PubMed · 265425
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J G Boyes, J P Hamilton. 1977. Macrodactylism.. https://pubmed.ncbi.nlm.nih.gov/265425/
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The ability of humans to detect striated stimuli on the distal phalanges was found to be highly anisotropic. Observers were much more sensitive to stripes presented in the proximal-distal orientation than to stripes in any other orientation. This tactile anisotropy was contrasted with the well-known visual anisotropy in which sensitivity is greatest for stripes at the horizontal and vertical orientations. We suggest that both the tactile anisotropy and the visual anisotropy are caused by corresponding anisotropies in the distribution of preferred orientations of orientation-selective neurons with in the respective modalities.
Perceived heaviness of a weight lifted by flexion of the distal joint of one digit increases when an adjacent digit concurrently lifts a weight. The present study confirmed this finding for relatively low weights (representing 3-5% maximal voluntary force) and a method was adapted to show that this effect occurs for much larger weights (20-25% maximal force). Thus, the increase in perceived heaviness is likely to operate over a wide range of muscle force generated by the hand. As perceived heaviness is biased by the magnitude of the central motor commands, these findings may reflect a lack of complete independence of motor commands to the long flexor muscles acting on the digits.