Abstract
When the two eyes’ processing streams meet in visual cortex, two things can happen: sufficiently similar monocular inputs are combined into a fused representation, whereas markedly different inputs engage in rivalry. Interestingly, the emergence of rivalry appears to require attention. Withdrawing attention causes the alternating monocular dominance that characterizes rivalry to cease, apparently allowing both monocular signals to be processed simultaneously. What happens to these signals in this case, however, remains something of a mystery; are they fused into an integrated representation? In a set of experiments, we show this not to be the case: visual aftereffects are consistent with the simultaneous yet separate presence of two segregated monocular representations, rather than a joint representation. These results provide evidence that dichoptic vision without attention prompts a third and previously unknown mode, where both eyes’ inputs receive equal processing, but escape interocular fusion.
Highlights
When the two eyes’ processing streams meet in visual cortex, two things can happen: sufficiently similar monocular inputs are combined into a fused representation, whereas markedly different inputs engage in rivalry
We found that some participants had a systematic response bias in the sense that the reported motion aftereffect (MAE) direction, when averaged across two mirror reversed versions of a given adapter, was not vertical
The adapter effect was significant and the post hoc analysis showed that the unattended superimposed condition had a significantly less vertical MAE angle than each of the other two unattended presentation conditions, but that there was no significant difference in MAE angle between the unattended dichoptic condition and the unattended sequential condition
Summary
When the two eyes’ processing streams meet in visual cortex, two things can happen: sufficiently similar monocular inputs are combined into a fused representation, whereas markedly different inputs engage in rivalry. Withdrawing attention causes the alternating monocular dominance that characterizes rivalry to cease, apparently allowing both monocular signals to be processed simultaneously What happens to these signals in this case, remains something of a mystery; are they fused into an integrated representation? In a set of experiments, we show this not to be the case: visual aftereffects are consistent with the simultaneous yet separate presence of two segregated monocular representations, rather than a joint representation These results provide evidence that dichoptic vision without attention prompts a third and previously unknown mode, where both eyes’ inputs receive equal processing, but escape interocular fusion. The central question, becomes: what MAE direction is observed after presenting these two gratings to separate eyes, and without attention? If such dichoptically presented images are fused under this condition, MAE directions should match that of the moving plaid, rather than that of the individual gratings
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