Jane F. MacNeil
Elzbieta B. Slawinski
Dept. of Psychol., Univ. of Calgary, 2500 University Dr., NW, Calgary, AB T2N 1N4, Canada
The relationship between frequency glide discrimination and frequency resolution was investigated among a group of normal hearing individuals aged 20 to 75 years. Frequency glide discrimination for 60-ms stimuli was determined at two frequency regions (1000 and 2500 Hz) for both upward and downward trajectories; converging or diverging offset frequencies; and in quiet and background noise. Psychophysical tuning curves were measured in a forward masking paradigm at both 500 and 4000 Hz. Relative to young adults, the elderly displayed larger just noticeable differences, greater effects for frequency region, noise, and transition direction. Though there was a significant effect for age, the results indicate that hearing sensitivity was the most important variable explaining more of the variance in the data than age. Even within normal limits, sensitivity still decreased with increasing age and therefore discrimination performance and shape of the tuning curves varied as a function of age. Consequently, the effect of age is confounded with sensitivity levels despite normal audiological profiles. Altered tuning curves are present before clinical evidence of cochlear damage indicating an impaired processing of complex signals.