Changing patterns of cognitive-motor interference (CMI) over time during recovery from stroke

Objective: To explore the extent and nature of change in cognitive-motor interference (CMI) among rehabilitating stroke patients who showed dual-task gait decrement at initial assessment. Design: Experimental, with in-subjects, repeated measures design. Setting: Rehabilitation centre for adults with acquired, nonprogressive brain injury. Subjects: Ten patients with unilateral stroke, available for reassessment 1-9 months following their participation in a study of CMI after brain injury. Measures: Median stride duration; mean word generation. Methods: Two x one-minute walking trials, two x one-minute word generation trials, two x one-minute trials of simultaneous walking and word generation; 10-metre walking time; Barthel ADL Scale score. Results: Seven out of ten patients showed reduction over time in dual-task gait decrement. Three out of ten showed reduction in cognitive decrement. Only one showed concomitant reduction in gait and word generation decrement. Conclusion: Extent of CMI during relearning to walk after a stroke reduced over time in the majority of patients. Effects were more evident in improved stride duration than improved cognitive performance. Measures of multiple task performance should be included in assessment for functional recovery.

Do children with Williams syndrome really have good vocabulary knowledge? Methods for comparing cognitive and linguistic abilities in developmental disorders

The comparison of cognitive and linguistic skills in individuals with developmental disorders is fraught with methodological and psychometric difficulties. In this paper, we illustrate some of these issues by comparing the receptive vocabulary knowledge and non-verbal reasoning abilities of 41 children with Williams syndrome, a genetic disorder in which language abilities are often claimed to be relatively strong. Data from this group were compared with data from typically developing children, children with Down syndrome, and children with non-specific learning difficulties using a number of approaches including comparison of age-equivalent scores, matching, analysis of covariance, and regression-based standardization. Across these analyses children with Williams syndrome consistently demonstrated relatively good receptive vocabulary knowledge, although this effect appeared strongest in the oldest children.

Inverse problems in dynamic cognitive modeling

Inverse problems for dynamical system models of cognitive processes comprise the determination of synaptic weight matrices or kernel functions for neural networks or neural/dynamic field models, respectively. We introduce dynamic cognitive modeling as a three tier top-down approach where cognitive processes are first described as algorithms that operate on complex symbolic data structures. Second, symbolic expressions and operations are represented by states and transformations in abstract vector spaces. Third, prescribed trajectories through representation space are implemented in neurodynamical systems. We discuss the Amari equation for a neural/dynamic field theory as a special case and show that the kernel construction problem is particularly ill-posed. We suggest a Tikhonov-Hebbian learning method as regularization technique and demonstrate its validity and robustness for basic examples of cognitive computations.