This article describes the procedures for conducting a verbal operant analysis (VOA), calculating the stimulus control ratio equation (SCoRE), and developing individualized verbal behavior treatment plans, specifically significant to address the deficits characteristic of autism.
Verbal operant analyses are the extension of functional analysis technology to the field of verbal behavior, of particular relevance to autism spectrum disorders and associated developmental disabilities. Similarly, a verbal operant analysis carefully controls specific environmental factors that influence language, and measures strength of responding across four verbal operant classes: tact, mand, echoic, and sequelic. The frequency of each independent verbal operant is then measured against one another using the stimulus control ratio equation (SCoRE) to summarize the relative strength of the speaker’s repertoire. The verbal behavior SCoRE yields a statistic that can be compared against itself (e.g., for the purposes of pre/post testing) or against others (e.g., for the purposes of randomized controlled trials). The results of this evaluation provide an individualized hierarchy for diverging stimulus control across the verbal operants, from which a treatment plan for errorless language learning may be prescribed.
Functional analyses are commonly employed as part of behavior-analytic interventions to identify the environmental variables responsible for maintaining behavioral excesses (problem behavior) and deficits (e.g., communication skills) necessary to developing appropriate and effective individualized behavior intervention plans. The functional independence of verbal operants has provided a revolutionary framework for treating autism and other language disorders1,2,3. Unlike prior attempts to analyze language as a cognitive phenomenon or structural framework, language is better described as operant behavior4, subject to the same principles of reinforcement5,6, extinction7,8, and punishment9. In doing so, six elementary verbal operants were identified, which work in various ways to extend control of the environment for the speaker.
Definitionally, the verbal behavior of a speaker is consequated by another individual as part of a social episode. Individuals who fail to develop a functional speaking repertoire are frequently diagnosed with autism spectrum disorder, of which the core symptoms include persistent deficits in communication and social interaction, in addition to restricted, repetitive behavior patterns10.
Over the past 60 years, behavior-analytic researchers have primarily focused on four of these operants in remediating the communicative deficits of autism spectrum disorder: mands, tacts, echoics, and sequelics. Strengthening each of these four language skills has been shown to be foundational to developing a fluent verbal repertoire for children with autism11. Procedures such as functional communication training have found that increasing language can lead to a corresponding decrease in challenging behavior. Moreover, when compared to neurotypical speech, disproportionality between the four verbal operants is a characteristic of autistic speech patterns12,13.
Mands are verbal behavior under the control of restricted access to reinforcers. Accordingly, the speaker must demand or command access to these items. For instance, to obtain a glass of water, one may state “May I have some water?”, “Would you mind getting us something to drink?”, or “Water, now!”, all of which are consequated similarly, and therefore belong to the same operant class of manding. Research on mand training has demonstrated its use in functional communication training14, removing aversive stimuli5, and requesting information15.
Tacts are verbal behavior under the control of physical properties of the environment with which we come into contact. For instance, taking a bath, feeling a drop of rain, or smelling the ocean air may all occasion the response, “Water.” Verbal responses under the control of nonverbal stimuli are consequated similarly, and therefore belong to the same operant class of tacting. Research on tact training has demonstrated its use in labeling visual stimuli16, interoceptive feelings17, and parts of a whole18.
Echoics and sequelics are both verbal behavior in response to other verbal behavior (i.e., intraverbal). Echoics are verbal behavior that echoes the verbal stimulus. For instance, upon meeting some who says, “Hi,” the individual is more likely to reply, “Hi.” Upon meeting some who says, “Hello,” the individual is more likely to reply, “Hello”. Research on echoic training has demonstrated its use in increasing the mean length of utterance19, prosody20, and use of sign language21. Individuals with autism may demonstrate echolalia, in which scripted vocalizations are repeated after an extended latency. However, these vocalizations are not maintained by reinforcement from a listener, and therefore need not be considered verbal.
On the other hand, sequelics share no such correspondence with its precipitating verbal stimulus. For instance, to the colleague who says, “How are you today?”, the individual may reply, “Fine.” Research on sequelic training has demonstrated its use in conversational turns22, categorization23, and fill-in-the-blanks tasks24. While echoic intraverbals and sequelics intraverbals are consequated similarly, the different antecedent stimuli create distinct operant classes.
Having verified the functional distinction of the primary verbal operants25, verbal behavior interventions have primarily focused on treatments to address each individual operant. The success of each of these individual lines of research has likely perpetuated their narrow scope. However, researchers have recently begun to emphasize the importance of multiple control over verbal behavior. Interdependence among the verbal operants is requisite for developing fluent speech26. Moreover, those who fail to consider multiple controls are unlikely to demonstrate adequate explanations, prediction, and control over verbal behavior27.
The verbal behavior stimulus control ratio equation (SCoRE)12 is a procedure for quantitively synthesizing an individual’s functional speaking repertoire and yielding a statistic comparing the relative proportionality of the four primary verbal operants. The SCoRE analyzes mand, echoic, tact, and sequelics response populations in relation to one another, and allows for idiographic and nomothetic comparisons to be drawn between autistic speech patterns and those of typically developing speakers. Additionally, the SCoRE prescribes an individualized prompt hierarchy for strengthening individual operants in proportion to one another. Accordingly, “The score may be used to predict some aspect of the larger universe of behavior from which the test is drawn”28. The SCoRE also yields a metric for differentiating the repertoire strength of verbal operants across effect sizes. The goal of the SCoRE assessment is to provide a model of language deficit that: (1) pinpoints the degree to which the autistic repertoire differs from a typical speaking repertoire, (2) identifies areas of insufficient stimulus control, and (3) provides an individualized treatment plan for remediation.
The following procedures were carried out under the oversight of The University of Texas at San Antonio’s Institutional Review Board.
NOTE: The verbal behavior SCoRE procedure is appropriate for early childhood learners with language deficits who emit topography-based or selection-based verbal behavior. Individuals beyond the early childhood age range, as well as young speakers who emit non-communicative vocalizations are excluded from this analysis.
1. Conduct a verbal operant analysis.
2. Calculate the verbal behavior stimulus control ratio equation (SCoRE).
Trials | Tact | Mand | Echoic | Sequelic |
1 - 10 | 6 | 2 | 6 | 2 |
11 - 20 | 4 | 2 | 10 | 0 |
21 - 30 | 4 | 4 | 6 | 2 |
Totals | 14 | 8 | 22 | 4 |
Table 1: The sum of responses across all three rounds of the assessment provide a sufficient response population for conducting further statistical analyses. Analyzing the variance across operants leads to an individualized prompt hierarchy for errorless language learning.
Operation | Tact | Mand | Echoic | Sequelic |
Sum | 14 | 8 | 22 | 4 |
Divide | 48 | 48 | 48 | 48 |
Equals | 0.29 | 0.17 | 0.46 | 0.08 |
Table 2: The mathematical operations used to determine the relative strength of each of the four verbal operants. The number of responses for each operant is divided by the sum of responses across all operants to yield a relative value for each operant.
Figure 1: A model of an autistic verbal repertoire demonstrating disproportionate levels of strength across tacts (29.2%), mands (16.7%), echoics (45.8%), and sequelics (8.3%). The four operants combine to account for 100% of the environmental variables that control verbal behavior. Please click here to view a larger version of this figure.
Figure 2: A model of the null verbal repertoire demonstrating proportionate strength across all four verbal operants at 25% each. Typically developing speakers show no variation in strength across tacts, mands, echoics, and sequelics. Please click here to view a larger version of this figure.
Figure 3: A demonstration of agreement between the observed response strength and the null hypothesis. A primary assumption in the SCoRE calculation is that any overlap between the observed repertoire (a) and null repertoire (25%; b) represents agreement, while nonoverlap represents disagreement. Please click here to view a larger version of this figure.
3. Abstract stimulus control.
Environmental Variable(s) | Environmental Control (%) |
METS | 100 |
MET | 91.67 |
ETS | 83.33 |
ET | 75 |
MES | 70.83 |
ME | 62.5 |
MTS | 54.17 |
ES | 54.17 |
MT | 45.83 |
E | 45.83 |
TS | 37.5 |
T | 29.17 |
MS | 25 |
M | 16.67 |
S | 8.33 |
Table 3: The strength of each verbal operant is converged with one another in all possible combinations to provide a rank order of strength from greatest to least. By converging various operants we can control a greater amount of the speaker’s environment. M = mand, E = echoic, T = tact, S = sequelic.
Tact | Mand | Echoic | Sequelic |
METS (100%) | METS (100%) | METS (100%) | METS (100%) |
MET (91.67%) | MET (91.67%) | MET (91.67%) | ETS (83.33%) |
ETS (83.33%) | MES (70.83%) | ETS (83.33%) | MES (70.83%) |
ET (75.00%) | ME (62.50%) | ET (75.00%) | MTS (54.17%) |
MTS (54.17%) | MTS (54.17%) | MES (70.83%) | ES (54.17%) |
MT (45.83%) | MT (45.83%) | ME (62.50%) | TS (37.50%) |
TS (37.50%) | MS (25.00%) | ES (54.17%) | MS (25.00%) |
T (29.17%) | M (16.67%) | E (45.83%) | S (8.33%) |
Table 4: To condition each individual operant, mands, echoics, tacts, and sequelics are systematically converged and diverged with one another to provide a framework for most-to-least prompting. Relational flexibility is established by varying the irrelevant variables that help support each of the individual operants. M = mand, E = echoic, T = tact, S = sequelic.
Figure 4 shows the results of a VOA conducted with Aron, a five-year-old Hispanic male diagnosed with ASD, prior to the onset of intervention. These data confirm the utility of the VOA for assessing disproportionate levels of verbal operant strength. Echoics were found to have the greatest strength and were emitted for half of all trials (48.4%). Tacts showed the next greatest strength with responses for 1/3 of all trials (32.3%). Mands were emitted for 1/6 of all trials (16.1%), while only one sequelic response was recorded (3.2%).
Figure 4: The observed verbal repertoire of a speaker diagnosed with autism spectrum disorder. Data for this model were obtained from a pretest VOA. Each of the four operants were assessed at disproportionate strength ranging from echoic (greatest) to sequelic (weakest). Please click here to view a larger version of this figure.
The strength of each operant was compared against the null repertoire’s proportionate strength of 25% each. For each comparison, the smaller of the two numbers represents agreement and was placed in the numerator, while the larger of the two numbers represents agreement plus disagreement and was placed in the denominator.
By comparing the observed data against the null repertoire, Aron’s pretest SCoRE was calculated as 0.53.
In addition to summarizing the verbal repertoire, the SCoRE serves as a judgmental aid for making programmatic decisions. Table 5 shows a prompt hierarchy to support Aron’s verbal repertoire across multiple and singular control.
Controlling Variables | Strength (%) |
M+E+T+S | 100 |
M+E+T | 96.8 |
E+T+S | 83.9 |
E+T | 80.7 |
M+E+S | 67.7 |
M+E | 64.5 |
M+T+S | 51.6 |
E+S | 51.6 |
M+T | 48.4 |
E | 48.4 |
T+S | 35.5 |
T | 32.3 |
M+S | 19.3 |
M | 16.1 |
S | 3.2 |
Table 5: An individualized hierarchy of transference across multiple and singular sources of control derived from Figure 2. M = mand, E = echoic, T = tact, S = sequelic.
The results of Table 5 prescribe an individualized prompt hierarchy to strengthen the singular control of each verbal operant (see Table 6). By systematically programming for multiple arrangements of the target operant through converging combinations, verbal “[b]ehavior may be brought under the control of a single property or a special combination of properties of a stimulus while being freed from the control of all other properties”28.
Mand | Echoic | Tact | Sequelic |
M+E+T+S | M+E+T+S | M+E+T+S | M+E+T+S |
M+E+T | M+E+T | M+E+T | E+T+S |
M+E+S | E+T+S | E+T+S | M+E+S |
M+E | E+T | E+T | M+T+S |
M+T+S | M+E+S | M+T+S | E+S |
M+T | M+E | M+T | T+S |
M+S | E+S | T+S | M+S |
M | E | T | S |
Table 6: A systematic progression for abstracting functional independence across each of the verbal operants. M = mand, E = echoic, T = tact, S = sequelic.
After 13 weeks of referent-based instruction, a posttest VOA was conducted with Aron, using the same procedures described above. In comparison to the pretest, Figure 5 shows greater proportionality across each of the four operants: mand (27.1%), echoic (34.1%), tact (23.5%), and sequelic (15.3%). By comparing these results to the null hypothesis, Aron’s SCoRE was calculated as 0.80. A pre/post analysis of Aron’s verbal repertoire with the SCoRE shows that his language increased by 0.27 over the course of the intervention.
Figure 5: The observed verbal repertoire of a speaker diagnosed with autism spectrum disorder after 13 weeks of referent-based verbal behavior instruction. Data for this model were obtained from a posttest VOA, illustrative of increased proportionality of the four verbal operants. Please click here to view a larger version of this figure.
It has been said that “the ‘meaning’ for a speaker of a word or sentence is, of course, defined by the sum total of conditions under which it is emitted”32. In the natural environment, the typically developing speaker’s verbal behavior is simultaneously under multiple sources of strength. Consequently, the dysfunctional speech of individuals with autism and other verbal behavior disorders may be explained as faulty stimulus control that prohibits the convergence of environmental variables.
Functional speech is predicated on behavioral fluency across learning channels33. Typically developing speakers will respond dog in the presence of a dog as well as they will when asked what kind of pet they own. Proportionate strength over various input modalities establishes the relational flexibility of fluent language. On the other hand, a visual stimulus may have a more profound effect than an auditory stimulus on the verbal behavior of individuals with autism. The aforementioned procedures were designed to isolate controlling relations to allow for a relative comparison of verbal operant strength.
Each of the four conditions lasts approximately five minutes in duration. Within the tact condition, access to the object is not restricted, as in the mand condition; the assessor does not name the object, as in the echoic condition; and no other statements are made about the object, as in the sequelic condition.
Of critical importance to this methodology is the isolation of verbal relations during each phase of the VOA. Within the mand condition, the item is not present, as in the tact condition; the assessor does not name the object, as in the echoic condition; and no other statements are made about the object as in the sequelic condition. Notably, the type of stimulus preference assessment employed as part of the mand condition may be substituted for one more suitable to the needs of the individual participant34.
Within the echoic condition, access to the object is not restricted, as in the mand condition; the item is not present, as in the tact condition; and no other statements are made about the object, as in the sequelic condition.
Within the sequelic condition, access to the object is not restricted, as in the mand condition; the item is not present, as in the tact condition; the assessor does not name the object, as in the echoic condition.
The SCoRE assessment prescribes an individualized prompt hierarchy for conditioning proportionate response strength across mands, echoics, tacts, and sequelics. If strength is assessed for all four operants on the VOA, there will be 15 possible combinations, and fading from multiple to isolated control will consist of eight steps for each operant. If strength is assessed for three operants, there will be seven possible combinations, and fading from multiple to isolated control will consist of four steps for each of the assessed operants. If strength is assessed for two operants, there will be three possible combinations, and fading from multiple to isolated control will consist of two steps for each assessed operant. If strength is assessed for only one operant, there is only one possible combination and no fading will occur. Any operants that are not assessed with strength during the VOA may be prompted using the greatest source of multiple control, and subsequently faded using the errorless language learning procedures described above.
By measuring rates of responding against one another, the SCoRE predicts the relative control of converging variables in the natural environment. Its utility for assessing disproportionate stimulus control over the verbal behavior of children with autism has been well demonstrated35. Moreover, SCoRE has implications for idiographic progress monitoring to document the effects of verbal behavior training. Future applications of the verbal behavior SCoRE may show its utility for group comparisons, such as randomized clinical trials, for demonstrating treatment efficacy as a pre- and post-measure, and may also be used to synthesize data in meta analyses.
The primary limitation of the verbal behavior SCoRE is its restriction to participants with non-fluent verbal behavior. Approximately 30% of individuals with autism are considered nonverbal36. For this population, the SCoRE targets may be modified to assess proportionality across manded stimulus selection, motor imitation, matching to sample, and other component skills. Additionally, the verbal behavior of fluent speakers may still show disproportionate strength across levels of derivational stimulus control37. Accordingly, SCoRE targets may be modified to assess reflexivity, symmetry, and transitivity.
As an alternative to the descriptive assessments generally used to measure language, the SCoRE’s experimental analysis affords the advantages of efficiency, objectivity, and quantitative precision. The SCoRE protocol can be readily implemented in a variety of settings (e.g., clinical or educational), making it ideal for use by behavior analysts, educators, and others trained in the use of functional analysis technology. As a data-based judgmental aid, the verbal behavior SCoRE offers a convenient, yet precise way of speaking about language.
The authors would like to acknowledge Mtra. Mariana de los Santos for her assistance with video production.
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