Human InformationProcessing

Li Liu

Human Computer Interaction

How much information canshe receive?

”Human InformationProcessing”

Case 1

Personal Area Network

Principle

Speech – Control Technology

Name Dialing

Hand Free

Speech Recognizer

SpeechRecognizer

”repeat”

Speech Signal Waveform

Effect of Background Noises

Performance

Speech-to-Noise Ratio (dB)

Word

s C

orr

ect

Rate

(%

)

-30 0

100

0

Lip Tracker

Performance of Speech Recognition

Speech-to-Noise Ratio (dB)

Word

s C

orr

ect

Rate

(%

)

-30 0

100

0

Auditorycues only

Auditory andvisual cues

How to Design A Headset?

Tip ?

Mobile Phones

Braille Code for English

Tactile Display

Problem: Usable?

Efficiency?

Reliability?

Braille Code for English

How Many Letters Can be Represented?

Combination

Tactile Pins

Braille Code for English

W=2.4093The average number of active tactile pins.

Wopt=1.2118Letters in written English

New Code

W=1.2316

Information

If all eight horses are equally good, then the chance for a horse to win the race is 1/8!

Information Theory

What is the probability?

The probability for a horse to win is

Pi=1/8

Information Theory

If a horse wins the game, how much information is it given?

How to measure information?

Measure of information

• A source A={a1,a2…aN} the probability of each event P={P1,P2…PN}

• More information if Pi is low, less information is Pi is high

• I(ai)=log(1/Pi) is called self information1/81/41/2 1/1

6

1/81/81/8 1/8

Entropy

Taking the mean value over all symbols with the alphabet

i 2 iH(x) P log P (bits / symbol) 1/81/41/2 1/1

6

1/81/81/8 1/8

Communication Theory I

If R < H error-free representation impossible!

H

source

R

Coding

1/81/81/8 1/8

000 001 010 111

1/81/41/2 1/16

0 10 110 1110111100111101111110111111

How much information does a picture contain?

255

254

0

How much information does a picture contain?

Suppose the size of a picture is 256 x256,And each pixel is represented by 8 bits, thenTotal bits to represent such a picture is

8x256x256= 524288 bits/picture

How many pictures can be represented by a half Mbits?0100110101000011101110101010..............

Total number of pictures

2524288 = 10158000

How many pictures have human beings been perceived

Up to now, the number of all pictures which have been perceived by human beings is only1019.

Assume that 30 frames of pictures per second are perceived by human eyes. If the averagelife-span is 70 years and 8 hours per day are spent on sleep, then about 108 frames arereceived by one person in all his/her life. Furthermore, if the total number of human beings who lived in the earth is 1011, then, thetotal number of all pictures which have been perceived by human beings is only1019. 1019 <<< 10158000

Entropy of an image

H=6.9

45 001123 00010208 00011

intensity

probability

Entropy of human face images

A face image = 50 bytes (400 bits) !

Communication

Brain Wave

C

channelsource

H

Communication Channel

Abstract Channel Model

Ex. Noiseless Binary Channel

0

1 1

0Channel Capacity

C= 1 bit

Communication Channel

Abstract Channel Model

Ex. Noisy Binary Channel

Channel Capacity

C= 1 + p log2 p + (1-p) log2 (1-p) bits

1 1

0 0

p

p1-p

1-p

Communication & Design

transmittertransmitter

receiverreceiver

Different Decoders

”When a group of people look at an object, none of them sees exactly the same thing as anyone else. Even if they receive approximately the same image on their retina and interpret the image in basicallythe same way, this image is always revised by theobserver’s personality and situation.” Rune Monö

Real-World Channel Model

Ex. Band-limited Gaussian Channel

Z(t) Gaussian noise

X(t) Y(t)

C = Wlog2(1+P/N) bits/s

W: channel bandwidthP/N: signal to noise ratio

Telephone signals are band-limited to 3300Hz and have a SNR of 20 dB (P/N=100),

C=3,300 log (1+100)= 22,000 bits/s

Practical modems achieve transmission rates up to 19,200 bits/s

Real-World Channel Model

Communication Theory II

If H <= C lossless transmission possible

If H > C lossless transmission impossible!

C

Channel

RH

Source

Brain Wave

Information Rate

sensation perception cognitiondata information knowledge

CognitiveBandwidth

PerceptualBandwidth

SensoryBandwidth

Information Rates

Sense Information StreamBits/s

Vision 10.000.000

Hearing 100.000

Touch 10.000

Smell 1.000

Taste 1.000

Sense Bandwidth of consciousness bits/s

vision 40

hearing 30

touch 5

Taste and smell 1

Channel=”Bandpass Filter”

Effect of degrading the speech signal by spectral filtering

The original speech signal contains significant energy up to 7 kHz

a) signal bandpass filtered (0.25 - 0.75 kHz)

b) signal bandpass filtered (1.0 – 3.0 kHz)

c) original signal

Effect of Bandpass

Bandpass System

Most long-haul transmission systems have a bandpassFrequency response

The transfer function can be written as

)(11)(

ffo

fofjQ

fH

where the resonant frequency fo and quality factor Q are

LCof

21 L

CRQ

ou l

fQB f f

The 3dB bandwidth between the lower and upper cutoff

frequencies is

=

R

L C

fl fo fu

f

1.00.707

B

Bandpass System

Since practical tuned circuits usually have 10 < Q <100,the fractional bandwidth B/fc should be kept within the range

c

B0.01 0.1

f

As a rough rue of thumb, the carrier frequencies and corresponding nominal bandwidth can be

cB 0.02f

Bandpass System

Frequency band Carrier frequency

Bandwidth

Longwave radio 100 kHz 2 kHz

Shortwave radio 5 MHz 100 kHz

VHF 100 MHz 2 MHz

Microwave 5 GHz 100 MHz

Millimeterwave 1 00 GHz 2 GHz

Optical 5x1014 Hz 1013 Hz

Selected carrier frequencies and nominal bandwidth