Abstract
Conventional pattern-reversal visual evoked cortical potential (VECP) shows positivity for luminance and chromatic equiluminant stimuli while conventional pattern-onset VECP shows positivity for luminance pattern-onset and negativity for chromatic pattern-onset. We evaluated how the presentation mode affects VECPs elicited by luminance and compound (luminance plus chromatic) pseudo-random stimulation. Eleven normal trichromats and 17 red-green color-blinds were studied. Pattern-reversal and pattern-onset luminance and compound (luminance plus red-green) gratings were temporally modulated by m-sequence. We used a cross-correlation routine to extract the first order kernel (K1) and the first and second slices of the second order kernel (K2.1 and K2.2, respectively) from the VECP response. We integrated the amplitude of VECP components as a function of time in order to estimate its magnitude for each stimulus condition. We also used a normalized cross-correlation method in order to test the similarity of the VECP components. The VECP components varied with the presentation mode and the presence of red-green contrast in the stimuli. In trichromats, for compound conditions, pattern-onset K1, K2.1, and K2.2, and pattern-reversal K2.1 and K2.2 had negative-dominated waveforms at 100 ms. Small negativity or small positivity were observed in dichromats. Trichromats had larger VECP magnitude than color-blinds for compound pattern-onset K1 (with large variability across subjects), compound pattern-onset and pattern-reversal K2.1, and compound pattern-reversal K2.2. Trichromats and color-blinds had similar VECP amplitude for compound pattern-reversal K1 and compound pattern-onset K2.2, as well as for all luminance conditions. The cross-correlation analysis showed high similarity between waveforms of compound pattern-onset K2.1 and pattern-reversal K2.2 as well as pattern-reversal K2.1 and K2.2. We suggest that compound pattern-reversal K2.1 is an appropriate response to study red-green color-opponent activity.
Highlights
Using pseudo-random stimulation it was possible to elicit negative-dominated visual evoked cortical potentials (VECP) for chromatic equiluminant contrast using both pattern-onset and pattern-reversal stimuli (Gerth et al, 2003)
Since the chromatic equiluminant pattern-onset VECP usually shows higher signal-tonoise ratio compared to chromatic equiluminant pattern-reversal VECP and exhibit inverse polarity compared to luminance pattern-onset VECP, many have used this stimulation mode to study the mechanism of chromatic equiluminant transient VECPs (Carden et al, 1985; Kulikowski and Parry, 1987; Murray et al, 1987; Berninger et al, 1989; Kulikowski et al, 1989, 1996; Rabin et al, 1994; Porciatti and Sartucci, 1999; Gomes et al, 2006, 2008, 2010; Souza et al, 2008)
For luminance pattern-reversal stimulation, K1 was very small or absent, K2.1 had a negative peak at about 85 ms followed by a double-peaked positivity between 100 and 120 ms, and K2.2 had a negative peak at 100 ms followed by a positive peak at 130 ms
Summary
Using pseudo-random stimulation it was possible to elicit negative-dominated visual evoked cortical potentials (VECP) for chromatic equiluminant contrast using both pattern-onset and pattern-reversal stimuli (Gerth et al, 2003). These findings differed from those obtained with conventional periodical stimulation (Carden et al, 1985; Suttle and Harding, 1999). McKeefry et al (1996) discussed about the activation of chromatic and achromatic mechanisms by pattern reversal and pattern onset–offset stimulations They based their suggestions in the features of response from tonic and phasic cells in the visual system
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