Hyper-arousal decreases human visual thresholds

Abstract

Arousal has long been known to influence behavior and serves as an underlying component of cognition and consciousness. However, the consequences of hyper-arousal for visual perception remain unclear. The present study evaluates the impact of hyper-arousal on two aspects of visual sensitivity: visual stereoacuity and contrast thresholds. Sixty-eight participants participated in two experiments. Thirty-four participants were randomly divided into two groups in each experiment: Arousal Stimulation or Sham Control. The Arousal Stimulation group underwent a 50-second cold pressor stimulation (immersing the foot in 0-2° C water), a technique known to increase arousal. In contrast, the Sham Control group immersed their foot in room temperature water. Stereoacuity thresholds (Experiment 1) and contrast thresholds (Experiment 2) were measured before and after stimulation. The Arousal Stimulation groups demonstrated significantly lower stereoacuity and contrast thresholds following cold pressor stimulation, whereas the Sham Control groups showed no difference in thresholds. These results provide the first evidence that hyper-arousal from sensory stimulation can lower visual thresholds. Hyper-arousal's ability to decrease visual thresholds has important implications for survival, sports, and everyday life.

Figure 1. Depth threshold device.

Participants viewed two white rods through an occluder placed at optical infinity (20 feet). Participants judged which rod (left or right) was closer in depth to their location. The maximum depth interval was 50 cm.

Figure 2. Stereoacuity thresholds.

Mean stereoacuity threshold from Baseline to Post-Stimulation for the Arousal Group and Sham Control Group. The left y-axis reports thresholds in units of linear separation (cm). The right y-axis reports thresholds in approximate units of angular separation (arcsec). Arcsec was calculated using an assumed average IPD of 6.3 cm. Baseline performance was not significantly different between groups (t = 1.02; DF = 32; p = .31). * = p<.05

Figure 3. Frequency plots for baseline stereoacuity thresholds by group.

Figure 4. Contrast threshold task.

A) Illustration of cue types. Gaussian + Noise example represents the highest contrast stimulus presented on the first trial of the test block. Noise only represents the noise stimulus common to all trials. B) Sequence of events in a trial. In the given example, Stimulus 1 represents the Gaussian + Noise example in 1a and Stimulus 2 represents the Noise only example. Feedback was given in white font as right or wrong based on the accuracy of the participant's response. In the given example, participants would click once to correctly identify the 1st stimulus presented as containing the stimulus with more contrast. ISI  =  inter-stimulus interval.

Figure 5. Contrast thresholds.

Mean contrast threshold from Baseline to Post-Stimulation for the Arousal Group and Sham Control Group. Baseline performance was not significantly different between groups (t = 1.29; DF = 32; p = .21). * = p<.05

Figure 6. Frequency plots for baseline contrast thresholds by group.