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This investigation compared the transparency of 11 different types of symbols representing objects with 40 nonspeaking subjects who experienced various degrees of intellectual disability. The subjects included a number of individuals with physical impairments or autism in addition to mild, moderate, or severe mental retardation. The symbol sets included: nonidentical objects, miniature objects, identical colored photographs, nonidentical colored photographs, black-and-white photographs, Picture Communication Symbols (PCS), Picsyms, Rebus, Self-Talk, Blissymbols, and written words. Statistical analyses indicated that real objects were more readily recognized than were any of the symbol sets and that Blissymbols and written words were more difficult than were any of the other sets. In addition, the results suggest the existence of a hierarchy of difficulty at the object (noun) level for the symbol sets assessed. The results are discussed in terms of their implications for selecting an initial symbol set for nonspeaking individuals. In addition, some suggestions for using the assessment protocols in clinical practice are presented, along with future research implications.
Mirenda et al. (Mon,) studied this question.