Precedence: Its Role in Recognizing Speech in Noise

University Of Massachusetts Amherst, Amherst MA

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Abstract

In a typical room, our ears receive not only the original source of sound, but numerous reflections off of surfaces in the room. Fortunately, through the precedence effect we are able to fuse a sound source and its reflections into a single image and locate that image near the original source of sound. The overall goal of the proposed research is to achieve a better understanding of the precedence effect and its importance in understanding speech in the presence of interfering noise or other speech. The primary assumption is that there are two types of masking of speech: (1) traditional energetic masking, and (2) informational masking, in which it is difficult for the listener to separate out the pattern of the target speech within a fluctuating pattern of interference. In non-reflective conditions, the horizontal separation of target and masking sources releases energetic masking, mostly because the head shadows the masker at one ear and because the brain compares the differences in inputs to the two ears. Unfortunately, this type of masking release is dramatically reduced by the reflections in a real room. The hypothesis tested in this research is that because the precedence effect preserves the perceived spatial distinctions between target and masker even in reverberation, release from informational masking is not reduced by room reflections. The studies will investigate the nature of informational masking and how the precedence effect and binaural hearing in general contribute to overcoming this type of masking. The study of binaural hearing is particularly important because many people with bilateral hearing impairment become effectively monaural listeners when they only wear one hearing aid. The results of these studies may well show how important it is to be able preserve binaural hearing and sound localization when prescribing auditory prostheses. The studies will also investigate the phenomena and mechanisms of the precedence effect on a more basic level, adding to our overall understanding of sound perception in typical reverberant spaces.