Processing of Binaural Pitch Stimuli in Hearing-Impaired Listeners

Binaural pitch is a tonal sensation produced by introducing a frequency-dependent interaural phase shift in binaurally presented white noise. As no spectral cues are present in the physical stimulus, binaural pitch perception is assumed to rely on accurate temporal fine structure coding and intact binaural integration mechanisms. This study investigated to what extent basic auditory measures of binaural processing as well as cognitive abilities are correlated with the ability of hearing-impaired listeners to perceive binaural pitch. Subjects from three groups (1: normal-hearing; 2: cochlear hearingloss; 3: retro-cochlear impairment) were asked to identify the pitch contour of series of five notes of equal duration, ranging from 523 to 784 Hz, played either with Huggins’ binaural pitch stimuli (BP) or perceptually similar, but monaurally detectable, pitches (MP). All subjects from groups 1 and 2 and some from group 3 could hear both MP and BP in more than 80% of all presentations; these subjects obtained similar contour identification scores for MP and BP. Other subjects from group 3 could hear most MP but none of the BP pitches. These other subjects obtained significantly lower binaural masking level differences and binaural intelligibility level differences than subjects from group 1, but did not necessarily show reduced scores in a lexical decision task and a reading span test. Overall, these findings confirm that binaural pitch perception is either immediate or absent in hearing-impaired listeners, and that its absence is not due to a general difficulty extracting tonal objects from noise; they also suggest that the absence of binaural pitch percept might be an indicator of retro-cochlear impairment. A total absence of binaural pitch percept was found to coexist with impaired lowlevel binaural processing, but not to imply reduced cognitive function.