Human InformationProcessing Li Liu

Human Computer Interaction How much information can she receive? ”Human Information Processing”

Case 1

Personal Area Network

Principle

Speech – Control Technology Name Dialing Hand Free

Speech Recognizer Speech Recognizer ”repeat”

Speech Signal Waveform

Effect of Background Noises

Performance Speech-to-Noise Ratio (dB) Words Correct Rate (%)

Lip Tracker

Performance of Speech Recognition Speech-to-Noise Ratio (dB) Words Correct Rate (%) Auditory cues only Auditory and visual 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= The average number of active tactile pins. W opt = Letters 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 P i =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={a 1,a 2 …a N } the probability of each event P={P 1,P 2 …P N } More information if P i is low, less information is P i is high I(a i )=log(1/P i ) is called self information 1/81/41/21/161/8

Entropy Taking the mean value over all symbols with the alphabet 1/81/41/21/161/8

Communication Theory I If R < H error-free representation impossible! H source R

Coding 1/ /81/41/21/

How much information does a picture contain?

How much information does a picture contain? Suppose the size of a picture is 256 x256, And each pixel is represented by 8 bits, then Total bits to represent such a picture is 8x256x256= bits/picture How many pictures can be represented by a half Mbits? Total number of pictures =

How many pictures have human beings been perceived Up to now, the number of all pictures which have been perceived by human beings is only Assume that 30 frames of pictures per second are perceived by human eyes. If the average life-span is 70 years and 8 hours per day are spent on sleep, then about 10 8 frames are received by one person in all his/her life. Furthermore, if the total number of human beings who lived in the earth is 10 11, then, the total number of all pictures which have been perceived by human beings is only <<<

Entropy of an image H= intensity probability

Entropy of human face images A face image = 50 bytes (400 bits) !

Communication

Brain Wave C channel source H

Communication Channel Abstract Channel Model Ex. Noiseless Binary Channel Channel Capacity C= 1 bit

Communication Channel Abstract Channel Model Ex. Noisy Binary Channel Channel Capacity C= 1 + p log 2 p + (1-p) log 2 (1-p) bits p p 1-p

Communication & Design transmitter receiver

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 basically the same way, this image is always revised by the observer’s personality and situation.” Rune Monö

Real-World Channel Model Ex. Band-limited Gaussian Channel Z(t) Gaussian noise X(t) Y(t) C = Wlog 2 (1+P/N) bits/s W: channel bandwidth P/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 R H Source

Brain Wave

Information Rate sensationperceptioncognition datainformationknowledge Cognitive Bandwidth Perceptual Bandwidth Sensory Bandwidth

Information Rates SenseInformation Stream Bits/s Vision Hearing Touch Smell1.000 Taste1.000 SenseBandwidth of consciousness bits/s vision40 hearing30 touch5 Taste and smell1

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 ( 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 bandpass Frequency response The transfer function can be written as where the resonant frequency f o and quality factor Q are The 3dB bandwidth between the lower and upper cutoff frequencies is = R LC flfl fofo fufu f B

Bandpass System Since practical tuned circuits usually have 10 < Q <100, the fractional bandwidth B/f c should be kept within the range As a rough rue of thumb, the carrier frequencies and corresponding nominal bandwidth can be

Bandpass System Frequency bandCarrier frequency Bandwidth Longwave radio 100 kHz 2 kHz Shortwave radio 5 MHz100 kHz VHF 100 MHz 2 MHz Microwave 5 GHz100 MHz Millimeterwave1 00 GHz 2 GHz Optical5x10 14 Hz Hz Selected carrier frequencies and nominal bandwidth