Backus, B.T. (2002) Perceptual Metamers in Stereoscopic Vision
Abstract
Theories of cue combination suggest the possibility of constructing
visual stimuli that evoke different patterns of neural activity in
sensory areas of the brain, but that cannot be distinguished by any
behavioral measure of perception. Such stimuli, if they exist,
would be interesting for two reasons. First, one could know that
none of the differences between the stimuli survive past the
computations used to build the percepts. Second, it can be
difficult to distinguish stimulus-driven components of measured
neural activity from top-down components (such as those due to
the interestingness of the stimuli). Changing the stimulus without
changing the percept could be exploited to measure the stimulusdriven
activity. Here we describe stimuli in which vertical and
horizontal disparities trade during the construction of percepts of
slanted surfaces, yielding stimulus equivalence classes.
Equivalence class membership changed after a change of vergence
eye posture alone, without changes to the retinal images. A formal
correspondence can be drawn between these “perceptual metamers”
and more familiar “sensory metamers” such as color metamers.
