Internal Spatial Organization of Receptive Fields of Complex Cells in the Early Visual Cortex

Abstract

Sasaki KS, Ohzawa I. Internal spatial organization of receptive fields of complex cells in the early visual cortex. J Neurophysiol 98: 1194 -1212, 2007. First published July 25, 2007; doi:10.1152/jn.00429.2007. The receptive fields of complex cells in the early visual cortex are economically modeled by combining outputs of a quadrature pair of linear filters. For actual complex cells, such a minimal model may be insufficient because many more simple cells are thought to make up a complex cell receptive field. To examine the minimalist model physiologically, we analyzed spatial relationships between the internal structure (subunits) and the overall receptive fields of individual complex cells by a two-stimulus interaction technique. The receptive fields of complex cells are more circular and only slightly larger than their subunits in size. In addition, complex cell subunits occupy spatial extents similar to those of simple cell receptive fields. Therefore in these respects, the minimalist schema is a fair approximation to actual complex cells. However, there are violations against the minimal model. Simple cell receptive fields have significantly fewer subregions than complex cell subunits and, in general, simple cell receptive fields are elongated more horizontally than vertically. This bias is absent in complex cell subunits and receptive fields. Thus simple cells cannot be equated to individual complex cell subunits and spatial pooling of simple cells may occur anisotropically to constitute a complex cell subunit. Moreover, when linear filters for complex cell subunits are examined separately for bright and dark responses, there are significant imbalances and position displacements between them. This suggests that actual complex cell receptive fields are constructed by a richer combination of linear filters than proposed by the minimalist model.

Complex Cells in the Cat Striate Cortex Have Multiple Disparity Detectors in the Three-Dimensional Binocular Receptive Fields

“…The geometric mean of the pooling ratio amounted to 1.80 for the Y direction and 1.30 for the X direction for our sample of complex cells. Sasaki and Ohzawa (2007) reported that the majority of complex cells in the early visual cortex pool subunits minimally in space to make up the monocular RFs (median of size ratio, ϳ1.21 in area), concluding that complex cells can be described adequately by the standard energy model without spatial pooling (Adelson and Bergen, 1985;Qian 1994;Fleet et al, 1996). An apparent contradiction with this report can be explained by a difference in the metric for evaluating the degree of spatial pooling.…”

“…Procedures for animal preparation and maintenance, surgery, single-unit recording, and experiment setup have been described in detail previously (Sasaki and Ohzawa, 2007). Only a brief account is provided here, with an emphasis on those aspects of the methodology most relevant to the present study.…”

“…For each cell, an XL-XR interaction map is also shown for a pair of Y positions that exhibited the strongest response among all pairs of Y positions (i.e., the XL-XR map obtained at the peak position in the interaction strength map in the YL-YR domain). The envelope of the XL-XR interaction profile was computed by using partial Hilbert transform for binocularly inseparable cells (Sasaki and Ohzawa, 2007) and by an equivalent method for binocularly separable cells (see supplemental material, available at www.jneurosci.org). The envelope of the XL-XR interaction profile may be regarded as an interaction strength map in the XL-XR domain and used to quantify to what extent binocular disparity detectors are pooled to make up the RF in the X direction.…”

Surround Suppression of V1 Neurons Mediates Orientation-Based Representation of High-Order Visual Features

“…Spatial frequency and orientation tunings were measured by subspace reverse correlation using rapidly flashed grating stimuli (Nishimoto et al 2005;Ringach et al 1997a). Dense-noise stimulus was presented to obtain receptivefield (RF) maps of CRF (linear kernel) using standard reverse correlation (Sasaki and Ohzawa 2007). Orientation and spatial-frequency tunings were also obtained using conventional drifting grating stimuli.…”

Orientation selectivity in cat primary visual cortex: local and global measurement

“…The shape (aspect ratio) and number of receptive fi eld subregions are major factors that affect the tuning width [18][19][20] . Orientation selectivity is also associated with a broader range of stimulus values (global measure).…”