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J. N. Nam, J. Gallardo, A. Jue, W. Seiple; Multifocal Visual Evoked Response: Evidence for Lateral Interactions. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3751.
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The functional consequences of lateral connection in the visual cortex have been demonstrated using psychophysical and electrophysiological methods. Zemon and Ratliff (1982) reported increases in second harmonic visual evoked response (VER) amplitude as the separation between modulated segments of a windmill-dartboard stimulus was increased. In this study we used the multifocal VER (mfVER) to quantify the local effects of lateral interaction.
Monocular multifocal VEPs (mfVEP) were recorded from four subjects using VERIS software and custom stimuli. Electrodes were placed on the mid-line (inion and inion plus 4 cm) and a forehead electrode served as the ground. The stimulus array consisted of two rings with four sectors per ring. Each sector contained 16 checks that pattern-reversed according to a pseudorandom (m-) sequence. The central ring had a radius of 1.75° and the outer ring had a radius of 2.6°. The inner and outer rings were separated by gaps ranging from 3 to 20 minarc.
Signal (45 to 150 ms) to noise (325 to 430 ms) RMS ratios were calculated for each subject for each condition. For the central ring, mfVEP amplitude ratios peaked near a gap size of 7 minarc and decreased with smaller and larger gap sizes. This trend was consistent for all subjects.
Consistent with previous studies, the presence of a surrounding patterned stimulus modulated the response amplitude of a more centrally located area.
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