Evidence that pupil dilation and cardiac afferent signalling differentially impact the processing of emotional intensity and racial bias

Interoceptive cardiac arousal signals (e.g., from baroreceptor firing at ventricular systole compared to diastole) have been found to enhance perception of fearful versus neutral faces. They have also been found to amplify racially biased misidentification of tools as weapons when preceded by facial images of Black versus White individuals. Since pupil size is strongly coupled to arousal, we tested if experimental manipulation of pupil size influences fear processing in emotional judgement and racial bias tasks involving measurement of cardiac signals. In a sample of 22 non-clinical participants in an emotional intensity judgement task, pupil size did not affect emotional intensity ratings. Nor did it interact with differential effects of cardiac systole versus diastole on intensity judgements of fearful and neutral faces, replicated here. In a sample of 25 non-clinical participants in a weapons identification task, larger pupil size resulted in faster response times and lower accuracy when identifying tools and weapons. However, pupil size did not interact with weapon versus tool identification, race of prime, or cardiac timing. We nevertheless replicated the observed increase in racially biased misidentification of tools as weapons following Black face primes presented at cardiac systole. Together our findings indicate that pupil dilation does not directly influence the processing of fear cues or perceived threat (as in racial bias) yet affects task performance by decreasing response times and accuracy. These findings contrast with the established effect of cardiac arousal signals on threat processing and may help focus interventions to mitigate related decision errors in high-pressure occupations.