Introduction to Skill Repertoire Building: Identifying What to Teach and How to Teach it

Verbal Behavior 2

Historically, when teaching language to children with autism considerable emphasis has been placed on teaching two types of behaviors or responses:

Receptive behavior:

Receptive behavior involves receiving an instruction and responding non-vocally. In other words, the child “hears” and instruction or “receives” it, but does not have to reciprocate with a vocal response. Rather, it involves engaging in a non-vocal action, such as matching or pointing to stimuli.

Examples:
Matching objects. In a matching task a child may be given an object and asked to match it to a similar or identical object. Let’s say that Callie is sitting at a table with three objects in front of her. A red apple, a yellow comb, and a blue baseball cap. Callie is handed a green apple and asked to “put with apple”. The expectation is that Callie will place the green apple next to the red apple on the table.

Identifying objects: In an identifying task a child is given an array of objects and asked to identify an object. Callie has the apple, the comb and the baseball cap. Callie is asked to “touch the apple”. The expectation is that Callie will touch the red apple. A non-vocal communication response.

Expressive behavior:

Expressive behavior however, involves the child receiving an instruction and responding vocally.

Example:
Vocally identifying. In an expressive identifying task Callie is shown an apple and asked to identify it, “What is this?”. The expected response is for Callie to say “apple”.

Expressive and Receptive behaviors are important elements of learning language, however to fully acquire language one must learn more than just the meaning of words. Expressive and receptive behaviors are topographies. Topographies are essentially descriptions of what language behavior looks like. The ability to match, point or speak when instructed or asked to do so does not mean that the child can use the word functionally in a variety of circumstances.

Think of Callie. Callie is hungry and would like an apple. She is unable to say “apple” to request an apple. Callie has learned the meaning of an apple, however she has not learned how to use it functionally across a variety of circumstances.

It is not enough to teach children receptive and expressive language. Because language is more than acquiring the meaning of words.

This is why EIBI programs focus on the function of behavior.

Function of Behavior

The function of behavior refers to the circumstances under which a behavior occurs. That is the antecedents and consequences to a particular behavior. In other words, the function of a behavior refers to a reason the behavior occurs. Focusing on the function of behavior increases the possibility the behavior will be used in all or most appropriate situations.

What is Verbal Behavior?

Verbal behavior is any behavior for which the consequence is mediated by the behavior of another person. In practice, verbal behavior is behavior that is reinforced by another person.

Example:

Antecedent: Callie is hungry.
Behavior: Callie asks her mom for an apple.
Consequence: Callie’s mom responds by giving her an apple.

The consequence for Callie’s requesting behavior was provided by another person, her mom. This requesting behavior is a verbal behavior.

A non-verbal behavior would be Callie being hungry, going to the refrigerator and getting and apple. Therefore the consequence of the behavior is not provided by another person.

It is important to note that verbal behavior is not the same as vocal behavior.

Extra Reading:  What is Verbal Behavior?

Vocal Behavior:

Is behavior that involves vocal output or speech. In practice, vocal behavior occurs when one speaks or produces sound with his or her voice. Vocal behavior can and often is a type of  verbal behavior, but there are forms of verbal behavior that are non-vocal.

Example:

Antecedent: Caiden is thirsty.
Behavior: Caiden shows his mom a picture of orange juice.
Consequence: Caiden’s mom gives him orange juice.

Caiden’s requesting behavior does not involve any vocal output or speech, therefore this behavior is not a vocal behavior. However, the consequence is provided by another person, so Caiden’s behavior is an example of verbal behavior.

Other methods of non-vocal verbal behavior are gesturing and sign language. The important thing to note is that behavior does not have to be vocal to be considered verbal.

B.F. Skinner

B.F. Skinner, behavioral pyschologist analyzed the antecedents and consequences to language and called this analysis of Verbal Behavior. Skinner’s Analysis of Verbal Behavior to classify and teach language to children with autism is a component of a strong EIBI program.

Extra Reading: B.F. Skinner Foundation

B.F. Skinner: Analysis of Verbal Behavior

Skinner’s analysis is a functional classification system.  Function refers to the circumstances under which a behavior occurs. This is determined by examining the antecedents and consequences associated with verbal behavior. Skinner identified several distinct functions of verbal behavior and titled them verbal operants. His analysis goes beyond the receptive/expressive classification system of language. It subdivides language or verbal behavior by function into verbal operants.

What are verbal operants?

The four most common are echoic, mand, tact and intraverbal. When considering verbal operants in terms of function the antecedents and consequences for each must be identified.

Echoic:

Vocal imitation. A verbal behavior that is controlled by and matches a verbal antecedent. The consequence for an echoic is nonspecific. A non specific consequence is not directly related to the verbal response through the child’s current desires. A nonspecific consequence is anything other than what is specified by the child’s verbal behavior. Echoic behavior occurs when a child imitates something heard and is then provided with an unrelated consequence.

Example:

Antecedent: Maura’s mom says “banana”
Behavior: Maura responds and says “banana”
Consequence: Maura’s mom praises Maura, “Excellent job, Maura!”

This is an example of echoic behavior because Maura’s response was controlled by and matched the verbal antecedent. And the consequence provided by her mom was nonspecific. Her mother did not provide Maura with a banana so the consequence was not directly related to Maura’s response.

An echoic behavior repertoire is very important to develop. An echoic repertoire can be used to develop other verbal operants: Mands, Tacts and Intraverbals. Because of this it is typically one of the first verbal operants taught in an EBEI

The echoic lesson in the Center for Autism and Related Disorders (CARD) language curriculum develops basic echoic behavior. The lesson typically involves four phases:

  1. Teaching a child to vocally imitate sounds: ie., buh for “b”, ah for “a” and ta for “t”. After acquiring several sounds, sound blends are taught.
  2. Teaching a child to vocally imitate sound blends: i.e., “at”, “wa”, “nt” After acquiring several sounds and sound blends, words are taught.
  3. Teaching a child to combine these sounds and blends together to form words: i.e., “bat”. After acquiring several words the child will be taught phrases and sentences.
  4. Teaching the child to link words together to form phrases and sentences. i.e., “I want bat” linking together the sounds and words to form the phrase, “I want bat”

Extra Reading: Center for Autism and Related Disorder Therapy Programs

Mand:

The term mand comes from the words Demand and Command. Manding behavior is often referred to as requesting or asking behavior and is directly related to the child’s desires. A mand is verbal behavior that is controlled by a motivative antecedent and followed by a consequence that is specific to that motivation. A specific consequence satisfies a current motivative antecedent and is specified in the response. In other words, the child specifies the desired consequence in his or her response. In practice, a mand occurs when a child wants or needs something, asks for it, and gets it.

Example:

Antecedent: Maura is hungry.
Behavior: Maura approaches her mom and asks for a banana.
Consequence: Maura’s mom gives Maura a banana.

This is an example of manding behavior because Maura’s response is controlled by a motivative antecedent or desire and followed by a consequence specific to that motivation. The consequence of receiving the banana is specific because receiving the banana is directly related to Maura’s desire and is specified in her response. In this example Maura directly stated the desired consequence in her response, although this often occurs in manding behavior, it is not necessary. For example, Maura could have slapped the counter instead of asking her mother. In both cases the consequence is specific, because the receipt of the banana satisfies Maura’s current desire and is specified or made clear by her response.

The development of a mand repertoire is crucial to a child’s success. There are several benefits associated with the acquisition of manding behavior. It decreases the frequency of inappropriate mands. Language is acquired faster by children when they are being taught to mand. Moreover, manding behavior facilitates the acquisition of other verbal operants. It is interesting to note that children tend to acquire mands faster than other forms of verbal behavior.

Manding can decrease the frequency of inappropriate mands. Many children with autism engage in problem behaviors which results in the receipt of a preferred item or the removal of a preferred item.

An example of an inappropriate mand: Brad and his grandmother are at the grocery store. There is candy at the register. Brad is hungry and wants candy. He cries. Grandmother gives Brad the Candy. In this situation, Brad’s crying behavior is a mand. His crying behavior is controlled by a motivative antecedent (He is hungry and wants some candy), it is followed by a consequence that is mediated by another person and is specific to his motivation when his grandmother gives him some candy. However, Brad’s crying behavior is a problematic and inappropriate mand. Over time, Brad’s grandmother stops taking him out in the community in order to avoid his crying behavior thus limiting Brad’s ability to participate in every day activities.

In Brad’s EIBI program, he is learning appropriate manding behavior. The Program Supervisor teaches Brad’s grandmother how to teach Brad to ask for candy instead of crying when standing in the supermarket check-out. Now, when Brad cries his grandmother does not give him candy. However, when Brad calmly asks for candy, he gets it. Over time, Brad learns to calmly ask for candy instead of crying when in the check-out line. Appropriate manding decreases the frequency of inappropriate mands.

Using Mand Behavior to develop Echoic Behavior:

Manding behavior facilitates acquisition of other verbal operants. Echoic behavior can be developed through teaching a child to mand.

  • Antecedent and consequence conditions for the man and echoic are initially combined.
  • Mand antecedent and consequence conditions are slowly removed over time.

Example:

Sophia’s therapist Stacey is teaching her to mand her favorite foods. Stacey is also teaching Sophia to vocally imitate sounds and words (echoic behavior). Initially, Stacey combines the antecedents and consequence conditions for these two verbal operants.

Sophia indicates her desire for a cracker by reaching for the cracker box. (The motivative antecedent for a mand). Stacey says “Cracker” (the vocal antecedent for an echoic). Sophia attempts to vocally imitate Stacey and says “Cacka” (The behavior). Stacey says, “Good job Sophia” the non specific consequence for the echoic, and then gives Sophia a cracker, the specific consequence for the mand.

Over time, Stacey slowly removes the mand antecedent and consequence conditions until only the echoic antecedent and consequence conditions remain. Of course, Stacey continues to teach Sophia to mand for her favorite foods, when Stacey is working on Sophia’s manding behavior she removes the echoic conditions for antecedent and consequence instead.

Manding behavior in the Center for Autism and Related Disorders (CARD) language curriculum is developed in several different lessons. Working on manding behavior within a lesson typically involves four phases:

  1. Teaching the child simple one-word mands: example within the objects lesson. A child is taught to mand for their favorite toys, using a one-word mand, “puzzle”. Once the child is taught to mand for several of their favorite toys, the lesson progresses to using mand frames.
  2. Teaching more complex mand frames: mand frames are short phrases such as “play with puzzle” or “I want puzzle”. Once the child learns to use mand frames, softened mands are taught.
  3. Teaching softened mand phrases and sentences: Softened mands are the inclusion of polite markers to the child’s mands, such as “please” and also using more complete sentences such as “Can I please play with the puzzle” Upon acquisition of softened mands, the lesson progresses to disguised mands.
  4. Teaching disguised mands: Teaching the child to show desire or interest through phrases like, “Wow, that’s a cool puzzle” or to stare longingly in the direction of the puzzle. Each of these would be disguised mands.

Mand behaviors are incorporated into many of the lessons of the CARD curricula.

Examples of Lessons within the Curricula:

  • In the people lesson, a child will be taught to ask for a specific person by name, such as “Mom”
  • In the actions lesson, a child will be taught to ask for assistance, such as “help open”
  • In the attributes lesson, a child will be taught to specify a preferred attribute, such as “red candy”
  • In the information lesson, a child will be taught to ask a question for information, such as “where are you going” or “when is dinner”

The development of a mand repertoire is crucial to a child’s success in that it results in a decrease of inappropriate and problematic mands, and facilitates the acquisition of other verbal operants as such manding behaviors. These are taught early in a child’s program. And an emphasis on manding behaviors continues through the initial months of treatment.

Tact:

The term tact comes from the phrase making contact with the environment and is often referred to as labeling. A tact is a verbal behavior that is controlled by a nonverbal antecedent and followed by a nonspecific consequence. In practice, tact behavior occurs when a child, sees, hears, smells, tastes, touches, or feels something and then says what has been seen, heard, smelled, tasted, touched or felt but does not receive it.

Returning to the example with Maura: Maura sees a banana in a decorative bowl on the counter (antecedent). Maura points to the banana and says, “banana” (behavior). Maura’s mom responds by saying, “That’s right Maura, it’s a banana” (consequence). This is a tact behavior because Maura’s verbal behavior is motivated by a nonverbal antecedent and followed by a nonspecific consequence (Maura does not get the banana, instead she receives social praise from her mom).

A tact benefits the listener because it provides information about what the speaker is seeing, hearing, smelling, tasting, touching or feeling. In this way, the development of a tact repertoire aids in the development of relationships and friendships.

Teaching tacting behavior involves:

  1. Starting with simple response forms: The child is taught to use one-word tacts, such as “hands”, “wash”, “bird”. Once this is acquired the child will learn complex tacts.
  2. Building the complexity of the response: this is putting together the action with the object, such as “wash hands” over time this will become more complex as the child learns to tact people, actions and objects, such as “mom is washing hands”. As this is developed the child will be able to add pronouns and prepositions, such as “mom is washing her hands in the sink”.

In the CARD language curriculum there are several lessons that develop tacting behavior.

  • Object lesson: a child may be taught to tact or label items while looking at a book.
  • Actions lesson: a child may be taught to tact by labeling the actions of a toy figure during pretend play
  • People lesson: a child may be taught to tact people by looking at photographs in a family photo album.

As a child progresses through their tacting lessons the tacting becomes more complex. Such as tacting an objects attributes, “big dog” to narrating a story by tacting the people, actions, emotions and location of a scene as the child looks at pictures in a book. Tacting an object that a child hears. Tacting the characteristic of an item that a child tastes. Or tacting a compliment by looking at the attributes of another’s work.

Tacting behavior is often one of the most difficult verbal operants to develop in a child with autism. Tacting behavior is followed by a nonspecific consequence, usually social praise. In some cases, non specific consequences may not be meaningful or important to a child with autism. In these cases, the nonspecific consequence is paired with a meaningful consequence, such as a food treat or favorite toy or activity. Over time, as the child develops a variety of tacts, the additional “meaningful” consequence is removed until only the nonspecific consequence remains.

Example of Tacting with additional meaningful consequence: Cora has not eaten in the past two hours and has indicated a desire for pretzels to her therapist. Cora is learning to tact different objects in her environment. Her therapist takes Cora outside to identify her neighbors dog. Cora says, “dog”. The therapist says, “good job Cora” and gives Cora a pretzel.

Over time as Cora learns to tact interesting things in her environment, the pretzel will slowly be removed until only the nonspecific consequence remains.

Intraverbal:

Intraverbal behavior is often referred to as conversational behavior. It is verbal behavior that is controlled by a verbal antecedent and does not match the the verbal antecedent. The consequence for intraverbal behavior is nonspecific. In practice, intraverbal behavior occurs when a child hears a question or comment, and then says something related to but different from what was heard, and does not get the item or thing named.

For example Olivia’s mom asks her, “what is your favorite fruit” (the antecedent). Olivia answers, “banana” (the behavior). Olivia’s mom says, “me too!” (the consequence). This is an example of intraverbal behavior because the verbal behavior is controlled by a verbal antecedent, the response or behavior does not match the antecedent and is followed by a nonspecific consequence.

Developing an intraverbal repertoire enables the child to talk about things that are absent. Much of what occurs in typical conversation is intraverbal behavior, two or more people discussing things that are absent.
Intraverbal behavior is also difficult to develop in children with autism. Like tacting behavior, it is maintained by social consequences and these consequences may not be meaningful to children with autism. If this is the case, like tacting, a specific consequence may be paired with the nonspecific consequence and over time the specific consequence will be removed until only the non specific consequence remains.

Another reason why intraverbal behavior is difficult is because things talked about are not physically present. Intraverbal behavior is controlled by a verbal antecedent alone. For this reason a non-verbal antecedent may be introduced when intraverbal behavior is first being taught and then one would systematically fade the non-verbal antecedent over time.

Example of Intraverbal: Jacob is teaching Grace to identify objects being described. Question: “What is green and hops” with the expected response, “Frog”. In the initial lesson Jacob will show Grace a picture of a frog and ask the question, “what is green and hops” (This is both a non-verbal and a verbal antecedent). Grace looks at the picture and says “Frog” (the behavior). Jacob says, “That’s right Grace!” (Consequence). Over time Jacob will fade out the non-verbal antecedent and until only the verbal antecedent remains. In this way Grace will learn to identify an absent item being described, an intraverbal behavior.

In the CARD Curricula there are several lessons that develop intraverbal behavior.

  • Music and Movement lesson: a child is taught to fill in the blank in familiar songs
  • Colors lesson: a child may be taught to identify the color of familiar objects
  • Episodic Memory lesson: a child may be asked to describe events that happened earlier, such as “what did you do at recess”
  • Statement – Question lesson: A child may be taught to answer a statement with a relevant question, such as “I went to the beach this weekend” and the child’s response, “Did you build a sandcastle?”

The incorporation of intraverbal behaviors into a child’s program plays an important role in the development of relationships and friendships.

Overview of B.F. Skinner’s Verbal Operants:

It is important that the child learn to use each word and concept across the functions of verbal behavior: Mand, Tact, Intraverbal and Echoic.

Pure and Impure Verbal Operants:

The four basic verbal operants are defined by specific controlling antecedents, and maintaining consequences. Only when these antecedent and consequence conditions are present the verbal operant is said to be pure. However, when the antecedent or consequence from two or more operants are present the verbal operant is said to be impure. In other words the use of a Mand, Tact and an Intraverbal antecedent to ellicit the desired behavior, resulting in specific consequence would be an impure operant.

It is important for a child to learn both pure and impure verbal operants. Both are necessary to communicate effectively in natural environments and every day circumstances.

 

Introduction to Behavioral Teaching Approaches and Procedures

When a child first enters a EIBI program, they are assessed by the BCBA to determine what skills need to be taught. Once these targets are identified the BCBA designs skill building lessons for teaching each individual skill target. Each lesson includes detailed instructions for teaching that specific lesson. Depending on the specific skill target and the unique needs of the child, the BCBA will identify the behavioral teaching approach to be used for each target.

Behavioral Approaches Used in EIBI Programs:

Discrete Trial Training

In discrete trial training the therapist or teacher guides the instruction by selecting a skill target to teach, and presents the instructions and or materials specified by the BCBA. Typically the child is presented with multiple opportunities to engage in the skill target. Additionally, training of the skill target is repeated until the child is able to respond independently and correctly (i.e, the target has been mastered according to the predetermined mastery criteria set by the BCBA). In discrete trial training skilled tasks are often taught in a specific sequence, building on each other to form more and more complex skills. In practice, discrete trial training as a teaching approach might look like:

  • The therapist selects a lesson and initiates the teaching interaction by presenting the specified instruction, question and/or an item.
  • Then the therapist helps the child engage in the specified response.
  • Finally, the therapist provides appropriate consequences based on the child’s response. 1) A reward for a correct response, or 2) An error correction procedure for an incorrect response. The consequence provided may or may not be a typical consequence  in the natural environment.

Example:

Julie is beginning a therapy session with Devon. Julie decides to begin the session by choosing the lesson, “following instructions”. One of the targets for the lesson is for Devon to sit when told to “sit down”. Julie approaches Devon and says, “Sit down” and then motions to a nearby chair. Devon sits in the chair. Julie then provides Devon with a piece of cookie and says, “Good sitting”.

This instructional sequence is initiated and directed by the adult. The small piece of cookie he receives as part of the consequence will not typically be provided in his natural environments. Over the course of the therapy session Julie will provide many opportunities for Devon to respond to the instruction. She will continue to work on the skill target until Devon is consistently responding independently and correctly.

Discrete trial training has been demonstrated to be successful in teaching a wide variety of skill targets in structured contexts. It is especially well suited for teaching skills that require repetition, such as learning to write and form letters correctly. It is also well suited for teaching skills that may not be intrinsically motivating to a child with autism such as tacting (identifying within environment) or responding to direction.

Natural Environment Training

In natural environment training the approach is largely directed by the child. This is because the child’s interests and motivations serve as the springboard for teaching skill targets. Natural environment training emphasizes the use of intrinsically motivating materials and considers the child’s current interests to guide instruction. The teaching is performed in the child’s every day natural settings. In practice, natural environment training as a teaching approach might look like:

  • The therapist joins the child in whatever the child is currently doing. The teaching is initiated by the child’s expression of interest in an item or topic.
  • Then the therapist helps the child engage in an expanded or more elaborate response related to that item or topic of interest.
  • Finally the therapist would provide a consequence related to the child’s interest that would typically follow the target response in the natural environment.

Example: 

Julie is beginning a therapy session with Devon. Julie walks into the kitchen and she sees Devon reaching for a cup of juice sitting on the kitchen counter. Julie says, “say juice”. Which Devon responds, “Ju”. Julie then gives Devon the cup of juice and he takes a drink. This instructional sequence occurs in a natural context, is initiated and directed by Devon’s current interest, and the consequence Devon receives for correct responding would typically follow this response in natural environments.

Natural environment training has been demonstrated to successfully build a wide variety of skills in the child’s natural environment, and is particularly well suited for teaching initiation skills, such as: gaining another’s attention, skills that are intrinsically motivating (i.e., juice for Devon).

Fluency Based Instruction

Fluency based instruction emphasizes responding accurately and quickly without hesitation. Typically the child is provided with several brief timed opportunities to practice the skill target. During each timing, the child repeatedly performs the skill target as quickly as possible while maintaining accuracy. Timed training is continued until the child can respond quickly and correctly. Similar to discrete trial training, fluency based training skill targets are often taught in a particular sequence, building speed and accuracy in basic skills before focusing on more complex skills. In practice, fluency based training as a teaching approach might look like:

  • The therapist selects a lesson, initiates the teaching interaction by presenting the specified instruction, question and/or item. The therapist also tells the child to perform the skill as quickly as possible.
  • The therapist then starts a timer according to the time specified for the target skill. Typically timing is very brief, ranging from 10 seconds to 1 minute. The therapist helps the child perform the skill quickly and repeatedly throughout the timing.
  • Finally, when the timing ends, the therapist provides appropriate consequences based on the child’s speed and accuracy. A reward for responding quickly and correctly, and an error correction procedure for any incorrect responses made during the timing. The consequence provide may or may not be a typical consequence in the natural environment.

Example:

Julie begins a session with Devon, with color lessons. Devon has learned to tact several different colors already.. The BCBA has determined using fluency based instruction to increase the speed at which Devon can name the colors. Julie hands Devon a stack of cards with several copies of the colors Devon has learned, she hands Devon the cards and says, “Say the colors as fast as you can”. She then starts a timer set for 15 seconds. During the timing Devon flips through the cards naming each one, while Julie cheers and reminds Devon to respond quickly. At the end of the timing, Devon had named all of the colors correctly and did so faster than he did the previous day. So Julie says, “Great job naming your colors so fast!” and lets Devon watch his favorite movie for several seconds. This instructional sequence involves responding both quickly and accurately during a timed practice, the timing is typically brief, and the skill is repeated multiple times for the duration of the timing. Over the course of the therapy session Julie will provide several opportunities for Devon to tact colors. She will continue to work on the skill target, increasing timing length and speed requirements until  Devon is consistently responding  quickly and accurately.

Fluency based instruction is particularly useful when teaching skills in which speed of responding is just as important as the accuracy of the response (i.e, reading, counting change, or riding a bike). It is problematic if a child can read accurately but so slowly that by the time he reaches the end of the sentence he has forgotten the words at the beginning, or counts change so slowly that a long line forms at the check-out counter, or pedals the bike too slowly to stay balanced. In these cases, fluency based instruction can be used to increase the child’s speed of responding to a point in which the child’s performance of the skill is considered truly competent. It is important to note that there is some overlap between discrete trial training and fluency based instruction.

Such overlap would be seen in learning to write. A child may learn to form letters in discrete trial training, but once a child has mastered forming their letters accurately the skill target would be better suited to fluency based instruction to increase speed and accuracy without hesitation.

Fluency based training also has several advantages beyond increasing the speed of skills that need to be performed quickly. First, when basic skills are learned to fluent levels, it is easier to learn related but more difficult skills later. Additionally, children who perform fluently are able to stay on task for longer periods of time  and retain information  longer. And finally, tasks that can be performed well are less aversive and less likely to occasion problem behavior.

Given these advantages, fluency based instruction is used to increase the speed and accuracy in a variety of skills in a variety of contexts.

Review:

Each of these behavioral teaching approaches provides instructional advantages for teaching specific skills to a child with autism. Because they compliment each other all three will likely be used during a child’s EIBI program. Each approach is a behavioral analytic approach scientifically validated to build particular skills in children with autism.  Each has its advantages and disadvantages. The BCBA will determine the approach used based on the skill target and the unique needs of each child. The BCBA will also provide detailed instruction on Behavioral Teaching Procedures for each target skill.

Behavioral Teaching Procedures:

  • Reinforcement
  • Prompt and Fading
  • Discrimination Training
  • Shaping
  • Chaining

Some of these will be used in every skill target that a child is taught, such as reinforcement. Others will only be used in a narrow set of specific circumstances.

Learn More…

The Discrete Trial

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