| Popis: |
Many behavioural measures of visual perception show continuous rhythmic fluctuations that reflect the influence of neural oscillations in the theta (4-7 Hz) and alpha frequency band (7-12 Hz). This thesis examines whether similar behavioural oscillations exist in audition and if so, how they may be linked to attention and sensory expectation. Three experiments are reported. All employed a similar design that involved the identification of the pitch (Experiment 1) or the ear of origin of a brief, monaural sinusoidal tone masked by uncorrelated broadband noise (Experiment 2 and 3). Experiment 1 confirmed oscillations in auditory sensitivity and revealed, for the first time, rhythmic fluctuations also in response bias. Sensitivity fluctuated at ~6 Hz, while bias exhibited slightly higher frequencies, ~8 Hz. The antiphase characteristic of the sensitivity oscillations between the ears were consistent with spatial attentional sampling. Additional results from Experiment 2 and 3 showed that oscillations in bias at ~9 Hz are related to sensory expectation arising from recent stimulus history. In particular, the oscillations in bias depended on the previous target occurring in the same ear as the current one. This suggests that sensory expectation is communicated through ear- or location-specific reverberations in the alpha band. Additionally, Experiment 3 revealed a new oscillatory effect in auditory behaviour related to unexpected stimulus changes: one trial after an infrequent target occurred, accuracy fluctuated rhythmically at ~7 Hz. These findings highlight the strong influence of oscillatory neural activity on auditory perception. In particular, they show that neural oscillations underlie important aspects necessary to maintain a continuous and coherent percept of the world, by anticipating forthcoming sensory input, sampling the relevant information and updating internal predictions. |
