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effect is evident when an attempt to reinforce a particular behavior through reward; when the rewards are finally withdrawn or reduced the subject is even less likely to exhibit that behavior than if he/she had never been rewarded.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 an 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 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. 
For example, at the beginning of a relationship one partner made 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.
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