Zentall, T.R. & Singer, R.A. (2007).
Within-trial contrast: when is a failure to replicate not a Type I error?
Journal of the Experimental Analysis of Behavior, 87, 401-404.
Vasconcelos, Urcuioli, and Lionello-DeNolf (2007) report the results of five experiments that fail to replicate
the results of our within-trial contrast study (Clement, Feltus, Kaiser, & Zentall, 2000) and suggest that our
results may represent a Type I Error. We believe that this conclusion is not warranted because (a) there is
considerable evidence in support of the effect and (b) the amount of training that they gave to their pigeons
prior to test may not have been sufficient to observe the effect reliably. We suggest that when sufficient
training is provided, reliable contrast can be found.
Key words: work ethic, simultaneous discrimination, within-trial contrast, Type I Error, overtraining, key peck, pigeons