Ambulatory activity classification with dendogram-based support vector machine: Application in lower-limb active exoskeleton

Publication date: October 2016
Source:Gait & Posture, Volume 50
Author(s): Oishee Mazumder, Ananda Sankar Kundu, Prasanna Kumar Lenka, Subhasis Bhaumik
Ambulatory activity classification is an active area of research for controlling and monitoring state initiation, termination, and transition in mobility assistive devices such as lower-limb exoskeletons. State transition of lower-limb exoskeletons reported thus far are achieved mostly through the use of manual switches or state machine-based logic. In this paper, we propose a postural activity classifier using a ‘dendogram-based support vector machine’ (DSVM) which can be used to control a lower-limb exoskeleton.A pressure sensor-based wearable insole and two six-axis inertial measurement units (IMU) have been used for recognising two static and seven dynamic postural activities: sit, stand, and sit-to-stand, stand-to-sit, level walk, fast walk, slope walk, stair ascent and stair descent. Most of the ambulatory activities are periodic in nature and have unique patterns of response. The proposed classification algorithm involves the recognition of activity patterns on the basis of the periodic shape of trajectories. Polynomial coefficients extracted from the hip angle trajectory and the centre-of-pressure (CoP) trajectory during an activity cycle are used as features to classify dynamic activities.The novelty of this paper lies in finding suitable instrumentation, developing post-processing techniques, and selecting shape-based features for ambulatory activity classification. The proposed activity classifier is used to identify the activity states of a lower-limb exoskeleton. The DSVM classifier algorithm achieved an overall classification accuracy of 95.2%.



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Quantifying intra-limb coordination in walking of healthy children aged three to six

Publication date: October 2016
Source:Gait & Posture, Volume 50
Author(s): Mingyu Hu, Nan Zhou, Bo Xu, Wuyong Chen, Jianxin Wu, Jin Zhou
The aim of this study was first to quantify intra-limb coordination and then to explore the gender differences of 180 healthy children aged 3–6. The children's joint Euler angles and angular velocities were measured and were used to calculate the phase angle (PA) and continuous relative phase (CRP). Firstly, a portrait of the mean and standard deviation (SD) of PA and CRP was applied to quantify coordination in the knees and ankles; then five key events in walking were selected and their inter-age differences were assessed by One-way ANOVA. Finally, gender differences were evaluated by GLM-Univariate. The significance level was 0.05 and confidence interval was 95%. Our results show that similar portraits of PA and CRP were found for knees and ankles from age 3–6; SD demonstrated that the PA and CRP in the knees and ankles were consistent with the increase in age. Moreover, θ_CRP(K-A) demonstrated that the direction reversal in heels off of those two joints in children aged 5 and 6 was earlier than those of age 3 and 4 and no inter-age significant differences were recorded for PA and CRP in either gait event. Finally, gender differences exist before the age of six, particularly in the transition period such as heel contact, toe off and during the mid swing. Overall, although further development such as gait control or balance is still improving, basic principle of intra-limb coordination has formed by the age of 3 and gender differences already existed before age of 6.



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Low-frequency bias tone suppression of auditory-nerve responses to low-level clicks and tones

Publication date: November 2016
Source:Hearing Research, Volume 341
Author(s): Hui Nam, John J. Guinan
We used low-frequency “bias” tones (BT's) to explore whether click and tone responses are affected in the same way by cochlear active processes. In nonlinear systems the responses to clicks are not always simply related to the responses to tones. Cochlear amplifier gain depends on the incremental slope of the outer-hair-cell (OHC) stereocilia mechano-electric transduction (MET) function. BTs transiently change the operating-point of OHC MET channels and can suppress cochlear-amplifier gain by pushing OHC METs into low-slope saturation regions. BT effects on single auditory-nerve (AN) fibers have been studied on tone responses but not on click responses. We recorded from AN fibers in anesthetized cats and compared tone and click responses using 50 Hz BTs at 70–120 dB SPL to manipulate OHC stereocilia position. BTs can also excite and thereby obscure the BT suppression. We measured AN-fiber response synchrony to BTs alone so that we could exclude suppression measurements when the BT synchrony might obscure the suppression. BT suppression of low-level tone and click responses followed the traditional pattern of twice-a-BT-cycle suppression with more suppression at one phase than the other. The major suppression phases of most fibers were tightly grouped with little difference between click and tone suppressions, which is consistent with low-level click and tone responses being amplified in the same way. The data are also consistent with the operating point of the OHC MET function varying smoothly from symmetric in the base to offset in the apex, and, in contrast, with the IHC MET function being offset throughout the cochlea. As previously reported, bias-tones presented alone excited AN fibers at one or more phases, a phenomena termed “peak splitting” with most BT excitation phases ∼¼ cycle before or after the major suppression phase. We explain peak splitting as being due to distortion in multiple fluid drives to inner-hair-cell stereocilia.



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