Description:
To determine whether the form of psychometric functions for 2I, 2AFC level discrimination changes with hearing impairment, measurements were obtained in listeners with cochlear impairments and normal listeners with impairments simulated by masking. Ten increment levels were presented in random order within blocks of 100 trials. Stimuli were tones at 0.25, 1, 8, or 14 kHz or white noises chosen to encompass a wide range of conditions and difference limens. Durations were either 10 or 500 ms and levels ranged from 50 to 90 dB SPL. For each condition, at least 20 blocks were presented in mixed order. Results show that the sensitivity d' is nearly proportional to ΔL(= 20 log [(p + Δp)/p], where p is pressure) over the entire range of difference limens for both simulated and real impairments as well as for normal listeners tested in the quiet. These results indicate that if the transformation from stimulus intensity to decision variable is affected by heating impairment or masking, the change affects both the mean and the standard deviation in the same manner. They also lend support to the notion that ΔL—plotted on a logarithmic scale—is an appropriate representation of level-discrimination performance. [Work supported by NIH.]