Orientation-selective inhibition from beyond the classic visual receptive field

Abstract

A considerable body of psychophysical literature indicates that the context in which a stimulus occurs can have striking effects on its appearance. In particular, one group of lines can distort the perceived orientation of other lines, as many figural illusions show. This suggests an orientation-selective interaction among contourdetecting cortical units 6,15. By surrounding the receptive field of one cell with contours which surely must have stimulated myriad others, we have been able to demonstrate a powerful, orientation-specific inhibitory input upon the cell under test. We have thus confirmed the report of Blakemore and Tobin 7 for one complex cell, and extended the findings to other common classes of visual receptive fields. Our primary aim in the present paper is to establish that the effect may be elicited when surrounding contours are prevented from directly stimulating any part of the receptive field. New, statistical techniques were therefore developed to delimit the maximum extent of the receptive field under test. Our ability to elicit an orientationselective inhibitory effect from beyond the classic receptive field limits strongly suggests an intracortical origin for the inhibitory input. Further properties of the effect itself, in particular its consequences for single unit orientation selectivity, will be explored elsewhere 17. Normally reared adult cats were anaesthetized with halothane in a 70:30 N20/02 gas mixture for major surgery, and anaesthesia maintained with 70:30 N20/O2 for subsequent recording with tungsten-in-glass electrodes from the central visual projection in Area 17. Surgical wounds were infiltrated with a long-acting local anaesthetic (bupivacaine, 0.5 ~) and treated with a topical antibiotic powder( Neosporin, Calmic Pharmaceuticals). Paralysis was maintained with a mixture of gallamine triethiodide (Flaxedil), approximately 6 mg/kg/h and toxiferin dichloride (Hoffman-La Roche), approximately 0.4 mg/kg/h. Coupled with bilateral sympathectomy, this paralytic cocktail makes accurate receptive field mapping possible by reducing eye movements to a slow drift of perhaps 6' arc/h is. We used limbic contact lenses, 3 mm artificial