# Pupil diameter as an indicator of sound pair familiarity after statistically structured auditory sequence

## TL;DR

The study found that pupil dilation can indicate familiarity with sound pairs in structured auditory sequences, but it doesn't always reflect statistical patterns in the sounds.

## Contribution

The study introduces pupil diameter as a potential indicator of sound pair familiarity in structured auditory sequences.

## Key findings

- Pupil dilation during a familiarity task showed participants learned structured sound pairs.
- Pupil diameter during structured sequences did not reflect statistical regularities.
- Results contrast with visual domain studies, highlighting auditory domain differences.

## Abstract

Inspired by recent findings in the visual domain, we investigated whether the stimulus-evoked pupil dilation reflects temporal statistical regularities in sequences of auditory stimuli. We conducted two preregistered pupillometry experiments (experiment 1, n = 30, 21 females; experiment 2, n = 31, 22 females). In both experiments, human participants listened to sequences of spoken vowels in two conditions. In the first condition, the stimuli were presented in a random order and, in the second condition, the same stimuli were presented in a sequence structured in pairs. The second experiment replicated the first experiment with a modified timing and number of stimuli presented and without participants being informed about any sequence structure. The sound-evoked pupil dilation during a subsequent familiarity task indicated that participants learned the auditory vowel pairs of the structured condition. However, pupil diameter during the structured sequence did not differ according to the statistical regularity of the pair structure. This contrasts with similar visual studies, emphasizing the susceptibility of pupil effects during statistically structured sequences to experimental design settings in the auditory domain. In sum, our findings suggest that pupil diameter may serve as an indicator of sound pair familiarity but does not invariably respond to task-irrelevant transition probabilities of auditory sequences.