Acta Psychologica 62 (1986) 89-100 North-Holland 89 WHAT IS CROSSED IN CROSSED-HAND EFFECTS? * Lucia RIGGIO, Luiz de Gonzaga GAWRYSZEWSKI ** and Carlo UMILTA Universitb di Parma, Italy Accepted August 1985 In choice RT tasks, when the subject crosses the hands two effects are observed: the direction of spatial compatibility reverses and response latency becomes overall longer. It has been proposed that the location of the response is compared to both its anatomical status (i.e., the hand that emits the response) and the location of the stimulus. When the hands are crossed, the former comparison yields the lengthening of RT while the latter yields the reversal in the direction of spatial compatibility. The present study aimed at testing the relative importance of two locational aspects of the response (i.e., the position of the effector and the position of the response goal) which were confounded in all previous studies. In both experiments the hands were always in anatomical uncrossed position but the position of the response goal might or might not be the same as that of the effector. In experiment 1 the responses were emitted by the index fingers, which were either uncrossed or crossed, whereas in experiment 2 the responses were emitted through two sticks, which again were either uncrossed or crossed. The results replicated both the reversal of spatial compatibility and the lengthening of RT. It was concluded that the effects of crossing the hands are due to the crossing of the response goals. In choice reaction time (RT) tasks response latencies to right-side stimuli are shorter when emitted with the right than the left hand and vice versa for left-side stimuli. This is true irrespective of whether the location of the stimulus is predictive of the correct response (i.e., the condition is that of spatial compatibility; Simon 1969; Nicoletti et al. 1982) or the locational cue provided by the stimulus is irrelevant for * The study was supported by funds from the Consiglio Nazionale delle Ricerche and the Minister0 della Pubblica Istruzione to Carlo Umilta. Luiz de Gonzaga Gawryszewski was postdoctoral fellow of CNPq-Brasil (proc. 200.049/82). The authors wish to thank Dr. A. Bullinger for helpful discussion of the experiments and Mr. G. Ianelli for writing and implement- ing the computer programs. ** Author’s present address: Universidade Federal Fluminense, Departamento de Neurobiologia, Niteroi, 24000 RI, Brasil. Requests for reprints should be addressed to C. Umilta, Istituto di Fisiologia Umana, Universita di Parma, via Gramsci 14, 43100 Parma, Italy. OOOl-6918/86/$3.50 0 1986, Elsevier Science Publishers B.V. (North-Holland)