Bilateral stimulation strengthens contralateral bias in extrastriate visual cortex J Reithler1, J Peters1, Y M van Someren2, R Goebel1 |
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1Cognitive Neuroscience, Maastricht University, Netherlands |
| Visual scenes are initially processed via segregated neural pathways dedicated to either of the two visual hemifields. In contrast, higher-order brain areas comprising the ventral visual stream are thought to utilize invariant object representations, abstracted away from low-level features such as stimulus position. Here, we assessed the nature of such higher-order object representations using fMRI-based multi-voxel pattern analyses, showing that their degree of position invariance is dependent on the encountered stimulus configuration. Under unilateral visual stimulation, fMRI activation in both the ipsilateral and contralateral hemisphere allowed nearly perfect classification of the presented object category (i.e, position invariant coding). However, adding a stimulus in the opposite hemifield elicited a very pronounced contralateral bias in activity patterns, re-establishing the segregation known to exist in earlier processing stages (i.e., position dependence). The contralateral emphasis under bilateral stimulation conditions likely reflects the brain’s common modus operandi given that natural visual scenes generally contain various objects simultaneously. The current findings extend previous work by showing that configuration-dependent modulations in representational invariance as previously observed in single neuron responses have a counterpart in human neural population coding. Moreover, they corroborate the emerging view that certain functional characteristics ascribed to ventral visual stream processing require reconsideration. |
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