Abstract

The incorporation of feedback into a person’s body schema is well established. The crossmodal congruency task (CCT) is used to objectively quantify incorporation without being susceptible to experimenter biases. This visual-tactile interference task is used to calculate the crossmodal congruency effect (CCE) score as a difference in response time between 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 CCT protocol that decreases the task exposure time. We show that the modified and shortened CCT protocol, which may be required to meet time or logistical constraints in laboratory or clinical settings, reduced the impact of the learning effect on CCT 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 CCT when designing experiments and suggests two mitigation strategies to improve the utility of this psychophysical assessment.

Highlights

  • There is an increasing interest concerning how the human brain represents the space surrounding its body due to converging findings from several different disciplines

  • In the present study we show evidence that congruency effect (CCE) scores decrease with repeated task exposure sessions and that this learning effect is persistent over time

  • To verify that the change in CCE score was due to a learning effect and not attributed to other interacting factors such as variability in motivation or baseline reactivity, we analyzed the congruency task (CCT) selection error rates, generalized reaction times measured from practice trials, and overall reaction times for congruent and incongruent stimuli

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Summary

Introduction

There is an increasing interest concerning how the human brain represents the space surrounding its body due to converging findings from several different disciplines. Other studies have investigated changes in the representation of peripersonal space that are elicited by the prolonged use of hand-held tools (Maravita et al, 2002; Holmes & Spence, 2004; Holmes, Calvert & Spence, 2007). It has been used in conjunction with the rubber hand illusion paradigm to investigate the degree of incorporation of a rubber hand into a person’s body schema (i.e., how strongly the rubber hand is experienced as one’s own hand) (Zopf, Savage & Williams, 2010; Zopf, Savage & Williams, 2013)

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