Enhanced perception of illusory contours in the lower versus upper visual hemifields.

The visual world consciously perceived is very different from the spatial array of photo-receptor activation present on our retinae; it is composed of segregated surfaces, organized into distinct objects. An important component of this organizational process, the segmentation of an image into figures and background, is shown to be performed much better in the lower visual field. This finding is demonstrated by the performance in two tasks that involve the perception of illusory contours. This asymmetry indicates a neural specialization that may be related to the anatomical discontinuity along the representation of the horizontal meridian in extrastriate visual cortex.