Threshold Shifts for Continuous or Pulsed Tones Produced by Contralateral Steady or Pulsed Noise

Abstract

Threshold shifts for either constant or pulsed pure tones were observed while a steady or pulsed narrow band of noise was delivered to the contralateral ear via an insert receiver. By means of an internal control circuit, the electronic switch channels for the pure tone and noise could pass stimuli continuously or pulsed at a switching rate of 1000 msec, with a rise-decay time of 50 msec. Thus, 12 subjects were tested during five experimental conditions: (1) continuous tone and continuous masker; (2) continuous tone and pulsed masker; (3), (4) pulsed-pulsed, simultaneously and alternating; and (5) pulsed tone and continuous masker. The masking was always a narrow band of noise centered around 4000 cps and presented at levels of 50, 70, and 90 dB SPL. Thresholds at 4000, 1000, or 250 cps were recorded via a graphic attenuator. The results show that greater contralateral masking occurs when the masker and tone are pulsed simultaneously than in the condition where the noise is steady and the tone pulsed. [Research supported by grant NB 04019 from the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]