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Taylor R. Hayes, Per B. Sederberg, Brian M. Siefke, Alexander A. Petrov; Pupillometry reveals role for norepinephrine in the isolation effect. Journal of Vision 2014;14(10):1142. doi: https://doi.org/10.1167/14.10.1142.
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In a rich, ever-evolving sensory environment taking note of incongruent events can be a powerful tool. Emerging evidence from animal electrophysiology and computational modeling suggests that norepinephrine may play a key role in how our brains process this type of unexpected uncertainty (Yu & Dayan, 2003). The locus coeruleus (LC) serves as the primary source of norepinephrine in the brain and LC activity is strongly correlated with the pupillary response (Samuels & Szabadi, 2008). Therefore, we used the pupillary response as a non-invasive proxy to assess fluctuations in LC activity during periods of unexpected uncertainty within an isolation effect paradigm. Twenty participants completed 12 blocks of an isolation effect task consisting of study, distraction, and test phases. During study participants viewed a series of 32 words presented on a static background context that would occasionally oscillate between either circles or stars. Participants then performed a math distractor task prior to being tested on each of the 32 studied items. Each test item was a studied word presented on a neutral gray background and participants were asked to indicate whether the word appeared on circles or stars during study. All experimental images were isoluminant and presented under consistent ambient lighting. Pupil diameter was measured continuously using an Eyelink 1000 eye tracker at a sampling rate of 500 Hz. A significant isolation effect was observed as background accuracy was significantly higher for words that occurred when the background context changed than no-change trials at test. More importantly, we observed significantly larger phasic pupillary responses on background change trials relative to no-change trials during study, suggesting a boost in LC/NE activity during these periods. These findings are consistent with the hypothesis that norepinephrine plays an important role in signaling periods of unexpected uncertainty in our sensory environment.
Meeting abstract presented at VSS 2014
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