2005). Therefore, the capacity to detect irregularities in global object structure is available early.
To investigate the perceptual mechanisms that support this capacity, we recorded eye movements as 4-month-olds viewed structurally matched line drawings of possible and impossible cubes. We reasoned that infants would provide evidence of active comparison of specific local regions in which depth order of junction parts was reversed in impossible relative to possible object displays and that “critical regions” in impossible cubes would recruit increased visual attention. Dwell times were reliably longer within critical regions in impossible relative to possible cubes (p < .01). Within each impossible cube, dwell times were longer in the critical region inconsistent with global coherence relative to other regions (p < .05). These results further document the ability of young infants to discriminate between possible and impossible objects, and extend our initial findings by providing insights into the mechanisms responsible for the effect. By 4 months of age, infants allocate attentional resources appropriately to register critical junctions, compute local relative depth of surfaces, and represent global 3-D object coherence.