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.
2
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