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Donatas Jonikaitis, Tirin Moore; Dissociating contributions of visual working memory and saccade preparation in V4 activity. Journal of Vision 2017;17(10):742. doi: 10.1167/17.10.742.
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© ARVO (1962-2015); The Authors (2016-present)
Visual spatial working memory and oculomotor control are processes thought to be highly interdependent and brought about by similar neural mechanisms. In humans and non-human primates visual cortex is known to show modulation during tasks requiring oculomotor selection. Further, human imaging studies demonstrate that in the absence of visual information, visual memory delay activity is observed in visual cortex. However, working memory representations, as measured by spiking activity in early visual cortex are largely absent. By adding an irrelevant background texture pattern to the display in order to evoke visual responses from neurons, we were able to unmask modulations in visual activity during memory task. During the task, while the monkey fixated a central spot, a briefly flashed peripheral visual cue indicated a location to be remembered. After a delay period, two stimuli appeared, one at the memorized location, and one at a new location. The monkey was rewarded for saccades either to the stimulus at the memorized location ('Look' blocks) or to the other location ('Avoid' blocks). Importantly, in both types of blocks, the monkey was required to remember the cue location, yet only in the 'Look' blocks could it prepare a saccade to that location. In the 'Avoid' blocks, saccade preparation was eliminated, as indicated by slow saccadic reaction times. During the task, we recorded from neurons in area V4 using linear array microelectrodes and measured their responses during the delay period. We observed clear working memory responses in neural receptive fields during trials on which the memory cue appeared in the neuronal receptive field compared to trials on which the cue appeared elsewhere. Further, memory responses were observed during 'Avoid' blocks, ruling out saccadic preparation as a cause for observed effects. We conclude that memory activity in visual area V4 can be observed independent of saccade preparation.
Meeting abstract presented at VSS 2017
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