Objective: The goal of this study was to investigate auditory function in individuals with deficits in musical pitch perception. We hypothesized that such individuals have deficits in nonspeech areas of auditory processing.
Design: We screened 865 randomly selected individuals to identify those who scored poorly on the Distorted Tunes test (DTT), a measure of musical pitch recognition ability. Those who scored poorly were given a comprehensive audiologic examination, and those with hearing loss or other confounding audiologic factors were excluded from further testing. Thirty-five individuals with tune deafness constituted the experimental group. Thirty-four individuals with normal hearing and normal DTT scores, matched for age, gender, handedness, and education, and without overt or reported psychiatric disorders made up the normal control group. Individual and group performance for pure-tone frequency discrimination at 1000 Hz was determined by measuring the difference limen for frequency (DLF). Auditory processing abilities were assessed using tests of pitch pattern recognition, duration pattern recognition, and auditory gap detection. In addition, we evaluated both attention and short- and long-term memory as variables that might influence performance on our experimental measures. Differences between groups were evaluated statistically using Wilcoxon nonparametric tests and t-tests as appropriate.
Results: The DLF at 1000 Hz in the group with tune deafness was significantly larger than that of the normal control group. However, approximately one-third of participants with tune deafness had DLFs within the range of performance observed in the control group. Many individuals with tune deafness also displayed a high degree of variability in their intertrial frequency discrimination performance that could not be explained by deficits in memory or attention. Pitch and duration pattern discrimination and auditory gap-detection ability were significantly poorer in the group with tune deafness than the normal control group. Approximately one-third of our participants with tune deafness displayed evidence of attention deficit with hyperactivity disorder on the Test of Variables of Attention. Test of Variables of Attention scores were significantly correlated with gap-detection scores, but not significantly correlated with any of the other experimental measures, including the DTT, DLF, and auditory pattern discrimination tests. Short- and long-term memory was not significantly related to any of the experimental measures.
Conclusions: Individuals with tune deafness identified by the DTT have poor performance on many tests of auditory function. These include pure-tone frequency discrimination, pitch and duration pattern discrimination, and temporal resolution. Overall, reduction in performance does not seem to derive from deficits in memory or attention. However, because of the prevalence of attention deficit with hyperactivity disorder in those with tune deafness, this variable should be considered as a potentially confounding factor in future studies of tune deafness and its characteristics. Pure-tone frequency discrimination varied widely in individuals with tune deafness, and the high degree of intertrial variability suggests that frequency discrimination may be unstable in tune-deaf individuals.