Attentional modulation and cue-specificity of cortical biases in favour of looming sounds

Our auditory sense allows us to constantly monitor our surroundings for potentially hazardous events. It may be for that reason that listeners are particularly sensitive to sounds indicating looming auditory objects. Researchers have elicited and studied the phenomenon of looming bias by creating moving stimuli through changes in either broadband or spectral intensity, thereby exposing this bias across various species and ages during attentive listening. For effective hazard protection, however, the bias should not require the listener's attention. In our present study, we directly compared the two cue types used to elicit the looming bias and looked into the role of attention: twenty-eight normal-hearing listeners were initially passively exposed to the stimuli, being directed to focus on a muted and dubbed movie. Subsequently, in a second condition, they were asked to discriminate sound motion by keypress. In both conditions, neural activity was recorded through high-density electroencephalography (EEG). Cortical source activity was localized based on individual brain anatomies and electrode positions. Behaviourally, we verify the presence of the looming bias and its manifestation in higher accuracies for spectral cues and faster responses for broadband cues. Neurally, we see the emergence of the bias as early as 80 ms after the change. The bias is evoked later but stronger for changes in broadband versus spectral intensity and, most importantly, present in both passive and active listening modes. At the level of the primary auditory cortex (PAC), the bias occurs most consistently on the right hemisphere. Together, our findings of early pre-attentive biases suggest a strong bottom-up directed prioritization in the neural processing of looming sounds.