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Cathy Clarke, Michael Paradiso; The complex spatial topography of attentional modulation in macaque V4. Journal of Vision 2004;4(8):7. doi: https://doi.org/10.1167/4.8.7.
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© ARVO (1962-2015); The Authors (2016-present)
We examined, at a fine spatial scale, perceptual sensitivity (d′) and V4 evoked responses in three attentional situations. Macaques were cued to attend to either a small or large spatial area in order to perform a threshold 2AFC color discrimination task, or performed a fixation task. Examined at a coarse spatial scale, our results agree with previous work showing that cueing improves performance. However, at the finer scale that our procedure provided, new features of attentional modulation were revealed. When the attended region was large, V4 firing rates were elevated and animals were more sensitive to stimuli presented further from the center of the cued location than when the attended region was small. In fact, retinotopic areas that elicited no response with a simple fixation paradigm did produce a response with widened attention, as if the RF had expanded beyond its canonical dimensions. To our knowledge this is the first demonstration of increases in V4 RF size as a consequence of widening attention. Previously we showed that performance improves at locations near the cued location in the narrow-attention task, but there is a paradoxical performance deficit at the cued location itself. Interestingly, neural responses for stimuli at the cued location in the narrow-attention task were inhibited relative to their responses when the same stimuli were presented with a fixation task (no attention). Comparing V4 activity in narrow and wide attention tasks paints a complex picture of attentional modulation in V4. For example, with widened attention, improved sensitivity was associated with greater neural activity whereas with narrow attention heightened sensitivity was sometimes associated with less activity. Taken together, our results show that V4 activity reflects shifts in the locus of attention, but at a finer spatial resolution it does not show a simple correlation with the spatial allocation of attention.
National Eye Institute
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