Auditory Fatigue Following Tone - Burst Trains At 2.2 Kc.

Abstract

Three hundred and two sailors were exposed by phones in groups of 11-20 men to 2.2 kilocycle/sec (kc) pulses (5 msec rise-fall time) of 37-250 msec pulse duration at 105-120 dB sound pressure level, duty cycle (on-time/total time) from 0.1 - 100%, and for 5-120 min/session. Permutations were selected to throw direct light on the four stimulus variables and on their interactions as well. Pulse-tone audiometry by magnetic tape was accomplished 7 times in 6 min at 2.5, 3, 4, 6, and 8 kc, before and immediately after exposure. The concept of a criterion temporary threshold shift (TTS) was developed in which 1 Kryt represents the area of TTS plotted on an audiometric chart from 2-8 kc. Any TTS can then be expressed in terms of the Kryt. Thus, for each of our subjects, for each of seven audiograms taken approximately once per minute, we have seven successive Kryt values. When plotted over recovery time, these values can be compared to the area enclosed on the graph representing 1 Kryt lasting for 2 min; this summation datum is termed the Nox. Mean Nox values for each experimental condition were determined. Within our data (1) each 5 dB SPL adds 0.5 Nox; (2) pulse duration as such is negligible; (3) each log session duration adds 0.65 Nox; and (4) the Nox is a linear function of duty cycle. Subjective and to some extent objective observations lead us to set a damage risk criterion of 2 Nox for pulsed stimulation at 2.2 kc. Graphs are provided by which any combination of stimulus parameters which would yield 2(+) Nox may be predicted. (Author)