Transcript Overview of Human

Overview of Human-Machine Systems
Muscular Feedback
Cognitive Functions
Sensory Systems:
Human Input
Motor Functions:
Human Output
The Human-Machine Interface
Displays:
Machine Output
Controls:
Machine Input
Feedback within Machine
Mechanisms of Machine:
Performs Task and Determines State
Physical
Stimulus
Light,
Sound,
Pressure,
Chemical substances,
Temperature, etc.
Perception/
Cognition
Our
experience
Accessory
Structures
Eye (cornea , lens …)
Ear (pinna, ossicles…)
Skin,
Tongue (tastebuds),
….
Receptors
(Transduction)
Neural
Processing
Locally and centrally
so many steps
Behavior
The output of all this
Rods,
Cones,
Hair cells
Chemoreceptors
Pacinian
corpuscles
…..
General Characteristics of Sensory Systems
Stimulus
In Vision
Light
In Audition
Sound

Receptor
Neural Relay
Cortex
Rods/Cones
LGN of Thalamus
Striate
Hair Cells
MGN of Thalamus
Sup.
Temp. G.
Other Generalities
 Always more than one pathway in brain
 Always more than one brain target
 Ultimately sensory information is combined
The Physical Stimulus for
Audition java illustration
•The sound wave is periodic changes in pressure
Air Pressure
1.5
Amplitude
or
Intensity
Wavelength
1
0.5
0
-0.5 0
90
180
270
360
-1
-1.5
Frequency =
1/Wavelength
Time
•Frequency = cycles/second = Hertz, Hz.
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.
 P12 
dB  10 log 2 
 Pr 
 P1 
dB  20 log  
 Pr 
Where P = air pressure; P2 = power
 dB SPL, P2=0.0002 dynes/cm2 which is near the absolute
threshold for hearing.
The Physical Stimulus for Audition - 3

Resonance
 All 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 <> pitch
 amplitude <> 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 - anvil
 Stapes - stirrup
○ Eustachian Tube
 Inner 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 like
 Basilar 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 Transduction
 Transduction 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 dB
Average Speaking Voice
=~60 dB
Heavy Traffic
=~80 dB
Rock Band
=~120 dB
Pain/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
1
0
-2
0.8
0.7
-4
0.6
0.5
-6
0.4
-8
0.3
0.2
-10
0.1
0
-12
Gain
dB
Gain vs. dB of 1000 Hz Tone at Half as Loud
dB
Gain at Half Loud (rel int)
0.9
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.
Air Pressure Level

0.9
0.4
-0.1 0
100
-0.6
-1.1
Time
How Fourier Analysis Works Briefly

The Frequency Domain
 Frequency of Sinewave along the x-axis
 Amplitude 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. 101100 = 1 Hz beats
3.5
Air Pressure Level

2.5
1.5
0.5
-0.5
-1.5
-2.5
105 Hz
0
0.5
1
1.5
100 Hz
2
Sum
-3.5
-4.5
-5.5
Time
2.5
3
3.5
4
Effects of Multiple Tones - 2

Missing fundamental
 Fundamental is lowest pitch of a tone
 higher frequencies called harmonics or
partials
 Perceive a same pitch even without
fundamental
 Allows 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 Differences
 Description - 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:
Present
Subject Present
Judges
Stimulus
Absent
to be:
Absent
Hit
False Alarm
Miss
Correct
Rejection