Geometrical illusions and the response of neurones in the cat's visual cortex to angle patterns

Abstract

SUMMARY1. This report describes the responses of thirty-six single neurones in the primary visual area of the cat's neurologically isolated and unanaesthetized forebrain, to movements of thin white lines across the visual field. The experiments were designed to record the effects upon the response to a single test line of an added line, which was either parallel to the test line or joined it, making an angle-pattern of 300. Unit responses were measured in terms of the peak probability of firing derived from a post-stimulus histogram.2. All of the cortical neurones tested exhibited a preferred orientation for stimulation by the test line, i.e. an orientation of the line which produced a maximal response when the line passed through the centre of the unit's receptive field.3. There was no evidence that the orientation of a single test line preferred by cortical neurones was different from that preferred by the same cell when excited by an angle pattern, one arm of which was the original test line.4. The position of a test line (with preferred orientation) in the visual field that produced a maximal response from cortical neurones, was not always the same as the position for maximal response, when a second line was added to make either an angle pattern or to make a pattern of two parallel lines.5. Where the two lines ofthese patterns were close together and separated by less than the radius of the receptive field, the position for maximal response to the test line was shifted towards the added line. Where the two lines were further apart than this but separated by less than a receptive field diameter, the optimal position for the test line was displaced away from the added line.

Assessing Poggendorff effects via collinearity, perpendicularity, parallelism, and Oppel (distance) experiments

“…Conforming with convention, counterclockwise angular errors are designated as positive errors. A plausible and widely held theory concerning the Poggendorff effect is that the transversal orientation is misperceived because acute angles are overestimated (Blakemore, Carpenter, & Georgeson, 1970;Burns & Pritchard, 1971). The explanation implies that contour repulsion exists between a transversal and attached parallel such that the transversal would appear tilted too far clockwise (a negative angular error).…”

“…Since transversal misorientation is not an acceptable explanation, the neurophysiological hypotheses leaning upon contour interactions producing overestimation of acute angles (Blakemore, Carpenter, & Georgeson, 1970;Burns & Pritchard, 1971) cannot apply. Versions of Gregory's (1963) misapplied-constancy scaling theory (Gillam, 1971;Green & Hoyle, 1964) might be modified by postulating that, in order for a parallelism judgment to be feasible for S, the free-standing dots are first unconsciously scaled in depth to the same extent as the transversal segment being evaluated.…”

“…Alternatively, the acute angle between transversal and parallels might appear too large, an instance of contour repulsion (Blakemore. Carpenter, & Georgeson, 1970;Burns & Pritchard, 1971).The initial experiments are direct offshoots of our previous work (Tong & Weintraub, 1974), attempting .to assess the parallels-attract hypothesis applied to the Poggendorff effect. If parallels between transversal segments are represented in experience as too close together, then the attached transversals will seem to be vertically misaligned when they are actually collinear.…”

“…Alternatively, the acute angle between transversal and parallels might appear too large, an instance of contour repulsion (Blakemore. Carpenter, & Georgeson, 1970;Burns & Pritchard, 1971).…”

Structural and cognitive components in the Müller-Lyer illusion assessed via Cyclopean presentation

“…Requests for reprints should be addressed to S. Coren, Department of Psychology, University of British Columbia, Vancouver,B.C.,Canada V6T lWS. tical blurring of the retinal image has been found to contribute to the magnitude of a number of intersecting line illusions, such as the Muller-Lyer and Poggendorf configurations (Coren, 1969;Coren, Ward, Porac, & Fraser, 1978;Ward & Coren, 1976). Neural interactions at the retinal level, in the form of lateral inhibition, and at the cortical level, between orientation-specific cells, also seem to play a role in illusion formation (Bekesy, 1967;Blakemore, Carpenter, & Georgeson, 1970;Burns & Pritchard, 1971;Coren, 1970). Other neural mechanisms that might contribute to illusory effects include those that may perform Fourier-like transforms of the retinal intensity patterns (Ginsburg, 1975).…”