What is learned when learning to point at "invisible" targets?

Abstract

Binocular masking is a particularly interesting means of suppressing human visual awareness, as images rendered subjectively "invisible" via binocular masking nonetheless excite robust activity in human visual cortex. Recently, binocular masking has been leveraged to show that people can be trained to better interact with inputs that, subjectively, remain invisible. Here we ask what is learned in such circumstances. Do people become more adept at using weak encoded signals to guide hand movements, or is signal encoding enhanced, resulting in heightened objective sensitivity? To assess these possibilities, we had people train on five consecutive days, to reach toward and point at a target presented in one of three masked locations. Target intensity was set to a fraction of a detection threshold determined pretraining for each participant. We found that people became better at selecting the target location with training, even when insisting they could not see the target. More important, posttraining we found objective thresholds had improved by an amount that was commensurate with an improvement in subjective visibility. Our data therefore show that training to coordinate with subjectively invisible targets can result in enhanced encodings of binocularly masked images.