Perspectives on Walkingin an Environment

Işık Barış Fidaner

BM 526 Project

BM 526 Project

HumanWalkingEnvironment

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LocomotionGait

A walkinghuman being

Body Soul____Central Nervous System

Walking - Bird’s eye view

Central Nervous System (CNS)

Body situated in the Environment

output channels

input channels

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 control

Visual awareness

• Three phases of locomotion:1.Perception and processing

of the visual information (pp phase)

2.Execute the movement(motor phase)

3.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(also near 120 BPM) (Styns et al. 2007)

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 style and tempo adapts to the time dynamics of GRF

(Racic et al. May 2009)

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 feedback loop

(Racic et al. May 2009)

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:a) Increased GSC (anxiety)b) Decreased mean COM and

COP in anterior direction(leaning backwards)

c) Decreased stdev of COP and COM (more control)d) Increase in mean power frequency of COP

• (c) and (d) Increased stiffness in ankle joint

(Brown et al. 2006)

Effect of anxiety, fear of falling

• No significant change dueto age difference

• Standing near height or edges causes anxiety

• Anxiety causes increasedcontrol 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

Behavioral scienceMusicology

Civil engineeringPsychology

….?

Biomechanics

Conclusion:

• Different perspectives, separate disciplines

• Common object of study• Multidisciplinary studies

of walking

Human

Behavioral scienceMusicology

Civil engineeringPsychology

….?

Biomechanics

Perspectives on Walkingin an Environment

Işık Barış Fidaner

BM 526 Project