Dissociable neural activations of conscious visibility and attention.

Abstract

Recent neuroimaging evidence indicates that visual consciousness of objects is reflected by the activation in the lateral occipital cortex as well as in the frontal and parietal cortex. However, most previous studies used behavioral paradigms in which attention raised or enhanced visual consciousness (visibility or recognition performance). This co-occurrence made it difficult to reveal whether an observed cortical activation is related to visual consciousness or attention. The present fMRI study investigated the dissociability of neural activations underlying these two cognitive phenomena. Toward this aim, we used a visual backward masking paradigm in which directing attention could either enhance or reduce the object visibility. The participants' task was to report the level of subjective visibility for a briefly presented target object. The target was presented in the center with four flankers, which was followed by the same number of masks. Behavioral results showed that attention to the flankers enhanced the target visibility, whereas attention to the masks attenuated it. The fMRI results showed that the occipito-temporal sulcus increased activation in the attend flankers condition compared with the attend masks condition, and occipito-temporal sulcus activation levels positively correlated with the target visibility in both attentional conditions. On the other hand, the inferior frontal gyrus and the intraparietal sulcus increased activation in both the attend flankers and attend masks compared with an attend neither condition, and these activation levels were independent of target visibility. Taken together, present results showed a clear dissociation in neural activities between conscious visibility and attention.