Sensation

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Sensation

• Psychology 1106

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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

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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
• Webers Law

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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

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What about subliminal messages?

• listen to these tapes, they are only 499.95
• We dont 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

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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 elses house smells
  funny and yours has no smell at all?

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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

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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.

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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

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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!

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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

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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

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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?

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More Feature Detectors

• Dave Perretts 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

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• Processing has to be parallel
• Imagine doing it serially!
• 130 000 000 receptors, one after the other
• You probably wouldnt live long enough to
  recognize a triangle
• The ability to process in this fashion could be
  blown out by a stroke

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Colour vision

• Trichromatic theory
• Opponent process theory
• Three types of cones
• Red-green
• Blue-yellow
• Black-white
• Explains afterimages

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• Stare at this

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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

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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

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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

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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

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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

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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

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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

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Taste

• Sweet
• Sour
• Bitter
• Salty
• Unami
• Carbohydrate?
• Makes lots of evolutionary sense
• Need the interaction with smell and vision