No abstract

Would a blind subject, on regaining sight, be able to immediately visually recognize an object previously known only by touch? We addressed this question, first formulated by Molyneux three centuries ago, by working with treatable, congenitally blind individuals. We tested their ability to visually match an object to a haptically sensed sample after sight restoration. We found a lack of immediate transfer, but such cross-modal mappings developed rapidly.

How the visual system comes to bind diverse image regions into whole objects is not well understood. We recently had a unique opportunity to investigate this issue when we met three congenitally blind individuals in India. After providing them treatment, we studied the early stages of their visual skills. We found that prominent figural cues of grouping, such as good continuation and junction structure, were largely ineffective for image parsing. By contrast, motion cues were of profound significance in that they enabled intraobject integration and facilitated the development of object representations that permitted recognition in static images. Following 10 to 18 months of visual experience, the individuals' performance improved, and they were able to use the previously ineffective static figural cues to correctly parse many static scenes. These results suggest that motion information plays a fundamental role in organizing early visual experience and that parsing skills can be acquired even late in life.

The human visual system is adept at detecting and encoding statistical regularities in its spatiotemporal environment. Here, we report an unexpected failure of this ability in the context of perceiving inconsistencies in illumination distributions across a scene. Prior work with arrays of objects all having uniform reflectance has shown that one inconsistently illuminated target can 'pop out' among a field of consistently illuminated objects (eg Enns and Rensink, 1990 Science 247 721 723; Sun and Perona, 1997 Perception 26 519-529). In these studies, the luminance pattern of the odd target could be interpreted as arising from either an inconsistent illumination or inconsistent pigmentation of the target. Either cue might explain the rapid detection. In contrast, we find that once the geometrical regularity of the previous displays is removed, the visual system is remarkably insensitive to illumination inconsistencies, both in experimental stimuli and in altered images of real scenes. Whether the target is interpreted as oddly illuminated or oddly pigmented, it is very difficult to find if the only cue is deviation from the regularity of illumination or reflectance. Our results allow us to draw inferences about how the visual system encodes illumination distributions across scenes. Specifically, they suggest that the visual system does not verify the global consistency of locally derived estimates of illumination direction.