Effects of aspirin on human psychophysical tuning curves in forward and simultaneous masking

Psychophysical tuning curves (PTCs) at 4 kHz were measured in forward and simultaneous masking under two experimental conditions: 1 h after listeners had ingested three 320 mg capsules of aspirin every 6 h for 3 days (3.84 g/day), and after an identical schedule of placebo ingestion. Aspirin and placebo allocation was double-blind. In addition to raising thresholds at several audiometric frequencies, aspirin elevated the tips and reduced the slopes of the PTCs, indicating a reduction in frequency selectivity. The aspirin-induced reduction in PTC slopes did not differ significantly between forward and simultaneous masking, nor did the overall reduction differ significantly between the low- and high-frequency side. However, a separate analysis of the data obtained in simultaneous masking indicated that the broadening in tuning caused by aspirin was greatest on the high-frequency side of the PTC.