A Bekesy descending-only procedure: effects of attenuation rate and step size, and starting level

Bekesy fixed-frequency thresholds for pulsed and continuous tones at 1 kc/s yielded by a descending-only technique were compared for suprathreshold starting levels of 38, 58, 78, and 98 db SPL, and attenuation rates of 1, 2, 4, and 8 db/sec with associated attenuation steps of 0.25, 0.5, 1, and 2 db, respectively, with 3 normal-hearing adults. For pulsed tones of 250 msec (duty cycle 50%), thresholds were not significantly affected by attenuation rate/step size or by starting level. However, for continuous tones, increasing attenuation rate/step size yielded better thresholds for a given starting level. Decreasing starting level yielded better thresholds for a given attenuation rate/step size. Thus, deteriorated thresholds were yielded by the slower attenuations/step sizes and by the higher starting levels. These data may be explained as a manifestation of normal adaptation. The similar relative effects found here of attenuation rate/step size and of starting level, as compared to the data of an earlier study (Harbert and Young, 1968) which used the traditional up-down Bekesy method of threshold tracing lend support to the possible future clinical use of a descending-only technique.