Morgan, Melmoth & Solomon (2013)

Linking Hypotheses Underlying Class A And Class B Methods

Michael J. Morgan, Dean R. Melmoth, and Joshua A. Solomon

Abstract

“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.”

Relation To Present Research

In the earlier stages of the project, it was difficult to say with certainty whether the effects observed were the result of a perceptual bias (from participants’ adaptation to different motion speeds) or of a choice bias (from participants’ discomfort choosing one option disproportionately, even when doing so is correct). Using the methodology described by Morgan et al. (2013), which does not allow for such choice biases to affect the results, allows for the two possible causes to be disentangled.

Reference

Morgan, M. J., Melmoth, D., & Solomon, J. A. (2013). Visual Neuroscience, 30 , 197–206.  doi:10.1017/S095252381300045X