Bimanual interference associated with the selection of target locations.

Diedrichsen, Joern; Ivry, Richard B.; Hazeltine, Eliot; Kennerley, Steven W.; Cohen, Asher · 2003 · Journal of Experimental Psychology Human Perception & Performance

DOI: 10.1037//0096-1523.29.1.64

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Summary

This study investigates the specific processing stage responsible for bimanual interference, the performance cost observed when individuals execute simultaneous movements with different spatial characteristics. While previous research attributed this interference to motor programming conflicts, the authors hypothesized that the bottleneck occurs earlier, during stimulus identification and response selection. To test this, three experiments examined whether interference arises from the kinematic properties of movements or the selection of target locations. Experiment 1 utilized a mirror-reflecting apparatus where participants reached toward colored targets. The design manipulated the congruency of movement amplitudes (same vs. different) and target colors (same vs. different). In a "crossed" condition, identical target colors required movements of unequal amplitude, while different colors required equal amplitudes. Results showed that reaction times were fastest when target colors were identical, regardless of movement amplitude. Conversely, when colors differed, reaction times slowed, even if movement amplitudes were congruent. This pattern contradicted the motor programming hypothesis, which predicted faster initiation for equal amplitudes. Instead, the data indicated that interference stems from the difficulty of selecting targets defined by different colors, suggesting a response-selection bottleneck. Experiment 2 refined these findings by removing explicit cues, requiring participants to select targets based on fixed rules amidst distractors. The study compared conditions where both hands targeted the same color versus different colors, and whether distractors were irrelevant or relevant (i.e., matching the target color of the opposite hand). Results confirmed that reaction time costs occurred when targets were defined by different colors. Crucially, interference was exacerbated when distractors were relevant, indicating that the cost arises from an assignment problem where response rules must be mapped to respective hands amidst competing visual information. The significance of these findings lies in redefining the locus of bimanual interference. The study demonstrates that the limitations in coordinating two hands are not primarily due to mechanical or programming conflicts between limbs, but rather cognitive constraints in selecting movement goals. This aligns bimanual coordination with dual-task paradigms in cognitive psychology, specifically highlighting a response-selection bottleneck. The results imply that the brain struggles to process and assign distinct response rules to two hands simultaneously when visual cues are not identical, rather than struggling to program different motor parameters.

Key finding

Bimanual interference during reaching movements originates from the selection of target locations and the assignment of response rules to hands, rather than from the motor programming of movement parameters.

Methodology

lab_experiment

Sample size: 26

Provenance

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Topics

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• dual task performance