The Effects of Reward and Incentive on Performance on the Symbol Digit Modalities Test (SDMT) in MS

Background: The Symbol Digit Modalities Test (SDMT) is one of the most commonly used measures in the evaluation of cognition in multiple sclerosis (MS); it is generally regarded as a measure of processing speed. Effort is an important component in the measurement of cognitive performance and the role of motivation in effort is well established.

Objectives: To examine the effect of a reward paradigm on patient performance at the SDMT in MS.

Methods: This research is being conducted as part of a large, ongoing, study at the MS Center of Holy Name Medical Center in Teaneck, NJ. N= 20 patients with definite MS have been recruited so far (current to the date of submission of this abstract). The study is being carried out using the Symbol Digit Modalities test (SDMT), a well validated cognitive measure in MS. Each patient is being administered the SDMT twice with approximately 3 to 5 minutes between each administration. The two administrations of the SDMT include a monetary reward condition, wherein performance is incentivized through financial reward, and a control condition, with no reward offered for performance. Individual performance on the SDMT is being compared between the reward and no reward administration. Counter-balancing is being employed to control for learning effects.

Results: Mean (and standard deviation) for total scores on all SDMT trials (N= 40) was 53.1(14.5). Mean total score for the control trial (n=20) and the reward trial (n=20) of the SDMT were 52.4(13.9) and 53.6(14.2) respectively. This difference was not significant (t= -1.035, p= .314).

Conclusions: Results are preliminary, due to the small sample size; however, the reward paradigm appears to have no significant effect on performance. It appears that the function measured by total performance on the SDMT is relatively stable in response to reward/incentive based motivation.