Godfrey, R., & Davison, M. (1998).
Effects of varying sample- and choice- stimulus disparity on symbolic matching-to-sample performance.
Journal of the Experimental Analysis of Behavior,
69, 311-326.
Six pigeons were trained on a typical two-stimulus two-response
symbolic matching-to-sample task involving the discrimination of
sample and choice stimuli that were signaled by different
probabilities that pixels in an area were lit on a computer
screen located behind the response keys. The disparities of the
sample and choice stimuli were systematically varied across five
experimental parts by manipulating the probabilities of pixel
illumination. Across conditions within parts, the ratio of
reinforcers obtainable for matching responses was varied over
five levels. A recent model of detection based on the
discriminability between the stimulus—response relations and
between response—reinforcer relations provided an effective
description of the data. Consistent with this model, changes in
the disparity of the sample stimuli led to decreases in
stimulus—response discriminability and left
response—reinforcer discriminability unchanged. Equally,
changes in choice-stimulus disparity caused a decrease in
estimates of response—reinforcer discriminability and not in
stimulus—response discriminability. Parameter invariance was
thus obtained, and the variables expected to affect these
parameters (sample and choice stimulus disparity) were correctly
identified. The reasons for the failure of two recently reported
studies to support parameter invariance under this model are
discussed.
Key words: detection, parameter invariance, matching to sample,
stimulus discriminability, response-reinforcer
discriminability, key peck, pigeons