Sign Language Studies

SLS 19 (1978), 95-110 0 William C. Stokoe 1 VISUAL CONSTRAINTS for SIGN LANGUAGE COMMUNICATION Patricia Siple Production of the signals of any language must to some extent depend on the modality of that production. The vocal apparatus can produce only a limited range of all the sounds that a human ear can detect, and there is certainly a limit to the possible duration and sequencing of these sounds. Similarly, the production of language signals must be related to the perceptual system receiving them. A difference between two sounds must be a difference that the hearer can immediately, accurately, and automatically detect before that difference can be used to convey a distinction between two elements of a language. The production of language signals, therefore, must be constrained by the apparatus used to receive them. We would expect that sign languages of the deaf would evolve in such a way that their units would become less perceptually ambiguous. Since sign languages are received and initially processed by the visual system, we would expect that the rules for the formation of signs of a sign language would be constrained by the limits of the visual system. One of the important limits of human vision is that it is not equally acute in all parts of the field it takes in. When we focus on a point, we can see a great deal of detail in the area immediately surrounding that point, because the image of the point and area falls on the most 1 The original version of this article was written in 1973. Brief as well as seminal, it quickly reached the small circle of sign language investigators then active and so escaped more formal publication until now. The author acknowledges help from Ursula Bellugi, Susan Fischer, and Robert Springer as well as NIH Grant NS 09811. [Editor's note] Sign Language Studies 19 sensitive part of the retina of the eye, the fovea. Farther away from the fixated point, we can see less and less fine detail. 2 We might then expect the formation of signs in a sign language to depend on where they are located in the visual field of the sign receiver. Further, if the person to whom the signs are addressed watches the signer by focusing on a particular spot, we might expect fine detail in the signs to be important in that location. Signs in that location should differ minimally from other signs made there by smaller changes than do signs made in places farther away from the point of fixation, where such fine detail would not be detected. Our observations indicate that signers do indeed have a fixed place of focus. When deaf signers are conversing , the receiver tends to look at the sender's face. Eye movements that do occur tend to be small excursions about the signer's face. This may seem strange, given that sign is a gestural language in which the hands have a large role, until we realize that the face gives very important cues to the meaning of a signed utterance (Bellugi & Fischer 1973, Liddell 1977, Baker 1976). We can use this information about where a person attending to signing habitually looks, along with the knowledge that we have about the human visual system, to make predictions about the form that signs will take in any sign language. Relative acuity. In order to recognize a sign, a viewer must be able to discriminate that sign from others similar to it. Stokoe (1960: 41f) posited three aspects as constituting the ways in which one sign (morpheme) can differ from another: configuration of the hand or dez, location or tab, and motion or sig. [More recently, what acts, where it acts, and its action (Stokoe, in press). ] We should expect the limits of the visual system for perception of fine detail to affect the degree to which these aspects of signs themselves are finely or grossly different. This is easily tested: Focus on a word in the middle of this page; words immediately around can be read easily without a shift in fixation, but those farther away are indistinct. Siple Visual acuity, one limit of the system, is measured...