Simple discrimination in ABA occurs when a learner responds differently across stimulus conditions because consequences differ. One stimulus signals reinforcement; another signals that the same response will not produce it. A sample does not change the correct comparison.
If touching green produces a point but touching red does not, green responding and red withholding may show discrimination. Verify response, consequence, and history rather than assuming color controls behavior.
What Is a Simple Discrimination in ABA?
A simple discrimination is stimulus control in which one stimulus condition or relevant dimension establishes differential responding. Responding is more likely with an SD correlated with reinforcement and less likely with an SΔ correlated with its absence.
“Simple” describes the stimulus relation, not task difficulty. Subtle cues or irrelevant features can make it hard; a complex task can still be simple if one condition signals reinforcement.
| Element | Question | Example |
|---|---|---|
| Stimulus condition | What antecedent stimulus is present or absent? | A green card is placed on the table. |
| Response | What observable behavior is being tested? | The learner touches the card. |
| SD relation | What happens when the response occurs in the SD condition? | Touching green produces a point. |
| SΔ relation | What happens in the comparison condition? | Touching red produces no point or programmed reinforcement. |
| Differential responding | Does response probability differ across conditions? | High responding to green and low responding to red. |
The BACB BCBA Test Content Outline, 6th edition addresses stimulus discrimination in B.13 and simple and conditional procedures in G.6.
SD, SΔ, and the Reinforcement Contingency
An SD does not force responding or mean the learner likes a stimulus. It signals a history of reinforcement for a response; an SΔ signals that the same response is not scheduled to produce it. Examine repeated consequences, not appearance.
A light may be an SD for pressing when pressing produces a message only while it is on, but an SΔ in another program. Functions depend on contingencies and history; always name the response and consequence.
| Term | Functional description | Example question |
|---|---|---|
| SD | A stimulus correlated with reinforcement for a specified response. | Does touching the green card produce the programmed point? |
| SΔ | A stimulus correlated with the absence of reinforcement for that response. | Does touching the red card fail to produce the point? |
| Reinforcement | A consequence that increases future probability of the response under relevant conditions. | Does the point or other consequence change later responding? |
| Differential reinforcement | Reinforcement is arranged for responding in one condition and not another. | Are the same response opportunities treated differently across stimuli? |
| Stimulus control | Behavior changes reliably as a function of the stimulus condition. | Is responding higher in the SD condition than in the SΔ condition? |
Absence of reinforcement is not punishment. No programmed consequence in SΔ may be discrimination training; an added aversive consequence is different. Distinguish planned SΔ from an implementation error.
Simple Versus Conditional Discrimination
In simple discrimination, one stimulus condition signals reinforcement. In conditional discrimination, a relation among multiple stimuli determines the correct response; in match-to-sample, the sample changes which comparison is correct.
Visual complexity is not enough. Ask whether one condition controls responding or another stimulus changes the options’ function. A choice array is not automatically conditional, and one card is not automatically simple.
| Feature | Simple discrimination | Conditional discrimination |
|---|---|---|
| Controlling relation | One stimulus condition directly signals reinforcement for a response. | A sample, context, or other stimulus changes which response or comparison is correct. |
| Typical arrangement | Go/no-go or SD versus SΔ training. | Match-to-sample or conditional selection. |
| Example | Press when the green light is on, not when it is off. | Select the comparison that matches the current sample. |
| Exam question | Which stimulus signals that the response will pay off? | Which stimulus changes the function of the available choices? |
| Common mistake | Calling every array or two-choice task conditional. | Ignoring the sample-to-comparison relation. |
See the conditional discrimination guide and simple-versus-conditional page for G.6 review.
Stimulus Control, Discrimination, and Generalization
Stimulus control is the broader relation in which a stimulus changes behavior probability. Discrimination is differential responding across conditions; generalization is responding across untrained stimuli or contexts. They are related but distinct.
A learner may discriminate green from red cards but fail to generalize the colors on a screen. Another may generalize across green stimuli while withholding for red. Program relevant control and prevent position, size, or adult movement from becoming the cue.
| Concept | What changes | Example |
|---|---|---|
| Stimulus control | The probability of a response changes in the presence of a stimulus. | Pressing is more likely when the light is on. |
| Stimulus discrimination | Responding differs across two or more stimulus conditions. | Pressing occurs with the on-light but not the off-light. |
| Stimulus generalization | The learned response occurs with similar untrained stimuli. | Pressing occurs with several similar lights. |
| Response generalization | New responses serving a similar function emerge. | The learner uses a switch, button, or gesture to request the same outcome. |
| Faulty stimulus control | An irrelevant feature controls responding instead of the intended stimulus. | The learner selects the left card regardless of its color. |
See the stimulus control and generalization guides. Identify the stimulus dimension and response pattern before choosing discrimination or generalization.
Examples of Simple Discrimination in ABA
Simple discrimination examples occur in teaching, communication, safety, and daily routines. Describe the contingency rather than apparent recognition. If a learner selects a blue cup because it is always on the left, rotate positions and test the relevant dimension.
In functional communication, a “break” card may signal a short break while a “finished” card signals another response. If the learner hands over either card to escape every task, discrimination is not established; measure correct and incorrect selections.
| Context | Possible SD and response | What to check |
|---|---|---|
| Safety | A stop sign signals stopping before crossing. | Whether the learner responds to the sign rather than an adult’s proximity. |
| Communication | A break card signals handing it over to access a break. | Whether the card produces the programmed outcome and alternatives are distinguished. |
| Sorting | A red item signals placing the item in a red bin. | Whether color, not position or bin size, controls sorting. |
| Technology | An illuminated button signals that pressing starts a device. | Whether the response changes when the light is absent. |
| Academic skill | A symbol signals selecting the matching written response. | Whether the learner can respond with varied materials and examples. |
| Daily living | A “wet hands” cue signals getting a towel. | Whether the cue functions in natural settings, not only during practice. |
A stimulus can have more than one function across programs. Tie the label to the response and consequence being analyzed.
Discrimination Training: A G.6 Implementation Sequence
Discrimination training begins with a clear target and repertoire assessment. Define stimuli, response, consequence, prompts, and mastery; arrange repeated SD/SΔ opportunities and evaluate differential responding.
Use errorless arrangements, prompt fading, differential reinforcement, or other individualized procedures. Avoid ambiguous arrays, undocumented consequence changes, and accidental cues.
| Step | Implementation question | Quality check |
|---|---|---|
| Define the target | What stimulus, response, and outcome are included? | Operational definitions and clear examples/nonexamples. |
| Assess prerequisites | Can the learner see, hear, attend, and emit the response? | Access, communication mode, motor demands, and response effort are considered. |
| Arrange the contingency | When is reinforcement available and when is it unavailable? | SD and SΔ conditions are consistent and feasible to implement. |
| Prompt strategically | How will errors be prevented or corrected? | Prompt hierarchy and fading plan are specified before teaching. |
| Reinforce discrimination | Is reinforcement differentially delivered for correct responses? | Consequence follows the target response promptly and reliably. |
| Probe without prompts | Does control persist when the teaching prompt is removed? | Independent performance is measured separately from prompted performance. |
Do not confuse prompting with final stimulus control. A prompt may guide responding temporarily; transfer control to the intended SD. If the learner responds only when an adult points, the prompt may still control behavior.
Measuring Discrimination and Detecting Errors
Data should show differential responding across conditions. Record opportunities, SD accuracy, SΔ responding, prompts, errors, and consequences; rotate positions and probe new examples.
Summaries can include percent correct, SΔ false alarms, latency, prompt level, and trial patterns. Add probes with new people, settings, positions, and materials; check integrity when data look flat or perfect.
| Measure | What it reveals | Possible interpretation |
|---|---|---|
| SD accuracy | Whether the learner responds correctly when reinforcement is available. | High accuracy suggests effective responding in the SD condition. |
| SΔ responding | Whether the learner withholds the response when reinforcement is unavailable. | High responding may indicate weak discrimination or a competing consequence. |
| Discrimination index | The difference between responding in SD and SΔ conditions. | A widening difference suggests stronger stimulus control. |
| Position analysis | Whether left, right, top, or bottom position controls selections. | Consistent position errors suggest faulty stimulus control. |
| Prompt level | How much assistance is needed for correct responding. | Accuracy with high prompts does not equal independent discrimination. |
| Generalization probe | Whether control transfers to untrained examples or contexts. | Performance may require additional programming even after acquisition. |
Position bias selects the left or first option; overselectivity uses a narrow irrelevant feature. Rotate positions, vary noncritical features, teach the intended dimension, and record errors.
Teaching Generalization, Flexibility, and Ethical Fit
After acquisition, vary materials and examples while preserving the relevant relation. Teach across people, settings, response forms, and natural routines; use safe realistic probes for safety skills.
Ethical fit includes communication mode, sensory access, preferences, culture, assent, and response effort. Do not force aversive or unsafe contact; use valid outcomes, protect refusal, and adapt inaccessible materials.
| Programming goal | Example strategy | Safeguard |
|---|---|---|
| Stimulus variation | Change color shade, size, font, voice, or material while preserving the relevant feature. | Confirm that the variation is accessible and not confusing beyond the target. |
| Position variation | Rotate the locations of choices across trials. | Keep the consequence relation consistent. |
| People and settings | Practice with different instructors and in natural environments. | Obtain assent and avoid unsafe community simulations. |
| Response flexibility | Accept equivalent communication responses when they serve the same function. | Do not treat one preferred motor or verbal form as the only valid response. |
| Maintenance | Thin programmed reinforcement while natural outcomes remain available. | Monitor whether performance and quality of life remain stable. |
| Self-advocacy | Teach the learner to ask for clarification or report a confusing cue. | Never reinforce discrimination by suppressing refusal or safety communication. |
Generalization should not be assumed because the learner performs in one room. Review the site’s generalization and maintenance guide; let data determine exemplars, prompts, consequences, or target revisions.
How to Analyze a Simple Discrimination Scenario
On a BCBA question, start with the contingency. Identify stimulus condition, response, and consequence, then ask whether one stimulus signals reinforcement or another changes which option is correct.
If blue alone signals reinforcement for touching a blue object, the relation may be simple. If a sample determines which comparison is correct, the relation is conditional.
| Scenario clue | Reasoning move | Likely conclusion |
|---|---|---|
| One light signals that pressing will produce a point. | Compare pressing with the light on and off. | Simple discrimination if the differential consequence establishes control. |
| A sample color changes which comparison earns reinforcement. | Ask whether the sample changes the function of the comparisons. | Conditional discrimination. |
| The learner always chooses the left card. | Check response pattern across rotated positions. | Possible position bias, not demonstrated color discrimination. |
| The learner responds correctly only after a point prompt. | Separate prompted accuracy from independent stimulus control. | Prompt control may still be present. |
| The learner responds to new examples without direct teaching. | Check whether the relevant stimulus dimension remains intact. | Stimulus generalization or generalized discrimination. |
| Consequences vary unpredictably across stimulus conditions. | Review implementation integrity and actual reinforcement history. | Weak or unstable stimulus control. |
The narrowest answer is best: identify SD, SΔ, simple or conditional discrimination, generalization, or faulty control from the stated antecedent and consequence.
BCBA Exam Traps, Checklist, and FAQ
Do not equate simple with easy, call every two-choice task conditional, label an SD without its response and consequence, or mistake a prompt or position cue for the intended stimulus.
| Exam wording | Concept to consider | Correction |
|---|---|---|
| “The response is reinforced in the presence of one stimulus.” | SD and simple discrimination. | Check the comparison condition and differential responding. |
| “The response is not reinforced in the presence of another stimulus.” | SΔ relation. | Do not call the absence of reinforcement punishment automatically. |
| “The sample determines which comparison is correct.” | Conditional discrimination. | Identify the relation among multiple stimuli. |
| “The learner chooses the first item every time.” | Faulty stimulus control or position bias. | Rotate positions and inspect error data. |
| “The learner responds to similar untrained stimuli.” | Stimulus generalization. | Do not confuse transfer with the original discrimination procedure. |
| “The learner is correct only with an adult prompt.” | Prompt control. | Measure independence and plan stimulus-control transfer. |
See the free BCBA mock exam after reviewing stimulus control and G.6. Checklist:
- Define the stimulus condition and response.
- Identify SD and SΔ consequences.
- Ask whether one stimulus or a relation controls responding.
- Check position bias and prompt control.
- Record SΔ withholding as well as correct responding.
- Vary irrelevant features.
- Probe novel relevant stimuli.
- Check generalization and maintenance.
- Protect assent, accessibility, refusal, and self-advocacy.
- Separate discrimination from conditional selection.
What is the simple discrimination definition in ABA? Differential responding because one stimulus signals reinforcement and another does not.
What is an SD? A stimulus correlated with reinforcement for a specified response; it does not force behavior.
What is the difference between simple and conditional discrimination? Simple uses one condition; conditional uses another stimulus or context to determine the correct response.
Is no reinforcement the same as punishment? No. No reinforcement in SΔ is not automatically punishment; punishment requires a consequence that decreases behavior.
How do I know whether discrimination is real? Measure SD/SΔ differences, rotate positions, remove prompts, vary irrelevant features, and probe novel examples.
A simple discrimination exists when one stimulus relation reliably changes whether a response produces reinforcement and data show intended control.
