On the summation of visual noise

Abstract

What information is used by the visual system to detect patterns? A standard model hypothesizes that both spatial frequency and orientation information are processed by independent channels, meaning there is no summation among channels. Despite consensus among researchers on how the visual system sums spatial frequency and orientation information there are data in the literature (Kersten, 1987) that ostensibly contradict the standard model. To resolve this conflict, we measured the efficiency of spatial frequency and orientation of filtered noise. To learn what information the visual system uses when detecting filtered noise, we applied a technique that can determine the information used to detect and discriminate filtered visual noise. In Chapter 2 the detection of spatial frequency filtered noise is not only efficient but remains so with stimulus uncertainty and extremely brief (10ms) stimulus duration. When the spatial frequency channel used was measured, we found a fixed bandwidth channel as the spatial frequency of the pattern was increased. To test the standard model, we implemented simulations of the standard model and contrary to the interpretation, the standard model could predict detection of spatial frequency filtered noise. Chapter 3 used spatial frequency filtered noise to relate the detection and discrimination of filtered visual noise. A simple rule relates what information observers use to detect and discriminate spatial frequency filtered noise. Chapter 4 extends the work of Chapter 2 to orientation information and found that orientation filtered noise is detected efficiently. We again measured what information observers used and found that, unlike SF filtered noise, observers use orientation in a flexible or adjustable manner.