Pupil dilation but not microsaccade rate robustly reveals decision formation

Christoph Strauch,Anke Huckauf,Lukas Greiter

doi:10.1038/s41598-018-31551-x

Abstract

Pupil dilation, an indicator of arousal that is generally regarded as unspecific, amongst others reflects decision formation and reveals choice. Employing letter selection in a Go/NoGo task, we show that choice can robustly be predicted by the pupillary signal, even under the presence of strong interfering factors such as changes in brightness or motor execution. In addition, a larger difference in pupil dilation between target and distractor conditions for NoGo compared to Go was demonstrated, underlining the particular appropriateness of the paradigm for decision research. Incorporating microsaccades, a variable that is suggested to covary with pupil diameter, we show that decision formation can only be observed in pupil diameter. However, microsaccade rate and pupil size covaried for motor execution and both reflected choice after key press with smaller effect size for microsaccade rate. We argue that combining pupil dilation and microsaccade rate may help dissociating decision-related changes in pupil diameter from interfering factors. Considering the interlinked main neural correlates of pupil dilation and microsaccade generation, these findings point to a selective role of locus coeruleus compared to superior colliculus in decision formation.

Highlights

Variations in pupil diameter, at constant brightness and viewing distance, are a popular but unspecific indicator of cognitive[1] and affective processing[2,3,4,5]
By means of a letter selection task including Go/NoGo-trials, we investigated whether and how robust decision formation and the outcomes of a binary decision process can be revealed by analyzing pupil diameter
We assessed microsaccade rate as a covariate in order to deepen the understanding of commonalities and differences in relation to pupil dilation

Summary

Introduction

Variations in pupil diameter, at constant brightness and viewing distance, are a popular but unspecific indicator of cognitive[1] and affective processing[2,3,4,5]. Two approaches might serve for compensating the missing specificity; firstly, one might disentangle interfering effects, or, secondly, one might add a further variable Both approaches were pursued by examining pupil responses in a decision task including strong interference factors such as a sudden change in brightness, a key press, a tone, and four directions of incoming saccades while simultaneously tracking microsaccade rate. Both dependent variables are hardly conjointly investigated for several psychological factors; a gap in existing research that we aim to close Besides this methodological contribution, we deepen the fundamental understanding of binary decision making and investigate the robustness of the effects of choice on pupil diameter in the presence of strong interfering variables. By combining these two ideas, application scenarios for pupil diameter and microsaccade rate in human-computer interaction could emerge, e.g. prediction of user intention[27]

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