Linear and nonlinear analysis of human postural sway

Çelik, Hüseyin
Human upright posture exhibits an everlasting oscillatory behavior of complex nature, called as human postural sway. Variations in the position of the Center-of-Pressure (CoP) were used to describe the human postural sway. In this study; CoP data, which has experimentally been collected from 28 different subjects (14 males and 14 females with their ages ranging from 6 to 84), who were divided into 4 groups according to their ages has been analyzed. The data collection from each of the subjects was performed in 5 successive trials, each of which has lasted for 180-seconds long. Linear analysis methods such as the variance/standard deviation, Fast Fouriér Transformation, and Power Spectral Density estimates were applied to the detrended CoP signal of human postural sway. Also the Run test and Ensemble averages methods were used to search for stationarity and ergodicity of the CoP signal respectively. Furthermore, in order to reveal the nonlinear characteristics of the human postural sway, its dynamics were reconstructed in m-dimensional state space from the CoPx signals. Then, the correlation dimension (D2) estimates from the embedded dynamics were calculated. Additionally, the statistical and dynamical measures computed were checked against any significant changes, which may occur during aging. The results of the study suggested that human postural sway is a stationary process when 180-second long biped quiet stance data is considered. In addition, it exhibits variable dynamical structure complex in nature (112 deterministic chaos versus 28 stochastic time series of human postural sway) for five successive trials of 28 different subjects. Moreover, we found that groups were significantly different in the correlation dimension (D2) measure (p≤0.0003). Finally, the behavior of the experimental CoPx signals was checked against two types of linear processes by using surrogate data method. The shuffled CoPx signals (Surrogate I) suggested that temporal order of CoPx is important; however, phase-randomization (Surrogate II) did not change the behavioral characteristics of the CoPx signal.


Transcriptomic insights into human brain evolution: acceleration, neutrality, heterochrony
Somel, Mehmet; Liu, Xiling (Elsevier BV, 2014-12-01)
Primate brain transcriptome comparisons within the last 12 years have yielded interesting but contradictory observations on how the transcriptome evolves, and its adaptive role in human cognitive evolution. Since the human-chimpanzee common ancestor, the human prefrontal cortex transcriptome seems to have evolved more than that of the chimpanzee. But at the same time, most expression differences among species, especially those observed in adults, appear as consequences of neutral evolution at cis-regulatory...
Investigation of control of human balance-recovery reactions
Bilgin, Nurdan; Özgören, Mustafa Kemal; Department of Mechanical Engineering (2015)
In this study, a natural control law has been conjectured, which is assumed to be applied by the central nervous system of a human being in order to maintain the erect posture after being exposed to a suddenly occurring impulsive disturbance. The control law is conjectured as PD (proportional-derivative) control, because it has to be compatible with the physiological facts. The conjectured control law has been validated by comparing a set of experimental results with the corresponding set of simulation resu...
Towards the Enhancement of Biped Locomotion and Control Techniques - Walking Pattern Classification
Yuksel, Basak; Leblebicioğlu, Mehmet Kemal (2011-01-29)
A new walking pattern classification method is proposed for uneven floor walking of 5-link 7 DOF biped robot. This method extracts the patterns as per the stance foot's current floor position and swing foot's transitioning floor conditions during locomotion. When a global path composed of stairs, obstacles, etc. and certain walking parameters, such as the speed of walking and total walking time, are given to the system, the guidance controller unit determines footstep trajectory in terms of step patterns by...
Acoustic surface perception from naturally occurring step sounds of a dexterous hexapod robot
Ozkul, Mine Cuneyitoglu; Saranlı, Afşar; Yazıcıoğlu, Yiğit (Elsevier BV, 2013-10-01)
Legged robots that exhibit dynamic dexterity naturally interact with the surface to generate complex acoustic signals carrying rich information on the surface as well as the robot platform itself. However, the nature of a legged robot, which is a complex, hybrid dynamic system, renders the more common approach of model-based system identification impractical. The present paper focuses on acoustic surface identification and proposes a non-model-based analysis and classification approach adopted from the spee...
Comparison of non-deterministic search techniques in the optimum design of real size steel frames
Hasançebi, Oğuzhan; Doğan, E.; Erdal, F.; Saka, M.P. (Elsevier BV, 2010-9)
There is a noticeable increase in the emergence of non-deterministic search techniques that simulate natural phenomena into a numerical optimization technique in recent years. These techniques are used for developing structural optimization algorithms that are particularly effective for obtaining solutions to discrete programming problems. In this study amongst these techniques genetic algorithms, simulated annealing, evolution strategies, particle swarm optimizer, tabu search, ant colony optimization and h...
Citation Formats
H. Çelik, “Linear and nonlinear analysis of human postural sway,” M.S. - Master of Science, Middle East Technical University, 2008.