Routes to action in reaction time tasks

Summary

Two-choice tactile RTs are no faster than 8-choice tasks, implying the existence of a ‘direct’ route. However, simple tactile RTs are much faster than choice tactile RTs (Leonard, 1959). In Experiment I we show that this is not due to subjects anticipating the stimulus in simple tactile RT tasks. Increasing probability of stimulus occurrence at a particular time led to equally decreased tactile RTs for simple and choice tasks.

We suggest that an alternative route is available for simple RTs which is faster than the ‘direct’ route available for choice tactile RTs. This route is faster because (a) the response can be specified in advance, and (b) the stimulus does not need to be identified. The subject needs merely to register that it has occurred. In Experiment II we show that simple RTs to a visual stimulus are decreased by a simultaneous uninformative tactile stimulus even when this is to the wrong finger. This confirms that exact stimulus identification is not necessary in the ‘fast’ route. In Experiment III we show that a secondary task slows down simple tactile RTs to the same level as choice tactile RTs while the latter are hardly affected. This suggests that focussed attention is not needed for the ‘direct’ route, but it is needed for the ‘fast’ route. We propose that a useful distinction can be made between action largely controlled by external stimuli (the ‘direct’ route) and action largely controlled by internal intentions of will (the fast route).