Stimulus length uncertainty with dichotic digit recognition

Dichotic digit listening was made more difficult by interleaving one-, two-, three-, and four-pair digits within a test list in which the subjects did not know a priori the number of digit pairs presented on a given trial, thereby introducing listener uncertainty. Twenty right-handed (mean age = 26.8 years) and 20 left-handed adults (mean age = 24.0) with normal hearing and 40 right-handed adults in the 60- to 75-years age range (mean age = 67.2) with mild-to-moderate sensorineural hearing loss were evaluated. Compared to traditional paradigms, the uncertainty of stimulus length (one, two, three, or four pairs) reduced overall recognition performance on stimuli presented to both ears of all groups, but the reduction was more pronounced for the left ear than for the right ear. The recognition performance of the right-handed subjects was more homogeneous than the performance of the left-handed subjects. In comparison to the young subjects, the 60- to 75-year-old group had substantially reduced recognition performance.