Longer duration intertrial intervals without visual stimuli have reinforcement value and increase the rate of reinforcement and punishment learning in computer-based discriminations in humans

Abstract

In two experiments, we examined the motivational value of the duration of intertrial intervals and/or task delays on responding in a computer-based task in humans. In both experiments, four color stimuli with different response contingencies were displayed. Participants freely decided if they want to make a response or not towards each stimulus. The outcome that followed was either a putatively pleasant visual feedback (a “smiley face” display) or a blank screen, which was contingent on whether a response was made or withheld differently for different color stimuli. Our key manipulation was whether this blank screen outcome was longer or shorter than the visual feedback, that is whether the blank screen outcome made the next trial start sooner, later, or with the same delay as earning the visual feedback. We found 1) increased reinforced responding for encouraging visual feedback and 2) faster reinforcement and punishment learning to respond or withhold responding for this visual feedback if there was a longer duration blank screen outcome on trials in which people did not earn the visual feedback. This effect appeared to be driven more by the absolute length of the blank screen stimulus rather than whether it increased the delay until the start of the next trial more than the visual feedback. Additional research is needed to investigate boundary conditions that may determine when these blank screens do/do not have this motivational effect. Our findings suggest that manipulating task delay may be a way to increase motivation in laboratory studies in humans and possibly minimize individual differences in motivation due to differing sensitivity to demand characteristics in individual participants. However, additional research is needed to eliminate alternative explanations for this effect, such as an effect in which longer blank screen presentations led to better learning by preventing poorer learning that can be observed after massed trial presentations.