Balance. When a human experiences a balance disturbance, muscles throughout the body are activated in a coordinated fashion to maintain an upright stance. Researchers at Lena Ting Laboratory for Neuro...

Balance. When a human experiences a balance disturbance, muscles throughout the body are activated in a coordinated fashion to maintain an

upright stance. Researchers at Lena Ting Laboratory for Neuro engineering at Georgia Tech are interested in uncovering the sensorimotor mechanisms responsible for coordinating this automatic postural response (APR). Their approach was to perturb the balance of a human subject standing upon a customized perturbation platform that translates in the horizontal plane. Platform motion characteristics spanned a range of peak velocities (5 cm/s steps between 25 and 40 cm/s) and accelerations (0.1 g steps between 0.2 and 0.4 g). Five replicates of each perturbation type were collected during the experimental sessions. Surface electromyogram (EMG) signals, which indicate the level of muscle activation, were collected at 1080 Hz from 11 muscles in the legs and trunk. The data in balance2.mat are processed EMG responses to backward directed perturbations in the medial gastrocnemius muscle (an ankle plantar flexor located on the calf) for all experimental conditions. There is 1 s of data, beginning at platform motion onset. There are 5 replicates of length 1024 each collected at 12 experimental conditions (4 velocities crossed with 3 accelerations), so the data set is 3-D 1024×5×12. For example, data(:,1,4) is an array of 1024 observations corresponding to first replicate, under the fourth experimental condition (30 cm/s, 0.2 g). Consider a fixed acceleration of 0.2g and only the first replicate. Form 1024 4-D observations (velocities 25, 30, 35, and 40 as variables) as a data matrix. For the first 16 observations find multivariate graphical summaries using MATLAB’s gplot matrix, parallel coords, andrewsplot, and glyphplot.