Speech intelligibility in various spatial configurations of background noise

This study is concerned with the influence of spatial
separation of disturbing sources of noise on the speech intelligibility. Spatial
separation of speech and disturbing sources without changing their acoustic
power may contribute to the significant improvement in the speech
intelligibility. This problem has been recently analysed in many papers [1-5].
These works have confirmed an important role of the spatial configuration of
sources. However, there have been no work investigating this problem for
nonsense words (logatoms) that may provide more rigorous tests of this
phenomenon. Moreover, this problem has not been analysed for Polish speech. It
is important to emphasize that the acoustic and phonetic properties of Polish
speech are somewhat different from those of English one. Therefore, the attempt
to investigate the influence of the spatial separation of sound sources was made
in this study. In the situation with more than one spatially separated
disturbances, there may occur a so-called spatial suppression phenomenon, that
is ``mutual suppression'' of disturbing sounds in the auditory system that
brings about an increase in the speech intelligibility. This phenomenon is also
called the spatial unmasking of speech [5, 6]. The research consist in
determination of the speech intelligibility in the presence of one or two
statistically independent speech-shaped noise sources varying in configuration.
Only two pairs of the spatial configurations were investigated. Character of the
dependences obtained in the study implies that the spatial suppression occurs in
certain configurations of sources only. This effect brings about an increase in
the speech intelligibility and can be explained on the basis of the binaural
masking level difference (BMLD). It seems then that the BMLD may be a more
general phenomenon and includes not only difference in the detection threshold
of a pure tone masked by noise but also the improvement in the speech
intelligibility, while speech is presented at the background of disturbing
signals. Key words: speech intelligibility, speech perception, spatial
separation, spatial suppression.