Flicker induces depth: Spatial and temporal factors in the perceptual segregation of flickering and nonflickering regions in depth

Abstract

If some regions of a random-dotfieldare flickered, then the nonflickering areas appear to stand out in depth in front of the flickering regions. This perception of depth is optimal within a limited range of temporal frequencies. The average temporal luminance of the flickering and nonflickering regions was kept equal, so the depth segregation is not due to a luminance difference. In fact, depth is seen even when the average temporal luminance of the flickering regions is twice that of the steadily presented regions. The magnitude of perceiveddepth is affected by the percentage of luminance modulation: depth is maximal at 100% modulation and diminishes as the percent modulation decreases. We charted the tuning function using alternating flickering and nonflickering random-dot bars and found it to be similar to those of visual channels most sensitive to high temporal frequency.If areas of a filled visual field are flickered, the fMckering regions appear to lie in depth well behind the nonflickering regions (Wong & Weisstein, 1983a). When parts of a random-dot field were flickered so that the display consisted of alternating flickering and non flickering "bars" composed of dots, the nonflickering "bars" were seen to stand out in front of the flickering "bars."The nonflickering "bars" appear to form coherent rectangular shapes located in front of a background of flickering dots. The impression is not different from that of a row of figures contrasted against a flickering backdrop. The perceived depth effect reminds one of random-dot stereograms in which an area of dots may appear to float out in space in front of a background. Figure 1 is a representation of what the percept looks like to an observer. The flickering areas appear to stay at a constant depth behind the nonflickering areas rather than receding and approaching with the on-and-off cycle of the flicker. In other words, once the area is flickered at the appropriate temporal frequency, the flickering area remains steadily at a constant depth behind the nonflickering areas.The depth segregation produced by flicker-flickerinduced depth-is not due to a luminance difference between the flickering and nonflickering areas, since the average temporal luminance of all the regions was kept equal. It is also not dependent on the textural elements making up the visual field, since we obtained the effect with dots, horizontal lines, and vertical lines; nor does it depend on a specific configuration of the flickering and nonflickering regions, since we obtained this effect with "bars" made up of different textures and with concentric squares. The effect is not dependent on the density of dots filling the flickering and nonflickering regions, provided there is an adequate number of dots to define a region. Moreover, we found that a temporal frequency of about 6 Hz produced the greatest depth separation between the flickering and nonflickering areas, suggesting that visual channels responding pri-229

Spatial and temporal frequency in figure-ground organization

“…They found that for a range of spatial frequencies, from 8 to 0.5 cycles per degree (cpd), the region filled with the relatively lower spatial frequency sine-wave grating tends to be seen as the background behind the region filled with the higher spatial frequency grating, which in tum tends to be seen as the figure (see Figure 1). Wong and Weisstein (1984 found that regions of flickering dots tend to be seen as the background behind regions of stationary dots, which in tum are seen as the figure. The transient-sustained continuum of visual response sensitivity (e.g., see Giaschi, Anstis, & Rogers, 1988;Hess & Plant, 1985;Kelly, 1972Kelly, , 1979Koenderink & van Doorn, 1979;Robson, 1966;van Nes, Koenderink, & Bouman, 1967;Watson & Nachmias, 1977), where visual responses to higher spatial frequencies are generally associated with responses to lower temporal frequencies and…”

“…As with the early investigations of visual sensitivity to spatial and temporal frequency (see Olzak &Thomas, 1986 andWatson, 1986 for reviews), the initial investigations of the visual system's responses to figure and ground considered only spatial or temporal frequency separately while holding the other physical dimension constant (Klymenko & Weisstein, 1986;Wong & Weisstein, 1984). Below, for suprathreshold stimuli, we systematically examine the combined influence of spatial and temporal frequency on figure-ground organization.…”

“…While the differential visual responses to contrasts for different spatial and temporal frequencies (Robson, 1966) become attenuated above threshold (Camisa, Zemon, & Conte, 1985;Georgeson & Sullivan, 1975;Kulikowski, 1976), the spatial and temporal frequency content of suprathreshold textures in adjacent regions reliably and systematically determines their figure-ground organization (Klymenko & Weisstein, 1986;Wong & Weisstein, 1984. As with the early investigations of visual sensitivity to spatial and temporal frequency (see Olzak &Thomas, 1986 andWatson, 1986 for reviews), the initial investigations of the visual system's responses to figure and ground considered only spatial or temporal frequency separately while holding the other physical dimension constant (Klymenko & Weisstein, 1986;Wong & Weisstein, 1984).…”

Influence of flicker on perceived size and depth

“…The usual paradigm involves a visual field divided into two or more areas flickering at different rates. Typically, flickering areas are perceived as more distant than nonflickering areas, and areas with higher flicker rates are perceived as more distant than areas of slower flicker Klymenko, Weisstein, Topolski, & Hsieh, 1989;Wong & Weisstein, 1984a, 1984b, 1985, 1987. These effects are quite robust, remaining unaffected by variations in texture (e.g., Wong & Weisstein, 1985) or in the shapes of the flickering and nonflickering areas (e.g., Wong & Weisstein, 1984b, 1985, 1987, or by the presence or absence of contours surrounding the areas (Wong & Weisstein, 1987).…”

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Previous research (e.g., Wong & Weisstein, 1984a, 1985 has shown that flickering stimuli appear to be more distant than nonflickering stimuli at the same physical distance. Given this relation between flicker and perceived depth, inappropriate constancy scaling theories predict that flickering stimuli should be perceived as larger than nonflickering ones.

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