Auditory dysfunction in subjects with normal hearing

For this investigation twenty-seven subjects with normal pure tone thresholds and speech discrimination scores were divided into two groups and studied. The first group (normal/normal-NN) consisted of 18 subjects with no complaints of difficulty hearing, and the second group (normal/abnormal-NA) consisted of nine subjects who complained of difficulty in hearing speech, especially in less than perfect listening conditions. Measures of frequency resolution, binaural release from masking and speech in noise and/or reverberation were used to determine if differences existed between the groups. Results indicated that the two groups investigated differed appreciably when more rigorous testing was conducted. These differences were determined with a combination of three assessment tools:

1) personal opinion of hearing ability;

2) response to a questionnaire;

3) performance on measures of MLD, slope and peak of the masking curve and discrimination of speech under reverberant conditions.

The eight subjects from subgroup NA shown to have hearing difficulties had smaller MLD's, greater upward spread of masking, and greater difficulty discriminating reverberant speech. These data suggest that the locus the auditory dysfunction for these NA subjects was in the cochlea.