New computerized Finnish speech in noise test and binaural hearing.

Aided and unaided binaural versus monaural recognition of speech has been studied with more or less laborious methods when speech and noise sources are spatially separated. The efficacy of the new Finnish speech in noise test to show binaural advantage was evaluated in free field conditions. Thirteen subjects with normal hearing were tested measuring speech recognition thresholds in noise (SRTN) in anechoic chambre with different situations of spatial separation of speech and noise sources monaurally and binaurally. The noise source was fixed above the head (treating both ears similarly) and equidistant speech was delivered at different azimuths. SRTNs with mixed speech and noise without spatial separation served as normalizing reference. Differencies in SRTNs consistently followed the changing head and pinna shadow effects on the speech-to-noise ratio with a smaller binaural advantage. This new test seems to give quite economically the same results as those of previous more sophisticated investigations on speech recognition in free field situations.