Averaged and single-trial brain responses in the assessment of human sound detection.

We investigated sound detection in humans with magnetoencephalography and behavioural measurements. Sounds with intensity increasing smoothly over 125-1000 ms elicited a transient response in auditory cortex with a peak latency in the 200-600ms range. Importantly, peak latency accurately predicted behavioural reaction time and was unaffected by attentional engagement. Peak amplitude was augmented when the study participants attended to the stimuli and when stimulus duration was decreased. For investigating the cause of these amplitude variations in the averaged response we designed a wavelet-based method for analysing single-trial responses. We found that attention affects the amplitude of the single-trial responses whereas the intensity slope of the stimulus modifies their latency distribution. The transient response reported here holds promise for rapid, objective hearing assessment not requiring a behavioural task.