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VACUUM ACTIVITY : an ethological term referring to a response (see FIXED ACTION PATTERN) occurring not in the presence of the stimulus that usually produces it (see RELEASER), but rather in the presence of one that usually produces some other response (cf. VACUUM ACTIVITY). Displacement activity and vacuum activity depend on deprivation of opportunities to complete the fixed action pattern, but displacement activity is likely to occur at lower levels of deprivation than vacuum activity.

VACUUM ACTIVITY : An ethological term referring to responding (see FIXED ACTION PATTERN) in the absence of the stimulus (see RELEASER) that ordinarily produces it. Cf DISPLACEMENT ACTIVITY.

VAGANOTIC MEASUREMENT : Measurement in which units are defined in a way such that their meaning can vary within or across applications. See Box 5. 1 and Reading 3 in Readings.

VALIDITY : The extent to which observed values represent what the events that are the focus of interpretation. See Indirect measurement and Box 7.3.

VALUE : A set of behaviors, public and private, which a society reinforces.

VALUE-ALTERING PRINCIPLE : The pairing procedure converts a neutral stimulus into a learned reinforcer or learned aversive condition.

VALUES : Learned and unlearned reinforcers and aversive conditions.

VARIABILITY : Any differences among events. With regard to behavior, variations in features of responding within a single response class, as well as variations in the summary measures of that class across sessions or entire phases.

VARIABILITY : See STATISTICS. Variability is the raw material upon which selection operates. It is also a property for which contingencies can be arranged, but no single response can have variability because variability can only be a property of a population of responses.

VARIABLE : Any condition in an experiment, whether manipulable or merely observed, which can be changed or changes.

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