To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.

The distribution of null arguments across languages has been accounted for in terms of two distinct strategies: licensing by agreement and licensing by topic. Lillo-Martin (1986 claims that American Sign Language (ASL) exploits both strategies for licensing null arguments, depending on the morphological characteristics of the verb. Here we show that this is incorrect. Once the nonmanual correlates of agreement features (comparable to the nonmanual expressions of other syntactic features) in ASL are recognized, it becomes apparent that null arguments in this language are systematically licensed by an expression of syntactic agreement.

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ASL syntax makes essential use of specific non-manual expressions of syntactic features (e.g., +neg, +wh) that co-occur with manual signs. These markings occur obligatorily with manual material contained in the node of origin and optionally extend over the c-command domain of that node, thus providing important evidence for hierarchical structure. In this article, we show that agreement features, both within the clause and the noun phrase, also have non-manual correlates that exhibit the predicted distribution. Interestingly, transitive IPs and possessive DPs pattern together in their manifestation of agreement marking, while intransitive IPs pattern with non-possessive DPs.

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