Despite the prevalent use of alerting sounds in alarms and human–machine interface systems and the long-hypothesized role of the auditory system as the brain's “early warning system,” we have only a rudimentary understanding of what determines auditory salience—the automatic attraction of attention by sound—and which brain mechanisms underlie this process. A major roadblock has been the lack of a robust, objective means of quantifying sound-driven attentional capture. Here we demonstrate that: (1) a reliable salience scale can be obtained from crowd-sourcing (N = 911), (2) acoustic roughness appears to be a driving feature behind this scaling, consistent with previous reports implicating roughness in the perceptual distinctiveness of sounds, and (3) crowd-sourced auditory salience correlates with objective autonomic measures. Specifically, we show that a salience ranking obtained from online raters correlated robustly with the superior colliculus-mediated ocular freezing response, microsaccadic inhibition (MSI), measured in naive, passively listening human participants (of either sex). More salient sounds evoked earlier and larger MSI, consistent with a faster orienting response. These results are consistent with the hypothesis that MSI reflects a general reorienting response that is evoked by potentially behaviorally important events regardless of their modality.SIGNIFICANCE STATEMENT Microsaccades are small, rapid, fixational eye movements that are measurable with sensitive eye-tracking equipment. We reveal a novel, robust link between microsaccade dynamics and the subjective salience of brief sounds (salience rankings obtained from a large number of participants in an online experiment): Within 300 ms of sound onset, the eyes of naive, passively listening participants demonstrate different microsaccade patterns as a function of the sound's crowd-sourced salience. These results position the superior colliculus (hypothesized to underlie microsaccade generation) as an important brain area to investigate in the context of a putative multimodal salience hub. They also demonstrate an objective means for quantifying auditory salience.

Acknowledgements:We are grateful to Makoto Yoneya (NTT) for initiating the pupillometry setup at UCL. This work was supported by an EC Horizon 2020 grant and a BBSRC international partnering award to MC.Significance statement: Microsaccades are small, rapid, fixational eye movements, measurable with sensitive eye-tracking equipment. We reveal a novel, robust link between microsaccade dynamics and the subjective salience of brief sounds (salience ranking obtained from a large number of participants in an online experiment): Within 300 ms of sound onset, the eyes of naïve, passively listening participants demonstrate different microsaccade patterns as a function of the sound's perceptual salience. These results position the Superior Colliculus (the generator of microsaccades) as an important brain area to investigate in the context of a putative multi-modal salience-hub and establish a robust objective means for quantifying auditory salience, critical in the development of sound-based human machine interfaces. AbstractDespite the prevalent use of alerting sounds in alarms and human-machine interface systems, we have only a rudimentary understanding of what determines auditory saliencethe automatic attraction of attention by sound -and the brain mechanisms which underlie this process. A major roadblock to understanding has been the lack of a robust, objective means of quantifying sound-driven attentional capture. Here we demonstrate that microsaccade inhibitionan oculomotor response arising within 300ms of sound onset -is a robust marker for the salience of brief sounds. Specifically, we show that a 'crowd sourced' (N=911) subjective salience ranking correlated robustly with the superior colliculus (SC) mediated ocular freezing response measured in naïve, passively listening participants (replicated in two groups of N=15 each). More salient sounds evoked earlier microsaccadic inhibition, consistent with a faster orienting response. These results establish that microsaccade-indexed activity within the SC is a practical objective measure for auditory salience.