Abstract
Although animal work suggests that arousal state has a profound impact on visual responses, the effects on human vision remain less well understood. To better characterize the mechanisms by which arousal affects perception, in this study we assessed the influence of task difficulty on the gain of human visuocortical contrast response functions (CRFs). To do so, we leveraged an adaptation paradigm that homogenizes population responses, allowing us to better measure compressive, nonlinear CRFs with fMRI. After adapting visual cortex (adapter: 16% contrast), we then measured BOLD responses in early visual cortex (V1-V3) while participants (n=14) viewed grating stimuli varying in contrast from trial to trial (9 contrast levels, 3% to 96% contrast). While viewing the stimuli, observers were instructed to concurrently solve auditory arithmetic problems which were categorized as either Easy (low arousal) or Hard (high arousal). To obtain population CRFs from the BOLD activity, we used a deconvolution analysis on a voxel-wise level. Our results revealed a surprisingly diverse pattern of modulatory effects across individuals: some individuals displayed enhanced gain of neural response with increased cognitive arousal, while others displayed the opposite effect: a decrease in gain of response with increased cognitive arousal. This diversity was not spurious: cross-validation analyses verified that these patterns were quite consistent within participants. Moreover, we found that an individual’s pattern of BOLD modulation correlated with arousal-driven changes in their pupil size, such that larger pupil differences between the two difficulty conditions corresponded to larger decreases in gain of neural response with increased cognitive arousal. We speculate that the polarity with which cognitive arousal modulates visuocortical responses may relate to individual differences in cognitive effort expended between the two difficulty conditions, with individuals falling on different points on the Yerkes-Dodson curve.