Dissociable neural mechanisms of selective visual information processing underlie the effects of attention on visual appearance and response bias

Abstract It has been debated if attention can penetrate early perceptual representations to alter visual appearance or it simply induces response biases. Here, we tested these alternative accounts by evaluating attentional modulations of EEG responses recorded from human subjects while they compared the perceived contrasts of cued and uncued visual stimuli of varying physical contrasts. We found that attention enhanced the response gain of neural contrast response functions (CRFs) computed based on the amplitude of the P1 component, an early visually evoked potential. Quantitative models suggested that the response gain of the P1-based CRFs could account for attention-induced changes in perceived contrast. Instead, attentional cues induced changes in the baseline offset of the CRFs based on 9-12Hz alpha-band oscillations and these baseline-offset changes better accounted for cue-induced response biases. Together, these results suggest that different neural mechanisms underlie the effects of attention on perceptual experience and on response biases.