Is the occurrence of two or more related stimuli eliciting the same reaction. In the context of an arbitrary matching to sample method, for example, if a stimulus is picked when it also appears as a sample, reflexivity has been demonstrated. The presence of stimulus reflexivity can be established by using multiple methods; for example, presenting several samples and comparing their properties with those of a single sample obtained via sampling.
Stimulus equivalence procedures are methods used to demonstrate that two or more stimuli are equivalent in some way. They can be divided into three broad categories: direct methods, indirect methods, and correlational methods. Direct methods test whether two items are actually the same object or not. If they are, then one would expect identical responses to be generated when each item is presented individually and as part of its pair. Indirect methods try to establish similarity between pairs of items without first determining whether they are the same object or not. For example, two objects may look the same but generate different responses when pressed with a key at exactly the same time. Correlational methods examine relationships between sets of variables. For example, if one increases value of one variable (such as price) another variable (such as profit) will usually increase as well. There is no reason why increased price should not lead to increased profits, but there may be factors other than price that influence sales.
If stimuli can be proved to display reflexivity, symmetry, and transitivity, they fulfill the mathematical concept of equivalence. The implication is that if one stimulus is presented long enough and frequently enough, it will elicit a response.
Stimulus equivalence occurs in animal behavior when an animal reacts equally to two or more stimuli. For example, if a dog is given two pieces of meat and then allowed to choose which he would like next, he will always pick the same piece each time. This means that the meat was not only tasty but also equivalent in his eyes. Stimuli that are equivalent should never be used together as this could lead to a repetition compulsion occurring. For example, if a person keeps giving a dog a bit of food after it has eaten already, this would be an improper use of food rewards because it would be triggering a response - eating more!
In ABA, stimulus equivalence is important because it is based on reflexive, symmetrical, and transitive properties. These are four-way relationships that can be established between any two items. If they display these characteristics, they are considered equal.
To fulfill the concept of equivalence, a positive evidence of reflexivity, symmetry, and transitivity is required. A sort of stimulus-to-stimulus interaction in which the learner exhibits the reversibility of matched sample and comparison stimuli without prior training or reinforcement. The term "associative" has been used instead, but this term has other meanings as well.
The concept of equivalence implies that there are similarities between two objects that are sufficient to consider them equal. These similarities can be visual (such as colors, shapes, and sizes), physical (for example, electrical charge), or conceptual (for example, political systems). Two objects are considered equivalent if there is no way to tell them apart without using information beyond their physical properties. For example, it would be impossible to distinguish red and green cars by looking at them, so they are considered equivalents. Objects that are not equivalents include identical items (i.e., pairs of shoes, pairs of pants), non-identical duplicates (i.e., copies of books, tapes, or videos), and substitutes (i.e., alternatives for something lacking a corresponding object; e.g., knives for spoons). Identical items and duplicates can be used as controls in experiments testing how people learn about new concepts or ideas. Substitutes can be used in teaching situations where one thing is replaced with another object that serves the same function.
The development of unreinforced or untrained responses based on a restricted group of learned responses is referred to as the derived stimulus relation of equivalence (Barnes-Holmes, Barnes-Holmes, & Cullinan, 2000; Barnes-Holmes, Finn, McEnteggart, & Barnes-Holmes, 2018). For example, if a dog learns that when he pulls down on his leash he will be given a toy, then when he pulls down on his leash in the presence of another dog, the other dog will also get excited and pull down on his leash. This is called a derived stimulus relation of equivalence between pulling down on one's leash and getting toys delivered.
Dogs also derive a stimulus relation from the pairing of a neutral stimulus with a rewarding one. For example, if a dog sees someone else being given a tasty food treat, he will come to expect food rewards for any neutral activity performed while standing next to the person giving out the treats. This is called a derived stimulus relation of association because the dog is learning that performing a neutral action leads to receiving a reward.
Finally, dogs can learn something about cause-and-effect by observing humans. If someone picks up something hot and yells "Ow!" then the dog learns that yelling "Ow!" causes people to give him attention and comfort, even if he has not done anything wrong. This is called a derived stimulus relation of consequence because the dog is learning that doing something dangerous leads to punishment.