Effects of aging and masker-level variability on backward-masked frequency discrimination

Backward-masked frequency discrimination thresholds (FDTs) were measured to probe the ability to ignore irrelevant auditory information in young and older adults. For 1500-Hz, 40- or 60-ms, 75-dB-SPL target tones, FDTs were measured unmasked and in three backward-masked conditions in which a 1500-Hz, 80-ms, 75-dB-SPL masking tone followed the target with 20–240-ms ISI. In two masked conditions, there was within-trial irrelevant variability in masker level, with negative or positive polarity (i.e., 75±5 or 10 dB SPL) but not in the third. The no-variability condition yielded more backward masking in older than in young adults. Irrespective of polarity, masker-level variability elevated the FDTs of both age groups, but relative to those of the young, the elders’ elevations were larger and did not decrease with training; elders had difficulty learning to ignore irrelevant variability. In young adults, the decrease in FDTs with training tended to be steeper with negative than with positive level variability. Memory capacity and long-term memory constraints seem to limit the elders’ ability to ignore irrelevant information.