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Valeria L. Fu; Effect of Visual Acuity on Suppressive and Facilitatory Cortical Interactions. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6342.
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Visual Evoked Potentials (VEPs) can be used to reflect cortical interactions that are highly localized (Zemon & Ratliff, 1982) and its responses can be dissected into different frequency components for analysis. Our study intended to employ the frequency-domain approach to investigate the effect of visual acuity on cortical interactions.
VEPs were recorded from six normal vision adults (acuity=0.093±0.07 Log MAR) under monocular and binocular viewing conditions. A 3-dioptre lens was placed in front of one eye in order to decrease the visual acuity. Stimuli were consisted of the windmill-dartboard (WMDB) patterns (Ratliff & Zemon 1982). VEP waveforms were quantified by Fourier analysis via two indices: 1) Facilitation index (FI): ratio of Fundamental (WMDB ON) and 2nd harmonic frequency (WMDB ON); 2) Suppression Index (SI): ratio of 2nd Harmonic (WMDB OFF) and 2nd Harmonic (WMDB ON) (Conte et al 2009).
In the monocular condition, there was a significant reduction of the SI when a 3-dioptre lens was used (t=2.71; p<0.05). In the binocular condition, there were no statistically significant changes either in the FI (t=0.48; p=0.64) or the SI (t=0.038; p=0.97) if the visual acuity of one eye was reduced by the lens. However, there was a significant difference in FI (t=3.05, p<0.05) but not SI (t=1.53; p=0.18) between the binocular and monocular conditions if 3-dioptre lens was placed in front of one eye. Allowing the fellow good eye to view the stimuli pattern simultaneously may improve visual acuity that may account for the changes in FI. Viewing the stimuli pattern only through the 3-dioptre lens which decreases visual acuity that may account for the changes in SI.
Decrease in visual acuity may be related to suppressive cortical interaction while improvement in visual acuity may be associated with facilitatory cortical interaction.
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