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Individuals with little or no functional speech as a result of autism spectrum disorders frequently rely on aided and unaided augmentative and alternative communication (AAC) symbols and signs to augment or replace natural speech. This has led investigators to identify the variables that are responsible for the acquisition and communicative use of graphic symbols and manual signs. The overall aim of this article is to evaluate the role of symbol, referent, and instructional variables on the acquisition of AAC symbols by individuals with autism and severe speech and language impairments.
Although augmentative and alternative communication (AAC) symbols have been used for the past two decades to improve the communicative abilities of individuals with severe speech and language impairments, to date only a few studies have focused on manipulating variables that possibly influence the acquisition and retention of AAC symbols by these individuals (Konstantareas, Oxman, & Webster, 1978; Koul & Lloyd, 1998; Kozleski, 1991; Luftig, 1983; Mirenda & Locke, 1989). These variables can be classified as symbol, referent, learner, instructional, partner, interactional, and community (Schlosser, Lloyd, & McNaughton, 1996). The primary focus of the present article is to provide a critical review of the role of symbol, referent, and instructional variables on the acquisition of aided and unaided AAC symbols by individuals whose primary diagnosis falls under the umbrella of autism spectrum disorders.
Symbol variables include iconicity (Bellugi & Klima, 1976; Brown, 1978; Fristoe & Lloyd, 1979; Lloyd & Fuller, 1990; Lloyd, Loeding, & Doherty, 1985) and complexity (Doherty, 1985; Fuller, 1977).
One of the core deficits in individuals with autism, autism spectrum, and pervasive developmental disorders is impairment in communication (Beukelman & Mirenda, 1998). Expressive speech function in individuals with autism ranges from total lack of speech to fluent speech (Wetherby, Schuler, & Prizant, 1997). Approximately 50% of individuals with autism are unable to develop speech that is sufficient to meet their daily communication needs (Wing & Atwood, 1987). Those who develop speech frequently have impairments in pragmatic aspects of speech (Baron-Cohen, 1988); they are unable to initiate or sustain communication. A typical characteristic of autistic language is immediate or delayed echolalia and impairment in language comprehension. Further, about 50% of all individuals with autism demonstrate subaverage intellectual functioning (Freeman, 1993). To remediate communicative deficits in individuals with autism, clinicians and researchers have used AAC symbols (in particular, manual signs) to augment or replace natural speech. However, an effective AAC intervention needs to go beyond simple modality exchange (i.e., replacement of natural language with manual signs or graphic symbols). It needs to take into account the underlying communicative and social-interactive deficits in individuals with autism. The effective use of AAC symbols will depend upon the ability of researchers to discover the variables that effect acquisition, retention, and communicative use of those symbols by individuals with autism.
Symbol Variables - The Difference Between a Transparent and an Opaque Symbol in Iconicity.
Several studies have attempted to establish the relationship between iconicity and learnability of graphic symbols by individuals with developmental disabilities and typical individuals (Ecklund & Reichle, 1987; Fuller, 1997; Goossens', 1983; Hurlbut, Iwata, & Green, 1982; Mirenda & Locke, 1989; Mizuko, 1987; Nail-Chiwetalu, 1991) and have supported the conclusion that iconicity facilitates the learning of graphic symbols. Specifically, Kozleski (1991) observed the effects of iconicity on graphic symbol learning in four individuals with autism. Her results indicated that all participants required fewer trials to criterion in symbol sets that are associated with a higher degree of iconicity.
Additionally, Mirenda and Locke (1989) compared the transparency of objects, photos, line drawings, Blissymbols, and written words using a match-to-sample task in individuals with autism, mental retardation, and multiple disabilities (i.e., mental retardation with cerebral palsy and/or autism). They observed the following hierarchy of symbol transparency from easiest to most difficult: objects, color photographs, black-and-white photographs, miniature objects, line drawings, Blissymbols (Bliss, 1965), and written words. Further, post hoc observations indicated that the performance of individuals with mild to moderate retardation and autism was superior to that of individuals with severe mental retardation.
Transparent and translucent graphic symbols or sets such as photographs, line drawings, Rebus (Clark, Davies, & Woodcock, 1974), Picture Communication Symbols (PCS; Johnson, 1994), and Picture Exchange Communication System (PECS; Frost & Bondy, 1994) have been used to teach specific communicative functions to individuals with autism with varying degrees of success (Kozleski, 1991; Reichle & Brown, 1986; Reichle, Barrett, Tetlie, & McQuarter, 1987; Rotholz, Berkowitz, & Burberry, 1989). Although these studies have not empirically demonstrated the effects of iconicity on graphic symbol learning, it can be hypothesized that iconicity had some role to play in the successful acquisition and use of symbols by individuals with autism in these studies.
In contrast to the facilitative effects of iconicity on graphic symbol learning, evidence for effects of iconicity on manual sign learning are equivocal. The natural sign languages and manual sign systems that parallel natural languages such as Signed English (Bornstein, 1990) are probably no more or less iconic than spoken languages (Bryen & Joyce, 1986). However, manual signs are taught to individuals with autism not as a part of a system, but rather as isolated signs in conjunction with speech and/or graphic symbols (Beukelman & Mirenda, 1998). Some manual signs produced in isolation may be iconic to individuals with autism as well as typical individuals. Konstantareas, Oxman, and Webster (1978) found that iconicity has a facilitative effect on receptive verb and adjective sign acquisition by individuals with autism. These results were supported by Doherty (1985) and Luftig (1983), who observed that individuals with moderate to severe mental retardation readily learned signs that were transparent or translucent. In contrast, studies by Kohl (1981) and Thrasher and Bray (1984) failed to demonstrate any facilitative effect of iconicity on sign acquisition in individuals with moderate to severe mental retardation. Further, not all of the signs that are included in the initial lexicon lists pass the "iconicity test" (Mirenda & Erickson, 2000). For example, the American Sign Language signs "help, ..... stop," and "toilet" are less iconic than the signs "eat" and "drink." However, all these five signs are included in many of the initial lexicon lists taught to nonspeaking individuals (Karlan, 1990).
In summary, the evidence on iconicity with respect to manual signs is equivocal. However, with respect to graphic symbols, this research suggested that clinicians and educators may wish to follow a hierarchy of symbol teaching. Transparent symbols may be taught initially, followed by high-translucent and low-translucent symbols. Symbols that have no visual or conceptual relationship to their referents may be selected and taught later.
Another symbol variable that may influence the acquisition and use of graphic symbols is complexity (Fuller, 1997). Complexity has been defined as the number of physical strokes or semantic elements that contribute to a depiction of a given symbol (Fuller & Lloyd, 1987). However, there is very little research regarding the effects of complexity on graphic symbol learning in individuals with severe speech and language impairments (Koul & Lloyd, 1993, 1998; Nail-Chiwetalu, 1991). The available data on complexity are equivocal, and further research is needed to explore the effects of complexity on graphic symbol acquisition and use in individuals with autism and other developmental disabilities.
Motor complexity of manual signs is another variable that may influence the acquisition and communicative use of manual signs (Bryen & Joyce, 1986). Past research has indicated that sign production is significantly associated with motor functioning in individuals with autistic disorder (McEvoy, Rogers, & Pennington, 1993; Seal & Bonvillian, 1997; Wing & Atwood, 1987). Thus, motor deficits (e.g., apraxia) observed in individuals with autism may account for some of their difficulties in acquiring manual signs. Clinicians need to conduct or obtain motor assessment before selecting manual signs to augment communicative abilities of individuals with autism.
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