The influence of catch trials on response caution – a diffusion model analysis

In typical response time tasks, catch trials are trials in which no stimulus is shown and participants accordingly do not have to respond. In previous studies, it has been assumed that stimulus expectancy–operationalized via the frequency of catch trials–affects response caution. For conditions with a higher proportion of catch trials enhanced response caution is expected. However, higher proportions of catch trials might also lead to less practice regarding the actual binary decision task, manifesting in reduced speed of information processing or longer encoding or motor execution times. By means of diffusion modeling we examine data from one of the studies that aimed at influencing response caution via a catch trial manipulation. Furthermore, we present data from a new study in which we systematically varied the proportion of catch trials. We consistently find longer non-decision times for conditions with higher proportions of catch trials, whereas the pattern is less clear-cut for drift rate and threshold separation. By means of a parameter recovery study, we further show that the effect in non-decision time is not driven by trade-offs in parameter estimation. In sum, the catch trial manipulation might be a questionable manipulation of response caution as it does not selectively influence threshold separation.