Effects of repeated trials on the strategy used for a hand laterality judgment task.

The hand laterality judgment task requires participants to determine whether a picture of a hand, presented at various rotational angles, depicts a left or right hand. Several strategies have been suggested to be involved in task performance: in particular, palm-view pictures are thought to rely on motor imagery (MI), whereas back-view pictures are thought to rely on 'nonMI' (i.e., without motor imagery) strategies, including visual imagery (VI). However, the influence of repeated task execution on performance strategies remains unclear. This study examined the relationship between self-reported strategies and response time (RT) profiles during a 512-trial hand laterality judgment task in 42 healthy adults. Based on post-task self-reports for palm-view pictures, participants were classified into the MI group, consistently using MI throughout the trials, and the MI-nonMI group, switching from MI to nonMI during the repeated trials. In the MI group, RT profiles consistently showed longer RTs for lateral palm-view pictures (outward-pointing fingers) than for medial orientations (inward-pointing fingers), characteristic of MI use, across both halves of the task. The MI-nonMI group showed similar RT patterns initially, but in the second half, RT differences between lateral and medial orientations diminished, suggesting a shift toward VI-like characteristics. These findings suggest that although both groups may have used MI, RT trends varied according to the participants' self-reported strategies. In the MI group, both explicit self-report and implicit RT profiles indicated sustained MI use, whereas the MI-nonMI group, self-reports indicated a strategy shift to nonMI, and their RT profiles suggest a combined use of MI and nonMI.