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. 2021 May:182:27-35.
doi: 10.1016/j.visres.2021.01.007. Epub 2021 Feb 13.

The effects of visual discomfort and chromaticity separation on neural processing during a visual task

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The effects of visual discomfort and chromaticity separation on neural processing during a visual task

Lisa C Lindquist et al. Vision Res. 2021 May.

Abstract

Visual stimuli that are uncomfortable to look at evoke a large neural response suggesting altered processing. While there is some evidence linking uncomfortable achromatic stimuli to impaired visual processing, the effect of uncomfortable chromatic patterns on visual cognition has yet to be explored. Large differences in chromaticity separation (e.g. red and blue) elicit visual discomfort, larger metabolic responses, larger visual evoked potentials, and greater alpha suppression compared to small chromaticity separations (e.g. pink and purple). We investigated the impact of stimuli that varied in their chromaticity separation (calculated in perceptual color space) on a visual task and their effect on neural responses across the cortex. Thirty participants completed a continuous pairs task (letters changed at 3 Hz) while grating patterns that differed in their chromaticity separation alternated with a grey screen at 5 Hz. The different temporal frequencies allowed for steady-state visual evoked potentials (SSVEPs) to the two stimulus-types to be measured simultaneously using electroencephalography (EEG). A subset of participants rated the gratings on a 9-point scale of discomfort. We observed greater ratings of discomfort and increased power at 5 Hz with the larger chromaticity separations. The increase in 5 Hz power with greater chromaticity separation was evident across the cortex. However, there was no significant effect of chromaticity separation on power at 3 Hz, or on reaction times, and no consistent effect on behavioral accuracy. Despite eliciting heightened neural responses across the cortex, short term exposure to uncomfortable chromatic stimuli does not adversely impact visual task performance.

Keywords: Chromaticity separation; Continuous pairs task; EEG; SSVEP; Visual discomfort.

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Conflict of interest statement

Declarations of Interest: None.

Figures

Figure 1.
Figure 1.. Colors used to create chromatic stimuli.
Colors used are plotted in CIE UCS (1976) space. Coordinates are adjusted for illustration purposes. Examples of how colors were presented as pairs in the grating patterns are shown.
Figure 2.
Figure 2.. Continuous Pairs Tasks (CPT).
An example of a “Hit” trial. The chromatic grating oscillates at a temporal frequency of 5Hz and letters are presented sequentially at a temporal frequency of 3 Hz. The trial continues for 2 seconds.
Figure 3.
Figure 3.. Electrode Montage used for analyses.
Electrode montage from which data were extracted (a) to assess responses from visual cortex, shown in white: Row 1 (top) = A18, A20 and A31; Row 2 (middle) = A17, A21 and A30; Row 3 (bottom) = A16, A22 and A29) and three columns (Left column = A18, A17 and A16; Central column = A20, A21 and A22; Right column = A31, A30 and A29. Electrodes in grey are a reference for reader orientation. (b) Positions of electrodes analyzed in follow-up analyses shown in white: Fz/C21, C3/D19, C4/B22. Additional electrodes were added in grey to be used as a reference for reader orientation.
Figure 4.
Figure 4.. Behavioral data for the Continuous Pairs Task (CPT).
D’ plotted as a function of chromaticity separation for each color pair with regression lines added to show general direction of trends. Error bars show one standard error.
Figure 5a.
Figure 5a.. Mean 5Hz SSVEP amplitude.
The 5Hz steady state visual evoked potential power as a function of chromaticity separation, shown separately for the three-color pairs (averaged over the responses from the nine electrodes).
Figure 5b.
Figure 5b.. Mean 3Hz SSVEP amplitude.
The 3Hz steady state visual evoked potential response to the CPT letter stimuli averaged over nine electrodes as a function of chromaticity separation, shown separately for the three-color pairs. Error bars show one standard error. Regression lines added to show general direction of trends for each color pair.
Figures 6.
Figures 6.. 5Hz and 3Hz SSVEP power at each cortical electrode.
The (a) 5Hz and the (b) 3 Hz steady state visual evoked potential power as a function of chromaticity separation, shown separately for the three-color pairs for each of the cortical electrodes (C3/D19 at the left temporal location, Fz/C21 at the front of the head, and C4/B22 at the right temporal location. Error bars show one standard error. Regression lines added to show general direction of trends for each color pair.
Figure 7.
Figure 7.. Ratings of visual discomfort for chromatic gratings.
Mean ratings of discomfort as a function of chromaticity separation for each color pair. Chromaticity separation calculated in CIE UCS 1976 space. Error bars show one standard error. Regression lines added to show general direction of trends for each color pair.

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