1. Sensation Psychology 1106

2. Introduction ► To talk to someone we have to hear what they say ► To catch a ball, we have to see it coming ► How does the external get internalized  That in essence, is what sensation is ► Bottom up vs. Top down processing  Sensation is bottom up  Perception is top down

3. Basic Principles ► Thresholds  We sense some things and not others  Faintest stimuli ► Absolute threshold  Difference thresholds or jnds ► Proportion ► Stimuli must differ by a constant proportion to be seen as different  Weber’s Law

4. Signal Detection Theory ► When will we detect stimuli? ► Have to filter out the background noise  Can be internal or external ► Hits vs. misses ► False alarms vs. rejections

6. What about subliminal messages? ► “listen to these tapes, they are only 499.95’ ► We don’t know what the stimulus is, and, it can affect our behaviour for a brief period ► Does it make us buy coke?  NO NO NO NO NO ► CBC Experiment ► WTWO experiment ► http://www.snopes.com/business/hidden/popcorn.asp http://www.snopes.com/business/hidden/popcorn.asp  What about backward masking… ► Umm, no

7. Sensory adaptation ► Getting used to something ► If you stop your eyes from moving, everything would go grey! ► Same thing if you give them constant stimulation, the ping pong ball trick ► Ever notice how everybody else’s house smells funny and yours has no smell at all?

8. Vision ► Like any sensory process, vision converts some energy to neural messages ► In this case, light ► Light is just a form of electromagnetic radiation ► So are x rays, micro waves, infra red, UV cosmic rays etc

10. I wish to hell I could see better…. ► Wavelength of light determines hue ► Intensity determines brightness ► Light enters the eye through the cornea and the pupil ► Pupil size regulated by iris ► Behind pupil, lens, which accomodates ► Light hits the retina ► Oh ya, it is upside down….

11. Acuity ► Acuity is affected by the shape of the eye ► Nearsighted, eye too long, or cornea too curved ► So far away stuff is blurry ► Image is in front of the retina ► Farsighted, opposite

12. The retina ► There are two kinds of receptors in the retina, rods and cones ► Rods for night, brightness ► Cones for day, colour ► When a photon hits a receptor it sends a message via the optic nerve to the brain ► Because of this, we have a blind spot!

13. Gotta love the retina ► Cones are for fine detail and colour ► Cones only really work in the light ► Concentrated in the fovea ► Rods are more evenly distributed ► Many rods to one bipolar cell, so you can see in dim light, but only in black and white ► One rod, one bipolar cell ► About 130 000 000 receptors per retina

14. Its all about me…. ► There are disorders that can lead to problems for the retina ► Albinism ► Pigment guides growth of visual system ► I have no fovea ► My eyes are wired ipsilaterally

15. And now we leave the eye.. ► Further up the system there are feature detectors ► Hubel and Wiesel and cats and Swedish Kings  Cells in cortex that respond to different line orientation  Truly cool, maybe they network together to recognize objects?

16. More Feature Detectors ► Dave Perrett’s work on face recognition in monkeys ► Monkeys have cells in their cortex that respond only to a specific monkey! ► Sort of like one of those ‘Grandmother’ cells.  Probably a hierarchical network  Hughlings-Jackson Principle

17. ► Processing has to be parallel ► Imagine doing it serially! ► 130 000 000 receptors, one after the other ► You probably wouldn’t live long enough to recognize a triangle ► The ability to process in this fashion could be blown out by a stroke

18. Colour vision ► Trichromatic theory ► Opponent process theory ► Three types of cones  Red-green  Blue-yellow  Black-white ► Explains afterimages

19. ► Stare at this

21. Colour constancy ► Weird thing is that we see things as having the same colour even if they move in to different light conditions ► So a gold coin, reflecting blue light, still looks gold ► More of a perceptual thing than anything else

22. Hearing ► Just like vision, we are converting one form of energy to another ► Sound is just changes in air pressure ► Sound pressure level ► dB ► 100 dB is 10 times louder than 90 dB

23. The Ear ► Outer ear sort of sucks sound in towards the eardrum ► Middle er transmits vibrations from the eardrum to hammer, anvil and stirrup ► Gets to the snail shaped cochlea in the inner ear ► Fluid vibrates ► Movement detected by hair like projections on the basilar membrane

24. Pitch ► Frequency of sound ► Place theory  Different frequencies make different parts of the membrane vibrate  High frequencies, start of cochlea  Hmm, low frequencies are less localized ► Frequency theory  Frequency of vibrations?  But how do we hear over 1000 Hz? ► Probably both

25. Sound Localization ► Sounds hit ears at different times, with different volumes ► So left right distinction is really pretty easy ► Up down is VERY hard, if not impossible ► We usually do up down in concert with other senses

26. Other senses ► Touch  Pressure  Warmth  Cold  Pain ► Pressure is easy to understand, 1 to 1 relationship ► There are more receptors some places than other places

27. Come on come on come on come on and touch me baby ► Pain  Probably a gate that selectively blocks pain  Stimulation  Cognitive effects ► Strangely enough there are different receptors for cold and warmth

28. Taste ► Sweet ► Sour ► Bitter ► Salty ► Unami ► Carbohydrate? ► Makes lots of evolutionary sense ► Need the interaction with smell and vision