Visual object processing as a function of stimulus energy, retinal eccentricity and Gestalt configuration: a high-density electrical mapping study.

To reveal the fundamental processes underlying the different stages of visual object perception, most studies have manipulated relatively complex images, such as photographs, line drawings of natural objects, or perceptual illusions. Here, rather than starting from complex images and working backward to infer simpler processes, we investigated how the visual system parses and integrates information contained in stimuli of the most basic variety. Simple scatterings of a few points of light were manipulated in terms of their numerosity, spatial extent, and organization, and high-density electrophysiological recordings were made from healthy adults engaged in an unrelated task. We reasoned that this approach permitted an uncontaminated view of the spatio-temporal dynamics of the related neural processes. We were guided in our predictions by the "frame-and-fill" model for object perception, whereby fast inputs to the dorsal stream of the visual "where" system first frame the spatial extent of visual objects, which are subsequently "filled-in" by the slower activation of the ventral stream of the visual "what" system. Our findings were consistent with this view, showing a rapidly-onsetting effect of spatial extent in dorsal stream sources, and later-onsetting effects due to dot number and symmetry, which were deemed to be more closely tied to the details of object identity, from ventral stream sources. This collection of observations provides an important baseline from which to understand the spatio-temporal properties of basic visual object perception, and from which to test dysfunction of this system in clinical populations.