valence: in psychology, especially in discussing emotions, means the intrinsic attractiveness (positive valence) or aversiveness (negative valence) of an event, object, or situation.

validity: the extent to a test measures what it claims and was intended to measure.

values: involves one's principles or standards or judgments about what is valuable or important in life.

variable: in an experimental setting, any measured factor which shows variation across cases or conditions.

variable interval schedule: in operant conditioning, a schedule of reinforcement determined by the average time interval which must elapse since the last reinforcerbefore a response will be reinforced.

variable ratio schedule:in operant conditioning, a schedule of reinforcement determined by the average number of responses required to receive a reinforcer.

variability:in statistics, the dispersion of scores within a set of data.

ventro-medial hypothalamus: section of the hypothalamus, that when lesioned in a rats brain, the rat will demonstrate abnormal appetitive behaviour.

vicarious learning: see observational learning.

vicarious reinforcement: learning behaviour by observing others being rewarded for the behaviour.

visual agnosia: a general term for disorders which occur as a result of disruption of visual recognition.

visual cliff: an apparatus used to assess an infant's perception of depth, comprised of a thick pane of glass that covers a shall drop and a deep drop. Surfaces of both are covered with the same chequered pattern; however children of six months and older will not explore the deep?side which demonstrates depth perception.

visual pathways: the routes by which nerve impulses travel from the retina to the visual areas of the brain.

visual perception: the process by which sensory information from the eyes is transformed to produce an experience of depth, distance, colour, etc.

volume:an increase in magnitude of vibration in the air (measured in decibels). Sounds increase in volume as the amplitude of the waves increases.

voluntary response: a response which is controlled by the individual rather than being elicited by specific stimuli as reflexes are.

volunteer bias: participants who volunteer for a research investigation may differ on particular characteristics from non-volunteers, therefore comprising a non-representative sample.