Simultaneous storage of two complex temporal sound patterns in auditory sensory memory.

We wished to determine whether multiple sound patterns can be simultaneously represented in the temporary auditory buffer (auditory sensory memory), when subjects have no task related to the sounds. To this end we used the mismatch negativity (MMN) event-related potential, an electric brain response elicited when a frequent sound is infrequently replaced by a different sound. The MMN response is based on the presence of the auditory sensory memory trace of the frequent sounds, which exists whether or not these sounds are in the focus of the subject's attention. Subjects watching a movie were presented with sound sequences consisting of two frequent sound patterns, each formed of four different tones and an infrequent pattern consisting of the first two tones of one of the frequent sound pattern and the last two tones of the other frequent sound pattern. The infrequent sound pattern elicited an MMN, indicating that multiple sound patterns are formed at an early, largely automatic stage of auditory processing.