Table 1.
Cognitive processes associated with pupil size dynamics
| Cognitive process | Key papers | Key findings |
|---|---|---|
| Mental effort | Kahneman and Beatty (1966); Kahnemann and Beatty (1967); Johnson (1971); Kramer et al. (2013) | Pupil size sensitive to variations in effort (greater effort, greater pupil size) |
| Attention (general) | Kahneman (1973); Hoeks and Levelt (1993); Iriki et al. (1996); Smallwood et al. (2011); Wierda et al. (2012) | Pupil signal indexes changes in attention over time. Pupil time course can be modeled via attentional pulses. Pupil exhibits greater spontaneous fluctuation when attention is decoupled from task |
| Attention (spatial) | Mathôt et al. (2013); Binda et al. (2013); Naber et al. (2013a) | When focusing attention on a visual object (even covertly), the pupil adjusts to the objects’ brightness |
| Uncertainty, decision-making | Friedman et al. (1973); Einhäuser et al. (2008); Jepma and Nieuwenhuis (2011); Laeng et al. (2012); de Gee et al. (2014); Urai et al. (2017); Kawaguchi et al. (2018); Colizoli et al. (2018a) | Pupil diameter increases prior to perceptual shifts and decision-making. Negative relationship between pupil size and decision confidence |
| Surprise, salience, orienting, prediction error | Beatty (1982a); Preuschoff et al. (2011); Wang et al. (2014); Fink et al. (2018); Alamia et al. (2019) | Pupil dilation response to surprising / alerting / salient stimuli, even when below perceptual threshold or unconscious and irrelevant to the task. Positive relationship between pupil size and prediction error |
| Sexual or emotional arousal | Hess and Polt (1960); Bradley et al. (2008) | Greater arousal correlated with greater pupil size. Heart rate and skin conductance also correlated with pupil activity |
| Response preparation, motor activity | Einhäuser et al. (2008); Reimer et al. (2014); McCloy et al. (2016) | Making a motor response (e.g., a button press) increases pupil dilation, which begins prior to the motor response. In mice, fluctuations in pupil size correlated with locomotion activity |
| Fatigue, task performance | Lowenstein et al. (1963); Beatty (1982a); Aston-Jones and Cohen (2005); Murphy et al. (2011); Eldar et al. (2013); McGinley et al. (2015); Knapen et al. (2016) | Performance on a task follows an inverse U-shaped function, with optimal performance at intermediate pupil sizes. Tonic pupil size decreases with time-on-task. Pupil size and behavior are correlated with changes in neural gain |
| Imagined arousal, effort, or brightness | Whipple et al. (1992); Laeng and Sulutvedt (2014); Sulutvedt et al. (2018); Kang and Banaji (2020) | Even during imagery or visual illusions, the pupil follows the same dilation patterns as observed during naturalistic conditions |
| Memory and familiarity | Võ et al. (2008); Kafkas and Montaldi (2011); Naber et al. (2013b); Papesh et al. (2012); Gomes et al. (2021) | Greater pupil size for greater familiarity; however, false alarms also produce pupil dilation (i.e., the pupil may not distinguish accurate familiarity, rather participants’ belief). Greater pupil size at encoding predicts greater retrieval success. cf. Beukema et al. (2019) and “Surprise” section above |