Issues Unresolved: New Perspectives on Language and Deaf Education

8. The Perception of Speech by Children with Hearing Loss

The Perception of Speech by Children with Hearing Loss Arthur Boothroyd 8 SPEECH CONSISTS of language patterns that are encoded as sound patterns by movements of the breathing and eating mechanisms. This is a broad definition that includes speech movements, speech sounds, and the language patterns they represent. Speech perception is defined here as the process by which a perceiver tries to identify the talker's underlying language patterns on the basis of speech sounds and movements. The ultimate goal of speech perception is to determine the meaning and intent behind the spoken message. In this chapter, however, speech perception is defined in terms of the more modest goal of identifying the talker's language patterns. SPEECH PERCEPTION There are four major components of speech perception-sensory evidence, contextual evidence, knowledge, and processing skill (Boothroyd 1993) (see Figure 8.1). 1. Sensory evidence is present in the patterns of neural activity generated by the perceiver's sense organs in response to patterns of speech sound and movement. The ears generate auditory evidence from speech sounds. The eyes generate visual evidence from speech movements. Under normal circumstances , auditory evidence dominates, but vision becomes increasingly important with increasing hearing loss. 2. Contextualevidence is any information within the context that can affect the interpretation of sensory evidence. It is of three basic kinds-linguistic, social, and physical. • Examples of language contexts are the phonemes in which contrasts occur, the words in which phonemes occur, and the sentences in which words occur. Numerous colleagues and associates have contributed to the work that provides the basis for this chapter. They include Tova Most, Teresa Hnath-Chisolm, Laurie Hanin, Liat Kishon-Rabin, Nancy Plant, Orna Eran, Eddy Yeung, Charlie Chen, Gary Chant, Vardit Lichtenstein, Doron Milstein, Robin Waldstein, Nina Guerrero, Susan Waltzman, Jean Moog, Ann Geers, Jill Firzst, Laura Mckirdy and Lisa Tonakawa. Their help is gratefully acknowledged. Preparation of this paper was supported, in part, by NIH grant #2P50DC00178. and NIDRR grant #H133E80019. 103 104 ARTHUR BOOTHROYD • Social context includes the people involved in the communicative exchange and the nature and purpose of that exchange. • Physical context involves the material surroundings. In addition to the specific context of a given interaction, there is also the general context of the language system within which it takes place, and of the social and physical worlds the talker and perceiver share (and to which the spoken messages refer). Contextual evidence is very important. In conversation , for example, topical and sentence context can convey five to ten times as much information about word identity as is available from sensory evidence in the words themselves (Boothroyd 1991). 3. Perceiver knowledge is information internal to the perceiver that affects the interpretation of sensory and contextual evidence. Like the context, it has linguistic, social, and physical components. Knowledge of speech, phonology and vocabulary provides the possible linguistic interpretations of sensory evidence. Knowledge of these and other aspects of language, knowledge of people, and knowledge of the physical world provide access to contextual evidence. Successful speech perception can only take place within theconstraints of the perceiver's knowledge. 4. Perceiver processing skill consists of attributes of the perceiver that affect the ease, accurac~ and speed of speech perception. The skillful perceiver makes inferential decisions rapidly using an appropriate balance of sensory evidence, contextual evidence, and prior knowledge, while maintaining a low probability of error, and often while completing other tasks such as determining meaning and formulating a response. The processing skills of evidence weighting, decision making, speed, and multitasking are easily taken for granted by those of us who have acquired them spontaneously by virtue of normal hearing and a lifetime of experience. EFFECTS OF CHILDHOOD HEARING Loss Sensorineural hearing loss in children has a direct effect on the available sensory evidence and indirect effects on contextual evidence, knowledge, and skill. Sensory Evidence Deficits of sensory evidence occur with sensorineural hearing loss for four reasons (see Figure 8.2): threshold elevation, reduced dynamic range, reduced discrimination, and increased noise susceptibility. Threshold Elevation Persons with normal hearing can (by definition) hear sounds whose intensity is greater than 0 dBHL.l A person with a hearing loss of x dB call, by Linguistic, social, and world context Figure 8.1. Schematic representation of the speech perception process. 10 Sound level in 5 dBHl Normal hearing Moderate loss Severe loss Profound loss Figure 8.2. Audibility of conversational speech in noise, with and without...