On the tangibility of letters and braille.

BraiWe characters and letters were presented to the senses of touch and vision of sighted observers. The optical stimuli were subjected to low-pass spatial filtering to the degree that visual spatial resolution closely matched tactile spatial resolution (re the size of characters presented). In one experiment, three sets of braille characters and five sets of Roman letters, varying in typography, were presented as stimuli. The variations in tangibility and legibility across the eight character sets were highly correlated (r = .98). In a second experiment, braille characters and letters were varied in size. The psychometric functions relating tangibility and legibility to character size were similar in both shape and position along the abscissa. The congruence of tangibility and legibility for these conditions, in which the senses were matched in spatial resolution, supports the idea that braille characters are more tangible by virtue of their greater distinctiveness after the low-pass spatial filtering of cutaneous processing.