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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.

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Psychology 1106


  • 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
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
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
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


    • What about backward masking…

      • Umm, no

Sensory adaptation
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?


  • 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
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 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
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
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
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
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
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
Colour vision

  • Trichromatic theory

  • Opponent process theory

  • Three types of cones

    • Red-green

    • Blue-yellow

    • Black-white

  • Explains afterimages

Colour constancy
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


  • 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
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


  • 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
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
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
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


  • Sweet

  • Sour

  • Bitter

  • Salty

  • Unami

  • Carbohydrate?

  • Makes lots of evolutionary sense

  • Need the interaction with smell and vision