Crossmodal congruency effect scores decrease with repeat test exposure

The incorporation of feedback into a person’s body schema is well established. The crossmodal congruency effect (CCE) task is used to objectively quantify incorporation without being susceptible to experimenter biases. This visual-tactile interference task is used to calculate the CCE score as a difference in response time for incongruent and congruent trials. Here we show that this metric is susceptible to a learning effect that causes attenuation of the CCE score due to repeated task exposure sessions. We demonstrate that this learning effect is persistent, even after a 6 month hiatus in testing. Two mitigation strategies are proposed: 1. Only use CCE scores that are taken after learning has stabilized, or 2. Use a modified CCE protocol that decreases the task exposure time. We show that the modified and shortened CCE protocol, which may be required to meet time or logistical constraints in laboratory or clinical settings, reduced the impact of the learning effect on CCE results. Importantly, the CCE scores from the modified protocol were not significantly more variable than results obtained with the original protocol. This study highlights the importance of considering exposure time to the CCE task when designing experiments and suggests two mitigation strategies to improve the utility of this psychophysical assessment.