Conde et al. (Exp Brain Res 233:3313–3321, 2015) found that the Simon effect for vertically arrayed stimuli and responses was reduced after 100 prior practice trials with an incompatible mapping of the stimulus locations and responses. This finding was contrary to Vu’s (Mem Cognit 35:1463–1471, 2007) finding of no transfer effect with 72 trials of prior practice. Conde et al. proposed that the different results were due to their responses being coded as top and bottom in the frontal plane, whereas Vu’s were coded as far and near in the transverse plane. We conducted four experiments to test this possibility in which participants responded with keypresses using their thumbs on a numeric keypad held vertically (upright in the frontal plane) or horizontally (flat in the transverse plane). Experiment 1 showed that, without any prior practice, a similar sized Simon effect was obtained when the response device was oriented in the transverse plane as when it was oriented in the frontal plane. In Experiments 2 and 3 participants performed with the same device orientation in the incompatible practice and Simon transfer tasks, with orientation manipulated between-subjects in the former and within-subjects in the latter. The Simon effect was reduced in both cases, with no significant difference in transfer effect for transverse and frontal planes. In Experiment 4, the device orientation differed between the incompatible practice and Simon transfer tasks, and the Simon effect was reduced similarly across both response-device orientations. Thus, the differences between Conde et al.’s and Vu’s findings cannot be attributed to the response-device orientation. Our results are consistent with the view that people code response locations in the transverse plane as top and bottom, rather than far and near, in agreement with the terminology of “top row” and “bottom row” for computer keyboards.
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