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Effects of Angle, Distance, and Illumination on Visual Reception of Speech by Profoundly Deaf Children

Two adult females presented lists of 240 common nouns to small groups of profoundly deaf children (N = 3 to 6). Lipreading performance was measured under several conditions of speaker angle, light-incidence angle, illumination, and distance. The best visual word-recognition scores were obtained for 0 or 45° horizontal observation angles. Mean scores were 14 to 22% lower when the angle was increased to 90°. For viewing angles within the range of 0 to 45°, the smaller the distance between the speaker and the lipreader, the greater was the visual intelligibility. Minor variations in vertical viewing angle (–30 to +30°) had little effect on lipreading performance. Within the 0 to 45° range of horizontal viewing angles, illumination conditions which shadowed the speaker's oral cavity (overhead lighting) lowered mean lipreading performance 3 to 12% below that which was obtained for 0 or +45° angles of light incidence. With frontal illumination of the speaker, a large reduction in facial luminance (from 30 to 0.03 footlamberts) produced only a 13% decrement in visual intelligibility. Under conditions of high background brightness, however, a reduction in facial luminance from 30 to 3 footlamberts produced a mean decrement of 41%. The data suggest that visual communication in classrooms for deaf children can be enhanced easily by positioning teachers so that they face the windows as they speak and by compressing the pattern of pupils' desks so that all children can observe their teacher from favorable angles.

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