Understanding Psychology (10th Ed)

validity

 
The property by which tests actually 
measure what they are supposed to measure 
(Module 26).

variability

 
The spread, or dispersion, of scores 
in a distribution (Module 57).

variable-interval schedule

 
A schedule by 
which the time between reinforcements varies 
around some average rather than being fi xed 
(Module 18).

variable-ratio schedule

 
A schedule by which 
reinforcement occurs after a varying number of 
responses rather than after a fi xed number 
(Module 18).

variables

 
Behaviors, events, or other charac-
teristics that can change, or vary, in some way 
(Module 5).

visual illusions

 
Physical stimuli that consis-
tently produce errors in perception (Module 13).

wear-and-tear theories of aging

 
Theories 
that suggest that the mechanical functions of 
the body simply stop working effi ciently 
(Module 39).

Weber’s law

 
A basic law of psychophysics stat-
ing that a just noticeable difference is a constant 
proportion to the intensity of an initial stimulus 
(rather than a constant amount) (Module 10).

weight set point

 
The particular level of weight 
that the body strives to maintain (Module 30).

working memory

 
A set of active, temporary 
memory stores that actively manipulate and 
rehearse information (Module 20).

zone of proximal development (ZPD)

 
Accord-
ing to Vygotsky, the level at which a child can 
almost, but not fully, comprehend or perform a 
task on his or her own (Module 37).