Experimental Finger Dyspraxia

Subjects were required to perform discrete finger movements in accordance with a pre-arranged sequence of instructions. In all cases, any movement made by any finger was recorded by means of a constant-speed kymograph equipped with levers designed to record separately the movements of the individual fingers. This experiment was carried out under three conditions: (a) with no vision of the hand; (b) with direct vision of the hand; and (c) with the hand presented in mirror-image. It was found that, whereas deprivation of visual control was without effect on the efficiency of finger movements, presentation of the hand in mirror-image gave rise to significant increases in reaction time of three fingers and to an increase in the percentages of prior and substitute movements of other digits. Phenomena akin to depersonalisation were reported in some cases. It was also found that the rank order of mean reaction times of the five digits was approximately constant under all conditions and that the two fingers with the shortest reaction times were preceded by the fewest movements of other digits. These two digits were also the most frequently moved in advance when movements of other digits were requested and it is suggested that they have a certain “signpost function” in guiding identification of the remaining fingers. Some implications of these results for an understanding of “finger agnosia” are briefly indicated in an Appendix.