Characterization of Visual Properties of Spatial Frequency and Speed in American Sign Language

Careful measurements of the dynamics of speech production have provided important insights into phonetic properties of spoken languages. By contrast, analytic quantification of the visual properties of signed languages remains largely unexplored. The purpose of this study was to characterize the spatial and temporal visual properties of American Sign Language (ASL). Novel measurement techniques were used to analyze the spatial frequency of signs and the speed of the hands as they move through space. In Study 1, the amount of energy (or “contrast”) as a function of spatial frequency was determined for various sign categories by applying a Fourier transform to static photographs of two ASL signers. In order to determine whether signing produces unique spatial frequency information, amplitude spectra of a person signing were compared to those of a “neutral” image of a person at rest (not signing). The results of this study reveal only small differences in the amplitude spectra of neutral versus signing images across various sign forms examined. In Study 2, three ASL signers wore small ultrasonic devices on the back of their hands during sign production, yielding measurements of hand position in 3-dimensional space over time. From these data, we estimated the speed of signs. Here, we found significant differences in speed between grammatically inflected signs and signs with no inflection. Overall, the spatial frequency content and speeds of signs were found to fall within a selective range, suggesting that exposure to signs is a specific and unique visual experience, which might alter visual perceptual abilities in signers, even for non-language