Overview of Human-Machine Systems: Muscular Feedback, Cognitive Functions, Sensory Systems

1. 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

2. Physical Stimulus Accessory Structures Light, Sound, Pressure, Chemical substances, Temperature, etc. Eye (cornea , lens …) Ear (pinna, ossicles…) Skin, Tongue (tastebuds), …. Receptors (Transduction) Rods, Cones, Hair cells Chemo- receptors Pacinian corpuscles ….. Perception/Cognition Neural Processing Our experience Locally and centrallyso many steps Behavior The output of all this

3. General Characteristics of Sensory Systems Stimulus Receptor Neural Relay Cortex In 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 brain • Always more than one brain target • Ultimately sensory information is combined

4. The Physical Stimulus for Audition java illustration • The sound wave is periodic changes in pressure Amplitude or Intensity Wavelength Frequency = 1/Wavelength • Frequency = cycles/second = Hertz, Hz.

5. 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.

6. 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

7. 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

8. 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

9. The Ear

10. 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

12. 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.

13. 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.

14. Half as Loud

15. 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.

16. 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.

17. 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.

18. 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.

19. Fourier Analysis • A mathematical procedure to break down complex waveforms in to simple components, usually sinewaves. • The ear does something like this.

20. Fourier Analysis - 2 • Let us use this stimulus as our complex wave. • It is called a square wave.

21. How Fourier Analysis Works - Briefly • The Frequency Domain • Frequency of Sinewave along the x-axis • Amplitude of Sinewave along the y-axis

22. How Fourier Analysis Works - Briefly 2 • Visual Illustration • Auditory online illustration

23. 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

24. 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.

25. The Missing Fundamental

26. Removing the Fundamental

27. Full vs. Octave

28. Octave vs. Missing Fundamental

29. 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.

30. 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?

31. 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

32. 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.

33. Signal Detection Theory • The Detection Situation The Stimulus is: Subject Judges Stimulus to be: