The Bergen left-right discrimination test: practice effects, reliable change indices, and strategic performance in the standard and alternate form with inverted stimuli.

Several authors pointed out that left-right discrimination (LRD) tasks may be entangled with differential demands on mental rotation (MR). However, studies considering this interrelationship are rare. To differentially assess LRD of stimuli with varying additional demands on MR, we constructed and evaluated an extended version of the Bergen right-left discrimination (BRLD) test including additional subtests with inverted stickmen stimuli in 174 healthy participants (50♂, 124♀) and measured subjective reports on participants' strategies to accomplish the task. Moreover, we analyzed practice effects and reliable change indices (RCIs) on BRLD performance, as well as gender differences. Performance significantly differed between subtests with high and low demands on MR with best scores on subtests with low demands on MR. Participants' subjective strategies corroborate these results: MR was most frequently reported for subtests with highest MR demands (and lowest test performance). Pronounced practice effects were observed for all subtests. Sex differences were not observed. We conclude that our extended version of the BRLD allows for the differentiation between LRD with high and low demands on MR abilities. The type of stimulus materials is likely to be critical for the differential assessment of MR and LRD. Moreover, RCIs provide a basis for the clinical application of the BRLD.