Previous studies have largely demonstrated the reliability of pupil diameter in acting as a reporter variable for LC activity in animal models, e.g. Rajkowski and colleagues recorded from a single LC neuron in the monkey, and used a remote eye-tracking camera to measure pupil dilation during a target detection task. This figure is adapted from Rajkowski, Kubiak, & Aston-Jones, and shows the close positive association between baseline locus coeruleus activity and tonic pupil diameter. The relationship between pupil diameter and baseline locus coeruleus activity. As the LC is the sole source of NE-releasing fibers to the forebrain, and pupils can dilate with latencies as short as 200 ms, pupil size over time should provide an overt and objective measure of NE levels in the forebrain on a sub-second time-scale.įigure 1. NE release in turn effects changes in individuals' attention and arousal by enhancing the synaptic responsivity of neurons to subsequent inputs. Pupil dilations have been shown to closely track norepinephrine (NE) release by the locus coeruleus (LC), (see Figure 1). There is ample reason to believe that the pattern of pupillary dilation dynamics, when recorded at high temporal resolution, can provide a continuous index of attention. easy mathematical calculations, ), these metrics ignore temporal information that could further elucidate the dynamics of attention to information. Although means and maxima are useful in discriminating responses between categories (e.g., emotional vs. Īlthough previous studies have been careful to control luminance to reveal salience-related dilations, the standard analysis of pupillometric data is often temporally coarse: averaging pupillary diameter across a trial or using the maximum dilation during a pre-defined temporal window for analysis, e.g.,, –. For this reason, pupil dilations that index informational salience are only reliably measured under conditions of controlled light, –. In contrast, luminance-related dilations index parasympathetic activation of the Edinger-Westphal nucleus and are generally between 2–4 mm. Information-related dilations are associated with sympathetic activation of the superior sympathetic ganglion, and rarely exceed. This difference in size reflects different biological pathways. Pupil dilations due to changes in informational salience are much smaller than pupil dilations due to changes in luminance. The pupil, especially, has been investigated as an index of mental states, given its tendency to dilate to salient stimuli such as emotionally arousing pictures, painful stimulation, and task-relevant numbers. Science supports this intuition: eyes broadcast mind and animacy better than any other facial feature, with specific ocular cues linked to emotion (scleral size, ), information processing (eye-blinks, ), and intention (gaze direction, ). ![]() Poets, philosophers, and artists throughout history have considered eyes to be portals to the mind. (2011) and clarifies their finding by demonstrating that stimulus-pupil coupling reflects online cognitive processing beyond sensory gain. ![]() When presented with isoluminant digit sequences, participants' pupillary dilations were synchronized with stimulus onsets when attending, but not when mind-wandering. (2011) while controlling for luminance changes. Here, we replicated the methodology and findings of Smallwood et al. However, because stimulus onsets in their study involved shifts in luminance as well as information, they could not determine whether this coupling of stimulus and pupillary dynamics reflected attention to low-level (luminance) or high-level (information) changes. This finding suggests that pupil dilations afford a dynamic readout of conscious information processing. ![]() (2011) demonstrated that pupil dilations not only provide an index of overall attentional effort, but are time-locked to stimulus changes during attention (but not during mind-wandering). Consistent with this intuition, empirical research has demonstrated that pupils dilate as a consequence of attentional effort. It has long been thought that the eyes index the inner workings of the mind.
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