2/9/2023 0 Comments Split pupilSeveral key features of these adaptive processes are reflected robustly in dynamic pupil fluctuations. In uncertain and changing environments, effective belief-updating strategies need to resist spurious noise while remaining flexible enough to adapt to real changes ( Behrens et al., 2007 Filipowicz et al., 2016 Nassar et al., 2010 O'Reilly, 2013). We build on studies of adaptive decision-making, in which past experiences are used flexibly to update beliefs about the world that guide decisions ( Filipowicz et al., 2016 Johnson-Laird, 2004 Tenenbaum et al., 2011). The goal of the present study was to reconcile these different views and synthesize a more comprehensive understanding of the role of pupil-linked arousal systems in cognition. This view emphasizes specific computations encoded in pupil size but lacks a clear link to idiosyncratic, cognitive processing. More recently, arousal-related pupil modulations have been shown to represent critical computations required to learn from, and adapt to, changes in our environment ( Krishnamurthy et al., 2017 Nassar et al., 2012 O'Reilly et al., 2013 Preuschoff et al., 2011). Pupil size is also sensitive to stimulus probabilities, typically increasing when unexpected stimuli are presented or expected stimuli are omitted ( Joshi et al., 2016 Murphy et al., 2014 Qiyang et al., 1985). This view emphasizes the idiosyncratic and cognitive nature of these pupil fluctuations but lacks a precise description of the computations being encoded. Several early studies ascribed arousal-related modulations of pupil size to the ‘mental effort’ required to, for example, solve an arithmetic problem or hold items in working memory ( Beatty, 1982 Mathôt, 2018). Pupil size changes primarily as a function of ambient light levels but also in the context of a host of other brain functions that often involve changes in arousal ( Joshi and Gold, 2020 Mathôt, 2018). ![]() Together these results demonstrate a central role for idiosyncratic cognitive processing in how arousal systems respond to new inputs and, via our complexity-based analyses, offer a potential framework for understanding these effects in terms of both inference processes aimed to reduce belief uncertainty and more traditional notions of mental effort. We further show that both baseline and evoked pupil diameter is modulated by the degree to which individual subjects use these violations to update their subsequent expectations, as reflected in the complexity of their updating strategy. Using an auditory adaptive decision-making task, we show that evoked pupil diameter is more parsimoniously described as signaling violations of learned, top-down expectations than changes in low-level stimulus properties. Pupils tend to dilate in response to surprising events, but it is not known whether these responses are primarily stimulus driven or instead reflect a more nuanced relationship between pupil-linked arousal systems and cognitive expectations.
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