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Michael-Paul Schallmo, Scott Sponheim, Cheryl Olman; Orientation Tuning in Schizophrenia Measured Using Reverse Correlation Psychophysics. Journal of Vision 2012;12(9):88. doi: 10.1167/12.9.88.
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Selectivity for visual stimulus orientation is observed in neurons within primary visual cortex (V1), and it is believed that feed-forward orientation tuning is shaped by both excitatory and inhibitory input. It has been recently demonstrated that for healthy adults, performance on an orientation discrimination task correlated with GABA concentrations in early visual cortex as measured by magnetic resonance spectroscopy. In schizophrenia, visual processing abnormalities have been observed that are consistent with dysfunctional GABAergic inhibition in visual cortex. Therefore, we were interested in examining how such ostensibly abnormal inhibition may affect orientation tuning in this disorder. We used the reverse correlation method of Ringach (1997, Vis. Res., 7, p. 963) to measure the ability of subjects with schizophrenia and healthy adults to detect vertically or horizontally oriented targets in a rapidly changing series of oriented grating stimuli. By calculating the distribution of orientations presented prior to each response, reaction times were estimated and the probability of responding to each of the ten stimulus orientations was measured. These probability distributions strongly resembled the orientation tuning curves of individual V1 neurons, as measured by electrophysiology in macaques. Data from each group were fit with a difference-of-von Mises function, yielding a positive and a negative component for each fit. For both groups, negative components were broader than positive components, demonstrating reduction below baseline of responses to orientations near the target. This result is consistent with the idea of sharpening orientation selectivity via broadly tuned inhibition, which suppresses responses to orientations near the target. Between groups, preliminary results indicate significantly narrower positive components in schizophrenia, consistent with sharper orientation tuning in this disorder. This may be evidence of a compensatory mechanism whereby orientation tuning sharpens for patients with schizophrenia, which may be related to known weaker contextual modulation effects.
Meeting abstract presented at VSS 2012
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