The Time Course of the Pupillary Response to Auditory Emotions in Pseudospeech, Music, and Vocalizations

Emotions can be communicated through visual and dynamic characteristics such as smiles and gestures, but also through auditory channels such as laughter, music, and human speech. Pupil dilation has become a notable marker for visual emotion processing; however the pupil's sensitivity to emotional sounds, specifically speech, remains largely underexplored. This study investigated the processing of emotional pseudospeech, which are speech-like sentences devoid of semantic content. We measured participants' pupil dilations while they listened to pseudospeech, music, and human vocalizations, and subsequently performed an emotion recognition task. Our results showed that emotional pseudospeech can trigger increases of pupil dilation compared to neutral pseudospeech, supporting the use of pupillometry as a tool for indexing prosodic emotion processing in the absence of semantics. However, pupil responses to pseudospeech were smaller and slower than the responses evoked by human vocalizations. The pupillary response was not sensitive enough to distinguish between emotion categories in pseudospeech, but pupil dilations to music and vocalizations reflected some emotion-specific pupillary curves. The valence of the stimulus had a stronger overall influence on pupil size than arousal. These results highlight the potential for pupillometry in studying auditory emotion processing and provide a foundation for contextualizing pseudospeech alongside other affective auditory stimuli.