Perspectives on Walking in an Environment

BM 526 Project

Perspectives on Walking in an Environment Işık Barış Fidaner

BM 526 Project

Environment

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Walking

Human

Gait Locomotion

A walking human being

Body

____ Soul Central Nervou s System

Walking - Bird’s eye view Central Nervous System (CNS) output channels

input channels

Body

situated in the Environment

Outputs of CNS • Motor signals – Contract muscles to move forward while controlling the body posture

• Auxilliary signals – Movements to enhance the input – Lifting head to see your path

Inputs to the CNS • Visual – Spatiotemporal awareness to predict near future

• Audio – Musical sounds to regulate the sense of time

• External forces – Ground reactions to optimize energy consumption

• Balance – Anxiety, fear of falling to increase posture

Visual awareness • Three phases of locomotion: • Perception and processing of the visual information (pp phase) • Execute the movement (motor phase) • Examine the consequences and adapt your behavior (Meschner 2008)

Visual awareness • Every pp phase must end before corresponding motor phase begins • Perceptions are buffered in short-term memory

(Meschner 2008)

Visual awareness • Locomotion is a complex variable behavioral contingency • Shares same structure with other activities that require “thinking ahead” such as – Reading out loud – Dancing – Foraging

(Meschner 2008)

Effect of music and rhythm • Effect of music vs. raw metronome ranging through 50 to 190 BPM on walking vs. tapping finger, in terms of • Synchronization – Adapting walking tempo to the music

• Spatialization – Effect on walking style, speed, step length etc.

(Styns et al. 2007)

Effect of music and rhythm • Synchronization – Better sync in tapping – An optimum musical tempo exists that maximizes sync in walking (near 120 BPM)

• Spatialization – Music makes us walk faster, compared to raw metronome at same tempo – An optimum walking tempo exists that maximizes step size (Styns et al. 2007) (also near 120 BPM)

Resonance behavior • Step size resonates with walking tempo • According to – fundamental frequency – damping factor

• 2 Hz (=120 BPM) resonance frequency in the long-term energy spectrum (Dougall et al. 2005) • Spontaneous or self-selected tempo of human locomotion

(Styns et al. 2007)

External forces • Ground reaction force acts on our body through feet • Body force acts on the ground • GRF on a solid ground: – GRF does not vary with time – Muscles react to preserve body posture

• GRF on a flexible ground: – Oscillating in vertical, anterior-posterior or lateral components – Walking tempo (Racic style et al.and May 2009) adapts to the time dynamics

The Millennium Bridge • Opening ceremony in London, June 2000

(Racic et al. May 2009)

The Millennium Bridge • Lateral oscillation up to 7 cm!

• Spontaneous walking tempo – Vertical / Anterior: 2 Hz – Lateral component: 1 Hz

• Same with the bridge’s natural frequency of lateral oscillation!

• People synchronized their tempo to each other and the bridge, forming a positive (Racic et al. May 2009) feedback loop

External forces • Force plates – Records single steps

• Instrumented treadmill – Records a sequence of steps – Vertical and lateral GRF increase with speed – Anterior GRF reaches a maximum at 5.6 kmph (spontaneous speed)

• Time / frequency domain • Deterministic / stochastic models (Racic et al. May 2009)

Effect of anxiety, fear of falling • Old and young subjects • Each stands on the platform – Higher or lower platform – At the edge or at the middle

• Recorded for each trial: – Galvanic skin conductance (GSC) to infer anxiety – Body center of mass (COM) and center of pressure (COP) to estimate motor behavior

(Brown et al. 2006)

Effect of anxiety, fear of falling • Standing on the edge, or higher platforms caused: – –

– –

Increased GSC (anxiety) Decreased mean COM and COP in anterior direction (leaning backwards) Decreased stdev of COP and COM (more control) Increase in mean power frequency of COP

• (c) and (d) ⇒ Increased stiffness in (Brown et al. 2006) ankle joint

Effect of anxiety, fear of falling • No significant change due to age difference • Standing near height or edges causes anxiety • Anxiety causes increased control on body posture • Contrary to previous work, fear may be beneficial to protect one’s body from falling (Brown et al. 2006)

Conclusion:

• Buffering, spatiotemporal awareness • Resonance in step size, optimum tempo of walking • Synchronize to structure, positive feedback loop • Anxiety, fear of falling, increased control

Biomechanics Behavioral science Musicology Civil engineering Psychology

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Conclusion:

• Different perspectives, separate disciplines • Common object of study • Multidisciplinary studies of walking

Human Biomechanics Behavioral science Musicology Civil engineering Psychology

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BM 526 Project

Perspectives on Walking in an Environment Işık Barış Fidaner