 
Summary: Psychological Review
1986, Vol. 93, No. 2, 154179
Copyright 1986 by the American Psychological Association, Inc.
0033295X/86/S00.75
Varieties of PerceptualIndependence
F. Gregory Ashby
Ohio State University
James T. Townsend
Purdue University
Several varieties of perceptual independence are investigated. These include sampling independence,
dimensional orthogonality, stimulus separability and integrality, and performance parity. A general
multivariate perceptual theory is developed, and a precise definition of perceptual independence is
offered. Each of these related concepts is then examined within the framework of this theory, and
their theoretical interrelationships are explicated. It is shownthat none of the concepts are equivalent
to perceptual independence but that if separability holds, then sampling independence is equivalent
to perceptual independence. Several simple tests of separability are suggested that can be applied to
the same data as sampling independence. Dimensional orthogonality isshownto test for independence
only if some strongdistributional assumptions are made about the perceptual effects of stimuli.Reaction
time and informationbasedperformance parity criteria are examined. The potential forempirically
testing each of these concepts is discussed.
