V

vaginismus A sexual dysfunction of women characterized by involuntary muscle spasms that cause the vagina to shut tightly so that penetration by a penis is extremely painful or impossible. 11

valid (validity) An essential criterion in determining the value of a test. A test is valid if it measures what it is supposed to measure. 14

variable-interval (VI) schedule An unpredictable and irregular partial reinforcement schedule in which there is no perceived relationship between the time elapsed and the frequency of rewards. 6

variable-ratio (VR) schedule An unpredictable and irregular partial reinforcement schedule in which there is no perceived relationship between the number of responses and the number of rewards. 6

variables Factors capable of change. 2

vicarious reinforcement and punishment Environmental consequences following the behavior of others that affect how an observer will behave. 6

violent pornography Material that combines sexual explicitness with violence. 18

volley principle A theory that explains why people can hear high-frequency sound. It is based on the assumption that the frequency of neural firing that the brain detects is determined not by the rate of firing of single neurons but rather by groups of neurons. 4