Pupillometry as an integrated readout of distinct attentional networks

The course of pupillary constriction and dilation provides an easy-to-access, inexpensive, and noninvasive readout of brain activity. We propose a new taxonomy of factors affecting the pupil and link these to associated neural underpinnings in an ascending hierarchy. In addition to two well-established low-level factors (light level and focal distance), we suggest two further intermediate-level factors, alerting and orienting, and a higher-level factor, executive functioning. Alerting, orienting, and executive functioning – including their respective underlying neural circuitries – overlap with the three principal attentional networks, making pupil size an integrated readout of distinct states of attention. As a now widespread technique, pupillometry is ready to provide meaningful applications and constitutes a viable part of the psychophysiological toolbox. Pupillometry provides a rich, (psycho)physiological readout of activity in specific brain networks. Highly interconnected but distinct neural circuits coordinate pupil responses.We propose a new taxonomy of five factors that drive pupil responses: the two well-established low-level factors – light level and focal distance, two intermediate-level factors – alerting and orienting, and a higher-level factor – executive control.Intermediate-level and higher-level factors and their underlying neural circuits closely correspond to established factors and networks of attention, suggesting that the pupil provides an integrated readout of distinct components of attention.Recent pupillometric discoveries are reviewed in the context of a comprehensive attention framework by providing examples of how high-level cognitive processes link to pupillary responses brought about by innervation of low-level pupil circuits via intermediate nuclei.