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Two psychophysical experiments were conducted on active tactual discrimination of line width using the method of constant stimuli with blind subjects. In Experiment I, 93 subjects made single judgments over each of five standards between 0.04 and 0.12 in. In Experiment II, 6 subjects were tested repeatedly over seven standards between 0.04 and 0.50 in. Over the range of standards common to both experiments, the Weber fractions decreased as the width of the standard increased. For two larger standards (0.25 and .50 in.I, the Weber fractions approached asymptote and then increased respectively suggesting a U-shaped function. No differences in accuracy of discrimination were found between males vs. females, age groupings, or grade groupings.Visually handicapped students use their fingertips to acquire information from tactile displays, either from braille characters (Fertsch, 1947; Nolan & Kederis, 19(9) or from nonpunctiform codes. such as the symbology used for maps (Bel'la' , 1972). A primary need in the education of these students is for readable tactile displays (maps, graphs, and diagrams). A method frequently used for designing tactile displays is to construct a tactile analogue of a visual display. However, given the disparity in resolving power between fingertips and eye, the results may be a symbology that is not discriminable by touch. For example. it has been reported that students cannot recognize basic geometric forms and patterns when they are reduced below .50 in.(1.27 em) in diam (Morris & Nolan, 1963; Zigler & Northrup. 1926). There is, however, a dearth of information on the tactual discriminatory capacity of the active fingertipts) for a variety of tactile parameters.The present investigation was concerned with the active tactual discrimination of line width by blind subjects. The stimuli were raised lines oriented perpendicularly away from the body. While the subject moved his index fingertip toward and away from the body along the length of the line. he had to judge the width of the line. A method of constant stimuli was used. In the first experiment. the subjects were limited in the amount of time they could participate; therefore, a large number (93) of subjects was used, each receiving each comparison pair once. In the second experiment, a repeated-trials procedure was used in which 6 subjects were repeatedly tested over a period of 8 weeks. EXPERIMENT I MethodSubjects. The subjects were 93 braille readers enrolled in the Ontario School for the Blind. The means and standard deviations of the ages of the students in each of three grade groupings (4·6, 7·9, 10-12) were, respectively: M = 11.94. SO = 1.42; M = 15.73. SO = 2.12; M = 18.49. SO = 1.70. There were approximately twice as many males as females in each grade grouping, with 28-33 subjects within each grade grouping. . Materials. Raised lines were made from cold rolled steel cut with a die and milled to the specified widths. The lines were polished with tine steel wool to reduce burrs. There were five standard line thicknesses of .0...

In response to an expressed need for inexpensive biological models for blind students, the American Printing House for the Blind has developed a set of 19 plastic models (schematics) which illustrate representative species of the major invertebrate phyla and component structures of flowering plants. The biological features depicted on the models were found to be highly discriminable in a test of legibility (95 percent overall correct responses) with 42 legally blind students (grades 7-12). The models emphasize simplicity, but offer additional cues where complexity occurs. Texture, size, shape, and relief were used for maximum legibility. Chromatic color coding was employed to maximize color and luminance contrasts for low vision students. The models averaged nine inches (22.9 cm) in length on their longest sides.