Color discrimination ellipses of trichromats measured with transient and steady state visual evoked potentials

Abstract

The purpose of this work is to investigate the use of different forms of visual evoked potentials (VEPs) to measure color discrimination thresholds and to plot color discrimination ellipses (MacAdam, 1942). Five normal trichromats (24.5 +/- 2.6 years-old) were monocularly tested. Stimuli consisted of sinusoidal isoluminant chromatic gratings made from chromaticity pairs located along four different color directions radiating from one reference point of the CIE 1976 chromaticity diagram (u' = 0.225; v' = 0.415). Heterochromatic flicker photometry (HFP) was used to obtain the isoluminance condition for every subject and for all chromaticity pairs. VEPs were elicited using two cycles per degree grating stimuli at three different temporal configurations: transient, onset (300 ms)/offset (700 ms), 1 Hz fundamental frequency; steady-state, onset (50 ms)/offset (50 ms), 10 Hz fundamental frequency; and steady-state pattern reversal at 5 Hz fundamental frequency (10 Hz phase reversal). VEP amplitude was measured using transient VEP N1-P1 components and steady state VEP first (10 Hz) and second (20 Hz) harmonics. VEP amplitude was plotted as a function of chromatic distance in the CIE 1976 color space and the data points were extrapolated to zero amplitude level to obtain chromatic discrimination thresholds. The results were compared with psychophysical measurements performed using the same stimulus configurations and with the pseudoisochromatic method of Mollon-Reffin (one-way ANOVA). For all subjects and all stimulation methods, the ellipses showed small sizes, low ellipticities, and were vertically oriented. Despite some consistent differences in the results obtained with different procedures, there was no statistical difference between ellipses obtained electrophysiologically and psychophysically. For steady state VEPs, ellipses obtained from second harmonic amplitudes were larger and more elongated in the tritan direction than those obtained with first harmonic amplitudes.

Cone contrast influence on components of the pattern onset/offset VECP

“…At the highest pooled cone contrast tested, N1 has a shorter latency than C1 (), but this difference disappears when similar contrast values are considered (). Using different experimental results and arguments, the identification of C1 and N1 with the P pathway has already been suggested in our previous work (Gomes et al. , 2006, 2008; Souza et al.…”

“…, 1994; Porciatti and Sartucci, 1999; Suttle and Harding, 1999; Gerth et al. , 2003; Gomes et al. , 2006, 2008; Souza et al.…”

“…, 1989; Porciatti and Sartucci, 1999; Suttle and Harding, 1999). These reports directly compared onset/offset pattern VECPs elicited by equiluminant chromatic contrast stimuli with those elicited by achromatic contrast stimuli using different luminance ratios of red‐green or blue‐yellow stimulus colour content (Suttle and Harding, 1999; Porciatti and Sartucci, 1999), or different colour distances in the colour space (Gomes et al. , 2006, 2008).…”

“…Visual evoked cortical potentials (VECP) due to luminance contrast and chromatic contrast mechanisms can be isolated by using pattern onset/offset sinusoidal gratings (Murray et al, 1987;Berninger et al, 1989;Crognale et al, 1993;Rabin et al, 1994;Porciatti and Sartucci, 1999;Suttle and Harding, 1999;Gerth et al, 2003;Gomes et al, 2006Gomes et al, , 2008Souza et al, 2008). A major difference between achromatic and chromatic VECPs is that the equiluminant chromatic onset VECP is characterized by a prominent negative componentnamed N1 -which progressively decreases in amplitude with the intrusion of luminance noise until it is completely replaced by a positive component named C1, that characterizes the onset response of luminance VECPs (Murray et al, 1987;Berninger et al, 1989;Porciatti and Sartucci, 1999;Suttle and Harding, 1999).…”

Contrast sensitivity of pattern transient VEP components: Contribution from M and P pathways.

“…The way in which VEP changes with stimulus contrast has been used to distinguish between the cortical activity of different visual pathways (Campbell & Maffei, 1970;Nakayama & Mackeben, 1982;Bobak, Bodis-Wollner, Harnois, & Harnois, 1984;Previc, 1988;Valberg & Rudvin, 1997;Rudvin, Valberg, & Kilavik, 2000;Ellemberg, Hammarrenger, Lepore, Roy, & Guillemot, 2001;Gomes, Souza, Rodrigues, Saito, Silveira, & da Silva Filho, 2006;Gomes, Souza, Lima, Rodrigues, Saito, da Silva Filho, & Silveira, 2008;Souza, Gomes, Saito, da Silva Filho, & Silveira, 2007;Souza, Gomes, Lacerda, Saito, da Silva Filho, & Silveira, 2008). Visual evoked potential amplitude linearly depends on the logarithm of stimulus contrast, sometimes with saturation at high contrasts.…”