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G.d. Souza, B.D. Gomes, C.A. Saito, L.C. L. Silveira, M. daSilvaFilho; Human Achromatic Spatial Contrast Sensitivity Measured With Transient Visual Evoked Cortical Potential: Comparison With Psychophysics Measurements . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5370.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate human achromatic spatial contrast sensitivity (CSF) with transient visual evoked cortical potential (tVECP). To compare electrophysiological and psychophysical measurements.
Six healthy subjects (21 ± 2 years–old) were monocularly tested. The stimuli were black and white horizontal sinusoidal gratings, 40 cd/m2 mean luminance, presented in a 5º circular patch. Six spatial frequencies were used: 0.4, 0.8, 2, 4, 8, and 10 cycles per degree (cpd), in 1 Hz squarewave reversal mode. Electrophysiological contrast thresholds were estimated by linear regressions fitted to data point representing P100 tVECP amplitude as a function of log contrast, extrapolated to zero amplitude. Psychophysics measurements were performed in the same spatial frequencies plus 1 and 6 cpd, using identical spatio–temporal configuration as used in tVECP experiments (dynamic presentation) and using stationary stimuli (static presentation). Psychophysical contrast sensitivity was obtained using the method of adjustment. We estimated CSF tuning by dividing peak sensitivity by sensitivity at the lowest spatial frequency tested.
Electrophysiology. Response amplitude changed as a function of contrast differently for different spatial frequencies. For 0.4–0.8 cpd, response amplitude saturated at high contrast. For 2–10 cpd, the function showed two limbs, one for low to medium contrasts, another for high contrasts. Contrast threshold was estimated by using only the low to medium contrast data. Electrophysiological CSF peaked at 2–4 cpd (2.13 ± 0.2 log units). CSF tuning was 1.09. Psychophysics. Dynamic psychophysical CSF peaked at 2–4 cpd (2.2 ± 0.1 log units) and its tuning was 1.11. Static psychophysical CSF peaked at 2–4 cpd (2.21 ± 0.2 log units) and its tuning was 1.31.
Electrophysiological CSF and dynamic psychophysical CSF were more similar to each other (r2 = 0.81) than to static pyschophysical CSF. Both had a more low pass tuning whilst static CSF had a more band pass tuning.
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