The major theories of aversive control consist of the two-factor theory, the operant theory, the cognitive theory and the biological theory. Of these four theories, it is generally accepted that the two-factor theory is the dominant theory within the group. This is largely because the theory views the avoidance and punishment aspects of aversive conditioning as belonging to both Pavlovian and operant influences, hence the two-factor theory of nomenclature. In the case of a bright light presented before a shock, the shock is then escaped, creating reinforcement: the shock is terminated. When each shock is avoided, Pavlovian conditioning begins to form through the association of the light with the shock until eventually a pairing forms. In this phase the light has come to represent fear for the subject, who will now try to escape the CS associated with the fear. However, fleeing the CS is essentially the same as avoiding the United States. As such, two-factor avoidance theory appears to show that avoidance is in fact not really avoidance, but rather escape from a CS paired with the initial shock. In other words, because escape is vital to successful avoidance behavior, the theory holds that the Pavlovian, as well as operant elements, manage and support avoidance. Indeed, the two-factor theory will explain a Pavlovian CS even when no stimulus is presented. In this case the time comes to represent the CS. If the US occurs at regular intervals, the simple passage of time will serve as the CS. As for punishment in the two-factor theory, this Pavlovian conditioning must arouse fear in the subject. When the punished response is given, the subject will experience fear, however, if the subject experiences a response other than punishment res… middle of paper… the theory resembles previous theories in many ways. Emphasis is the distinguishing factor of this theory, and that emphasis is on a set of defensive responses that Bolles argues that every species has. He called these species-specific defense reactions, or SSDFs. Although SSDFs can occur randomly, it is believed that they most likely follow a hierarchical scale. In biological theory a response similar to an SSDF would result in rapid learning, while a response that does not would result in the opposite. Looking more closely at the relationship between biological theory and cognitive theory we can see that, although similar in some respects, biological theory is decidedly distinct. In short, while cognitive theory addresses what happens after a response occurs, biological theory's focus lies in what determines the first occurrences of those responses..