Biomedical subjects
F A Geldard
Publications and source records attributed to F A Geldard.
The mutability of time and space on the skin.
Radical shifts in perceived spatial relations can occur through the operation of the principle of sensory saltation. In the realm of cutaneous sensation, where it was first encountered, and also in some auditory and visual situations, any brief stimulus preceding a second one by no more than about 300 ms will show apparent spatial displacement from its veridical position. The degree of deviation is determined primarily by temporal relations between the two stimuli but, secondarily, by intensive ones as well. Limits of the operation of the saltatory effect on the skin have been ascertained by employing a campimetric technique on representative body areas. From the results of such measurement, taken together with consideration of some aspects of the known neural substrate, it is possible to decide among several competing hypotheses concerning the essential seat of the phenomenon. The relation of the saltatory effect to the earlier tau and kappa effects is discussed, as are the possibilities offered by all three to the solution of tactual communication problems and the allied problem of tactile displays.
Cutaneous stimuli, vibratory and saltatory.
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The saltatory effect in vision.
Events in vision triggered by brief flashes in train prove to be strictly analogous to those generated in the skin by a succession of taps. A requisite condition for their appearance in vision is projection of the flashes into the peripheral retinal field. Experiments are described that establish the general relation between extent of saltatory leaping and degree of retinal eccentricity and between leaping and retinal subtense of stimulus patches. Additionally, a curious "dip" phenomenon and several qualitative experiments in which color has been used to "tag" the saltatory image are reported.
The cutaneous "rabbit": a perceptual illusion.
Anomalous localizations of mechanical and electrical cutaneous pulses are produced when widely separated bodily points are successively stimulated with trains of taps. The observer experiences a manifold of discrete "phantom" impressions connecting the points actually touched. The theoretical basis for this perceptual phenomenon is not understood, but some boundary conditions are specified.
Clarence Henry Graham: 1906-1971.
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Vision, audition, and beyond.
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