Certainties and mysteries in the within-trial contrast literature: A reply to Zentall (2008)

Contrary to Zentall’s (2008) hypothesis that extensive overtraining is required in order to obtain the work ethic effect in pigeons, we find no evidence of this in two separate paradigms designed to assess preference for stimuli encountered after high effort. In light of these findings, along with our previously published results and those of Arantes and Grace (2008), we maintain that the work ethic effect is not a reliable phenomenon in pigeons. On the other hand, we are uncertain about the reason(s) underlying the different preference profiles for high- versus low-deprivation stimuli as a function of successive versus simultaneous discrimination training (Vasconcelos & Urcuioli, 2008). Nevertheless, we disagree with Zentall that additional analyses of the sort he suggests support the conclusion that both training regimens yield within-trial contrast effects.     

Contrast and value: Beyond the work ethic effect. A reply to Zentall (2008)

Zentall (2008) challenges Arantes and Grace’s (2008) failure to replicate Clement, Feltus, Kaiser, and Zentall (2000) by suggesting that our results may have been due to insufficient training or to subjects’ experimental histories, and that our results are actually consistent with those of Clement et al. when examined closely. On the contrary, our pigeons received more training than Clement et al.’s did, and when an overall measure of preference on test trials was calculated, independent of the effect of initiating event that we reported, there was no evidence of preference for the stimulus preceded by the greater response requirement in our data. Although there have now been two unsuccessful attempts to replicate Clement et al.’s work ethic effect, there is evidence that in some situations, the value of a stimulus, as assessed by transfer tests, varies inversely with the context of reinforcement. It is important to look for convergent results using other procedures and transfer tests, such as resistance to change, to identify the principles that determine when contrast manipulations affect value and when they do not.     

Interpreting the differences: A reply to Kaufman

Kaufman's critique of our article was based on a misunderstanding of our purpose and procedures. This reply clarifies those points and suggests further areas of concern regarding the McCarthy Screening Test.