Dissociable neural mechanisms underlie effects of attention on visual appearance and response bias

Abstract

Researchers have long debated whether attention can change perception and alter visual appearance, or whether attention only induces response bias. Recent psychophysical findings suggest that attention can have both of these types of effects, depending on stimulus visibility and decision uncertainty of the behavioral task. While this evidence helps reconcile the two competing accounts, it is still unknown how these different effects of attention are implemented in the brain. Using EEG, we found that the two behavioral effects of attention could be explained via different patterns of attentional modulations on different neural markers of visual processing. Specifically, the early visually evoked potential at ~100ms post-stimulus (i.e., the P1 component) appeared to underly subjects’ changes in visual appearance, whereas alpha-band oscillations (i.e., the posterior occipital 10-12Hz activity) appeared to underly subjects’ response bias. Specifically, attention enhanced the multiplicative response gain (or the slope) of the early visual-cortical response (the P1-based contrast response function (CRF) or the P1 amplitude measured as a function of visual contrast). At the same time attention led to an additive shift of the neural CRF based on the posterior occipital alpha band activity, which appeared to be responsible for changes in the lateralized readiness potential and subjects’ response bias. These findings suggest that attention biases both early visual perception and later stages of decision-making. Moreover, these two effects of attention are supported by dissociable neural mechanisms at different stages of visual information processing.