Overview of Human-Machine Systems

The Human-Machine Interface

Cognitive Functions

Motor Functions:Human Output

Sensory Systems:Human Input

Controls:Machine Input

Displays:Machine Output

Mechanisms of Machine:Performs Task and Determines State

Feedback within Machine

Muscular Feedback

Physical Stimulus

Accessory Structures

Receptors (Transducti

on)

Neural Processing

Perception/

Cognition

Behavior

Light,Sound,Pressure,Chemical substances,Temperature, etc.

Eye (cornea , lens …)Ear (pinna, ossicles…)Skin,Tongue (tastebuds),….

Rods,Cones,Hair cellsChemo- receptorsPacinian corpuscles…..

Locally and centrallyso many steps

Our experience

The output of all this

General Characteristics of Sensory Systems

Stimulus Receptor Neural Relay CortexIn Vision

Light Rods/Cones LGN of Thalamus Striate

In Audition

Sound Hair Cells MGN of Thalamus Sup. Temp.

G. Other Generalities

Always more than one pathway in brainAlways more than one brain targetUltimately sensory information is combined

The Physical Stimulus for Audition java illustration

• The sound wave is periodic changes in pressure

• Frequency = cycles/second = Hertz, Hz.

Frequency =1/Wavelength

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The Physical Stimulus for Audition - 2 Amplitude is the difference in air pressure between the

compression and rarefaction. The measure of sound amplitude is the relative measure

called decibel or dB.

Where P = air pressure; P2 = power dB SPL, P2=0.0002 dynes/cm2 which is near the absolute

threshold for hearing.

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21log10rP

PdB

rP

PdB 1log20

The Physical Stimulus for Audition - 3

ResonanceAll physical mater will most easily vibrate at certain

frequencies.This is true of our ear.

○ Thus some frequencies will more easily enter our ear○ It helps us determine the frequencies of incoming

sounds as we shall see.

The physical dimensions are related to but not the same as the psychological dimensions:frequency <> pitchamplitude <> loudness

Anatomy and Physiology of the Ear Three Major Divisions

Outer Ear receives sound directs it to the rest of the ear.○ Pinna - directs sound

energy to middle ear and helps perception of the direction.

○ External Auditory Meatus or Canal - 2.5 to 3 cm long, 7 mm wide Resonates at about 2-4K Hz.

○ Tympanic Membrane

Anatomy and Physiology of the Ear - 2

Middle Ear transmits sound information to inner ear.○ Ossicles transmit and amplify sound energy.

Malleus - Hammer Incus - anvilStapes - stirrup

○ Eustachian TubeInner Ear is where transduction of sound

information occurs.○ Cochlea (snail) with the○ Oval Window○ Round Window

The Ear

The Cochlea and Sound Transduction

The Cochlea - Latin for snail which is what it looks likeBasilar membrane runs most of the length of the

cochlea dividing in the top and bottom.○ The base is right below the oval window where the

sound energy enters○ The apex is at the other end.

Hair Cells are the receptors and run the length of the Basilar Membrane in two sets○ inner 1 row ~ 3500○ outer 3 rows ~20000

Tectorial Membrane - across top of Hair Cells

The Cochlea and Sound Transduction - 2

Auditory TransductionTransduction is the conversion of energy from one

form to another, e.g., sound pressure to neural impulses

The Traveling Wave.○ Wave set up by action of stapes on oval window○ Point of Maximal Displacement depends upon the

frequency of the tone.High Frequencies near the base.Low frequencies near the apex.

The Shearing Force○ The traveling wave bends the basilar membrane ○ This bends the hair cells.

Loudness The experience of sound most closely related to

amplitude or intensity.Examples of sounds at different dB SPL levels for

comparison.Rustling Leaves =~20 dBAverage Speaking Voice =~60 dBHeavy Traffic =~80 dBRock Band =~120 dBPain/Damage Threshold =~130 to 140 dB

Loudness differs in many ways from intensity.○ The threshold depends upon intensity and frequency.○ Intensity doubles every 6 dB; loudness doubles

every ~8 dB.

Half as Loud

Gain dB0

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Gain vs. dB of 1000 Hz Tone at Half as Loud

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Pitch The dimension of sound that most closely relates to

frequency. The higher the frequency the higher the pitch. Discrimination between two pitches depends on the

frequency of the lower pitch:

Weber Fraction: (f1 - f2)/f2 = 0.004

e.g.

(251-250)/250= 0.004

(1004-1000)/1000=0.004

Pitch is not the same as frequency○ Pitch will change as intensity is increase and frequency is kept

constant.

The Interdependence of Loudness and Pitch

First studied by Fletcher and Munson (1933). Called Fletcher-Munson Curves or Equal

Loudness Contours.Method:

○ Subjects adjusted tone of different frequencies to match loudness of 1000 Hz tone

○ the intensity of 1000 Hz tone was varied over trials.Thus, all tones that match a 1K Hz tone of a

given intensity should all be equally loud and connecting those on a graph of intensity by frequency should give an equal loudness contour.

The Interdependence of Loudness and Pitch - 2

As intensity of the 1K Hz tone increase, the contours get flatter.

Relates to the Loudness button on your stereo.

This relationship again illustrates the difference between physical dimensions and psychological experience.

Application to Human Factors Sound Button on Stereo

Most recording are at region where loudness if fairly constant across frequency.

We may play at a lot lower level where loudness does depend on frequency

Alters what we hear because we lose sensitivity to low and high frequencies faster than middle frequencies.

Sound button compensates for this by boosting high and low frequencies.

Fourier Analysis A mathematical procedure to break down complex

waveforms in to simple components, usually sinewaves.

The ear does something like this.

Fourier Analysis - 2 Let us use this stimulus as our complex

wave.It is called a square wave.

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How Fourier Analysis Works - Briefly The Frequency Domain

Frequency of Sinewave along the x-axisAmplitude of Sinewave along the y-axis

How Fourier Analysis Works - Briefly 2

Visual Illustration Auditory online illustration

Effects of Multiple Tones Beats

Perception of intensity changes from two nearby frequencies

From constructive and destructive interference Frequency of beating is difference in

frequency between the two tones, e.g. 101-100 = 1 Hz beats

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Effects of Multiple Tones - 2

Missing fundamental Fundamental is lowest pitch of a tonehigher frequencies called harmonics or

partialsPerceive a same pitch even without

fundamentalAllows us to tell female vs. male voices on

the telephone.

The Missing Fundamental

Removing the Fundamental

Full vs. Octave

Octave vs. Missing Fundamental

Masking

DEFINITION: one tone is rendered less

perceptible by another auditory stimulus. Tone Masking

low tones will mask higher tones better. due to shape of traveling wave (skewed towards base,

higher frequencies). Noise Masking

Noise is sound energy that lacks coherence. Beyond a point adding more frequencies to the noise

does not increase masking. Critical bands: region of basilar membrane where sound

energy is summed together.

Application to Human Factors Consider Noisy Environments

How keep all the sounds distinguishable?

Consider sirens and other alerting sounds?Is simply loud enough or necessary?

The Perception of Auditory Direction Eyes can see only in one direction at a time.

Ears are not so limited. Interaural Time of Arrival Difference/Phase

Description - sound has to travel farther to ear on farther side of head

This difference can be detected if as small as 0.1 msec.

Works for clicks and tones with frequencies < 1000 Hz

Precedence Effect - Tendency to suppress later arriving parts of a sound

The Perception of Auditory Direction - 2

Interaural Intensity DifferencesDescription - Head shadows sound so that

farther ear will hear a slightly less intense sound.

Just as we suppress later sounds, we suppress less intense sounds.

Works best for relatively high frequencies.

This ability to hear sounds from all directions is useful to design alerts.

Signal Detection Theory The Detection Situation

The Stimulus is:

Subject

Judges

Stimulus

to be:

Present Absent

Present Hit False Alarm

Absent Miss CorrectRejection