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Carolina d. Araujo, Givago S. Souza, Bruno D. Gomes, Luiz Carlos L. Silveira; Contribution of P and M Pathways to Pseudo-Random Binary Sequence Visual Evoked Cortical Potential across the Contrast and Spatial Frequency Domains. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5718.
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© ARVO (1962-2015); The Authors (2016-present)
To study visual evoked cortical potential elicited by pseudo-random binary sequence stimuli (PRBS-VECP) at different contrasts and spatial frequencies.
Nine normal subjects (24.1 ± 6.2 years old) were tested at seven spatial frequencies ranging from 0.4 to 10 cpd and six Michelson contrasts (99%, 50%, 25%, 12.5%, 6.25%, and 3.125%). Sinusoidal gratings (8º visual angle) were modulated by a m-sequence to simulate pattern reversal presentation. The background had the same mean chromaticity and mean luminance of the stimulus. One channel recordings were obtained by using surface electrodes placed at Oz (active), Fz (reference), and Fpz (ground). A Veris system was used for visual stimulation, electrophysiological recording, and kernel extraction.
PRBS-VECP was found in the first slice of the second order kernel and they were composed by a negative component (N1) and a positive component (P2) at low spatial frequencies (0.4-0.8 cpd) at all contrasts. P2 increased when contrast was raised, saturating at high contrast. At intermediate spatial frequencies (2-6 cpd), N1 was followed by a small positivity (P1) and P2 at high contrasts. When the contrast was lowered, P1 became smaller and disappeared at intermediate contrasts, while P2 was present at medium and low contrasts. At high spatial frequencies (8-10 cpd), P1 was present only at high contrasts while P2 was less prominent but present at intermediate and high contrasts.
PRBS-VEP components had different spatial frequency and contrast tuning. We suggest that P2 results from M pathway contribution whilst P1 results from P pathway activity.
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