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Marina v. Camargo, Russell D. Hamer, Dora S. Ventura; Spatiotemporal Properties Of Human Cortical Vernier Responses Measured With The Sweep Visual Evoked Potential (svep). Invest. Ophthalmol. Vis. Sci. 2011;52(14):6094.
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© ARVO (1962-2015); The Authors (2016-present)
To begin construction of a spatiotemporal (ST) map of sVEP Vernier (VRN) responses. and relate the data to the hypothesis that magno- (M) but not parvocellular (P) ganglion cell output serves as the input to cortex used to extract hyperacuity VRN displacements (e.g., Sun et al. Vis Res 44: 19, 2004).
EEGs recorded from O1, Oz, O2 (re: to Cz,10/20 system) in 9 young adults. Stimuli: VRN protocol. Vertical VRN offsets were introduced to 14.5x19.5 deg achromatic horizontal squarewave gratings (64% contrast, mean lum = 161 cd/m^2), producing columns of moving and static bars. Gratings (1 or 8 c/d) alternated between 2 asymmetric states -- aligned (AL) and misaligned (MAL) -- at 3, 6 or 15 Hz. VRN offsets were swept logarithmically from 0.2’ to 6.4’ (<45 deg spatial phase; 1 c/d) or from 0.2’ to 1.88’ (90 deg spatial phase; 8 c/d). Motion control protocol. Offsets alternated between 2 symmetrical states (MAL/MAL). Data were analyzed at 1F and at the 2nd harmonic (2F). VRN and Motion thresholds (thd) were estimated by extrapolation of the vector-averaged 1F and 2F amplitudes to 0 microV, respectively (Norcia et al. Vis Neurosci 16:1123, 1999).
(1) The VRN protocol generates high-SNR amplitudes at both 1F and 2F; the Control protocol generates only 2F. (2) For 6 & 15 Hz, VRN thds decreased from ~0.75’ to 0.30’ between 1 & 8 c/d, matching psychophysical data of Bradley & Skottun (Vis Res. 27: 1817, 1987). For 3 Hz, the VRN thds matched the BS data at 1 c/d, but decreased by only 0.17 log units between 1 & 8 c/d. (3) VRN thds were thus TF-dependent at 8 but not at 1 c/d. (4) Motion thds depended less on SF than VRN thds (Motion VRN at 8 c/d) at 6 & 15 Hz, but not at 3 Hz, where VRN and Motion thds were equal at both SFs.
sVEP VRN thds decrease with SF as in psychophysical measures, but are TF-dependent. At 8c/d, VRN thds are ~equal for 6 and 15 Hz, but increase sharply at 3 Hz. The data thus suggest a shift of mechanism at low-TF/high-SF. Working interpretation: our sVEP VRN responses are dominated by the M signals at the 2 higher TFs, and by P signals at low TF, high SF.
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