The Detection of Orientation Continuity and Discontinuity by Cat V1 Neurons

Abstract

The orientation tuning properties of the non-classical receptive field (nCRF or “surround”) relative to that of the classical receptive field (CRF or “center”) were tested for 119 neurons in the cat primary visual cortex (V1). The stimuli were concentric sinusoidal gratings generated on a computer screen with the center grating presented at an optimal orientation to stimulate the CRF and the surround grating with variable orientations stimulating the nCRF. Based on the presence or absence of surround suppression, measured by the suppression index at the optimal orientation of the cells, we subdivided the neurons into two categories: surround-suppressive (SS) cells and surround-non-suppressive (SN) cells. When stimulated with an optimally oriented grating centered at CRF, the SS cells showed increasing surround suppression when the stimulus grating was expanded beyond the boundary of the CRF, whereas for the SN cells, expanding the stimulus grating beyond the CRF caused no suppression of the center response. For the SS cells, strength of surround suppression was dependent on the relative orientation between CRF and nCRF: an iso-orientation grating over center and surround at the optimal orientation evoked strongest suppression and a surround grating orthogonal to the optimal center grating evoked the weakest or no suppression. By contrast, the SN cells showed slightly increased responses to an iso-orientation stimulus and weak suppression to orthogonal surround gratings. This iso-/orthogonal orientation selectivity between center and surround was analyzed in 22 SN and 97 SS cells, and for the two types of cells, the different center-surround orientation selectivity was dependent on the suppressive strength of the cells. We conclude that SN cells are suitable to detect orientation continuity or similarity between CRF and nCRF, whereas the SS cells are adapted to the detection of discontinuity or differences in orientation between CRF and nCRF.

Silent suppressive surrounds and optimal spatial frequencies of single neurons in cat V1

“…Adult cats of both sexes were used for these experiments. Surgical procedures and animal preparation have been described previously [7].…”

“…Previous studies have suggested that the center responses of the majority of V1 cells are suppressed by the inclusion of surround stimuli. We named these neurons "surround-suppressive" (SS) cells [7].…”

“…Instead, in some cells, responses will saturate and exhibit a plateau-like tuning profile [1,4]. These cells we named "surroundnon-suppressive" (SN) cells [7].…”

“…Using the abbreviation "s" for suppressive and "n" for non-suppressive, four possible combinations of the integration of the side (width, W) and end (length, L) can be defined: the majority of cells [1,5]. Their feature-selective surround inhibition constitutes the neural basis of perceptual 'pop out' [14,15] and contour discrimination [5,7,10,13,16]. We, therefore, studied the optimal SF of this type of neuron and explored the various influences of end and side inhibition on optimal SF.…”

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

“…Detailed descriptions of animal surgery, anesthesia, and recording techniques can be found in previous studies [25,26] . Briefl y, cats were anaesthetized prior to surgery with ketamine hydrochloride (30 mg/kg, i.v.…”