Accuracy of tactual discrimination of letters, numerals, and geometric forms.

Abstract : The purpose of this experiment was to determine to what extent various letters, numerals, and geometric forms could be discriminated tactually with the index finger-tip. Two sets of stimulus figures were tested, one set of solid figures and one set which contained figures made up of points. Both sets included all the letters in the alphabet, the numerals 2 through 9, and various geometric forms. The stimulus figures were presented one at a time in random sequence to ten subjects. The experiment involved four conditions of presentation of the stimulus figures: (1) solid figures--no finger-tip movement permitted, (2) solid figures-movement, (3) point figures--no movement, and (4) point figures-movement. Of the four conditions tested, the solid figures-movement condition proved to be the most effective. Under the restrictions of this condition, approximately 60 per cent of the figures were discriminable at or above the 90 per cent level of accuracy, i.e., not more than one error from a total of ten subjects on each of the figures. These figures were the following: C, D, E, G, I, J, K, L, O, P, Q, T, U, V, W, X, Y, 2, 7, 9, diamond, right triangle, rectangle, crescent and half circle. No errors were made on the I or L throughout the experiment regardless of mode of presentation, and the C, I, L, O, T, and U met the 90 per cent accuracy criterion in each of the four conditions. Possible applications of tactual cues are suggested and three criteria for selecting the most effective figures are discussed. (Author)