Inhibition of return in single and dual tasks: examining saccadic, keypress, and pointing responses

Two experiments are reported in which inhibition of return (IOR)was examined wit h single-responsetasks (either manual responses alone or saccadic responses alone) and dual-response tasks (simultaneous manual and saccadic responses). The first experiment-using guided limb movements that require considerable spatial information-showed more IOR for saccades than for pointing responses. In addition, saccadic IOR was reduced with concurrent pointing movements, but manual IOR was not affected by concurrent saccades. Importantly, at the time of saccade initiation, the arm movements did not start yet, indicating that the influence on saccade IOR is due to arm-movement preparation. In the second experiment, using localization keypress responses that required only minimal spatial information, greater IOR was again found for saccadic than for manual responses, but no effect of concurrent movements was found. These findings add further support that there is a dissociation between oculomotor and skeletal-motor IOR. Moreover, the results show that the preparation manual responses tend to mediate saccadic behavior-but only when the manual responses require high levels of spatial accuracy-and that the superior colliculus is the likely neural substrate integrating IOR for eye and arm movements.