The effect of rhythmical violations on the pupillary response in unattended beat perception

It is far from resolved how unattended information operates in the multimodal attentional system. One of the aspects of this system is the perception of auditory stimuli as complex interactions between its elements and their subjective interpretation. For example, beat perception depends on various subdivisions of rhythm and listeners’ ability to infer regular pulse from it. However, it is still unknown how beat perception operates in the absence of attention, and how it relates to the subjectively established hierarchy of salience or meter. The current study addressed those questions by use of pupillometry. We investigated the pupillary response to omissions with three different salience levels in drum beats (high salience, low salience and polyrhythmic change), while participants (n=20) attended to a filler vigilance task. It was hypothesised that there would be significant pupil dilation to all rhythmical violations and that there would be a significant difference between pupillary responses that would correspond to the levels of salience. The results demonstrated that pupils dilate as a response only to the high salience rhythmic violation. Contrary to Damsma and van Rijn (2017), the results suggest that there may be a threshold to extend the unattended auditory information being reflected by the pupillary response. Overall, the findings suggest that pupils dilate as a response to the violation of expectation and indicates unattentive auditory processing.