Spatial Receptive Field Organization of Macaque V4 Neurons

Abstract

Subfield analysis of the receptive fields (RFs) of parafoveal V4 complex cells demonstrates directly that most RFs are tiled by overlapping second-order excitatory inputs that for any given V4 cell are predominantly selective to the same preferred values of spatial frequency and orientation. These results extend hierarchical principles of RF organization in the spatial, orientation and spatial frequency domains, first recognized in V1, to an intermediate extrastriate cortex. Spatial interaction studies across subfields demonstrate that the responses of V4 neurons to paired stimuli may either decrease or increase as a function of inter-stimulus distance across the width axis. These intra-RF suppressions and facilitations vary independently in magnitude and spatial extent from cell to cell. These results taken together with the relatively large RF sizes of V4 neurons - as compared with RF sizes of their afferent inputs - lead us to hypothesize a novel property, namely that classes of stimulus configurations that enhance areal summation while reducing suppressive interactions between excitatory inputs will evoke especially robust responses. We tested, and found support for, this hypothesis by presenting stimuli consisting of optimally tuned sine-wave gratings visible only within an annular region and found that such stimuli vigorously activate V4 neurons at firing rates far higher than those evoked by comparable stimuli to either the full-field or central core. On the basis of these results we propose a framework for a new class of neural network models for the spatial RF organizations of prototypic V4 neurons.

Spatial Summation Can Explain the Attentional Modulation of Neuronal Responses to Multiple Stimuli in Area V4

“…This neuron exhibited strong orientation tuning to single Gabors (top row and right column). Consistent with a previous report (Pollen et al, 2002), orientation tuning was similar at the two positions. When a single Gabor was presented in the receptive field, average responses were consistently higher when attention was directed within the receptive field (solid lines) than when it was directed outside of the receptive field (dashed lines).…”

“…For such stimulus pairs, the attended position dominates the response (A, center and right). The paired response surface for attend out shows that responses to pairs of stimuli are not necessarily simply predicted from single-stimulus responses (Pollen et al, 2002). For example, a simple averaging model is inadequate because, with such a model, the strongest response would be limited to preferred stimuli in both positions (top left corner).…”

Predictions of a model of spatial attention using sum- and max-pooling functions

“…Our approach is similar, but competition occurs after pooling. It is based on lateral short-range excitory and long-range inhibitory connections within the population, which is in accordance with ÿndings in V4 [8,29]. With respect to pooling, our simulations suggest that an additional max-like competition among a erents would prevent a bias due to the fact that multiple distractors add up their competitive weight.…”

“…The V4 layer is simulated by a single population of the same size on which the V2 populations project. We consider feedforward, lateral excitory and inhibitory input and spatially organized attentional feedback as relevant factors (see [29]), but do not model feedback from IT. Each V4 cell receives a weighted input from each V2 population (Eq.…”

Receptive Field Properties of Neurons in the Early Visual Cortex Revealed by Local Spectral Reverse Correlation

“…Rather, visual stimuli must contain the essential parts simultaneously in order for the summed excitation to overcome the spiking threshold. This type of nonlinearity is thought to be a source of the problem in mapping response profiles in a part-by-part manner using elementary stimuli such as a bar or a patch of grating (Pollen et al, 2002). The LSRC method may, at least partly, overcome this difficulty.…”