Subjective Magnitude Estimation

ECE 511: Guest Lectureby Ali Israr

School of Mechanical EngineeringPurdue University

October 31, 2006

© 2006 Ali Israr

Outline

IntroductionBasic conceptScaling ExperimentsRobustness of subjective scales ApplicationsMotorcycle vibration model

© 2006 Ali Israr

Introduction

“subjective” and “magnitude”subjective magnitude is the mental size of a physical stimulusclosely related to the perceived intensitysubjective magnitude estimation resulted in a function that relates physical intensity of the stimulus to the sensation magnitude

© 2006 Ali Israr

Basic idea

Define a scale (such as that of numbers) in your mind that corresponds to the sensation magnitude of a physical variable.

for example, line length, line thickness, intensity of tone, hardness or roughness etc.

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• Line lengths

for example

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Scaling Experiment

Objective:

Estimate subjective magnitude of a physical stimulus

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Scaling ExperimentProcedure:

Select a range of a stimulus and choose about 10-20 test stimuli within this rangeIn a trial, randomly select one stimulus and present it to a subjectAsk the subject to rate the stimulus from a predefined range of numbersThe numbers can be positive integers, fractions, or decimal numbersContinue this until each stimulus is presented at least 8 or 10 times

© 2006 Ali Israr

3.3

• Line lengths

for example

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103512

Trial 1Trial 2Trial 3Trial 4

Scaling ExperimentResults:

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Zwislocki and Goodman (1980)

Murray et al. (2003)

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other exampleVibrotactile loudness of 250 Hz vibration

Subjective magnitude scale…

1. does not depend on the experience of the subject.

2. does not depend on the intensity of the first stimulus presented.

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Robustness of subjective scales

3. Subjective magnitude scale does not depend on the extent of the physical intensity and number ranges.

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Robustness of subjective scalesZwislocki and Goodman (1980)

4. Subjective magnitude scale does not depend on the group of subjects.

Note: The magnitude estimates may be different among subjects and in different sessions of one subject. “Normalize” the data in each test session with respect to the overall mean.

© 2006 Ali Israr

Robustness of subjective scales

Applications

Determine human behavior and perceived intensity of a physical stimulusDesign new and intelligent products that incorporates perceptual attributes

Need to have a baseline function, such as detection thresholds, to determine the perceived intensity of the stimulus

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Motorcycle handlebar design

Magnitude estimation of handlebar vibrations

Determination of a function that relates the physical vibrations to the sensation energy

Design a motorcycle handlebar mount for a comfort ride

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Test rigTest rig: 2005 Victory motorcycle frame

Actuator, accelerometer, front screen, foot pedals

Data acquisition by Siglab

Controller in dSPACE

LEDs on the screen

Head phones with pink noise

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Procedure10 participants (5M-5F)

15 broadband test stimuli

30 trials in a session and each test stimulus was randomly presented twice

Participants rated test stimulus between 0-100

Four sessions per participant

© 2006 Ali Israr 6th7515

5th7514

4th7513

6th6512

5th6511

4th6510

6th559

5th558

4th557

5th456

4th455

4th354

3rd353

3rd252

2nd251

GearSpeed (MPH)

Stimulus ID

Instructions/training

Participants were instructed to “rate the vibration between 0 and 100, where 0 being no vibration and 100 being the most discomforting vibration”

Before the testing a light, a mediocre and an intense test stimuli were presented to participants and they were told to relate small numbers to light vibrations and large numbers to intense vibrations

© 2006 Ali Israr

Data analysisPerceived intensity of each test stimulus was calculated by detection thresholds reported in Bolanowski et al. and critical band model of Makous et al. That is,

Data was normalized among participants and sessions.

© 2006 Ali Israr

2 22 22 2 2 2

i

s s i iis ifs f

A fA fT f T f

⋅⋅ =⋅ ⋅∑

Psychophysical model

© 2006 Ali Israr

Normalized Rating vs. Perceived Energy

1

1.5

2

10 15 20 25 30 35Perceived Energy - dB

Nor

mal

ized

d R

atin

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mic

)

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( )0.051×dB + 0.28normalized rating=10

p < 0.0010.94r =

ReferencesZwislocki, J. J., and Goodman, D. A. (1980), “Absolute scaling of sensory magnitudes: A validation”, Perception & Psychophysics, 28(1), pp. 28-38.

Murray, A. M., Klatzky, R. L., and Khosla, P. K. (2003), “Psychophysical Characterization and Testbed Validation of a Wearable Vibrotactile Glove for Telemanipulation”, Presence: Teleoperators and Virtual Environments, 12 (2), pp. 156-182.

Bolanowski, S. J., Gescheider, G. A., Verrillo, R. T., and Checkosky, C. M. (1988), “Four channels mediate the sense of touch”, The Journal of the Acoustical Society of America, 84 (5), pp.1680-1694.

Makous, J. C., Friedman, R. M., and Vierck, C. J. Jr. (1995), “A critical band filter in touch”, The Journal of Neuroscience, 15 (4), pp. 2808-2818.

© 2006 Ali Israr

Finis

© 2006 Ali Israr