Academic journal article The Psychological Record

Tactual Equivalence Class Formation and Tactual-to-Visual Cross-Modal Transfer

Academic journal article The Psychological Record

Tactual Equivalence Class Formation and Tactual-to-Visual Cross-Modal Transfer

Article excerpt

Sensory Modalities and Equivalence Classes

An equivalence class consists of at least three stimuli (N), none of which need to resemble each other, but all of which become interchangeable following the establishment of (N-l) stimulus-stimulus relations (Fields & Verhave, 1987; Sidman, 1994; Sidman & Tailby, 1982). Although equivalence classes have been established using a variety of stimuli within and between modalities, no single study has determined the stimulus modalities that must be included to form classes.

The initial demonstrations of equivalence class formation used both visual and auditory stimuli: the picture and written name of an object, as well as its name as heard (Sidman, 1971; Sidman & Cresson, 1973). Citing Geschwind (1965), Sidman and Cresson (1973) suggested that both visual and auditory stimuli might be required to establish equivalence classes. This position was not supported by subsequent demonstrations of equivalence class formation consisting of visual stimuli only such as arbitrary or abstract line drawings (Bush, Sidman, & De Rose, 1989; Hayes, Kohlenberg, & Hayes, 1991; Lazar, 1977; Saunders, Saunders, Kirby, & Spradlin, 1988; Sigurdardottir, Green, & Saunders, 1990; Spencer & Chase, 1996; Spradlin, Cotter, & Baxley, 1973; Wetherby, Karlan, & Spradlin, 1983; Wulfert, Greenway, & Dougher, 1994; Wulfert & Hayes, 1988) and nonsense syllables (Fields, Adams, Verhave, & Newman, 1990; Fields, Newman, Adams, & Verhave, 1992; Fields, Reeve, Adams, & Verhave, 1991). These results also showed that equivalence classes can be formed from stimuli in only one sensory modality. Finally, these data showed that auditory stimuli are not required for equivalence class formation. Recently, Dube, Green, and Serna (1993) demonstrated the formation of equivalence classes consisting of auditory stimuli only. In addition to extending the range of equivalence classes that can be formed using stimuli in only one modality, this experiment also demonstrated that visual stimuli were not required for equivalence class formation.

A few studies have explored the formation of equivalence classes that contained auditory or visual stimuli plus additional stimuli from other sensory modalities. Thus, equivalence classes have been formed with one gustatory and two visual stimuli (Hayes, L. J., Tilley, & Hayes, 1988), one interoceptive (a drug reaction) and two visual stimuli (DeGrandpre, Bickel, & Higgins, 1992), one olfactory and two visual stimuli (Annett & Leslie, 1995), one haptic and two visual stimuli (Tierney, De Largy, & Bracken, 1995), or one auditory and two tactual stimuli (Bush, 1993). Even though these studies included stimuli sensed through two sensory modalities, each study included at least one auditory or visual stimulus per class. These data suggest that at least one visual or auditory stimulus might have to be present for the emergence of equivalence classes. They also suggest it might not be possible to form equivalence classes without the presence of at least one visual or auditory stimulus. One recent study, however, showed the emergence of equivalence classes comprised of tactual stimuli only (O'Leary & Bush, 1996). These data contradict the view that the inclusion of at least one visual or auditory stimulus is needed to establish an equivalence class. Indeed, they show that equivalence classes can be formed in the absence of visual and auditory stimuli.

O'Leary and Bush demonstrated the formation of tactual equivalence classes with a small number of subjects (3), sampled from one subpopulation (typically developing young children), and used only one procedure for training and testing (a complex to simple protocol (Adams, Fields, & Verhave, 1993). Thus, the generality of the effect may be limited. As such, the theoretical implications of the data for determining whether visual or auditory stimuli are necessary for the formation of equivalence classes may also be limited. …

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