Effect of Contralateral Noise on Speech Detection and Speech Reception Thresholds

Abstract

Speech detection thresholds (SDT) and speech reception thresholds (SRT) for spondee words were obtained on 20 normal hearing listeners while white or speech noise masking was presented to the contralateral ear. Each masker was presented continuously or pulsed simultaneously with the onset of each spondee word. Several masker sensation levels (SL) of 30, 40, 50, 60, 70, and 80 dB were employed, and the amount of masking (threshold shift) was determined for each condition. Small but consistent SDT and SRT shifts were apparent at low masker SLs (30 dB). The shifts increased approximately 1 dB for each 10-dB increase in masker SL between 30 and 60 dB. For 60-80 dB masker SLs, the shifts were about 3.5 dB for each 10-dB increase in the masker. The greater threshold shifts at the higher masker SLs may have resulted from transcranial conduction and/or activation of the acoustic reflex. The pulsed masker condition had more of an effected on the SDT than on the SRT; SDT shifts were consistently larger for each masker SL when the masker was pulsed compared to continuous presentation. Overall, the average threshold shifts ranged from about 1 to 11 dB as the masker SL was increased from 30 to 80 dB. These data suggest that central masking is operating for masker SLs below 60 dB; for higher masker SLs, the increased threshold shifts probably result from a combination of central masking, transcranial conduction, and acoustic stapedius reflex action. The clinical implications of central masking are also discussed

Key Words:

• Auditory masking
• Central masking
• Speech audiometry
• Speech detection
• Speech reception