Dichotic pitch discrimination

Abstract

Dichotic Huggins pitch was produced by generating broadband noise stimuli with narrow sections of the noise (bandwidths of 2, 4, 8, 16, 32, 64, and 128 Hz) interaurally phase shifted (by 90°, 135°, or 180°). The center frequencies of the narrow dichotic bands to which the interaural phase shifts were added were varied to change the value of the Huggins pitches. The just discriminable differences (obtained in a two-alternative, forced-choice adaptive procedure) in center frequency were determined for six listeners and at four (250, 400, 500, and 750 Hz) base center frequencies in an attempt to describe the pitch discrimination of dichotic Huggins pitches. For some listeners, at base center frequencies of 250 and 400 Hz and when the interaural phase shift used to produce the pitch was 180°, discrimination was almost as acute for these dichotic pitches (Δf/f=0.05%) as it was for diotically produced pitches. Pitch discrimination became more difficult as the center frequency increased to 500 and 750 Hz, the bandwidth of the interaurally altered band decreased from 128 to 2 Hz, or the interaural phase shift was reduced from 180° to 135° and 90°. The results will be discussed in terms of models of binaural processing and the use of interaural variables to segregate one sound image from other sound images. [Work supported by the NIDCD and the AFOSR.]