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Givago S. Souza, Veronica R. da Silva, Carolina S. Araujo, Barbara B. Risuenho, Bruno D. Gomes, Luiz Carlos L. Silveira; Effects of the presentation mode and color contrast in visual evoked potential elicited by pseudo-random stimuli. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5717.
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© ARVO (1962-2015); The Authors (2016-present)
To study the role of presentation mode and color contrast on visual evoked cortical potential elicited by pseudo-random binary sequence stimuli (PRBS-VECP).
Normal trichromats (23.2 ± 7.4 years old) were tested in four different protocols of stimulation: achromatic pattern reversal (n = 11), achromatic pattern onset (n = 4), achromatic pattern offset (n = 4); red-green chromatic pattern onset (n = 6), red-green chromatic pattern onset (n = 6). Sinusoidal gratings (8º visual angle) were modulated by an m-sequence to simulate pattern reversal, pattern onset and pattern offset presentation modes. Achromatic stimuli had high contrast (>90%) and were presented in seven spatial frequencies (0.4 to 10 cpd). The background had the same mean chromaticity and mean luminance. Chromatic stimuli were presented at 2 cpd and the colors had the same mean chromaticity and mean luminance of the background. One channel recording was obtained using surface electrodes placed at Oz (active), Fz (reference), and Fpz (ground). A Veris system was used for visual stimulation, VECP recording, and kernel extraction.
Achromatic pattern reversal PRBS-VECP changed across the stimulus spatial frequency domain. At low spatial frequencies (0.4-0.8 cpd) a negative component (N1) was followed by a positive component (P2), while at intermediate spatial frequencies (2-6 cpd) N1 was followed by an earlier positive component (P1) and a later positive component (P2) which corresponded to the positivity observed at low spatial frequencies. At high spatial frequencies P1 dominates the recordings. Achromatic pattern onset PRBS-VECP at low spatial frequencies (0.4-0.8 cpd) had a positive component (C1) followed by a dominant negative component (C2) and a second positivity (C3). From 2 to 10 cpd C1 decreases while C2 and C3 dominate the PRBS-VECP waveform. Achromatic pattern offset PRBS-VECP from 0.4 to 10 cpd showed similar waveforms composed by an earlier positivity (C1) followed by a dominant negativity (C2), and a later positivity (C3). Chromatic pattern reversal and pattern onset PRBS-VECPs had both N1 followed by a P1.
The changes in the spatial frequency domain may reflect the influence of different visual pathways on the cortical activity. Presentation modes elicited different waveforms indicating different contrast detection mechanisms for achromatic stimulation. Nevertheless of the presentation mode, chromatic PRBS-VECP had inverted polarity compared to achromatic PRBS-VECP, suggesting predominance of the color-opponent pathways in VECP generation.
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