When does cortical arousal enhance performance in visual perception tasks?

Abstract

Intro: Cold pressor stimulation (CPS, immersing the foot in ice-water for 50 seconds) decreases contrast thresholds without changing verbal distance estimates (Woods et al., 2009). Apparently, enhancing cortical arousal influences some visual tasks but not others. The factors that elicit this influence remain unclear. To begin investigating this issue, we conducted two experiments representing intermediate steps between the contrast threshold and verbal distance estimation methodologies: a Depth Threshold task (modeled on the 2AFC contrast threshold methodology, but in the depth domain) and a Distance Difference Threshold task (similar to the Depth task but with targets presented successively rather than in pairs). Methods: Depth Threshold: Two groups (N's = 18) underwent either CPS or “Sham” stimulation (immersing the foot in room temperature water for 50 seconds). On each trial participants binocularly viewed two white rods against a black background and judged which rod was closer, with depth separation being adjusted adaptively across trials. Threshold (82% correct criterion) was estimated before and after stimulation. DistanceDifference Threshold: Seventeen participants sequentially viewed 2 cones in identical checkerboard-covered alleyways (interstimulus interval ≈ 1.5s), judging which cone was closer. Thresholds were determined before and after CPS. Distance difference was adjusted adaptively across trials. Results: Depth thresholds decreased following CPS (t=3.4, p=0.003), but remained unchanged following Sham stimulation (t=0.19, p=0.84). Distancedifference thresholds did not change from Baseline to Post-Stimulation (t=0.21, p=0.83). Discussion: When present, arousal-related affects could stem from either enhanced attention or bona-fide changes in visual appearance. These factors are difficult to tease apart. In a separate experiment, we found that CPS did not affect contrast thresholds in a 2AFC task when the interstimulus interval was increased to 1.5 s. Thus, our results suggest that some aspect of the simultaneous or near-simultaneous comparison between stimuli may be crucial for eliciting arousal-related effects in visual tasks.