The effects of force and direction uncertainty of choice reaction time in an isometric force production task

The two experiments reported examined the temporal organization of force and direction motor-programming processes in a step-input tracking type task. Both experiments observed a reduction in reaction time in the direction-uncertain conditions compared to the direction-certain ones. Thus it seems as though the direction decision does not have to precede the selection of the proper amount of forces. Experiment 2 observed an under-additive interaction between levels of direction uncertainty (certain or uncertain) and levels of force uncertainty (certain or uncertain). This interaction was interpreted as support for the programming of force and direction and thus, strongly supports the parallel model of programming recently proposed by Klapp (1977a,b).