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Clinton Cooper, Benjamin Ramsden; Color modulation of temporal response to oriented stimulation in macaque V2. Journal of Vision 2008;8(6):359. doi: 10.1167/8.6.359.
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© ARVO (1962-2015); The Authors (2016-present)
In daily vision, we use color and orientation to aid rapid identification of visual forms. Neurons in the second visual cortical area of the primate (V2) preferentially fire to signature colored and oriented stimulus combinations, but the modulation of temporal response to oriented stimuli by color, and its associated mechanisms, is still not well characterized. To investigate these possible modulatory effects, we presented luminance-controlled colored and/or oriented stimuli to anesthetized macaque monkeys during single unit electrophysiological and intrinsic optical imaging recordings in V2. We have applied several quantification methods, including Surprise and spike density function (SDF) threshold, to objectively quantify the characteristics of neuronal temporal response. These methods provide estimates of response latency and allow quantification of the temporal evolution of response to presentations of oriented, color, and color/oriented stimuli. Here, we show and contrast examples of temporal response of firing that were obtained following colored/oriented stimulation. With strong responses, Surprise and SDF measures showed comparable latency values, however sensitivity rapidly declined when responses were relatively weak. We found that latency reliability significantly improved when we controlled for mean post-stimulus spike firing. A broad distribution of response latencies were observed across the population of recorded V2 neurons (cf. Munk et al 1995; Schmolesky et al 1998). Therefore, color-induced temporal modulation of oriented response was optimally detected using a within-unit design. We observed significant advances in latency to oriented stimulus presentations, with supplementary specific color modulations. Interestingly, color inclusion was sometimes also associated with extended (rather than advancing) response latency, suggesting that color/orientation induced response in V2 may arise from a balance of excitatory and inhibitory neurophysiological mechanisms (cf. Anzai et al 2007). These data suggest that color inclusion produces identifiable temporal response modulations in V2 that may be important for efficient early visual processing and later perception.
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