Abstract
Recent theories of embodied perception posit that emotion and physiological effort influence early (contrast threshold) and late (egocentric distance perception) visual perception, respectively. Manipulations of effort and emotion may have their effect by indirectly altering cortical arousal. However, quantifiable measures of arousal have been lacking, and the linkage between cortical arousal and changes in visual perception is poorly understood. METHOD: In two groups, we administered a stimulus commonly used in clinical settings to increase physiological arousal (cold pressor stimulation [CPS]—immersing the foot in iced water for 50 seconds): One group completed a two-alternative forced choice contrast threshold task (n=17), while the other group verbally estimated egocentric distances (n=18). Participants were tested at 3 time points: pre-CPS, immediate-post-CPS, and 20-minutes post-CPS. To prevent the “distance perception” group from associating specific verbal estimates with particular local features across time points, we alternated the viewing location for each time point. RESULTS: Contrast thresholds improved upon application of CPS (t=2.38, pt=−0.02, p=0.9). Although there were some changes between immediate- and 20-minutes post-CPS performance for both tasks, only the contrast threshold changes were consistent with an arousal effect. To verify that arousal was indeed enhanced by CPS, participants in the contrast threshold group underwent EEG recording to measure P50 amplitude—an established physiological marker of cortical arousal. The EEG data confirmed that CPS enhanced arousal, with a significant treatment effect in P50 amplitude from pre- to post-CPS (t=2.24, p[[lt]]0.05). CONCLUSION: The increase in arousal post-CPS was associated with significant decreases (improvements) in contrast threshold, but no change in verbal distance estimates. To our knowledge, this is the first evidence that early visual processes can be influenced by changes in cortical arousal. However, more complex forms of visual perception may be resistant to alterations in cortical arousal.
Research supported in part by a National Science Foundation Graduate Research Fellowship and research enhancement funding provided by the George Washington University (AJ Woods).