Aging Impairs the Ability to Ignore Irrelevant Information in Frequency Discrimination Tasks

Age effects on the ability to ignore irrelevant auditory information were studied using frequency discrimination threshold (FDT) tasks. FDTs were determined in an unmasked condition with target tones in isolation, and in two backward-masked conditions with a nontarget masking tone presented 20 to 240 ms after the target.One masked condition included irrelevant variability in the masker frequency, but the other did not. The no-variability condition yielded more masking in older than in young adults. Masker variability induced large FDT elevations in both groups; however, the improvement in FDTs with training was large in young but only minimal in older adults.

This research project was supported by a seed grant from the College of Allied Health, University of Oklahoma Health Sciences Center awarded to B. Espinoza-Varas (PI). The authors would like to thank the older and young adults for their willingness and enthusiasm to participate in this research project and complete the test schedules.

Notes

¹The effects of signal duration on FDTs of older adults have not been studied in detail. Larger FDTs for older than for young adults have been reported (Abel, Krever, & Alberti, 1990), but for tones of much shorter duration than the ones used here (20 versus 40 ms); in the Abel et al. study, the amount of training in the discrimination task was also much smaller than in the present study.

²Because frequency discrimination improves when T increases from 40 to 60 ms (e.g., Liang & Chistovich, 1961), E1 had a slight advantage relative to the other study participants (nevertheless, her FDTs were among the highest).

Target duration (ms): a = 80; b = 60; c = 40.

T = target tone; NT = nontarget tone; ISI = interstimulus interval.

³Previous research (e.g., He, Dubno, & Mills, 1998) shows that, for frequencies higher than 1000 Hz, FDTs are only slightly larger for older than for young adults. In the present study, FDTs were measured with an adaptive procedure implemented on a 3I/2AFC task and, prior to estimating baseline FDTs, the older adults underwent many hours of training. Both of these factors could account for the small differences between the young and older adults' FDTs.

⁴The effects of hearing sensitivity on frequency-discrimination thresholds depend mainly on the target sensation level; that is, on the amount by which the target exceeds the detection threshold at the target frequency (e.g., Wier, Jesteadt, & Green, 1977). Frequency discrimination thresholds decrease as the sensation level increases up to 35 to 40 dB; above this level, frequency discrimination thresholds remain nearly constant with sensation level. In the present study, the target sensation level was 50 to 55 dB in all subjects; therefore, the discrimination thresholds could not have been affected by differences in hearing sensitivity across age groups. In order to elevate the FDTs, the elevation of detection thresholds (i.e., decrease in sensitivity) has to be more 40 to 50 dB (e.g., Freyman & Nelson, 1991); that is, the elevation has to be clearly in the abnormal sensitivity range; in the present study, the detection thresholds at the target frequency were within the normal range in all subjects.