Abstract
Single cell recordings in cat and monkey (e.g., Knierim & van Essen 1992) have shown that the response to an oriented line in the receptive field center of a neuron is strongest, when it is orthogonal to line elements in the receptive field surround. When the orientation is the same, the response is weak. We devised texture patterns to test whether there is a psychophysical correlate of this neuronal behavior when different orientations in the center are pitted against same orientations in the surround and vice versa. Two stimuli were used: one with randomly oriented bars in the center and vertical bars in the surround and a second that was its converse. The mean spacing of the bars was the same in center and surround, and stimuli were positioned at 8 deg from fixation. Fading time was measured. In 10 observers we found that the first stimulus was not only perceptually more salient, but required also more time for the center to fade into the background (“filling-in”). This finding is consistent with the assumption that a random texture elicits activity in all orientation channels and thus produces a strong response, whereas a uniform texture elicits activity only in a single channel and therefore produces a weak response. As a consequence, the percept of a randomly oriented center would be sustained, while the percept of a uniformly oriented center would be suppressed. In a second experiment, we used dots, instead of bars, in the center and again found longer fading times for stimuli having uniformly oriented as opposed to randomly oriented bars in the surround. However, when we reduced the surround area while keeping the size of the center constant, we found no systematic change of fading time. Instead, fading increasingly occurred in the opposite direction (“filling-out”). The data suggest a correlation of fading time with perceptual salience and the presumed neuronal response, with a modulating influence by the relative size of center and surround.
Supported by DFG-grant SP 67/8-2