Spectrotemporal window of integration of auditory information in the human brain

The human auditory system is adapted to integrate temporally successive sounds into meaningful entities, that is, acoustic information units. Hence, sound sequences falling within the temporal window of integration should be coded holistically as unitary representations in the human auditory cortex. Although it is well established that the auditory system operates in the frequency-temporal domain, many previous studies only focused on the temporal domain of the window of integration. Therefore, in the current study we investigated the relationship between the short-term temporal integration and the frequency integration. Event-related magnetic fields in response to infrequent omission of the second tone in repetitive tone pairs composed of two closely spaced tones of different frequencies were recorded. This omission elicited the magnetic counterpart (MMNm) of the electric mismatch negativity (MMN), a change-specific component mainly generated in the auditory cortex, when the interval between the two successive tones was extremely short or when the frequency difference between the two tones was small. These findings suggest that two stimuli presented in close succession might be represented in the auditory system as a unitary integrated event. In addition, as the distance between the two successive tones decreased in the spectrotemporal dimensions, the magnitude of the MMNm increased. Behavioral data also supported these neurophysiological phenomena. This work shows the first neurophysiological evidence that the two-dimensional (spectrotemporal) window of integration, which provides important constraints for the neural processing of the acoustic environment, exists in the human brain.