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Luke Hallum, Christopher Shooner, Romesh Kumbhani, Najib Majaj, J. Anthony Movshon, Lynne Kiorpes; Altered balance between excitation and suppression in visual cortex of amblyopic macaques. Journal of Vision 2016;16(12):1123. doi: 10.1167/16.12.1123.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is a developmental disorder leading to form vision deficits in the affected eye and interocular perceptual suppression. Monocular testing has revealed neuronal response patterns that can partly account for the form deficits, but few have studied amblyopic cortical responses under binocular viewing conditions. We wondered whether dichoptic testing could improve response field (RF) characterization and furnish a more complete account of the cortical deficit. We recorded from 96-electrode "Utah" arrays straddling the V1/V2 border (eccentricities: 0.5 to 7 degrees) in each hemisphere of seven anesthetized macaques: six behaviorally assessed amblyopes and one visually-normal control. We presented large, contrast-modulated gratings to both eyes simultaneously. Grating parameters were chosen to vigorously drive overall responses. Data revealed dichoptic suppression: increasing contrast in the amblyopic eye (AE) decreased responses at binocular cortical sites. We modeled RFs using a difference of Gaussian envelopes (Hallum & Movshon, Vision Research, 2014), estimating the magnitudes of central excitation and surrounding suppression. To quantify the excitation/suppression balance, we used indices of the form V = (A-B)/(A+B). Within eye, A and B were model-based estimates of the magnitudes of excitation and suppression, respectively. For fellow (FE) and control eyes, excitation dominated suppression, while for AEs, suppression dominated excitation. V was associated with depth of amblyopia. Between eyes, A and B were model-based estimates of either (1) FE excitation and AE excitation, respectively, or (2) FE suppression and AE suppression, respectively. For the control macaque, excitation and suppression were balanced. Between the eyes of amblyopes, FE excitation dominated AE excitation; V tended toward higher values in severe amblyopia. Suppression appeared unaffected by amblyopia. These response patterns likely reflect the mechanisms mediating interocular perceptual suppression.
Meeting abstract presented at VSS 2016
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