Behavioral contrast

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Behavioral contrast or behavioural contrast (also known as negative contrast effect and positive contrast effect} is the change of response rate or response latency following changes in one component of a multiple operant discrimination schedule of reinforcement.

Behavioral contrast refers to a change in the strength of one response that occurs when the rate of reward of a second response, or of the first response under different conditions, is changed. It occurs in some two choice discrimination tasks where increased response rates to one stimulus (S1) are accompanied by a decreased response rate to the other stimulus(S2) and vice versa. Where a changed shedule of reinforcement is introduced for S1 , to either increase or decrease the reponse rate, a contrasting change is seen in responses to S2.

For example, suppose that a pigeon in an operant chamber pecks a key for food reward. Sometimes the key is red, sometimes green, but food comes with equal frequency in either case. Then suddenly pecking the key when it is green brings food less frequently. Positive contrast is seen when the rate of response to the red key goes up, even though the frequency of reward in red remains unchanged. Likewise, increasing the reward to green tends to reduce the response rate to red (negative contrast). This sort of contrast effect may occur following changes in the amount, frequency, or nature of the reward, and it has been shown to occur with various experimental designs and response measures (e.g. response rate, running speed).

History of contrast effects

The phenomenon was first identified by G.S. Reynolds. In 1942, Crespi measured the speed of rats running to various amounts of reward at the end of an alley. He found that the greater the magnitude of reward, the faster the rat would run to get the reward. In the middle of his experiment Crespi shifted some of his animals from a large reward to a small reward. These animals now ran even more slowly than control animals that had been trained on small reward throughout the experiment. This overshoot is an example of successive negative contrast. Likewise, other animals shifted from small to large reward ran faster than those trained on the larger reward throughout (successive positive contrast). Crespi originally called these effects depression and elation respectively, but, in 1949, Zeaman suggested changing the names to negative contrast and positive contrast. In 1981, Bower discovered that positive contrast may be reduced because the response measure hits a ceiling. Thus, reward sizes need to be adjusted to keep the response below such a ceiling. In 1996, Flaherty suggested that negative contrast was related to frustration; that is, the sudden shift to a low reward causes frustration for the person or the animal, and this frustration interferes with the behavior the subject is performing.

Negative (Positive) Contrast Effect in Operant Conditioning

In the behavioral theory of operant conditioning, the negative contrast effect is evident when an attempt to reinforce a particular behavior through reward, when the rewards are finally withdrawn or reduced the subject is even less likely to exhibit that behavior than if he/she had never been rewarded. The theory is that the subject will view the task as work, for which he is only temporarily rewarded, rather than enjoyable or and end in itself such as play. For example rewarding children for reading may be counter-productive in the long run, as they may view it as a chore

Conversely, the positive contrast effect is that when rewards are increased, the subject shows an even greater frequency of the behavior than subjects who had been rewarded with the higher quantity all along.

Negative (Positive) Contrast Effect in Relationships

In the assessment of interpersonal relationships, this would be the tendency for an individual to utilize the history of a performance (by an individual or a process) to determine their expectations relative to a current level of performance. A form of behavioral ‘compare and contrast’; in that if an individual’s history of a particular behavior improves (increases), this will be perceived by the receiving individual as a positive contrast effect. If a person’s behavior (or some process) diminishes or is degraded in any fashion historically related to a similar event or set of events, this will be perceived as a negative contrast effect.

In example, at the beginnings of a relationship one partner put forth significant efforts in supplying love, care or attention to another person and the receiving party enjoyed and reacted positively to these efforts. However, at a later date, these practices diminished or were omitted to some degree (the expectation of the other partner not being met or the behavior not persisting or increasing), the receiving partner would experience a negative contrast effect.

However, if the reverse was to happen and the partner started out with a lesser degree of love, care or attention and were to increase the practice over time, the receiving person would experience a positive contrast effect.

Thus the adage, “Don’t pick up his socks the first time unless you intend to pick them up forever!”

See also

• Behaviour
• Reinforcement
• Reinforcement in operant conditioning
• Response frequency
• Stimulus discrimination