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Jordan R. Wagge, Lynn A. Olzak; Contributions of contrast gain and response gain in pattern masking. Journal of Vision 2008;8(17):89. doi: 10.1167/8.17.89.
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Biologically and psychophysically, response as a function of contrast can be characterized by an ogive that accelerates at low contrasts and saturates at high contrasts. Recently, Huang & Dobkins (2005) found that the psychometric curve will shift under different testing conditions (transient versus sustained attention). A lateral shift indicates a change in the semisaturation constant and is suggestive of contrast gain, or gain set by the stimulus; a vertical shift indicates a change in maximum response (Rmax) and is suggestive of response gain, or gain set by the system and not the stimulus (Sengpiel et al, 1998; Webb et al, 2003). Shifts in the psychometric function can be used to test whether the responses of the system in pattern masking are due to response gain or contrast gain. In other words, does the psychometric function shift laterally or vertically when an abutting annulus is added to a central sinusoid? Preliminary data was gathered from 3 subjects in a 2AFC suprathreshold orientation discrimination; in this experiment, we added a surround mask to a central stimulus and examined the shift of the curve. With the addition of a low-contrast mask, two subjects demonstrated a horizontal shift, indicating contrast gain, and the other subject did not demonstrate any shift. One subject participated in a high-contrast mask condition and demonstrated both vertical and horizontal shifts. Further data will be used to study the relative contributions of response gain and contrast gain in pattern masking.
HuangL.DobkinsK. R. (2005). Attentional effects on contrast discrimination in humans: evidence for both contrast gain and response gain. Vision Research, 45, 1201–1212.
SengpielF.BaddeleyR. J.FreemanT. C. B.HarradR.BlakemoreC. B. (1998). Different mechanisms underlie three inhibitory phenomena in cat area 17. Vision Research, 38, 2067–2080.
WebbB. S.TinsleyC. J.BarracloughN. E.ParkerA.DerringtonA. M. (2003). Gain control from beyond the classical receptive field in primate primary visual cortex. Visual Neuroscience, 20, 221–230.
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