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David L. Sheinberg, Ryan E. B. Mruczek, Britt Anderson, Keisuke Kawasaki; Effects of long term image familiarity in monkey temporal cortex. Journal of Vision 2006;6(6):617. doi: 10.1167/6.6.617.
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© ARVO (1962-2015); The Authors (2016-present)
Recognition of repeatedly encountered visual objects must be accompanied by the modification of neural circuits, but where in the brain this occurs is not well understood. In previous studies in monkeys, we found that visual evoked potentials recorded from skull electrodes revealed enhanced responses to highly familiar images starting between 120ms and 140ms after stimulus onset. In the present study, we investigated the extent to which these changes could be traced to events occurring in the inferior temporal cortex (IT). Three monkeys were each trained to recognize 100 visual images of real world objects using a 2AFC classification task. Following extensive training, we obtained simultaneously recorded local field potentials and single unit activity from between one and four electrodes lowered into visually responsive regions of IT. Sites were selected by monitoring responses to a neutral set of trial unique patterns. We then interleaved presentations of highly familiar objects with totally unfamiliar objects during a viewing only task. In all three animals, significant effects of image familiarity were observed in the stimulus aligned LFPs starting 150–170ms after stimulus onset. Single unit responses had typical onset latencies around 110ms, and preliminary analysis suggests that robust, selective responses were much more common for familiar objects compared to novel ones. We never encountered single neurons that encoded stimulus familiarity, per se. We hypothesize that large populations of single neurons in IT become tuned to repeatedly encountered objects, and that the integrated output of these cells will, in turn, present a signal of familiarity.
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