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Emergent symbolic relations in speakers and nonspeakers
Research in Developmental Disabilities 21 (2000) 197–214
Emergent symbolic relations in speakers and nonspeakers夞 Nancy C. Brady*,1, Lee K. S. McLean2 University of Kansas Life Span Institute, Parsons, KS 67357, USA
Abstract Eight adults with developmental disabilities and four typically developing preschool children participated in an experiment studying emergent stimulus–stimulus relations after match-to-sample instruction. Participants were taught to match lexigrams (arbitrary graphic stimuli) to objects. Each object was functionally related to another object in the teaching set. For example, brush and comb were members of the teaching set. Most participants were able to select objects when the objects were named in pretests. Postteaching probes assessed emergent relations between spoken names and lexigrams. In addition, we included probes to detect emergent relations between related lexigrams. That is, would participants select the lexigram for comb when the experimenter displayed the lexigram for brush (without explicit teaching)? Two preschool children and five adults with developmental disabilities showed emergent relations between lexigrams and spoken words. However, only two preschool children showed the emergent lexigram to related lexigram relations. © 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction Individuals with developmental disabilities are frequently taught to communicate by selecting graphic stimuli (e.g. pictures or printed words) that represent objects or events (e.g. Calculator & Dollaghan, 1982; Glennen & Calculator, 1985; Hamilton & Snell, 1993). Typically, an anticipated outcome of such instruction is the selection of the graphic stimuli in a variety of functional 夞 This research was supported by Grant number 5 PO1 HD18955 from NICHD. * Corresponding author. Tel.: ⫹1-612-624-3322; fax: ⫹1-612-624-7586. 1 Nancy Brady is currently affiliated with the University of Minnesota, Twin Cities campus. 2 Lee McLean is currently affiliated with University of Connecticut, Storrs. 0891-4222/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 1 - 4 2 2 2 ( 0 0 ) 0 0 0 3 4 - 2
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communicative situations (McIlvane et al., 1993; Reichle & Sigafoos, 1991). The degree to which the graphic stimuli are selected across multiple contexts may reflect the degree to which an individual learner recognizes the stimuli as representations of specific objects or events. For example, if a symbol for “dog” is highly representative, we would expect the symbol to be used in the same contexts that a speaker says “dog,” including naming a live animal, naming a picture, answering a question about favorite animals, etc. One way to determine whether an individual learns to view a graphic as a representational symbol for an object or event is to evaluate the degree to which the individual substitutes the graphic for the object (Bates,1979). For example, an individual may indicate the item desired at a restaurant by pointing to the name of the food item. In this context, the printed word is substitutable for the object and the spoken word. The substitutability of symbols for objects has been addressed by recent work in the area of stimulus equivalence (Sidman, 1994). Stimuli that are members of the same equivalence class are related to each other by the properties of reflexivity, symmetry, and transitivity (Sidman & Tailby, 1982). Reflexivity denotes that a participant will match a stimulus to an identical stimulus. Symmetry denotes that a participant who has learned to match a given sample stimulus (e.g., symbol A) to a comparison stimulus (e.g., symbol B) will also match these stimuli when B is the sample and A is a comparison stimulus. The transitivity test determines whether two stimuli are substitutable in their relationship to a third stimulus. For example, if a participant selects an object in the presence of a specific spoken name and then learns to select a written symbol in the presence of the object, transitivity is assessed by asking if the participant will now select the printed symbol when the specified name is spoken. This transitive relation between the spoken name and the written symbol must emerge without instruction in order for the stimuli involved to be considered members of a stimulus equivalence class. The research in stimulus equivalence appears extremely relevant for analyzing acquisition of graphic symbols by individuals with developmental disabilities (Goldstein, 1985; Remington, 1994). For example, Sidman’s classic study in 1971 demonstrated that matching-to-sample tasks could be used to teach learners with developmental disabilities to read and comprehend printed words. These learners could already match spoken names to pictures and name the pictures. Sidman demonstrated that after learning to match dictated names to the printed words, the participants were able to name the printed words (read) and match printed words to pictures (comprehend). This demonstration of emergent relations in learners with developmental disabilities is important for a number of reasons. First, it shows that many individuals with developmental disabilities do not have to be explicitly taught every relationship. Teaching that results in emergent relations saves teaching time. Second, stimulus equivalence research has provided a method to determine whether an individual’s learning extends beyond the relations specifically taught. That is, there are predictable relationships that may emerge after match-to-sample instruction. Thus far, the majority of emergent relations examined in participants with
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developmental disabilities include relations such as those described in Sidman’s original experiment (Sidman, 1971)—relations between objects (or pictures of objects), auditory names and an arbitrary visual stimulus. The term “arbitrary” indicates that there is not a physical resemblance between the stimulus and its referent. The present study extends the analysis to emergent relations between familiar, related objects. The objects in the present study were all related to another object through functional use, or temporal contiguity (e.g., shoe–sock; comb– brush). The experiment was designed to determine whether participants would show emergent relationships between arbitrary symbols that represented pairs of related objects. For example, if an individual identified two real objects as going together (e.g., a shoe and a sock) and then learned to match graphic stimuli to each of these objects, would the individual then also match the graphics as going together? Goldstein (1985) and others have suggested that the stimulus equivalence paradigm can be used to analyze larger categories of stimuli representing conceptually related objects. Demonstrating complex emergent relations, such as those investigated in the present study, offers an important step in the development of behavioral models for symbolic communication by individuals with developmental disabilities. Learning to use an augmentative symbol system parallels the tasks investigated in this study in a number of ways. Many individuals learning an augmentative system comprehend some spoken words. In addition, teaching almost invariably introduces new symbols for familiar objects. Teachers may assume that the newly learned symbols will be equivalent to the auditory names and the objects themselves, but this may not always be the case. In addition, we considered whether participants’ verbal abilities were related to their demonstration of emergent relations including equivalence classes. Several researchers have recently discussed whether naming is a prerequisite skill for demonstrating stimulus equivalence (Horne & Lowe, 1996; Saunders et al., 1995; Stromer et al., 1996). Horne and Lowe (1996) contend that naming is essential for equivalence class formation because stimulus class formation requires verbal mediation. In support of their theory, Horne and Lowe point to research that has shown poor performance on stimulus equivalence tasks by individuals who can’t name. Devany et al. (1986) reported that young children who could speak and older children with developmental disabilities who could speak, showed emergent performances on stimulus equivalence tests. Children with developmental disabilities who could not speak did not show these emergent performances. Eikeseth and Smith (1992) studied equivalence class formation in four children with autism and limited expressive and receptive language skills. All four participants had acquired “some language” at the time of the experiment. Initially, Eikeseth and Smith found that none of the four participants demonstrated the emergence of equivalence classes. After participants were taught to say the same name for each member of a class, two participants’ performances demonstrated the emergence of an equivalence class. Thus, naming appears to at least facilitate stimulus class formation in some participants.
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1.1. Purpose One purpose of the present study was to investigate emergent relations between objects, spoken words, and graphics after match-to-sample instruction. In addition to the critical tests for demonstrating a stimulus equivalence class, we added a test to determine whether participants would also show emergent relations between graphics representing objects functionally related to each other. A second purpose was to determine whether performances on each of these tasks would differ for participants with different language skills. Toward this end, we performed more extensive measures of participants’ expressive and receptive language than typically reported in studies of emergent relations. We wanted to compare performance by participants who were able to speak to performances by participants who did not speak, use sign language, or a graphic selection communication board. Receptive vocabulary abilities were also measured in order to obtain a broader picture of participants’ language skills.
2. Methods 2.1. Participants Eight adults with severe developmental disabilities and four typically developing children participated. The adult participants lived in a large residential facility for individuals with developmental disabilities. The classification of severe mental retardation was made by staff psychologists using the criteria of the American Association on Mental Retardation (Grossman, 1983). Four of the adults communicated with spoken sentences. The remaining four adults did not communicate with spoken words or with an augmentative communication system. Further descriptions of the expressive communication abilities of these eight participants were based on an interactive communication assessment completed by the first author. This assessment consisted of 10 different tasks designed to evoke specific types of communication, including requests for objects (mands), and comments about atypical events (tacts). The following is an example of a task designed to evoke a request for an object: The experimenter and participant take turns filling cups with juice and drinking juice. The experimenter puts some more juice in her cup and then passes the (now empty) pitcher to the participant. Another pitcher that visibly contains juice is within sight, but out of reach for the participant. The following is an example of a task designed to evoke a comment about an atypical event: At some point during the assessment, a small plastic alligator attached to a clear fishline is dangled from the ceiling behind the experimenter’s head. The assessment lasted about 30 min. A complete description is presented in McLean et al.(1991).
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Table 1 Participant descriptions Participant
Age
Adults with developmental disabilities Speakers TC 33 FR 45 VB 26 WB 52 Gesture users RG 30 LT 31 BJ 31 BD 28 Typically developing children TJ 6 JE 4 BK 3 MA 3
Gender
Receptive Vocabulary Age1
Expressive Communication Level2
F M M M
3-7 2-8 2-8 4-11
MLU MLU MLU MLU
7.0 3.0 3.1 7.1
F F M M
4-2 4-2 2-8 2-8
distal distal distal distal
gesture gesture gesture gesture
M F M F
4-5 4-5 4-1 3-6
NT3 MLU 4.28 MLU 2.92 MLU 3.74
1
Age equivalent according to the Peabody Picture Vocabulary Test. Reported in years-months. MLU ⫽ Mean length of words per utterance. Expressive language level was determined by performance on the scripted communication protocol. 3 Not tested. 2
The four adult participants who could talk and three of the four typically developing children were engaged in additional conversation in order to collect a sample of their speech sufficient to analyze with the Systematic Analysis of Language Transcripts (Miller & Chapman, 1985). All speaking participants produced grammatically correct sentences, some of which included embedded clauses. These participants’ mean number of words per utterance are reported in Table 1. We did not complete a formal assessment of participant TJ’s expressive communication, but he also communicated with complex spoken sentences. None of the five typically developing children had any speech or language delays or disorders. The four adult participants who did not speak communicated with both contact and distal gestures. Contact gestures directly contact the referent object (e.g., giving an object to the adult). Distal gestures are gestures, such as a point, that are distanced from the referent by at least 6 inches. Other examples of distal gestures include reaches or open palm requests that are distanced more than 6 inches from the referent. For example, in the dangling alligator task described above, participants frequently pointed at the alligator while vocalizing to gain the experimenter’s attention. Thus, while these participants did not speak or use other symbolic communication means, they communicated with a variety of nonsymbolic gestures. In addition to expressive communication, receptive vocabulary was measured
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Fig. 1. Relations taught and tested in this experiment. Bold lines represent relations participants showed in pretests, or were taught during the experiment. Dotted lines represent relations tested in post-test probes.
with the Peabody Picture Vocabulary Test (PPVT-R). Table 1 describes each participant’s expressive communication and receptive vocabulary levels. 2.2. Setting and materials All assessments, pretests, teaching, and post-tests were conducted in a laboratory room at a university research center located on the grounds of a large residential facility where the adult participants lived. This room contained all stimulus items, two chairs, and a table. During the expressive communication assessment, some items were arranged on open shelving so that they were visible, yet beyond immediate reach. Communication assessments, pretests, post-tests, and some teaching sessions were videotaped through a one-way mirror from an adjacent observation room. 2.3. Procedures The relations tested in pretests and post-tests and taught are diagrammed in Fig. 1. All matching tasks were completed by the experimenter placing the stimuli on the table. The sample stimulus was then either displayed in the experimenter’s hand or spoken by the experimenter. The experimenter was instructed to look at the participant’s face while the participant was selecting a comparison stimulus or naming a stimulus. In addition, the first author periodically watched sessions through a one-way mirror in order to determine whether
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Table 2 Teaching sets used for each participant Participant
TC, FR, GR, LT, BJ, BD, TJ, JE, BK VB WB MA
Objects in teaching sets Obj 1
Obj 2
Obj 3
Obj 4
Obj 5
Obj 6
cup
brush
shoe
straw
comb
sock
car car car
pan bowl pan
chair chair table
tire wheel tire
spoon spoon spoon
table table chair
the experimenter was in any way cueing the participant’s responses. The experimenter was not aware of these observations. No experimenter cueing was observed. 2.4. Pretests All participants completed pretests 1– 4. In addition, participants with developmental disabilities completed an identity matching task (pretest 5) to ensure that the lexigrams were discriminable. All pretests except the naming pretest followed a match-to-sample format. The experimenter set out three comparison stimuli in a horizontal array in front of the participant and then held up a sample stimulus above the center comparison. The participant was then asked to select the comparison stimulus that went with the sample. The first comparison stimulus pointed to or touched by the participant was recorded by the experimenter. The experimenter did not provide feedback regarding correct or incorrect responses. Positive remarks about the participants’ involvement were provided intermittently during the pretests. Pretest 1 assessed participants’ abilities to match objects to associated objects. For example, participants were shown a brush and asked to select what “goes with” the brush from the following array: comb, sock, and straw. Real, full-sized objects were used for brush, comb, shoe, sock, cup, and straw. Toy objects were used for pan, spoon, car, tire/wheel, chair, and table. If a participant identified the same comparison object as going with the sample object on 4 out of 5 trials, the two objects were used in future match-to-sample teaching and testing. This procedure was used to identify three sets of two related objects for each participant. These six objects will henceforth be referred to as the teaching set. Each participant’s teaching set is identified in Table 2. Pretests 2 through 5 consisted of 30 trials each. Pretest 2 assessed selecting objects in the teaching set in response to their spoken names. Objects were presented in a three-choice array and the experimenter said “Find the (name of object).” The third pretest asked speaking participants to name these same objects. The experimenter held up each stimulus from the training set and asked “What’s this?” The fourth and fifth pretests were identity matching pretests. We assessed matching each object from the training set to an identical object, and
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Table 3 Sample and comparison stimuli used in pretests Pretest
Sample
Correct Response
Distracters
Object to associated object matching
Obj 1 Obj 2 Obj 3 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6
Obj 4 Obj 5 Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6
Obj Obj Obj Obj Obj Obj Obj Obj Obj
Spoken name to object matching
Object naming
Object to identical object matching
Lexigram to identical lexigram matching
name” name” name” name” name” name”
5 4 4 2 1 1 5 4 4
Obj Obj Obj Obj Obj Obj Obj Obj Obj
6 6 5 3 3 2 6 6 5
name” name” name” name” name” name” Obj 2 Obj 1 Obj 1 Obj 5 Obj 4 Obj 4 Lex 2 Lex 1 Lex 1 Lex 5 Lex 4 Lex 4
Obj 3 Obj 3 Obj 2 Obj 6 Obj 6 Obj 5 Lex 3 Lex 3 Lex 2 Lex 6 Lex 6 Lex 5
each lexigram used in object–lexigram matching (described below) to an identical lexigram. The instructions for Pretests 4 and 5 were “Find the same.” The array of stimuli presented as samples, correct comparisons, and distracter comparisons for each pretest are shown in Table 3. 2.5. Object–lexigram teaching We taught participants to select each lexigram in response to an object from the teaching set, presented as sample. Lexigrams are arbitrary, visual graphics originally developed by Rumbaugh (1977). Lexigrams have been taught to children with severe developmental disabilities as part of an augmentative communication system (Romski & Sevcik, 1992). Two, three, or four geometric elements are overlaid to form each lexigram (Romski et al., 1985). The average number of elements for lexigrams taught in this study was 2.8. The participants had no previous history with lexigrams. Each lexigram was printed on a 7.6 cm ⫻ 12.7 cm card. The average height of each lexigram was 8.9 cm, and the average width was 6.4 cm. Fig. 2 shows each lexigram taught in this study.
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Fig. 2. Lexigrams taught in this experiment. (Note that this figure was also presented in Brady and McLean, 1996.)
We taught participants to match lexigrams to objects in a match-to-sample format, with objects as samples and lexigrams presented in a three-choice array. Teaching began with three sample stimuli presented in quasi-random order, with the stipulation that the same sample was not presented more than twice consecutively. Spoken instructions were kept to a minimum. The experimenter said, “Find this” or “Point to this” while holding up an object. Participants responded by touching a lexigram from the comparison array (see Table 4). Each compar-
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Table 4 Sample and comparison stimuli used in teaching object-lexigram matching Sample
Correct response
Distracters
Obj Obj Obj Obj Obj Obj
Lex Lex Lex Lex Lex Lex
Lex Lex Lex Lex Lex Lex
a
1 2 3 4 5 6
1 2 3 4 5 6
2, 1, 1, 1, 1, 1,
Lex Lex Lex Lex Lex Lex
Order of introduction 3 3 2 2, Lex 3a 2, Lex 3, Lex 4a 2, Lex 3, Lex 4, Lex 5a
1 1 1 2 3 4
Two distracter stimuli were randomly selected from the listed stimuli.
ison stimulus was presented an equal number of times in each position (i.e., left, center, and right). Comparison stimuli were not presented in the same position on more than two consecutive trials. Correct responses were reinforced with either edibles, pennies, or praise depending on individual preference. We determined preference by asking staff or parents what motivated the participants. A pass criterion was set at 90% or greater correct trials for two consecutive sessions, and a fail criterion was set at or below 50% correct trials on two consecutive sessions. After the participant met criterion selecting lexigrams in response to three objects in a mixed presentation, a fourth object and its lexigram were introduced. Teaching trials for the new stimulus were intermixed with the three previously learned object–lexigram relations. Roughly equal numbers of trials for all four stimuli were presented. After the participant’s responses reached criterion levels, the fifth object and lexigram were added; and following criterion with five lexigrams, the sixth object–lexigram relation was added. Table 4 shows the sequence used in teaching participants to match six objects to lexigrams. If a participant met the fail criterion with mixed presentation, we sequenced trials so that the same correct response was targeted in blocks of consecutive trials (Saunders & Spradlin, 1993). The initial size of blocks was individualized and varied between 5 and 15 trials. If the participant met the pass criterion with the initial block size, the size of the block was systematically decreased until the sample stimuli were presented in quasi-random order. If the participant met the fail criterion, the block size was increased by 5, up to a maximum of 30 trials (the entire session). If participants met the fail criterion with block sizes of 30, teaching of lexigrams was discontinued (this only occurred for participant BD). Table 5 shows the number of trials per participant, per teaching condition, and the total number of trials to reach criterion with all six lexigrams. Data on the acquisition of the first three lexigrams in each set were previously presented in Brady and McLean (1996).
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Table 5 Number of trials by procedures and total trials to criterion for teaching six object-lexigram relations Participant
Mixed trials
Participants with severe developmental disabilities Speakers TC 255 FR 180 VB 270 WB 750 Gesture users LT 805 BJ 1,080 BD 120 RG 210 Typically developing participants TJ 240 JE 180 BK 180 MA 120
Blocked trials
Trials to criterion
0 1,197 0 0
255 1,377 270 750
0 1,060 3,930 0
805 2,140 — 210
0 0 0 0
240 180 180 120
2.6. Posttests After meeting criterion with six object–lexigram relations, 11 participants completed Posttests 1– 4. Participant BD did not participate in posttests because he did not meet criterion for learning to match objects to lexigrams. The first posttest assessed whether participants would match lexigrams to lexigrams, as they matched objects to related objects. For example, if the participants matched the real shoe to the real sock, the first posttest determined whether they would now match the lexigram for shoe to the lexigram for sock. Participants were asked, “What goes with this?” while the experimenter held up a lexigram. Table 6 shows which lexigrams were presented as comparisons for each sample lexigram, as well as the sample and comparison stimuli presented in Posttests 2–5. Posttest 2 was a symmetry test. The lexigrams now appeared in the sample position and objects were presented in the three-choice comparison array. Participants were told, “Find this one.” The third and fourth posttests assessed transitivity between spoken words and lexigrams. In Posttest 3, three lexigrams were presented to the participant on each trial and the participant was asked to “Find (name of object).” In Posttest 4, participants who could speak were presented with lexigrams, one at a time, and asked to name the lexigram (“What is this?”). Participants TC, FR, VB, BJ, BK, MA, JE, and TJ had 30-trial posttests in which all 30 trials were presented consecutively. The experimenter did not provide feedback regarding correct or incorrect responses to the participants on any of the trials. As in the pretest, the experimenter intermittently made noncontingent positive statements about the participants’ involvement. Posttest 1
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Table 6 Sample and comparison stimuli used in posttests Post-testa
Sample
Correct response
Distracters
Lexigram-associated lexigram
Lex 1 Lex 2 Lex 3 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6
Lex 4 Lex 5 Lex 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6
Lex 5, Lex 6 Lex 4, Lex 6 Lex 4, Lex 5 Obj 2, Obj 3 Obj 1, Obj 3 Obj 1, Obj 2 Obj 5, Obj 6 Obj 4, Obj 6 Obj 4, Obj 5 Lex 2, Lex 3 Lex 1, Lex 3 Lex 1, Lex 2 Lex 5, Lex 6 Lex 4, Lex 6 Lex 4, Lex 5
Lexigram-object matching (symmetry)
Spoken name-lexigram
Lexigram naming
a
name” name” name” name” name” name”
name” name” name” name” name” name”
The stimulus described first is the sample stimulus, followed by comparison stimuli.
trials (matching lexigrams to associated lexigrams) were embedded in reinforced baselines for Participants WB, RG, and LT. For example, on Trial 1, pointing to a shoe when sock was the sample was reinforced. On Trial 2, pointing to the lexigram for shoe with the real shoe as sample was reinforced. On Trial 3, pointing to the lexigram for sock with the real sock as sample was reinforced. Trial 4, the probe trial, presented the lexigram for shoe as sample and the lexigram for sock as one of the comparisons. Responses to the probe trials were not reinforced. This 4-trial sequence was repeated for the remaining items in the training set. WB had 24 embedded Posttest 1 trials. RG and LT both had 30 embedded Posttest 1 trials. 2.7. Reliability Videotapes of 13 sessions were independently scored by a second observer. The reliability observations included at least one session from each pretest, posttest, and object–lexigram training. Percentage agreement scores between the two observers were calculated by dividing the number of trials both observers scored the same response by the total number of trials in a session. The percentage agreement scores ranged from 87% to 100% with a mean of 97%.
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Table 7 Results of protests Participant
Objectassociated object
Spoken nameobject
Adults with developmental disabilities Speakers TC 100% 100% VB 100% 80% FR 93% 100% WB 93% 100% Gesture users RG 100% 93% LT 100% 100% BJ 80% 100% BD 87% 100% Typically developing children TJ 93% 100% JE 100% 100% BK 87% 100% MA 100% 100%
Objectnaming
Objectidentical object
Lexigramidentical lexigram
100% 67% 100% 100%
100% 100% 93% 100%
100% 93% 93% 100%
NT NT NT NT
100% 100% 93% 90%
100% 100% 100% 97%
100% 100% 100% 100%
100% 93% 100% 100%
3. Results 3.1. Pretests Table 7 shows each participant’s percentage correct scores for each pretest. All but one of the participants were highly accurate on all pretests. Participant VB was only 67% correct in the object naming pretest. VB correctly named car, chair, and tire on 100% trials; spoon 80% trials; and table 0% trials (VB called table “chair” on all trials). With this exception, participants who could speak were able to name all six objects before lexigram teaching. All of the participants were highly accurate selecting the objects when presented with the spoken name. High scores on the identity matching pretests indicated that participants with developmental disabilities could visually discriminate the objects and lexigrams. 3.2. Teaching With the exception of BD, all participants learned to select six lexigrams in response to six objects. Table 5 shows the number of trials required for each participant to reach criterion with all six objects. 3.3. Post-tests Table 8 shows each participant’s percentage correct for each posttest. Scores on posttests greater than 85% correct were considered to be demonstrative of the emergence of one of the tested relations.
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Table 8 Results of posttests Participant
Lexigram– associated lexigram
Adults with developmental disabilities Speakers TC 27% VB 47% FR 37% WB 46% Gesture users RG 47% LT 50% BJ 37% BD * Typically developing children TJ 100% JE 100% BK 40% MA 37%
Lexigram– object (symmetry)
Spoken name– lexigram (transitivity)
Lexigram– naming (transitivity)
100% 100% 70% 90%
100% 100% 87% 50%
100% 100% 87% 70%
100% 93% 97% *
87% 40% 90% *
NT NT NT *
100% 90% 100% 100%
100% 100% 77% 67%
100% 100% 77% 93%
* Did not meet criterion for object–symbol training. NT, Not tested because participants could not speak.
Results for Posttest 1, matching lexigrams to related lexigrams indicated that only two participants, TJ and JE, demonstrated the emergence of relations between symbols for related objects. For example, they selected the lexigram that matched brush in response to the lexigram that matched comb. Results for Posttest 2, however, indicated that all of the tested participants demonstrated symmetry between lexigrams and objects. Posttests 3 and 4 assessed emergent transitive relations between speech and lexigrams. The results of Posttest 3 show that seven participants showed emergence between spoken-name samples and lexigram comparisons. It should be noted that two of these successful participants, RG and BJ, were nonspeaking individuals. The results of Posttest 4 show that six of the eight speaking participants also showed transitivity by naming the lexigrams. 3.4. Error analyses Participant MA was highly accurate naming the lexigrams and on the symmetry post-test but was only 67% accurate selecting lexigrams in response to spoken names. Further analysis indicated that MA was correct on all but one trial for Set 1 (car, table, and pan). MA was only correct 40% of trials for Set 2 (tire, spoon, and chair), however. Participant BK was 77% correct selecting lexigrams in response to spoken names and naming lexigram posttests. In the Lexigram Naming Post-test, BK was 100% correct naming lexigrams that matched shoe, cup, straw, sock, and comb. However, he named the brush lexigram “shoe” on all
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five trials. BK missed only one trial selecting lexigrams that matched straw, sock, and comb in response to spoken names. His other errors occurred in Set 1 (cup, brush, and shoe). We analyzed participants’ selections in the Lexigram–Lexigram Posttest to determine whether participants selected comparisons that shared physical features with the sample (i.e., a “feature-based” selection). The degree of featurebased responding in this study was difficult to determine, however, because there were no controls made for the number of common elements in sample and comparison stimuli. In addition, a single feature (e.g., a squiggly line or a filled triangle) could be a salient basis for discrimination for a particular participant. For example, VB selected “pan” as going with “tire” on 9 of 10 trials. Both stimuli had a squiggly line across the middle. Participants TC and BJ most often selected “sock” when “cup” was the sample. As can be seen in Fig. 2, “sock” and “cup” share three elements. Outside of these examples, feature-based responding was difficult to determine.
4. Discussion We set out to investigate emergent relations in speakers and non-speakers with developmental disabilities. Specifically, we extended the research on stimulus equivalence classes to classes of functionally related objects. Two participants, TJ, and JE, showed emergent relations between lexigrams and spoken names, and between lexigrams depicting related objects (e.g., lexigram for shoe and lexigram for sock). These two participants were typically developing children with receptive vocabulary ages above 4 years and with complex expressive language. Other participants who also had high levels of expressive language did not, however, identify lexigrams as going with related lexigrams in posttests. Several factors may have contributed to these results. First, as mentioned previously, the geometric composition of the lexigrams apparently predisposed some participants to respond based on similar features. Second, the lexigram-toassociated lexigram test was the first in a series of unreinforced posttest sessions, and only one test session was presented. Test performance often improves after repeated testing (Sidman et al., 1985; Spradlin et al., 1973). Third, the lexigramassociated lexigram matching test assessed the emergence of a class composed of all visual stimuli. Classes that include auditory samples, such as spoken names, have been found to emerge more often than classes consisting entirely of visual stimuli (Green, 1990; Sidman et al., 1986). Fourth, the teaching and testing sessions were all conducted with a human experimenter rather than through a computerized apparatus. Tabletop procedures such as those employed in this study are particularly vulnerable to inadvertent cueing by the experimenter (Williams & Saunders, 1998). Therefore, participants may have learned to respond to some inadvertent cue during teaching that was not present during testing. In addition to the aforementioned testing and stimulus variables that may have
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affected results, the match-to-sample teaching procedure may have played an important role. It may be that if learners were taught to use the lexigrams in communicative tasks, rather than match lexigrams to objects in a massed trial situation, they would associate lexigrams to lexigrams in post-tests. Research is needed to explore this possibility. The second purpose of this study was to investigate the importance of naming for the emergence of relations between arbitrary visual stimuli, objects, and auditory names. The results of this study offer important evidence that naming is not a critical variable in stimulus equivalence class emergence. Two participants who did not name objects in our pretests and who did not speak at all according to their history and an interactive communication evaluation, demonstrated reflexivity, symmetry, and transitivity relations between objects, spoken words, and lexigrams. These findings contradict earlier theories proposing that naming is a prerequisite for stimulus equivalence class formation (Devany et al., 1986; Horne & Lowe, 1996). However, the two nonspeaking participants who demonstrated equivalence in the current study were able to comprehend the names of the object stimuli at the outset of the experiment. Either receptive or expressive naming may be sufficient to support the emergence of equivalence classes. Further research is needed to investigate the role of receptive naming abilities. We introduced this study by discussing the implications of stimulus equivalence research for understanding symbolic communicative behavior. The development of symbolic behavior has been analyzed by child language researchers (Bates, 1979; Bruner, 1975; Werner & Kaplan, 1984), language disorders specialists (Mirenda & Locke, 1989; Romski et al., 1985; Wetherby et al., 1988), and primate language researchers (Premack, 1976; Savage–Rumbaugh, 1981, 1984). Although there are many differences in terminology and methodologies between the language research referenced in the previous sentence and stimulus equivalence research, there is often a similar purpose in understanding beginning symbol use (Goldstein, 1985; Remington, 1994). It is hoped that by blending the experimental methodologies of stimulus equivalence research with real language learning tasks, experiments such as the present investigation will further our understanding of symbol learning and use. Acknowledgment We acknowledge the helpful suggestions regarding this manuscript provided by Kathryn Saunders and Joe Spradlin. References Bates, E. (1979). The Emergence of Symbols: Cognition and Communication in Infancy. New York: Academic Press. Brady, N. C. & McLean, L. K. (1996). Arbitrary symbol learning by adults with severe mental retardation: comparison of lexigrams and printed words. Am J Ment Retard, 100, 423– 427.
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Bruner, J. S. (1975). The ontogenesis of speech acts. J Child Lang, 2, 1–19. Calculator, S. & Dollaghan, C. (1982). The use of communication in a residential setting: an evaluation. J Speech Hearing Disord, 47, 281–287. Devany, J. M., Hayes, S. C., & Nelson, R. O. (1986). Equivalence class formation in language-able and language-disabled children. J Exper Anal Behav, 46, 243–257. Eikeseth, S. & Smith, T. (1992). The development of functional and equivalence classes in highfunctioning autistic children: the role of naming. J Exper Anal Behav, 58, 123–133. Goldstein, H. (1985). Enhancing language generalization using matrix and stimulus equivalence training. In S. F. Warren & A. K. Rogers–Warren (Eds.). Teaching functional language (pp. 225–251). Baltimore: University Park Press. Glennen, S. L. & Calculator, S. N. (1985). Training functional communication board use: a pragmatic approach. AAC: Augment Altern Commun, 1, 134 –142. Green, G. (1990). Differences in development of visual and auditory–visual equivalence relations. Am J Ment Retard, 95, 260 –270. Grossman, H. J. (1983). Classification in mental retardation. Washington, DC: American Association on Mental Deficiency. Hamilton, B. L. & Snell, M. E. (1993). Using the milieu approach to increase spontaneous communication book use across environments in an adolescent with autism. AAC Augmen Altern Commun, 9, 259 –272. Horne, P. J., & Lowe, C. F. (1996). On the origins of naming and other symbolic behavior. J Exper Anal Behav, 65, 185–241. McIlvane, W., Dube, W., Green, G., & Serna, R. (1993). Programming conceptual and communication skill development: a methodological stimulus-class analysis. In A. P. Kaiser & D. B. Gray (Eds.). Enhancing children’s communication: research foundations for intervention (pp. 243– 285). Baltimore: Paul H. Brookes. McLean, J. E., McLean, L. K. S., Brady, N. C., & Etter, R. (1991). Communication profiles of two types of gesture using nonverbal persons with severe to profound mental retardation. J Speech Hearing Res, 34, 294 –308. Miller, J. F. & Chapman, R. S. (1985). Systematic analysis of language transcripts. Madison: Waisman Center on Mental Retardation and Human Development, University of Wisconsin. Mirenda, P. & Locke, P. A. (1989). A comparison of symbol transparency in nonspeaking persons with intellectual disabilities. J Speech Hearing Disord, 54, 131–140. Premack, D. (1976). Language and intelligence in ape and man. Am Sci, 64, 674 – 683. Reichle, J. & Sigafoos, J. (1991). Establishing an initial repertoire of requesting. In J. Reichle, J. York, & J. Sigafoos (Eds.). Implementing augmentative and alternative communication: strategies for learners with severe disabilities (pp. 89 –114). Baltimore: Paul H. Brookes. Remington, B. (1994). Augmentative and alternative communication and behavior analysis: a productive partnership? AAC: Augment Altern Commun, 10, 3–13. Romski, M., & Sevcik, R. (1992). Developing augmentative language in children with severe mental retardation. In S. Warren & J. Reichle (Eds.), Causes and effects in communication and language intervention (pp. 113–130). Baltimore: Paul H. Brookes. Romski, M., Sevcik, R., Pate, J., & Rumbaugh, D. (1985). Discrimination of lexigrams and traditional orthography by nonspeaking severely mentally retarded persons. Am J Ment Defic, 90, 185–189. Romski, M., Sevcik, R., & Rumbaugh, D. (1985). Retention of symbolic communication skills by severely mentally retarded persons. Am J Ment Defic, 89, 441– 444. Rumbaugh, D. M. (Ed.). (1977). Language learning by a chimpanzee: the Lana project. New York: Academic Press. Saunders, K. J., & Spradlin, J. E. (1993). Conditional discrimination in mentally retarded participants: programming acquisition and learning set. J Exper Anal Behav, 60, 571–585. Saunders, K. J., Williams, D. C., & Spradlin, J. E. (1995). Conditional discrimination by adults with mental retardation: establishing relations between physically identical stimuli. Am J Ment Retard, 99, 558 –563.
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Savage–Rumbaugh, E. S. (1981). Can apes use symbols to represent their world? Annals NY Acad Sci, 364, 35–59. Savage–Rumbaugh, S. E. (1984). Acquisitions of functional symbol usage in apes and children. In H. L. Rotblat, T. G. Bever, & H. S. Terrace (Eds.). Animal cognition (pp. 291–310). Hillsdale, NJ: Erlbaum. Sidman, M. (1971). Reading and auditory–visual equivalences. J Speech Hearing Res, 14, 5–13. Sidman, M. (1994). Equivalence relations and behavior: a research story. Boston, MA: Authors Cooperative. Sidman, M., Kirk, B., & Willson–Morris, M. (1985). Six-member stimulus classes generated by conditional– discrimination procedures. J Exp Anal Behav, 43, 21– 42. Sidman, M., & Tailby, W. (1982). Conditional discrimination vs. matching to sample: an expansion of the testing paradigm. J Exper Anal Behav, 37, 5–22. Sidman, M., Willson–Morris, M., & Kirk, B. (1986). Matching-to-sample procedures and the development of equivalence relations: the role of naming. Anal Interv Develop Disabil, 6, 1–19. Spradlin, J. E., Cotter, V. W., & Baxley, N. (1973). Establishing a conditional discrimination without direct training: a study of transfer with retarded adolescents. Am J Ment Defic, 77, 556 –566. Stromer, R., Mackay, H. A., & Remington, B. (1996). Naming, the formation of stimulus classes, and applied behavior analysis. J App Behav Anal, 29, 409 – 431. Werner, H., & Kaplan, B. (1984). Symbol formation. Hillsdale, NJ: Lawrence Erlbaum. (First published in 1963). Wetherby, A., Cain, D. H., Yonclas, D. G., & Walker, V. G. (1988). Analysis of intentional communication of normal children from the prelinguistic to the multiword stage. J Speech Hearing Res, 31, 240 –252. Williams, D. C., & Saunders, K. J. (1998). Stimulus control procedures. In K. A. Lattal, I. H. Iversen, & M. Perone (Eds.), Handbook of research methods in human operant behavior. New York: Plenum.
Emergent symbolic relations in speakers and nonspeakers夞 Nancy C. Brady*,1, Lee K. S. McLean2 University of Kansas Life Span Institute, Parsons, KS 67357, USA
Abstract Eight adults with developmental disabilities and four typically developing preschool children participated in an experiment studying emergent stimulus–stimulus relations after match-to-sample instruction. Participants were taught to match lexigrams (arbitrary graphic stimuli) to objects. Each object was functionally related to another object in the teaching set. For example, brush and comb were members of the teaching set. Most participants were able to select objects when the objects were named in pretests. Postteaching probes assessed emergent relations between spoken names and lexigrams. In addition, we included probes to detect emergent relations between related lexigrams. That is, would participants select the lexigram for comb when the experimenter displayed the lexigram for brush (without explicit teaching)? Two preschool children and five adults with developmental disabilities showed emergent relations between lexigrams and spoken words. However, only two preschool children showed the emergent lexigram to related lexigram relations. © 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction Individuals with developmental disabilities are frequently taught to communicate by selecting graphic stimuli (e.g. pictures or printed words) that represent objects or events (e.g. Calculator & Dollaghan, 1982; Glennen & Calculator, 1985; Hamilton & Snell, 1993). Typically, an anticipated outcome of such instruction is the selection of the graphic stimuli in a variety of functional 夞 This research was supported by Grant number 5 PO1 HD18955 from NICHD. * Corresponding author. Tel.: ⫹1-612-624-3322; fax: ⫹1-612-624-7586. 1 Nancy Brady is currently affiliated with the University of Minnesota, Twin Cities campus. 2 Lee McLean is currently affiliated with University of Connecticut, Storrs. 0891-4222/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 1 - 4 2 2 2 ( 0 0 ) 0 0 0 3 4 - 2
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communicative situations (McIlvane et al., 1993; Reichle & Sigafoos, 1991). The degree to which the graphic stimuli are selected across multiple contexts may reflect the degree to which an individual learner recognizes the stimuli as representations of specific objects or events. For example, if a symbol for “dog” is highly representative, we would expect the symbol to be used in the same contexts that a speaker says “dog,” including naming a live animal, naming a picture, answering a question about favorite animals, etc. One way to determine whether an individual learns to view a graphic as a representational symbol for an object or event is to evaluate the degree to which the individual substitutes the graphic for the object (Bates,1979). For example, an individual may indicate the item desired at a restaurant by pointing to the name of the food item. In this context, the printed word is substitutable for the object and the spoken word. The substitutability of symbols for objects has been addressed by recent work in the area of stimulus equivalence (Sidman, 1994). Stimuli that are members of the same equivalence class are related to each other by the properties of reflexivity, symmetry, and transitivity (Sidman & Tailby, 1982). Reflexivity denotes that a participant will match a stimulus to an identical stimulus. Symmetry denotes that a participant who has learned to match a given sample stimulus (e.g., symbol A) to a comparison stimulus (e.g., symbol B) will also match these stimuli when B is the sample and A is a comparison stimulus. The transitivity test determines whether two stimuli are substitutable in their relationship to a third stimulus. For example, if a participant selects an object in the presence of a specific spoken name and then learns to select a written symbol in the presence of the object, transitivity is assessed by asking if the participant will now select the printed symbol when the specified name is spoken. This transitive relation between the spoken name and the written symbol must emerge without instruction in order for the stimuli involved to be considered members of a stimulus equivalence class. The research in stimulus equivalence appears extremely relevant for analyzing acquisition of graphic symbols by individuals with developmental disabilities (Goldstein, 1985; Remington, 1994). For example, Sidman’s classic study in 1971 demonstrated that matching-to-sample tasks could be used to teach learners with developmental disabilities to read and comprehend printed words. These learners could already match spoken names to pictures and name the pictures. Sidman demonstrated that after learning to match dictated names to the printed words, the participants were able to name the printed words (read) and match printed words to pictures (comprehend). This demonstration of emergent relations in learners with developmental disabilities is important for a number of reasons. First, it shows that many individuals with developmental disabilities do not have to be explicitly taught every relationship. Teaching that results in emergent relations saves teaching time. Second, stimulus equivalence research has provided a method to determine whether an individual’s learning extends beyond the relations specifically taught. That is, there are predictable relationships that may emerge after match-to-sample instruction. Thus far, the majority of emergent relations examined in participants with
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developmental disabilities include relations such as those described in Sidman’s original experiment (Sidman, 1971)—relations between objects (or pictures of objects), auditory names and an arbitrary visual stimulus. The term “arbitrary” indicates that there is not a physical resemblance between the stimulus and its referent. The present study extends the analysis to emergent relations between familiar, related objects. The objects in the present study were all related to another object through functional use, or temporal contiguity (e.g., shoe–sock; comb– brush). The experiment was designed to determine whether participants would show emergent relationships between arbitrary symbols that represented pairs of related objects. For example, if an individual identified two real objects as going together (e.g., a shoe and a sock) and then learned to match graphic stimuli to each of these objects, would the individual then also match the graphics as going together? Goldstein (1985) and others have suggested that the stimulus equivalence paradigm can be used to analyze larger categories of stimuli representing conceptually related objects. Demonstrating complex emergent relations, such as those investigated in the present study, offers an important step in the development of behavioral models for symbolic communication by individuals with developmental disabilities. Learning to use an augmentative symbol system parallels the tasks investigated in this study in a number of ways. Many individuals learning an augmentative system comprehend some spoken words. In addition, teaching almost invariably introduces new symbols for familiar objects. Teachers may assume that the newly learned symbols will be equivalent to the auditory names and the objects themselves, but this may not always be the case. In addition, we considered whether participants’ verbal abilities were related to their demonstration of emergent relations including equivalence classes. Several researchers have recently discussed whether naming is a prerequisite skill for demonstrating stimulus equivalence (Horne & Lowe, 1996; Saunders et al., 1995; Stromer et al., 1996). Horne and Lowe (1996) contend that naming is essential for equivalence class formation because stimulus class formation requires verbal mediation. In support of their theory, Horne and Lowe point to research that has shown poor performance on stimulus equivalence tasks by individuals who can’t name. Devany et al. (1986) reported that young children who could speak and older children with developmental disabilities who could speak, showed emergent performances on stimulus equivalence tests. Children with developmental disabilities who could not speak did not show these emergent performances. Eikeseth and Smith (1992) studied equivalence class formation in four children with autism and limited expressive and receptive language skills. All four participants had acquired “some language” at the time of the experiment. Initially, Eikeseth and Smith found that none of the four participants demonstrated the emergence of equivalence classes. After participants were taught to say the same name for each member of a class, two participants’ performances demonstrated the emergence of an equivalence class. Thus, naming appears to at least facilitate stimulus class formation in some participants.
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1.1. Purpose One purpose of the present study was to investigate emergent relations between objects, spoken words, and graphics after match-to-sample instruction. In addition to the critical tests for demonstrating a stimulus equivalence class, we added a test to determine whether participants would also show emergent relations between graphics representing objects functionally related to each other. A second purpose was to determine whether performances on each of these tasks would differ for participants with different language skills. Toward this end, we performed more extensive measures of participants’ expressive and receptive language than typically reported in studies of emergent relations. We wanted to compare performance by participants who were able to speak to performances by participants who did not speak, use sign language, or a graphic selection communication board. Receptive vocabulary abilities were also measured in order to obtain a broader picture of participants’ language skills.
2. Methods 2.1. Participants Eight adults with severe developmental disabilities and four typically developing children participated. The adult participants lived in a large residential facility for individuals with developmental disabilities. The classification of severe mental retardation was made by staff psychologists using the criteria of the American Association on Mental Retardation (Grossman, 1983). Four of the adults communicated with spoken sentences. The remaining four adults did not communicate with spoken words or with an augmentative communication system. Further descriptions of the expressive communication abilities of these eight participants were based on an interactive communication assessment completed by the first author. This assessment consisted of 10 different tasks designed to evoke specific types of communication, including requests for objects (mands), and comments about atypical events (tacts). The following is an example of a task designed to evoke a request for an object: The experimenter and participant take turns filling cups with juice and drinking juice. The experimenter puts some more juice in her cup and then passes the (now empty) pitcher to the participant. Another pitcher that visibly contains juice is within sight, but out of reach for the participant. The following is an example of a task designed to evoke a comment about an atypical event: At some point during the assessment, a small plastic alligator attached to a clear fishline is dangled from the ceiling behind the experimenter’s head. The assessment lasted about 30 min. A complete description is presented in McLean et al.(1991).
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Table 1 Participant descriptions Participant
Age
Adults with developmental disabilities Speakers TC 33 FR 45 VB 26 WB 52 Gesture users RG 30 LT 31 BJ 31 BD 28 Typically developing children TJ 6 JE 4 BK 3 MA 3
Gender
Receptive Vocabulary Age1
Expressive Communication Level2
F M M M
3-7 2-8 2-8 4-11
MLU MLU MLU MLU
7.0 3.0 3.1 7.1
F F M M
4-2 4-2 2-8 2-8
distal distal distal distal
gesture gesture gesture gesture
M F M F
4-5 4-5 4-1 3-6
NT3 MLU 4.28 MLU 2.92 MLU 3.74
1
Age equivalent according to the Peabody Picture Vocabulary Test. Reported in years-months. MLU ⫽ Mean length of words per utterance. Expressive language level was determined by performance on the scripted communication protocol. 3 Not tested. 2
The four adult participants who could talk and three of the four typically developing children were engaged in additional conversation in order to collect a sample of their speech sufficient to analyze with the Systematic Analysis of Language Transcripts (Miller & Chapman, 1985). All speaking participants produced grammatically correct sentences, some of which included embedded clauses. These participants’ mean number of words per utterance are reported in Table 1. We did not complete a formal assessment of participant TJ’s expressive communication, but he also communicated with complex spoken sentences. None of the five typically developing children had any speech or language delays or disorders. The four adult participants who did not speak communicated with both contact and distal gestures. Contact gestures directly contact the referent object (e.g., giving an object to the adult). Distal gestures are gestures, such as a point, that are distanced from the referent by at least 6 inches. Other examples of distal gestures include reaches or open palm requests that are distanced more than 6 inches from the referent. For example, in the dangling alligator task described above, participants frequently pointed at the alligator while vocalizing to gain the experimenter’s attention. Thus, while these participants did not speak or use other symbolic communication means, they communicated with a variety of nonsymbolic gestures. In addition to expressive communication, receptive vocabulary was measured
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Fig. 1. Relations taught and tested in this experiment. Bold lines represent relations participants showed in pretests, or were taught during the experiment. Dotted lines represent relations tested in post-test probes.
with the Peabody Picture Vocabulary Test (PPVT-R). Table 1 describes each participant’s expressive communication and receptive vocabulary levels. 2.2. Setting and materials All assessments, pretests, teaching, and post-tests were conducted in a laboratory room at a university research center located on the grounds of a large residential facility where the adult participants lived. This room contained all stimulus items, two chairs, and a table. During the expressive communication assessment, some items were arranged on open shelving so that they were visible, yet beyond immediate reach. Communication assessments, pretests, post-tests, and some teaching sessions were videotaped through a one-way mirror from an adjacent observation room. 2.3. Procedures The relations tested in pretests and post-tests and taught are diagrammed in Fig. 1. All matching tasks were completed by the experimenter placing the stimuli on the table. The sample stimulus was then either displayed in the experimenter’s hand or spoken by the experimenter. The experimenter was instructed to look at the participant’s face while the participant was selecting a comparison stimulus or naming a stimulus. In addition, the first author periodically watched sessions through a one-way mirror in order to determine whether
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Table 2 Teaching sets used for each participant Participant
TC, FR, GR, LT, BJ, BD, TJ, JE, BK VB WB MA
Objects in teaching sets Obj 1
Obj 2
Obj 3
Obj 4
Obj 5
Obj 6
cup
brush
shoe
straw
comb
sock
car car car
pan bowl pan
chair chair table
tire wheel tire
spoon spoon spoon
table table chair
the experimenter was in any way cueing the participant’s responses. The experimenter was not aware of these observations. No experimenter cueing was observed. 2.4. Pretests All participants completed pretests 1– 4. In addition, participants with developmental disabilities completed an identity matching task (pretest 5) to ensure that the lexigrams were discriminable. All pretests except the naming pretest followed a match-to-sample format. The experimenter set out three comparison stimuli in a horizontal array in front of the participant and then held up a sample stimulus above the center comparison. The participant was then asked to select the comparison stimulus that went with the sample. The first comparison stimulus pointed to or touched by the participant was recorded by the experimenter. The experimenter did not provide feedback regarding correct or incorrect responses. Positive remarks about the participants’ involvement were provided intermittently during the pretests. Pretest 1 assessed participants’ abilities to match objects to associated objects. For example, participants were shown a brush and asked to select what “goes with” the brush from the following array: comb, sock, and straw. Real, full-sized objects were used for brush, comb, shoe, sock, cup, and straw. Toy objects were used for pan, spoon, car, tire/wheel, chair, and table. If a participant identified the same comparison object as going with the sample object on 4 out of 5 trials, the two objects were used in future match-to-sample teaching and testing. This procedure was used to identify three sets of two related objects for each participant. These six objects will henceforth be referred to as the teaching set. Each participant’s teaching set is identified in Table 2. Pretests 2 through 5 consisted of 30 trials each. Pretest 2 assessed selecting objects in the teaching set in response to their spoken names. Objects were presented in a three-choice array and the experimenter said “Find the (name of object).” The third pretest asked speaking participants to name these same objects. The experimenter held up each stimulus from the training set and asked “What’s this?” The fourth and fifth pretests were identity matching pretests. We assessed matching each object from the training set to an identical object, and
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Table 3 Sample and comparison stimuli used in pretests Pretest
Sample
Correct Response
Distracters
Object to associated object matching
Obj 1 Obj 2 Obj 3 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6
Obj 4 Obj 5 Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6
Obj Obj Obj Obj Obj Obj Obj Obj Obj
Spoken name to object matching
Object naming
Object to identical object matching
Lexigram to identical lexigram matching
name” name” name” name” name” name”
5 4 4 2 1 1 5 4 4
Obj Obj Obj Obj Obj Obj Obj Obj Obj
6 6 5 3 3 2 6 6 5
name” name” name” name” name” name” Obj 2 Obj 1 Obj 1 Obj 5 Obj 4 Obj 4 Lex 2 Lex 1 Lex 1 Lex 5 Lex 4 Lex 4
Obj 3 Obj 3 Obj 2 Obj 6 Obj 6 Obj 5 Lex 3 Lex 3 Lex 2 Lex 6 Lex 6 Lex 5
each lexigram used in object–lexigram matching (described below) to an identical lexigram. The instructions for Pretests 4 and 5 were “Find the same.” The array of stimuli presented as samples, correct comparisons, and distracter comparisons for each pretest are shown in Table 3. 2.5. Object–lexigram teaching We taught participants to select each lexigram in response to an object from the teaching set, presented as sample. Lexigrams are arbitrary, visual graphics originally developed by Rumbaugh (1977). Lexigrams have been taught to children with severe developmental disabilities as part of an augmentative communication system (Romski & Sevcik, 1992). Two, three, or four geometric elements are overlaid to form each lexigram (Romski et al., 1985). The average number of elements for lexigrams taught in this study was 2.8. The participants had no previous history with lexigrams. Each lexigram was printed on a 7.6 cm ⫻ 12.7 cm card. The average height of each lexigram was 8.9 cm, and the average width was 6.4 cm. Fig. 2 shows each lexigram taught in this study.
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Fig. 2. Lexigrams taught in this experiment. (Note that this figure was also presented in Brady and McLean, 1996.)
We taught participants to match lexigrams to objects in a match-to-sample format, with objects as samples and lexigrams presented in a three-choice array. Teaching began with three sample stimuli presented in quasi-random order, with the stipulation that the same sample was not presented more than twice consecutively. Spoken instructions were kept to a minimum. The experimenter said, “Find this” or “Point to this” while holding up an object. Participants responded by touching a lexigram from the comparison array (see Table 4). Each compar-
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Table 4 Sample and comparison stimuli used in teaching object-lexigram matching Sample
Correct response
Distracters
Obj Obj Obj Obj Obj Obj
Lex Lex Lex Lex Lex Lex
Lex Lex Lex Lex Lex Lex
a
1 2 3 4 5 6
1 2 3 4 5 6
2, 1, 1, 1, 1, 1,
Lex Lex Lex Lex Lex Lex
Order of introduction 3 3 2 2, Lex 3a 2, Lex 3, Lex 4a 2, Lex 3, Lex 4, Lex 5a
1 1 1 2 3 4
Two distracter stimuli were randomly selected from the listed stimuli.
ison stimulus was presented an equal number of times in each position (i.e., left, center, and right). Comparison stimuli were not presented in the same position on more than two consecutive trials. Correct responses were reinforced with either edibles, pennies, or praise depending on individual preference. We determined preference by asking staff or parents what motivated the participants. A pass criterion was set at 90% or greater correct trials for two consecutive sessions, and a fail criterion was set at or below 50% correct trials on two consecutive sessions. After the participant met criterion selecting lexigrams in response to three objects in a mixed presentation, a fourth object and its lexigram were introduced. Teaching trials for the new stimulus were intermixed with the three previously learned object–lexigram relations. Roughly equal numbers of trials for all four stimuli were presented. After the participant’s responses reached criterion levels, the fifth object and lexigram were added; and following criterion with five lexigrams, the sixth object–lexigram relation was added. Table 4 shows the sequence used in teaching participants to match six objects to lexigrams. If a participant met the fail criterion with mixed presentation, we sequenced trials so that the same correct response was targeted in blocks of consecutive trials (Saunders & Spradlin, 1993). The initial size of blocks was individualized and varied between 5 and 15 trials. If the participant met the pass criterion with the initial block size, the size of the block was systematically decreased until the sample stimuli were presented in quasi-random order. If the participant met the fail criterion, the block size was increased by 5, up to a maximum of 30 trials (the entire session). If participants met the fail criterion with block sizes of 30, teaching of lexigrams was discontinued (this only occurred for participant BD). Table 5 shows the number of trials per participant, per teaching condition, and the total number of trials to reach criterion with all six lexigrams. Data on the acquisition of the first three lexigrams in each set were previously presented in Brady and McLean (1996).
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Table 5 Number of trials by procedures and total trials to criterion for teaching six object-lexigram relations Participant
Mixed trials
Participants with severe developmental disabilities Speakers TC 255 FR 180 VB 270 WB 750 Gesture users LT 805 BJ 1,080 BD 120 RG 210 Typically developing participants TJ 240 JE 180 BK 180 MA 120
Blocked trials
Trials to criterion
0 1,197 0 0
255 1,377 270 750
0 1,060 3,930 0
805 2,140 — 210
0 0 0 0
240 180 180 120
2.6. Posttests After meeting criterion with six object–lexigram relations, 11 participants completed Posttests 1– 4. Participant BD did not participate in posttests because he did not meet criterion for learning to match objects to lexigrams. The first posttest assessed whether participants would match lexigrams to lexigrams, as they matched objects to related objects. For example, if the participants matched the real shoe to the real sock, the first posttest determined whether they would now match the lexigram for shoe to the lexigram for sock. Participants were asked, “What goes with this?” while the experimenter held up a lexigram. Table 6 shows which lexigrams were presented as comparisons for each sample lexigram, as well as the sample and comparison stimuli presented in Posttests 2–5. Posttest 2 was a symmetry test. The lexigrams now appeared in the sample position and objects were presented in the three-choice comparison array. Participants were told, “Find this one.” The third and fourth posttests assessed transitivity between spoken words and lexigrams. In Posttest 3, three lexigrams were presented to the participant on each trial and the participant was asked to “Find (name of object).” In Posttest 4, participants who could speak were presented with lexigrams, one at a time, and asked to name the lexigram (“What is this?”). Participants TC, FR, VB, BJ, BK, MA, JE, and TJ had 30-trial posttests in which all 30 trials were presented consecutively. The experimenter did not provide feedback regarding correct or incorrect responses to the participants on any of the trials. As in the pretest, the experimenter intermittently made noncontingent positive statements about the participants’ involvement. Posttest 1
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Table 6 Sample and comparison stimuli used in posttests Post-testa
Sample
Correct response
Distracters
Lexigram-associated lexigram
Lex 1 Lex 2 Lex 3 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6
Lex 4 Lex 5 Lex 6 Obj 1 Obj 2 Obj 3 Obj 4 Obj 5 Obj 6 Lex 1 Lex 2 Lex 3 Lex 4 Lex 5 Lex 6 “Obj 1 “Obj 2 “Obj 3 “Obj 4 “Obj 5 “Obj 6
Lex 5, Lex 6 Lex 4, Lex 6 Lex 4, Lex 5 Obj 2, Obj 3 Obj 1, Obj 3 Obj 1, Obj 2 Obj 5, Obj 6 Obj 4, Obj 6 Obj 4, Obj 5 Lex 2, Lex 3 Lex 1, Lex 3 Lex 1, Lex 2 Lex 5, Lex 6 Lex 4, Lex 6 Lex 4, Lex 5
Lexigram-object matching (symmetry)
Spoken name-lexigram
Lexigram naming
a
name” name” name” name” name” name”
name” name” name” name” name” name”
The stimulus described first is the sample stimulus, followed by comparison stimuli.
trials (matching lexigrams to associated lexigrams) were embedded in reinforced baselines for Participants WB, RG, and LT. For example, on Trial 1, pointing to a shoe when sock was the sample was reinforced. On Trial 2, pointing to the lexigram for shoe with the real shoe as sample was reinforced. On Trial 3, pointing to the lexigram for sock with the real sock as sample was reinforced. Trial 4, the probe trial, presented the lexigram for shoe as sample and the lexigram for sock as one of the comparisons. Responses to the probe trials were not reinforced. This 4-trial sequence was repeated for the remaining items in the training set. WB had 24 embedded Posttest 1 trials. RG and LT both had 30 embedded Posttest 1 trials. 2.7. Reliability Videotapes of 13 sessions were independently scored by a second observer. The reliability observations included at least one session from each pretest, posttest, and object–lexigram training. Percentage agreement scores between the two observers were calculated by dividing the number of trials both observers scored the same response by the total number of trials in a session. The percentage agreement scores ranged from 87% to 100% with a mean of 97%.
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Table 7 Results of protests Participant
Objectassociated object
Spoken nameobject
Adults with developmental disabilities Speakers TC 100% 100% VB 100% 80% FR 93% 100% WB 93% 100% Gesture users RG 100% 93% LT 100% 100% BJ 80% 100% BD 87% 100% Typically developing children TJ 93% 100% JE 100% 100% BK 87% 100% MA 100% 100%
Objectnaming
Objectidentical object
Lexigramidentical lexigram
100% 67% 100% 100%
100% 100% 93% 100%
100% 93% 93% 100%
NT NT NT NT
100% 100% 93% 90%
100% 100% 100% 97%
100% 100% 100% 100%
100% 93% 100% 100%
3. Results 3.1. Pretests Table 7 shows each participant’s percentage correct scores for each pretest. All but one of the participants were highly accurate on all pretests. Participant VB was only 67% correct in the object naming pretest. VB correctly named car, chair, and tire on 100% trials; spoon 80% trials; and table 0% trials (VB called table “chair” on all trials). With this exception, participants who could speak were able to name all six objects before lexigram teaching. All of the participants were highly accurate selecting the objects when presented with the spoken name. High scores on the identity matching pretests indicated that participants with developmental disabilities could visually discriminate the objects and lexigrams. 3.2. Teaching With the exception of BD, all participants learned to select six lexigrams in response to six objects. Table 5 shows the number of trials required for each participant to reach criterion with all six objects. 3.3. Post-tests Table 8 shows each participant’s percentage correct for each posttest. Scores on posttests greater than 85% correct were considered to be demonstrative of the emergence of one of the tested relations.
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Table 8 Results of posttests Participant
Lexigram– associated lexigram
Adults with developmental disabilities Speakers TC 27% VB 47% FR 37% WB 46% Gesture users RG 47% LT 50% BJ 37% BD * Typically developing children TJ 100% JE 100% BK 40% MA 37%
Lexigram– object (symmetry)
Spoken name– lexigram (transitivity)
Lexigram– naming (transitivity)
100% 100% 70% 90%
100% 100% 87% 50%
100% 100% 87% 70%
100% 93% 97% *
87% 40% 90% *
NT NT NT *
100% 90% 100% 100%
100% 100% 77% 67%
100% 100% 77% 93%
* Did not meet criterion for object–symbol training. NT, Not tested because participants could not speak.
Results for Posttest 1, matching lexigrams to related lexigrams indicated that only two participants, TJ and JE, demonstrated the emergence of relations between symbols for related objects. For example, they selected the lexigram that matched brush in response to the lexigram that matched comb. Results for Posttest 2, however, indicated that all of the tested participants demonstrated symmetry between lexigrams and objects. Posttests 3 and 4 assessed emergent transitive relations between speech and lexigrams. The results of Posttest 3 show that seven participants showed emergence between spoken-name samples and lexigram comparisons. It should be noted that two of these successful participants, RG and BJ, were nonspeaking individuals. The results of Posttest 4 show that six of the eight speaking participants also showed transitivity by naming the lexigrams. 3.4. Error analyses Participant MA was highly accurate naming the lexigrams and on the symmetry post-test but was only 67% accurate selecting lexigrams in response to spoken names. Further analysis indicated that MA was correct on all but one trial for Set 1 (car, table, and pan). MA was only correct 40% of trials for Set 2 (tire, spoon, and chair), however. Participant BK was 77% correct selecting lexigrams in response to spoken names and naming lexigram posttests. In the Lexigram Naming Post-test, BK was 100% correct naming lexigrams that matched shoe, cup, straw, sock, and comb. However, he named the brush lexigram “shoe” on all
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five trials. BK missed only one trial selecting lexigrams that matched straw, sock, and comb in response to spoken names. His other errors occurred in Set 1 (cup, brush, and shoe). We analyzed participants’ selections in the Lexigram–Lexigram Posttest to determine whether participants selected comparisons that shared physical features with the sample (i.e., a “feature-based” selection). The degree of featurebased responding in this study was difficult to determine, however, because there were no controls made for the number of common elements in sample and comparison stimuli. In addition, a single feature (e.g., a squiggly line or a filled triangle) could be a salient basis for discrimination for a particular participant. For example, VB selected “pan” as going with “tire” on 9 of 10 trials. Both stimuli had a squiggly line across the middle. Participants TC and BJ most often selected “sock” when “cup” was the sample. As can be seen in Fig. 2, “sock” and “cup” share three elements. Outside of these examples, feature-based responding was difficult to determine.
4. Discussion We set out to investigate emergent relations in speakers and non-speakers with developmental disabilities. Specifically, we extended the research on stimulus equivalence classes to classes of functionally related objects. Two participants, TJ, and JE, showed emergent relations between lexigrams and spoken names, and between lexigrams depicting related objects (e.g., lexigram for shoe and lexigram for sock). These two participants were typically developing children with receptive vocabulary ages above 4 years and with complex expressive language. Other participants who also had high levels of expressive language did not, however, identify lexigrams as going with related lexigrams in posttests. Several factors may have contributed to these results. First, as mentioned previously, the geometric composition of the lexigrams apparently predisposed some participants to respond based on similar features. Second, the lexigram-toassociated lexigram test was the first in a series of unreinforced posttest sessions, and only one test session was presented. Test performance often improves after repeated testing (Sidman et al., 1985; Spradlin et al., 1973). Third, the lexigramassociated lexigram matching test assessed the emergence of a class composed of all visual stimuli. Classes that include auditory samples, such as spoken names, have been found to emerge more often than classes consisting entirely of visual stimuli (Green, 1990; Sidman et al., 1986). Fourth, the teaching and testing sessions were all conducted with a human experimenter rather than through a computerized apparatus. Tabletop procedures such as those employed in this study are particularly vulnerable to inadvertent cueing by the experimenter (Williams & Saunders, 1998). Therefore, participants may have learned to respond to some inadvertent cue during teaching that was not present during testing. In addition to the aforementioned testing and stimulus variables that may have
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affected results, the match-to-sample teaching procedure may have played an important role. It may be that if learners were taught to use the lexigrams in communicative tasks, rather than match lexigrams to objects in a massed trial situation, they would associate lexigrams to lexigrams in post-tests. Research is needed to explore this possibility. The second purpose of this study was to investigate the importance of naming for the emergence of relations between arbitrary visual stimuli, objects, and auditory names. The results of this study offer important evidence that naming is not a critical variable in stimulus equivalence class emergence. Two participants who did not name objects in our pretests and who did not speak at all according to their history and an interactive communication evaluation, demonstrated reflexivity, symmetry, and transitivity relations between objects, spoken words, and lexigrams. These findings contradict earlier theories proposing that naming is a prerequisite for stimulus equivalence class formation (Devany et al., 1986; Horne & Lowe, 1996). However, the two nonspeaking participants who demonstrated equivalence in the current study were able to comprehend the names of the object stimuli at the outset of the experiment. Either receptive or expressive naming may be sufficient to support the emergence of equivalence classes. Further research is needed to investigate the role of receptive naming abilities. We introduced this study by discussing the implications of stimulus equivalence research for understanding symbolic communicative behavior. The development of symbolic behavior has been analyzed by child language researchers (Bates, 1979; Bruner, 1975; Werner & Kaplan, 1984), language disorders specialists (Mirenda & Locke, 1989; Romski et al., 1985; Wetherby et al., 1988), and primate language researchers (Premack, 1976; Savage–Rumbaugh, 1981, 1984). Although there are many differences in terminology and methodologies between the language research referenced in the previous sentence and stimulus equivalence research, there is often a similar purpose in understanding beginning symbol use (Goldstein, 1985; Remington, 1994). It is hoped that by blending the experimental methodologies of stimulus equivalence research with real language learning tasks, experiments such as the present investigation will further our understanding of symbol learning and use. Acknowledgment We acknowledge the helpful suggestions regarding this manuscript provided by Kathryn Saunders and Joe Spradlin. References Bates, E. (1979). The Emergence of Symbols: Cognition and Communication in Infancy. New York: Academic Press. Brady, N. C. & McLean, L. K. (1996). Arbitrary symbol learning by adults with severe mental retardation: comparison of lexigrams and printed words. Am J Ment Retard, 100, 423– 427.
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Bruner, J. S. (1975). The ontogenesis of speech acts. J Child Lang, 2, 1–19. Calculator, S. & Dollaghan, C. (1982). The use of communication in a residential setting: an evaluation. J Speech Hearing Disord, 47, 281–287. Devany, J. M., Hayes, S. C., & Nelson, R. O. (1986). Equivalence class formation in language-able and language-disabled children. J Exper Anal Behav, 46, 243–257. Eikeseth, S. & Smith, T. (1992). The development of functional and equivalence classes in highfunctioning autistic children: the role of naming. J Exper Anal Behav, 58, 123–133. Goldstein, H. (1985). Enhancing language generalization using matrix and stimulus equivalence training. In S. F. Warren & A. K. Rogers–Warren (Eds.). Teaching functional language (pp. 225–251). Baltimore: University Park Press. Glennen, S. L. & Calculator, S. N. (1985). Training functional communication board use: a pragmatic approach. AAC: Augment Altern Commun, 1, 134 –142. Green, G. (1990). Differences in development of visual and auditory–visual equivalence relations. Am J Ment Retard, 95, 260 –270. Grossman, H. J. (1983). Classification in mental retardation. Washington, DC: American Association on Mental Deficiency. Hamilton, B. L. & Snell, M. E. (1993). Using the milieu approach to increase spontaneous communication book use across environments in an adolescent with autism. AAC Augmen Altern Commun, 9, 259 –272. Horne, P. J., & Lowe, C. F. (1996). On the origins of naming and other symbolic behavior. J Exper Anal Behav, 65, 185–241. McIlvane, W., Dube, W., Green, G., & Serna, R. (1993). Programming conceptual and communication skill development: a methodological stimulus-class analysis. In A. P. Kaiser & D. B. Gray (Eds.). Enhancing children’s communication: research foundations for intervention (pp. 243– 285). Baltimore: Paul H. Brookes. McLean, J. E., McLean, L. K. S., Brady, N. C., & Etter, R. (1991). Communication profiles of two types of gesture using nonverbal persons with severe to profound mental retardation. J Speech Hearing Res, 34, 294 –308. Miller, J. F. & Chapman, R. S. (1985). Systematic analysis of language transcripts. Madison: Waisman Center on Mental Retardation and Human Development, University of Wisconsin. Mirenda, P. & Locke, P. A. (1989). A comparison of symbol transparency in nonspeaking persons with intellectual disabilities. J Speech Hearing Disord, 54, 131–140. Premack, D. (1976). Language and intelligence in ape and man. Am Sci, 64, 674 – 683. Reichle, J. & Sigafoos, J. (1991). Establishing an initial repertoire of requesting. In J. Reichle, J. York, & J. Sigafoos (Eds.). Implementing augmentative and alternative communication: strategies for learners with severe disabilities (pp. 89 –114). Baltimore: Paul H. Brookes. Remington, B. (1994). Augmentative and alternative communication and behavior analysis: a productive partnership? AAC: Augment Altern Commun, 10, 3–13. Romski, M., & Sevcik, R. (1992). Developing augmentative language in children with severe mental retardation. In S. Warren & J. Reichle (Eds.), Causes and effects in communication and language intervention (pp. 113–130). Baltimore: Paul H. Brookes. Romski, M., Sevcik, R., Pate, J., & Rumbaugh, D. (1985). Discrimination of lexigrams and traditional orthography by nonspeaking severely mentally retarded persons. Am J Ment Defic, 90, 185–189. Romski, M., Sevcik, R., & Rumbaugh, D. (1985). Retention of symbolic communication skills by severely mentally retarded persons. Am J Ment Defic, 89, 441– 444. Rumbaugh, D. M. (Ed.). (1977). Language learning by a chimpanzee: the Lana project. New York: Academic Press. Saunders, K. J., & Spradlin, J. E. (1993). Conditional discrimination in mentally retarded participants: programming acquisition and learning set. J Exper Anal Behav, 60, 571–585. Saunders, K. J., Williams, D. C., & Spradlin, J. E. (1995). Conditional discrimination by adults with mental retardation: establishing relations between physically identical stimuli. Am J Ment Retard, 99, 558 –563.
214
N. Brady et al. / Research in Developmental Disabilities 21 (2000) 197–214
Savage–Rumbaugh, E. S. (1981). Can apes use symbols to represent their world? Annals NY Acad Sci, 364, 35–59. Savage–Rumbaugh, S. E. (1984). Acquisitions of functional symbol usage in apes and children. In H. L. Rotblat, T. G. Bever, & H. S. Terrace (Eds.). Animal cognition (pp. 291–310). Hillsdale, NJ: Erlbaum. Sidman, M. (1971). Reading and auditory–visual equivalences. J Speech Hearing Res, 14, 5–13. Sidman, M. (1994). Equivalence relations and behavior: a research story. Boston, MA: Authors Cooperative. Sidman, M., Kirk, B., & Willson–Morris, M. (1985). Six-member stimulus classes generated by conditional– discrimination procedures. J Exp Anal Behav, 43, 21– 42. Sidman, M., & Tailby, W. (1982). Conditional discrimination vs. matching to sample: an expansion of the testing paradigm. J Exper Anal Behav, 37, 5–22. Sidman, M., Willson–Morris, M., & Kirk, B. (1986). Matching-to-sample procedures and the development of equivalence relations: the role of naming. Anal Interv Develop Disabil, 6, 1–19. Spradlin, J. E., Cotter, V. W., & Baxley, N. (1973). Establishing a conditional discrimination without direct training: a study of transfer with retarded adolescents. Am J Ment Defic, 77, 556 –566. Stromer, R., Mackay, H. A., & Remington, B. (1996). Naming, the formation of stimulus classes, and applied behavior analysis. J App Behav Anal, 29, 409 – 431. Werner, H., & Kaplan, B. (1984). Symbol formation. Hillsdale, NJ: Lawrence Erlbaum. (First published in 1963). Wetherby, A., Cain, D. H., Yonclas, D. G., & Walker, V. G. (1988). Analysis of intentional communication of normal children from the prelinguistic to the multiword stage. J Speech Hearing Res, 31, 240 –252. Williams, D. C., & Saunders, K. J. (1998). Stimulus control procedures. In K. A. Lattal, I. H. Iversen, & M. Perone (Eds.), Handbook of research methods in human operant behavior. New York: Plenum.