Faculty Bibliography

This paper proposes a parametric model for saccadic waveforms. The model has a small number of parameters, yet it effectively simulates a variety of physiologic saccade properties. In particular, the model reproduces the established relationship between peak saccadic angular velocity and saccadic amplitude (i.e., the saccadic main sequence). The proposed saccadic waveform model can be used in the evaluation and validation of methods for quantitative saccade analysis. For example, we use the proposed saccade model to evaluate four well-known saccade detection algorithms. The comparison indicates the most reliable algorithm is one by Nystrom et al. We further use the proposed saccade model to evaluate the standard technique used for the estimation of peak saccadic angular velocity. The evaluation shows the occurrence of systematic errors. We thus suggest that saccadic angular velocity values determined by the standard technique (low-pass differentiation) should be interpreted and used with caution.

Vision impairments are highly prevalent after acquired brain injury (ABI). Conceptual models that focus on constructing intellectual frameworks greatly facilitate comprehension and implementation of practice guidelines in an interprofessional setting. The purpose of this article is to provide a review of the vision literature in ABI, describe a conceptual model for vision rehabilitation, explain its potential clinical inferences, and discuss its translation into rehabilitation across multiple practice settings and disciplines.

Although primary dystonia is defined by its characteristic motor manifestations, non-motor signs and symptoms have increasingly been recognized in this disorder. Recent neuroimaging studies have related the motor features of primary dystonia to connectivity changes in cerebello-thalamo-cortical pathways. It is not known, however, whether the non-motor manifestations of the disorder are associated with similar circuit abnormalities. To explore this possibility, we used functional magnetic resonance imaging to study primary dystonia and healthy volunteer subjects while they performed a motion perception task in which elliptical target trajectories were visually tracked on a computer screen. Prior functional magnetic resonance imaging studies of healthy subjects performing this task have revealed selective activation of motor regions during the perception of 'natural' versus 'unnatural' motion (defined respectively as trajectories with kinematic properties that either comply with or violate the two-thirds power law of motion). Several regions with significant connectivity changes in primary dystonia were situated in proximity to normal motion perception pathways, suggesting that abnormalities of these circuits may also be present in this disorder. To determine whether activation responses to natural versus unnatural motion in primary dystonia differ from normal, we used functional magnetic resonance imaging to study 10 DYT1 dystonia and 10 healthy control subjects at rest and during the perception of 'natural' and 'unnatural' motion. Both groups exhibited significant activation changes across perceptual conditions in the cerebellum, pons, and subthalamic nucleus. The two groups differed, however, in their responses to 'natural' versus 'unnatural' motion in these regions. In healthy subjects, regional activation was greater during the perception of natural (versus unnatural) motion (P < 0.05). By contrast, in DYT1 dystonia subjects, activation was relatively greater during the perception of unnatural (versus natural) motion (P < 0.01). To explore the microstructural basis for these functional changes, the regions with significant interaction effects (i.e. those with group differences in activation across perceptual conditions) were used as seeds for tractographic analysis of diffusion tensor imaging scans acquired in the same subjects. Fibre pathways specifically connecting each of the significant functional magnetic resonance imaging clusters to the cerebellum were reconstructed. Of the various reconstructed pathways that were analysed, the ponto-cerebellar projection alone differed between groups, with reduced fibre integrity in dystonia (P < 0.001). In aggregate, the findings suggest that the normal pattern of brain activation in response to motion perception is disrupted in DYT1 dystonia. Thus, it is unlikely that the circuit changes that underlie this disorder are limited to primary sensorimotor pathways.

Healthy individuals appear to use both vector-coded reach plans that encode movements in terms of their desired direction and extent, and target-coded reach plans that encode the desired endpoint position of the effector. We examined whether these vector and target reach-planning codes are differentially affected after stroke. Participants with stroke and healthy controls made blocks of reaches that were grouped by target location (providing target-specific practice) and by movement vector (providing vector-specific practice). Reach accuracy was impaired in the more affected arm after stroke, but not distinguishable for target- versus vector-grouped reaches. Reach velocity and acceleration were not only impaired in both the less and more affected arms poststroke, but also not distinguishable for target- versus vector-grouped reaches. As previously reported in controls, target-grouped reaches yielded isotropic (circular) error distributions and vector-grouped reaches yielded error distributions elongated in the direction of the reach. In stroke, the pattern of variability was similar. However, the more affected arm showed less elongated error ellipses for vector-grouped reaches compared to the less affected arm, particularly in individuals with right-hemispheric stroke. The results suggest greater impairment to the vector-coded movement-planning system after stroke, and have implications for the development of personalized approaches to poststroke rehabilitation: Motor learning may be enhanced by practice that uses the preserved code or, conversely, by retraining the more impaired code to restore function.

OBJECTIVE: The aim of this study was to evaluate the effects of a novel divided attention task, walking under auditory constraints, on gait performance in older adults, and to determine whether the effect was moderated by cognitive status. DESIGN: Validation Cohort SETTING: General Community PARTICIPANTS: 104 older non-demented and ambulatory older adults INTERVENTIONS: Not applicable MAIN OUTCOME MEASURE(S): In this pilot study, we evaluated walking under auditory constraints (WUAC) in 104 older adults who completed three pairs of walking trials on a gait mat under one of three randomly assigned conditions: one pair without auditory stimulation, and two pairs with emotionally charged auditory stimulation with happy or sad sounds. RESULTS: The mean age of subjects was 80.6+/-4.9 years and 63% were women. The mean velocity during normal walking was 97.9+/-20.6 cm/sec and the mean cadence was 105.1+/-9.9 steps/min. The effect of walking under auditory constraints on gait characteristics was analyzed using a two factorial ANOVA with a 1-between factor (cognitively intact and minimal cognitive impairment groups) and a 1-within factor (type of auditory stimuli). Under both happy and sad auditory stimulation trials, cognitively intact older adults (n=96) showed an average increase in gait velocity of 2.68 cm/s (F[1.86, 191.71](1, 2)=3.99, p=0.02) and an average increase in cadence of 2.41 steps/min (F[1.75, 180.42]=10.12, p<0.001) compared to trials without auditory stimulation. In contrast, older adults with minimal cognitive impairment (Blessed test score 5-10, n=8) showed average reduction in gait velocity of 5.45 cm/s (F[1.87, 190.83]= 5.62, p=0.005) and in cadence of 3.88 steps/min (F[1.79, 183.10]=8.21, p=0.001) under both auditory stimulation conditions. Neither baseline fall history nor performance on activities of daily living accounted for these differences. CONCLUSIONS: Our results provide preliminary evidence of the differentiating effect of emotionally charged auditory stimuli on gait performance in older individuals with minimal cognitive impairment compared to those without. A divided attention task using emotionally charged auditory stimuli might be able to elicit compensatory enhancement in gait performance in cognitively intact older individuals, but lead to decompensation in those with minimal cognitive impairment. Further investigation is needed to compare gait performance with this task to other dual-task paradigms, and separately examine the effects of physiological aging versus cognitive impairment on gait performance under auditory constraints.

The purpose of this study was to investigate the potential of a high-throughput, easily implemented, cost-effective, video analysis software-based mobility protocol to quantify spine kinematics. This prospective cohort study of clinical biomechanics implemented 2-dimensional (2D) image processing at a tertiary-care academic institution. Ten healthy, able-bodied volunteers were recruited for 2D videography of gait and functional motion. The reliability of a 2D video analysis software program for gait and range of motion metrics was evaluated over 2 independent experimental sessions, assessing for inter-trial, inter-session, and inter-rater reliability. Healthy volunteers were evaluated for simple forward and side bending, rotation, treadmill stride length, and more complex seated-to-standing tasks. Based on established intraclass correlation coefficients, results indicated that reliability was considered good to excellent for simple forward and side bending, rotation, stride length, and more complex sit-to-standing tasks. In conclusion, a cost-effective, 2D, video analysis software-based mobility protocol represents a feasible and clinically useful approach for objective spine kinematics and gait metrics. As the complication rate of operative management in the setting of spinal deformity is weighed against functional performance and quality of life measures, an objective analysis tool in combination with an appropriate protocol will aid in clinical assessments and lead to an increased evidence base for management options and decision algorithms.