Sensation Psychology 1106
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
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
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
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 • What about backward masking… • Umm, no
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?
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
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….
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
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!
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
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
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?
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
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
Colour vision • Trichromatic theory • Opponent process theory • Three types of cones • Red-green • Blue-yellow • Black-white • Explains afterimages
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
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
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
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
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
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
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
Taste • Sweet • Sour • Bitter • Salty • Unami • Carbohydrate? • Makes lots of evolutionary sense • Need the interaction with smell and vision