Neural and Cardiac Contributions to Perceptual Suppression During Cycling

Figures

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  FIGURE 1. GFS trial types, block design, experimental setup. (A) Time courses of GFS, catch, and RDMOFF trials. GFS trials began with a 2 s central fixation, followed by the onset of a salient red target in the upper left visual hemifield. After 2 s of target presentation, a random dot motion (RDM) stimulus was presented for a further 2 s, resulting in the disappearance of the target in a subset of trials. During catch trials, the target was physically removed at RDM onset. During RDMOFF trials, the RDM pattern was never presented. Subjects reported their detection of the target by pressing and holding the button for as long as they could see it, and releasing the button to indicate its disappearance. A blank screen was presented for 3 s as the inter‐trial interval (ITI). (B) The three rest (R) blocks each consisted of 61 trials: 44 GFS, 10 catch, and 7 RDMOFF. The four cycling blocks (2 low‐resistance (L) and 2 high‐resistance (H)) each consisted of 90 trials: 65 GFS, 15 catch, and 10 RDMOFF. Each cycling block began with a 3‐min warm‐up period before the GFS paradigm was presented. (C) The experimental setup consisted of the subject seated at a desk facing a computer screen where the…

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  FIGURE 2. Disappearance probability decreases for cycling conditions compared to rest. (A) Violin plots showing the mean disappearance probabilities during GFS performed at rest (blue), low‐resistance (orange), and high‐resistance (green) cycling. Statistical significance between the conditions, as assessed by post hoc Bonferroni‐corrected pairwise comparisons, is indicated at the p ≤ 0.05 (*) level. (B) Violin plots showing the percent change in disappearance probability for low‐resistance (orange) and high‐resistance (green) cycling compared to rest. Statistical significance, as assessed by one‐sample t‐tests, is indicated at the p ≤ 0.01 (**) level. For both panels, vertical gray boxes indicate the interquartile range (IQR), with gray whiskers indicating 1.5 × IQR, surrounded on each side by the kernel density estimation in the color corresponding to each group. Horizontal lines, in the color corresponding to each group, denote means, and white dots indicate medians. Each dot in a given condition represents the average value of a single subject. N = 30 for all plots.

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  FIGURE 3. Decreased parieto‐occipital alpha amplitude during cycling compared to rest. Average time courses of alpha band (8–12 Hz) amplitudes for GFS performed during (A) low‐resistance (orange) and (B) high‐resistance (green) cycling compared to rest (blue) (N = 30). The shaded areas denote the SEM for each time course. The zero mark denotes the onset of the RDM stimulus, after which the target was potentially perceptually suppressed. The data represent the mean of all parieto‐occipital electrodes. Statistical significance between the conditions for different time windows, as assessed by Bonferroni‐corrected Wilcoxon signed‐rank tests, is indicated at the p ≤ 0.05 (*), p ≤ 0.001 (***), and p ≤ 0.0001 (****) levels.

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  FIGURE 4. Decreased pre‐RDM parieto‐occipital alpha power for cycling conditions compared to rest. (A) Violin plots showing the mean pre‐RDM parieto‐occipital alpha during GFS performed at rest (blue), low‐resistance (orange), and high‐resistance (green) cycling. Vertical gray boxes indicate the interquartile range (IQR), with gray whiskers indicating 1.5 × IQR, surrounded on each side by the kernel density estimation in the color corresponding to each group. Horizontal lines, in the color corresponding to each group, denote means, and white dots indicate medians. Each dot in a given condition represents the average value of a single subject. Statistical significance between conditions, as assessed by Bonferroni‐corrected Wilcoxon signed‐rank tests, is indicated at the p ≤ 0.05 (*) and p ≤ 0.001 (***) levels. Power spectra for the second preceding the RDM stimulus for GFS performed at rest and during (B) low‐resistance and (C) high‐resistance cycling across subjects. Topographies of the (D) low‐resistance − rest and (E) high‐resistance − rest differences in 8–12 Hz amplitude in the second prior to RDM onset. N = 30 for all plots.

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  FIGURE 5. No correlation between pre‐RDM parieto‐occipital alpha amplitude and disappearance probability. Correlations, as assessed by Kendall's Tau‐b, between percent change in parieto‐occipital alpha amplitude from rest and percent change in disappearance probability from rest for (A) low‐resistance and (B) high‐resistance cycling. N = 30 for all plots.

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  FIGURE 6. Pre‐RDM parieto‐occipital alpha amplitude as a function of perceptual suppression and cycling. Average time courses of alpha band (8–12 Hz) amplitudes for GFS trials where the target remained visible and trials where the target was rendered invisible, when the task was performed during (A) rest, (B) low‐resistance, and (C) high‐resistance cycling. The SEM is plotted for each time course in corresponding color. The zero mark denotes the onset of the RDM stimulus, after which the target was potentially perceptually suppressed. The data represent the mean of all parieto‐occipital electrodes. Statistical significance between the conditions for different time windows, as assessed by Wilcoxon signed‐rank tests, is indicated at the p ≤ 0.05 (*) level. (D) Bonferroni‐Holm‐corrected Wilcoxon signed‐rank test p‐values for pairwise comparisons reflecting the effect of target visibility and exercise intensity on parieto‐occipital alpha amplitude in the second prior to RDM onset (Rest—R, Low‐resistance—L, High‐resistance—H, Visible—vis, Invisible—inv). (E) Violin plots showing the visible—invisible difference in mean pre‐RDM alpha during GFS performed at rest (blue), and during low‐resistance…

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  FIGURE 7. Heart rate increases with cycling intensity. (A) Violin plots showing the pre‐RDM instantaneous heart rate during GFS performed at rest (blue), low‐resistance (orange), and high‐resistance (green) cycling. Vertical gray boxes indicate the interquartile range (IQR), with gray whiskers indicating 1.5 × IQR, surrounded on each side by the kernel density estimation in the color corresponding to each group. Horizontal lines, in the color corresponding to each group, denote means, and white dots indicate medians. Each dot in a given condition represents the average value of a single subject. Statistical significance between the conditions, as assessed by a post hoc analysis with a Bonferroni adjustment, is indicated at the p ≤ 0.0001 (****) level. Correlations as assessed by Kendall's Tau‐b between percent change in heart rate from rest and percent change in disappearance probability from rest for (B) low‐resistance and (C) high‐resistance cycling. Correlations between percent change in heart rate from rest and percent change in alpha amplitude from rest for (D) low‐resistance and (E) high‐resistance cycling. None of the correlations are significant. N = 30 for all plots.

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  FIGURE 8. Heartbeat‐evoked potential amplitudes decrease during cycling. (A) Topographical map of heartbeat‐evoked potential (HEP) amplitude difference between low‐resistance and rest conditions in the 152–203 ms post‐T‐peak time window during which a statistically significant difference was observed. White labels indicate the channels contributing to the significant cluster. (B) Pre‐RDM HEPs for the two conditions averaged across the cluster. The shaded areas denote the SEM for each time course. The signal contaminated by T‐wave and P‐wave cardiac artifacts appears in a lighter color. The gray bar highlights the time window in which a significant difference was observed as the p ≤ 0.05 (*) level. (C) Violin plots of the HEP amplitude averaged across the cluster for rest (blue) and low‐resistance cycling (orange). Vertical gray boxes indicate the interquartile range (IQR), with gray whiskers indicating 1.5 × IQR, surrounded on each side by the kernel density estimation in the color corresponding to each group. Horizontal lines, in the color corresponding to each group, denote means, and white dots indicate medians. Each dot in a given condition represents the average value of a single…

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  FIGURE 9. Heartbeat‐evoked potentials as a function of perceptual suppression and cycling. Pre‐RDM HEPs averaged across the significant cluster for the trials where the target remained visible and those where it was rendered invisible during GFS are shown for (A) rest and (B) low‐resistance cycling conditions. (C) Bonferroni‐corrected Wilcoxon signed‐rank test p‐values for pairwise comparisons reflecting the effect of target visibility and exercise on pre‐RDM HEP amplitude (Rest—R, Low‐resistance—L, Visible—vis, Invisible—inv). (D) Violin plots showing the visible—invisible difference in mean pre‐RDM HEP amplitude (from the same time window as the exercise intensity analysis) during GFS performed at rest (blue) and during low‐resistance (orange) cycling. Vertical gray boxes indicate the interquartile range (IQR), with gray whiskers indicating 1.5 × IQR, surrounded on each side by the kernel density estimation in the color corresponding to each group. Horizontal lines, in the color corresponding to each group, denote means, and white dots indicate medians. Each dot in a given condition represents the average value of a single subject. N = 29 for all plots.