Shifts in auditory thresholds produced by ipsilateral and contralateral maskers at low-intensity levels.

Abstract

The present investigations were conducted to determine and describe some of the acoustic parameters of central masking. Shifts in threshold were observed during the following monotic and dichotic conditions: (1) pulsed pulsed, in which both test signal and masker were pulsed simultaneously; (2) pulsed continuous, in which the test tone was pulsed but the masker was continuous; and (3) continuous-continuous, in which both test tone and masker were steady. Test signals of 250, 1000, and 4000 cps were used. It was found that the degree of threshold shift resulting from central masking factors was dependent on the temporal presentation of the test signal and masker (whether pulsed or steady). Threshold shifts due to central masking increased with frequency and were related to the spectrum level of the masker. The largest shifts in threshold were found for a 4000 cps test signal when the masker was a pure tone close in frequency. In these instances, lateralization of the test signal toward the midline was observed as the threshold shift increased and, at times, subjects were unable to distinguish between the test tone and pure-tone masker. Although the results can be explained on the basis of central masking factors, the manner in which the subjects traced their thresholds during the condition where both test signal and masker tone were continuous suggested that all observed shifts in threshold may not be clue to masking alone.