Signal Detection as a Function of Contralateral Sinusoid-to-Noise Ratio

Detection of a masked signal (500 Hz) at one ear was measured while a sinusoid of the same frequency and a noise were presented to the contralateral ear. Both the signal and the contralateral sinusoids were pulsed, and they were either in phase or inverted. The noise at the signal ear was presented continuously at a spectrum level of 40 dB. In Expt. 1, the same continuous noise was presented to the contralateral ear at a spectrum level of 40 dB and in phase with the noise in the signal ear. The contralateral sinusoid-to-noise ratio was varied by changing the level of the sinusoid. In Expt. 2, the contralateral sinusoid-to-noise ratio was held constant while the levels of both the contralateral sinusoid and the contralateral noise were varied. When the contralateral sinusoid and noise are intense, a 50-dB increase in the contralateral sinusoid-to-noise ratio causes a 25- to 35-dB change in the signal-to-noise ratio required for detection. The results show that contralateral stimulation can either enhance or degrade detection of a monaural signal. The results are compared to data from investigations of masking-level difference, central masking, and monarual detection with contralateral cue.