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J.C. Rabin; Spatial Frequency Doubling Transcends the Cardinal Directions of Color Space . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3190.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: When a low spatial frequency sine wave grating is counterphase flickered at a high rate, the perceived spatial frequency appears 2X higher than that perceived under stationery conditions. This spatial "frequency-doubling effect," initially described by Kelly (JOSA 1966;56:1628), has been attributed to nonlinear response properties, originating in a subset of magnocellular-projecting (M) ganglion cells. However, recent evidence indicates that M cell activity per se does not underlie frequency doubling; the effect presumably is seated at a higher level (White et al, IOVS 2002;43:3590). Our purpose is to determine whether frequency doubling transcends the cardinal directions of color space, which include both M and parvocellular (P) pathways. Methods: Stimuli were generated with a Cambridge Research Graphics (VSG 2/4) calibrated display system. Vertical sinusoidal gratings were displayed in a 10 degree square surrounded by a field of the same mean luminance and chromaticity. Contrast was modulated along the three cardinal directions: achromatic luminance (LUM), equiluminant S (stimulates only S cones), and equiluminant LM (stimulates L and M cones out of phase). Stimuli were presented at equal multiples of resolution threshold to achieve approximately equal levels of visibility, regardless of color direction. On each trial the subject adjusted spatial frequency to maintain a constant perception of five vertical bars on the display. Color direction (LUM, LM or S) and temporal frequency (stationery or flicker; 25 Hz flicker for LUM; 15 Hz flicker for S and LM directions) were varied between trials. Results: Consistent with previous research (Dobkins et al IOVS 1999;40:S355; Abstract 1886), our preliminary results indicate that the spatial frequency doubling effect occurs at all color directions (achromatic luminance, S cone equiluminant, LM equiluminant; mean ratio of perceived spatial frequency: flicker/stationary = 2.0). The effect persists across a range of luminance and chromatic contrasts with stimuli equated for relative visibility. Conclusions: Spatial frequency doubling transcends the cardinal directions of color space, thought to be fundamental in early stages of visual processing. The illusion may be seated at higher levels of processing, accessible to M and P information streams. These findings are relevant to the design of clinical testing, including frequency-doubling perimetry.
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