Pupil Diameter Tracks the Exploration-Exploitation Trade-off During Analogical Reasoning and Explains Individual Differences in Fluid Intelligence

The ability to adaptively shift between exploration and exploitation control states is critical for optimizing behavioral performance. Converging evidence from primate electrophysiology and computational neural modeling has suggested that this ability may be mediated by the broad noradrenergic projections emanating from the locus coeruleus (LC-NE; Aston-Jones & Cohen, 2005). There is also evidence that pupil diameter covaries systematically with LC activity. Though imperfect and indirect, this link makes pupillometry a useful tool for studying the LC-NE system in humans and in high-level tasks. Here we present a novel paradigm that examines how the pupillary response during exploration and exploitation covaries with individual dif-ferences in fluid intelligence during analogical reasoning on Raven’s Advanced Progressive Matrices (APM). Pupillometry was used as a non-invasive proxy for LC activity, and concur-rent think-aloud verbal protocols were used to identify exploratory and exploitative solution periods. This novel combination of pupillometry and verbal protocols from 40 participants revealed a decrease in pupil diameter during exploitation and an increase during exploration. The temporal dynamics of the pupillary response was characterized by a steep increase during the transition from exploitative to exploratory periods, sustained dilation for many seconds afterwards, followed by gradual return to baseline. Moreover, the individual differences in the relative magnitude of pupillary dilation accounted for 16 % of the variance in APM scores. Assuming that pupil diameter is a valid index of LC activity, these results establish promising preliminary connections between the literature on LC-NE mediated cognitive control and the literature on analogical reasoning and fluid intelligence