Ten participants (6 male, 4 female) with intellectual disabilities were enrolled. presents information about participant gender, diagnostic/etiological information, intelligence quotient, and receptive vocabulary levels. Intelligence quotient scores were derived either from the Leiter International Performance Scale–Revised (Roid & Miller, 1997
) or the Test of Nonverbal Intelligence (Brown, Sherbenou, & Johnson, 1997
). The scores ranged from low/mild to severe levels of intellectual disability. Three individuals were not testable with these instruments.
Receptive vocabulary was evaluated with the Peabody Picture Vocabulary Test–Revised (Dunn & Dunn, 1985
) or the Peabody Picture Vocabulary Test–Third Edition (Dunn & Dunn, 1997
). All participants scored in the lowest 1% on these assessments. Participants received a mean raw score of 36, with 5 participants receiving raw scores under 20. When converted into standard scores (taking age as well as raw score into consideration), 9 of the 10 participants’ performances were at floor level (standard score = 40). Thus, although there was a fairly broad range of overall intellectual functioning in the sample, virtually all participants exhibited severe disabilities in acquisition of vocabulary.
Diagnoses and etiological information were obtained through a review of participants’ medical records after informed consent was obtained. Standardized testing was conducted at the outset of the study, in all but one case no more than 2 months before formal data collection commenced. All participants attended schools for individuals with developmental and/or behavioral disorders, and all had prior experience with matching-to-sample procedures.
Stimuli were either familiar (baseline) stimuli or novel (target) stimuli. All stimuli were presented on a computer screen and were contained within a 2 × 2-in. square. Baseline stimuli depicted familiar objects from everyday life. The baseline set consisted of spoken words, color photographs scanned into the computer, and black and white symbols taken from the Mayer-Johnson Picture Communication Symbols (PCS; Mayer-Johnson, 1992
). Examples of these stimuli are presented in . All participants underwent preliminary assessment to ensure that they could match the photographs and the line drawings to one another and to the spoken word (thus, photograph-to-line-drawing matching, described below). Only stimuli on which participants demonstrated reliable selections served as baseline stimuli.
Figure 1 Baseline stimuli. Note. From Picture Communication Symbols, by R. Mayer-Johnson, 1992, Solana Beach, CA: Mayer-Johnson. Copyright 1981–2003 by Mayer-Johnson. Used with permission.
For target stimuli, three simple three-stimulus categories were created, shown in . Color photographs of unfamiliar/hard-to-name objects (Set B) were scanned into the computer and modified to have a white background. Lexigrams (Set C) were created by combining three graphical elements (e.g., a triangle, a horizontal line) from a small set of choices, through procedures described by Romski and her colleagues (1996)
. Spoken labels (Set A) were nonsense words that adhered to the phonology of English created by a speech–language pathologist. Auditory stimuli were prerecorded into the controlling software (described in the following section). Because three sets of relations between the stimuli in Sets A and B (see ) were taught, as well as three sets of relations between stimuli in Sets B and C, a total of six relations were targeted in this study (these six taught relations are indicated by plain arrows). also shows emergent relations that might be expected to occur as a result of training (these emergent relations are indicated by dashed arrows).
Three stimulus categories. Solid line arrows indicate relations directly taught and tested. Dashed arrows indicate emergent relations tested.
Participants were tested in a quiet room at school during regularly scheduled free time. During the sessions, the experimenter sat just behind the participant and interacted with the participant as little as possible. Participant responses were touches to a touch-sensitive computer screen mounted on a Macintosh computer monitor. Stimulus presentation and response recording were controlled by software designed for this research (Dube, 1991
). When a stimulus appeared as a sample, it was presented in the center of the screen. Comparison stimuli appeared in the upper and lower corners.
Two types of feedback were given. First, computer-generated auditory feedback was provided through an external speaker to indicate whether or not a given response was correct. The type of auditory feedback depended in part on the protocol and the participant needs. In general, feedback ranged from prerecorded spoken words such as “wow” to computer-generated sounds like tones or musical notes. Participants also received tangible reinforcers on an individualized schedule that would maintain accurate responding for each participant. presents the reinforcement schedule and type for each participant.
Three sessions of preliminary assessment were conducted. Examples of trials in these sessions are presented in the top panel of .
Trial structure in preliminary assessment and instruction sessions.
The first session tested the participants’ ability to match the PCS symbols and the color photographs depicting the same referent. Referents included toothbrush, horse, hamburger, tissues, sunglasses, banana, sweater, guitar, hat, brownie, comb, bus, crayon, peach, and the familiar McDonald’s symbol. Fifteen trials presented photographs of familiar objects as the sample and PCS symbols as comparisons. Fifteen other trials presented a PCS symbol as the sample and photographs as comparisons.
The second session tested the ability to match the PCS symbols and the photographs to their spoken labels. This session consisted of 28 auditory-visual matching trials. Fourteen trials presented photographs as comparisons, and 14 trials presented PCS symbols as comparisons. One of the stimuli used in the first session (a toothbrush) was eliminated in this session.
The third session presented just six stimuli—those chosen to serve as baseline stimuli in subsequent testing. Most participants performed well with six of the stimuli used in the first two assessments: sweater, comb, hat, peach, hamburger, and tissues. The third session consisted of 27 auditory-visual matching trials with the photographs and PCS symbols randomly alternating as comparison sets. All but one participant performed without error during this session. Participant YCD, however, showed less reliable selections (81% accuracy). Consequently, she was tested on a different subset, including horse, bus, and guitar. Her performance on this assessment was satisfactory (98% accuracy), and she was tested with this baseline for the remainder of her participation.
Instruction Using the Exclusion/Adapted Fast-Mapping Procedure
Instruction was conducted in two components. The order of instruction is presented in the second and third panels of , as are examples of important trials. In the first component (second panel), the targeted novel auditory-visual (photograph-to-word) relations were taught. After acquisition of these new auditory-visual relations, participants entered the second phase in which visual-visual (symbol-to-photograph) relations were taught (third panel).
Teaching auditory-visual relations
The successive introduction procedure described by Wilkinson et al. (1998)
and Wilkinson and McIlvane (2001)
was modified for the purpose of teaching three new dictated auditory-visual stimulus relations. illustrates the three critical trial types used. In the top panel is an example of a disambiguation
trial, in which the first novel word is introduced (see Wilkinson, 2005
, for a discussion of the use of this term). As in typical fast-mapping/exclusion procedures, exposure to the first novel word and referent made use of the contrast of the single novel item against well-established baseline items. The middle panel of illustrates modified disambiguation
trials, in which the second novel word-referent relation is introduced. For this second word/referent pair, the contrast items in the array included one baseline item and the just-learned (just-labeled) item. To perform correctly on trials with the second novel word/referent, participants had to attend to the differences in the two novel stimuli. Finally, the bottom panel of illustrates the tests for learning/retention (i.e., learning outcome
tests; McIlvane, Kledaras, Lowry, & Stoddard, 1992
). In these learning outcome tests, both novel items are presented together and the participant is asked to select between them on the basis of each novel word (cf. Dixon, 1977
; McIlvane & Stoddard, 1981
Illustration of the successive introduction procedure.
In the current adaptation of the original methods, five training phases were scheduled. In all sessions, disambiguation and modified disambiguation (exclusion teaching) trials were interspersed within baseline trials, the number of which was adjusted to reflect the teaching needs. presents the total number of each trial type in each session. The first phase introduced the first target dictated word–visual stimulus pair. Six disambiguation trials for this pair (the stimuli under the “roke” class) were interspersed within 15 baseline trials (see for trial structures). The second phase reviewed the roke stimulus pair on three trials during the first half of the session and introduced the second target word–photograph pair (the stimuli under the “chiz” class) in the second half of the session. In this second block, three review trials for the roke class were interspersed within baseline trials and modified disambiguation teaching trials for the chiz stimulus pair (see for trial structures).
Example of Trial Structure for Sessions
The third phase began with a review of the instruction and testing to determine how well participants were learning. The beginning of this session was structured identically to the second session, just described. Interspersed within 18 baseline trials were six exclusion teaching trials for the roke class and three for the chiz class. At the end of the session, however, was an additional block in which 6 trials presented the roke class stimulus and the chiz class stimulus together, and the participant was required to make selections between them based on the sample stimulus (learning outcome trials).
The fourth phase evaluated how well participants retained the Pair 1 versus Pair 2 relations when no review was presented. Only learning outcome trials were presented (interspersed within baseline trials), with no exclusion teaching review. If participants selected reliably between the roke and the chiz class stimuli, it indicated that they had learned the specific relations between each targeted stimulus pair. Up to this point, the procedures were direct replications of earlier successive introduction methods (Wilkinson & Green, 1998
; Wilkinson, 2005
Upon reliable selection in the fourth phase, participants continued to the fifth phase. This phase was conducted to teach the third new pair, from the “teng” class of stimuli. Because the roke and chiz class stimulus relations had been learned, they now could serve as contrasts in the exclusion teaching. Thus, the exclusion teaching trials for the teng class stimuli were structured identically to learning outcome trials; the teng stimulus was contrasted against the roke and chiz stimuli (see ). There were 36 trials in this phase. Interspersed among 18 baseline trials were 6 roke, 6 chiz, and 6 teng outcome trials. Participants were given three different variations of sessions during the fifth phase, in order to ensure that all three targeted auditory-visual stimulus relations were established prior to testing for emergent equivalence relations.
Teaching visual-visual relations
This teaching followed the same format as the teaching of the auditory-visual relations. The teaching goal was to establish relations between lexigram comparisons with photograph samples via exclusion of Mayer-Johnson symbols. In all phases, if one or two errors were made on exclusion or outcome trials, participants repeated the prior session to ensure they had learned the novel pair. After teaching was completed for both the auditory-visual and visual-visual relations, two “mixed” sessions were scheduled consisting of all of the taught relations. These sessions were given to familiarize participants with the baseline that was to be used during subsequent tests for defining properties of equivalence relations.
Testing for category formation
After the exclusion/adapted fast-mapping instruction, the formation of simple categories was evaluated using two defining properties of equivalence relations. illustrates how taught relations and potentially emergent relations were evaluated using the stimulus class roke as an example. Symmetry probes consisted of trials in which the sample and comparison positions were reversed from training; participants were required to select among photographs when presented with a lexigram sample. Transitivity probes consisted of trials in which the participant was required to select among lexigrams upon hearing dictated sample stimuli. All symmetry and transitivity probe trials were interspersed into a baseline of previously known and directly taught relations. Two symmetry test sessions and two transitivity test sessions were conducted. In each session, there were 24 baseline trials and 6 probe trials (2 per stimulus).
Trial structure for equivalence testing.
Tests were not conducted for the combined symmetry and transitivity test (cf. Sidman & Tailby, 1982
). Doing so would have required a different design, for example, teaching relations A-B and A-C and testing for B-C and C-B or teaching relations A-B and C-B and testing for A-C and C-A. The former procedure would not have allowed an examination of both auditory-visual and visual-visual exclusion in the same participants and their staged use within an integrated teaching path—the primary purpose of the study. The latter procedure was not feasible because the auditory A stimuli could not be presented simultaneously as comparison stimuli while retaining their intelligibility. Thus, we can report here only behavioral patterns consistent with acquisition of equivalence relations rather than the full complement of documenting tests. This limitation, however, does not seriously compromise our main intent—to demonstrate successively emergent auditory-visual and visual-visual relations via exclusion learning in persons with intellectual and related language disabilities. Moreover, we think it likely that seemingly alternative associative and/or Pavlovian process accounts of data like ours may be explained ultimately in terms of stimulus equivalence and associated transfer and/or transformation of functions (cf. Sidman 1994