The effects of temporal modulation and spatial location on the perceived spatial frequency of visual patterns

Abstract

The perceived spatial frequency of a visual pattern can increase when a pattern drifts or is presented at a peripheral visual field location, as compared with a foveally viewed, stationary pattern, We confirmed previously reported effects of motion on foveally viewed patterns and of location on stationary patterns and extended this analysis to the effect of motion on peripherally viewed patterns and the effect of location on drifting patterns. Most central to our investigation was the combined effect of temporal modulation and spatial location on perceived spatial frequency. The group data, as well as the individual sets of data for most observers, are consistent with the mathematical concept of separability for the effects of temporal modulation and spatial location on perceived spatial frequency. Two qualitative psychophysical models suggest explanations for the effects. Both models assume that the receptive-field sizes of a set of underlying psychophysical mechanisms monotonically change as a function of temporal modulation or visual field location, whereas the perceptual labels attached to a set of channels remain invariant. These models predict that drifting or peripheral viewing of a pattern will cause a shift in the perceived spatial frequency of the pattern to a higher apparent spatial frequency.Several investigators have observed that changes in the perceived spatial frequency or apparent size of visual patterns may be produced by temporal modulation of the stimulus (Ansbacher, 1944;Gelb & Wilson, 1983;Kelly, 1966;Parker, 1981Parker, , 1983Tolhurst, 1975;Tyler, 1974) and by varying visual-field location (Davis, 1990;Davis, Yager, & Jones, 1987;Georgeson, 1980;James, 1890;Newsome, 1972).For example, a drifting grating viewed at the fovea has a higher perceived spatial frequency than does a foveally viewed stationary grating of the same physical spatial frequency (i.e., the foveal motion effect, FME). These shifts in perceived spatial frequency can increase up to 1 octave as the temporal frequency of the drifting grating is increased (e.g., see Parker, 1983). The effects of temporal modulation are most salient for low spatial frequency patterns.Similarly, a stationary peripheral sinewave grating may have a higher perceived spatial frequency than does a stationary foveal pattern of the same physical spatial frequency (i.e., the location effect for stationary stimuli, LES). These shifts in perceived spatial frequency can be This research is based on a paper submitted by Lynn Marran in partial fulfillment of the Master of Science degree requirements. The research was supported in part by NIH Grants EY05360 and EY05586, and by a Matching Funds Grant from the Research Foundation of the State University of New York to Elizabeth T. Davis. We thank Angela Brown, Ellen Ettinger, Phil Kruger, Bill Swanson, Dean Yager, and an anonymous reviewer for their helpful comments on earlier versions of the manuscript. Correspondence may be addressed to either author, Department of Visual Sciences, SUNY State College of Optom...