The Relationship Between Reward-Related Motor Adaptation and Sensitivity to Punishment and Reward

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Table 1.1

Demographics of Participants

Male

Female

Age (avg)

Right-Handed

Left-Handed

28

123

20.52

134

16

Design

This was a quasi-experiment, meaning there was no random assignment to different groups as participants’ predispositions were different prior to the study and could not be manipulated. The between-groups design involved a single assessment and enabled predictions between innate tendencies and real-time actions. The sensitivity to either reward or punishment was the independent variable, measured by The Sensitivity to Punishment and Sensitivity to Reward Questionnaire (SPSRQ), while the dependent variable was the ability to adapt to the motor output requirement to achieve points, examined using the synchronous bimanual force task (Motor Adaptation Task (MAT)).

Materials

The SPSRQ (Torrubia, Avila, Moltò, & Caseras, 2001) was used to group participants based on either being more sensitive to reward or to punishment. To measure voluntary contraction through the squeezing of force transducers, the MAT was used, with participants completing 130 trials, scoring a point each time they adapted correctly.

Procedure

Commencing the study, participants were seated at a computer in a testing room and given two force transducers (one for each hand). Participants then squeezed the transducers as hard as they could to calibrate the individual’s strength, measuring for Maximum Voluntary Contraction (MVC). Students then completed a trial of the transducers to help participants acclimatise to the task’s requirements. During the test, participants had to produce a specific force (over 130 trials) within a zone in response to a high-pitched tone (500ms after). If they adapted correctly, they scored 1 point for each hand. Once concluded, participants completed a questionnaire measuring their sensitivity to reward and punishment.

Results

The raw data acquired from the scores on the MAT and SPSRQ were computed and analysed using the Statistical Package for the Social Sciences (SPSS). An independent samples t-test (alpha=.05) was used to assess MA between those who were more sensitive to reward (n=56) and those more sensitive to punishment (n=95). It was shown that approach learners scored higher (M=154.59, SD=43.48) on the MAT compared to avoidance learners (M=139.58, SD=39.07), t(149)=2.19, p=.015, one-tailed, 95% CI [-28.58,-1.44]. This test had small-medium effect size, d=0.37, and showed statistical significance. Levene’s test was found to be non-significant, allowing for equality of variance to be assumed. Using Pearson’s correlation, the strength and direction of the relationship between sensitivity to punishment/reward and scores on the MAT was measured. A significant positive relationship was observed for the sensitivity to reward correlation, r(151)=.27, p=.001, one-tailed. Sensitivity to punishment showed no correlation however, r(151)=.01, p=.954, one-tailed. To test the second hypothesis, a linear regression analysis was used, analysing whether scores on the sensitivity to reward questionnaire, could be used to predict corresponding scores on the MAT. It was found that results on the SR questionnaire did significantly predict scores on the MAT, F(1,149)=11.99, p=.001, accounting for 7.4% of the variability in MAT scores (adjusted R^2=.07). Contrastingly, for the third hypothesis, tests for normality, linearity and homoscedasticity were not supported. It was found that scores on the SP questionnaire did not significantly predict scores on the MAT, so a linear regression was not included.

Discussion

The results of the study, as was hypothesised, revealed that participants showing greater sensitivity to reward display better motor adaptation than those who were more sensitive to punishment. This would suggest that like what was predicted, dopaminergic pathways and positive reinforcement may play a more vital role in the speed and accuracy of adaptation (Awenowicz & Porter, 2002). Similarly, as hypothesised, scores on the sensitivity to reward questionnaire did accurately and significantly predict corresponding scores on the MAT. Following this, scores on the sensitivity to punishment questionnaire did not accurately predict comparable scores on the MAT, which was expected.

The results showed, as well as reward being better than punishment at improving the rate of adaptation, that scores on the sensitivity to reward questionnaire were a better predictor of corresponding scores on the MAT. This was abnormal in the context of past research, with previous studies' results indicating that the systems involved with punishment in the form of feedback contributed more to the rate of learning, or in this case, adaptation. It also contrasts the results of (Wachter et al. 2009) study, which stated that although positive reinforcement contributed to motor adaptation, it improved the retention of the motor action, rather than the speed of adaptation. However, this experiment's results did coincide with the theory that the dopamine-reward system was largely associated with learning, contributing to both the speed and retention (Awenowicz & Porter, 2002).

Despite this study providing significant results on the intricacies of motor adaptation, there were some factors that could have limited the study's replicability and external validity. The major gender difference, highlighted by having three times more females, could have heavily influenced the results, as the average adaptation scores for each gender could have been significantly different. For future research, the use of convenience sampling may need to be reconsidered, as a different sampling method (e.g. random sampling) may be able to provide a more generalisable and valid sample.

The study's main aim was to analyse sensitivity to reward in relation to MA, however, the 'reward' used to act as motivational feedback was not a strong stimulus, with 'scoring a point' deemed the reward. This could have been detrimental as sensitivity to reward was being used as an IV, and the reward may not have been