Non-conscious choice in cutaneous backword masking

A simple but effective method has been devised to explore backward masking in cutaneous sensation. In this method a weak electrical shock to the palm (test stimulus) is followed by a stronger shock to the same site (masking stimulus). By combining this stimulation strategy with a choice reaction time paradigm, it has been possible to show that the nervous system responds to the test stimuli even though they are not consciously perceived. Further, the distribution of errors in the different types of trial suggests that, under these experimental conditions, the identification of the stimulus and the choice of response may also be made at a non-conscious level. A tentative scheme for the timing of the various neural events is proposed.