The temporal dynamics of adaptation to background noise

The auditory system’s remarkable ability to adapt its processing to the statistical properties of background noise is a key contributor to its ability to facilitate hearing in complex acoustic environments. However, the temporal dynamics of this process of adaptation and the precise acoustic features that influence them are not fully characterised on a perceptual level, particularly in response to complex, naturalistic sounds. This thesis aimed to comprehensively characterise the time course of perceptual adaptation to naturalistic background noise and the factors influencing its build-up and reset, as well as investigate the causal role of the non-primary auditory cortex in this process. I conducted a series of psychophysical experiments in human listeners, using a behavioural paradigm in which continuous background noises switched in spectrotemporal identity and/or spatial location between trials. By systematically varying the target onset delay (0–1750 ms) relative to this change, I mapped the time course of adaptation. To test the causal contribution of non-primary auditory cortex to this process, I then adapted this paradigm in ferrets while incorporating optogenetic inactivation. Human listeners consistently demonstrated a rapid perceptual benefit, developing over several hundred milliseconds and plateauing around 1000 ms. This adaptive benefit was reset by changes in both spectrotemporal and spatial shifts. Acoustic feature analysis of 109 naturalistic noises revealed that the magnitude of adaptation was strongly modulated by the temporal statistics of noise, with less stationary noises benefiting from a greater adaptive benefit. This time course was also found to be largely preserved in older listeners, irrespective of age-related hearing loss. In contrast, I was not able to demonstrate the same perceptual benefit in ferrets, likely due to attentional confounds, and consequently, cortical inactivation was inconclusive.