Binaural information can converge in abstract memory traces

Neural representations for abstract features of auditory stimuli were studied by presenting reading subjects with stimulus blocks composed of pairs of two closely spaced tones. There were frequent ascending standard pairs (i.e., the second tone was higher in frequency than the first tone) and occasional descending deviant pairs. Both types of pairs varied randomly over a wide frequency range. In separate blocks, the tones forming a pair were presented either to the same ear or to opposite ears. The deviant pairs elicited the mismatch negativity (MMN) in all conditions, which indicates that the brain can automatically extract and represent an abstract invariant feature (rise or fall) of stimulation above the point of binaural convergence and detect violations against it. Poor behavioral performance in an active discrimination task suggested that conscious discrimination processes can only partially use the outcome of the preattentive discrimination processes reflected by the MMN.