Visual evoked cortical potential elicited by pseudoisochromatic stimulus
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Visual evoked cortical potentials (VECPs) are useful for investigating the mechanisms and dysfunctions of color vision. Chromatic sinusoidal gratings are generally used to elicit VECPs, but they require long psychophysical measurements to match the perceptual luminance between their stripes. An alternative method is to use pseudoisochromatic stimuli, which makes use of luminance noise to mask luminance clues and force the target perception to be dependent on chromatic contrast. In this study, we compared VECPs generated by sinusoidal gratings and pseudoisochromatic gratings. Contrary to chromatic sinusoidal gratings, pseudoisochromatic stimuli do not require the use of previous methods to find the equiluminance of the stimulus.
Normal trichromats were recruited to be tested with red–green chromatic sinusoidal gratings and pseudoisochromatic gratings presented by pattern onset–offset and pattern reversal modes in five spatial frequencies. In addition, we also tested four different chromatic contrast pairs in pattern onset–offset mode presentation in five trichromats and one colorblind subject (deuteranope).
Pattern onset–offset VECPs elicited by sinusoidal gratings had a larger amplitude than those obtained with pseudoisochromatic stimuli, whereas pattern reversal VECPs elicited by pseudoisochromatic gratings had similar amplitudes compared to those elicited by sinusoidal gratings. We found no difference between the VECP amplitudes elicited by sinusoidal and pseudoisochromatic gratings containing different chromatic contrast. Color-blind subjects displayed absent or small responses to the stimuli.
Pseudoisochromatic stimulus can be an alternative stimulus to generate VECPs dominated by the chromatic mechanism.
KeywordsColor Luminance VECP Visual cortex Visual perception Pseudoisochromatic stimulus
This research was supported by the following grants: CAPES, CAPES-Pro-Amazônia, CNPq # 431748/2016-0. RCS, ICVSM, and BBOR received CAPES fellowships for graduate students. DFV and LCLS are CNPq research fellows. LCLS passed away during the process of manuscript writing.
Compliance with ethical standards
Conflict of interest
All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.
Statement of human rights
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee (Tropical Medicine Center Committee) and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.
Statement on the welfare of animals
No animals were used in this study.
Informed consent was obtained from all individual participants included in the study.
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