The purpose of the study was to examine recognition of degraded melodic stimuli in dichotic listening with or without frequency-place mismatch.
Melodic stimuli were noise vocoded with various number-of-channel conditions in a dichotic and monaural processor. In the dichotic zipper processor, the odd-indexed channels were tonotopically matched and presented to the left ear while the even-indexed channels were tonotopically matched or upward shifted in frequency and presented to the right ear. In the monaural processor, all channels either unshifted or shifted were presented to the left ear alone. Familiar melody recognition was measured in 16 normal-hearing adult listeners.
Performance for dichotically presented melodic stimuli did not differ from that for monaurally presented stimuli even with low spectral resolution (8 channels). With spectral shift introduced in one ear, melody recognition decreased with increasing spectral shift in a nonmonotonic fashion. With spectral shift, melody recognition in dichotic listening was either not different or superior in a few cases relative to the monaural condition.
With no spectral shift, cohesive fusion of dichotically presented melodic stimuli did not seem to depend on spectral resolution. In spectrally shifted conditions, listeners may have suppressed the partially shifted channels in the right ear and selectively attended only to the unshifted ones, resulting in dichotic advantages for melody recognition in some cases.