Attentional Effect on Contrast Appearance: From Enhancement to Attenuation

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Does attention alter appearance? Recent studies have shown that an exogenous cue tends to increase the perceived contrast of a low-contrast stimulus. In the present study we systematically studied the attentional effect over a wide range of contrast levels (15% to 60%). Besides replicating the enhancement at lower contrast levels with higher comparative tasks (Experiment 1), the data revealed a cue-induced attenuation in apparent contrast at higher contrast levels with lower comparative tasks (Experiment 2) and same/different judgment task (Experiment 3). This attenuation effect was robust at the individual level, and it was not due to response bias or sensory interactions (Experiments 3 and 4). These results suggest that attention modulates contrast appearance and this effect depends on both the contrast level and the type of judgment task used. We propose that our findings can be understood through contrast gain mechanism on supersatuating neurons, whose response increases first as the stimulus intensity increases, but decrease the responses after the peak. This surprising phenomenon offers insights for the underlying neural mechanisms of visual processing.

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