Frank A. Geldard

The cutaneous saltatory area and its presumed neural basis

The saltatory area, defined as that region of the skin within which two successive and spatinily separated signals will interact to produce apparent mislocalization of the prior signal, is measured by a campimetric technique applied to the palm, finger pad, and volar forearm. As contrasted with earlier measures on larger anatomical units, saltatory areas of the hand region are considerably compressed. Comparisons between cortical receptive fields and saltatory areas lead to speculation concerning the operation of the neural principle of “magnification” in the establishment of saltatory limits. The correspondence of configurational properties of both receptive fields and saltatory areas suggests a commonality of principles underlying both, but demands more information on the temporal dimensions of cortical interaction to confirm the parallelism.

Multiple Cutaneous Stimulation: The Discrimination of Vibratory Patterns

In an effort to supply widespread cutaneous stimulation and thus make possible systematic study of the limits of spatial discrimination through this channel, there has been devised a multiple contactor system permitting application of vibratory signals to 10 bodily loci simultaneously. Patterns comprising from 1 to 9 stimuli were presented in successive pairs, the subjects task being to report whether the patterns were perceived as “same” or “different.” Members of pairs were separated by 500 msec and burst duration was 200 msec. Two synchronized Western Union tape transmitters presented 20 programs of 50 pairs of patterns, 500 “same” and 500 “different” pairs being randomly intermixed in the 1000 presentations. A pilot experiment, in which many types of pattern changes were explored, revealed errors to be associated with (a) relative pattern complexity (large numbers of vibrators) and (b) high degree of communality (many elements in common). A formal experiment, involving a stratified sample with all co...

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 bodily 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 τ and κ effects is discussed as are also the possibilities offered by all t...

Cutaneous coding of optical signals: the optohapt

Means of transmuting optical signals into cutaneous patterns are sufficiently rare to warrant a fresh attempt at devising one. An instrument called the “optohapt” is described. It converts printed or typed characters into tactual signals having various spatial and temporal properties. These are impressed on nine widely scattered bodily loci. Data on discriminability of a wide range of patterns are reported, and there is proposed a promising coding system for the instrument.

Vision-from a wide mantel

Graham’s contributions to visual science are summarized. The emphasis is on his research in color vision, but work on stereoscopic vision is also mentioned.