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Stuart G. Fuller, Marisa Carrasco; Hue-contrast is invariant with attention. Journal of Vision 2005;5(8):1001. doi: https://doi.org/10.1167/5.8.1001.
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Background: Transient covert attention enhances contrast sensitivity and spatial resolution, and alters both apparent contrast and spatial frequency. We have shown that transient attention also changes apparent color saturation (Fuller et al., VSS 2004). Here we examine whether attention affects hue-contrast sensitivity. Hue discrimination thresholds are a function of angular separation in colorspace, independent of saturation (Sankeralli & Mullen, 1999). We hypothesized that attention enhances the saturation of two simultaneously presented hues without changing the subjective hue difference between them.
Method: Observers performed a 2AFC orientation discrimination task, reporting the orientation (45° right or left tilt) of one of two stimuli presented simultaneously at 4° eccentricity on the horizontal meridian. The stimuli were 2° Gabors modulated in hue (polar angle in colorspace) with fixed luminance and saturation. Hue modulation was identical for both patches in each trial, with tilt varying independently. We employed a range of hue modulations to elicit a psychometric function. Stimulus presentation (50 ms) was preceded by a brief (60 ms) uninformative precue appearing at the center fixation point (neutral cue) or adjacent to one of the stimuli (peripheral cue). At stimulus offset, a central arrow indicated the stimulus for which the observer was to report orientation.
Results: The psychometric function did not change with cueing condition, indicating that sensitivity to hue difference is invariant with attention, and that hue remains independent from saturation. This result differs from previous findings regarding the effect of attention on the appearance of contrast and spatial frequency. For color, whereas attention affects saturation, it does not affect hue.
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