Linking hypotheses underlying Class A and Class B methods.
Class A psychophysical observations are based on the linking hypothesis that perceptually distinguishable stimuli must correspond to different brain events. Class B observations are related to the appearance of stimuli not their discriminability. There is no clear linking hypothesis underlying Class B observations, but they are necessary for studying the effects of context on appearance, including a large class of phenomena known as "illusions." Class B observations are necessarily measures of observer bias (Fechner's "constant error") as opposed to Class A measures of sensitivity (Fechner's "variable error"). It is therefore important that Class B observations distinguish between response biases, decisional biases, and perceptual biases. This review argues that the commonly used method of single stimuli fails to do this, and that multiple-alternative forced choice (mAFC) methods can do a better job, particularly if combined with a roving pedestal.
Max-Planck Institute for Neurological Research, Cologne, Germany.
M J
MJ
Morgan
Division of Optometry and Visual Science, City University London, London, UK.
D
D
Melmoth
Division of Optometry and Visual Science, City University London, London, UK.
J A
JA
Solomon
D006801:Humans; D007088:Illusions / Q000145:classification / Q000502:physiology*; D009039:Motion Perception / Q000145:classification / Q000502:physiology*; D011601:Psychophysics / Q000145:classification* / Q000379:methods* / Q000592:standards