Sensation and Perception

Sensation and Perception

1. Taste

   • The physical stimuli for taste are chemicals that can be dissolved in water.
     • Gustatory receptors are taste buds that line the trenches around tiny bumps on the tongue called papillae
       • Four primary types of taste
         • Sweet
           • Sour
             • Bitter
               • Salty
   • People are born with certain density of taste buds on the tongue.
     • Supertasters have 4 times as many taste buds as nontasters. These are two extremes on a continuum. Women are more likely to be supertasters then men
       • Supertasters are often less fond of sweets and high fat foods, dislike veggies, alcohol and smoking

2. Stimulus Intensity

   • Threshold
     • Absolute threshold
       • The stimulus intensity that is detected 50% of the time
     • Dividing point between energy levels that do and do not have detectable effect

3. Weber's Law

   • The size of JND is a constant proportion of the size of the initial stimulus and is known as "Weber's Fraction"
     • This applies to all the senses

4. Fechner's Law

   • The amount of your sensory experience is proportional to the number of JND's that the stimulus above absolute threshold
     • The same amount of increase in the stimulus brings about smaller and smaller increases in the perceived increase

5. Sensory Adaptation

   • The gradual decline in sensitivity to prolonged stimulation
     • Not noticing the ring on your finger / do not notice the smell of garbage after a while because you don't get any new stimulation from your sensory receptors

6. The Eye

   • Lens
     • Transparent structure with muscles attached to it focus the light
   • Pupil
     • The opening of the Iris, it determines how much light is let into the eye
   • Retina
     • Rods
       • Specialized visual receptors that play a key role in night and peripheral vision and are sensitive to dim light
     • Cones
       • Specialized visual receptors that play a key role in daylight and colour vision
     • The neural tissue lining the inside of the back surface of the eye

7. Definitions

   • Sensation
     • A physical feeling or perception resulting from something that happens to / or comes into contact with the body
   • Perception
     • Ability to see, hear, or become aware of something through the senses
   • Psychophysics
     • Study of how physical stimuli are translated into psychological experience

8. The Brain

   • The optic nerve is a collection of axons that connect the eye with the brain
     • The receptive field of a visual cell is the retinal area that when stimulated affects the firing of that cell
       • The optic nerve leaves the retina, goes to the thalamus and on to the visual cortex in the occipital lobe
         • Optic nerve is divided and crosses at the optic chiasm the point where the optic nerves from inside half of each eye cross over and go to the other side of the brain
           • Information from the outside of each eye goes straight to the same side of the brain.

9. Theories of Colour

   • Trichromatic Theory
     • Hermann von Helmholtz (1852) stated that the human eye hasthree types of receptors with different sensitivities to different light wavelengths, specifically red, blue, and green.
       • The eye mixes theses three colours to make any colour that we can see
         • Televisions work this way
     • ( Tri ; Three, Chroma : colour )
   • Opponent Theory
     • Ewald Hering (1878) proposed the theory that colour perception depends on receptors that make opposite responses to the three pairs of colours
       • Blue / Yellow
         • Red / Green
         • Black / White
         • These are also the colours of the afterimages you get.
   • Colour Vision
     • The visible spectrum, the shortest wavelengths appear violet and the longest appear red
       • It is a psychological interpretation because colour is not a physical property of light so the colour simply appears to us

10. Top-down Processing

    • Bottom-up Processing
      • Used in feature analysis. Start at parts and build towards the whole
    • Brain uses this also like reversible figures or when we perceive a word before we know all the individual letters

11. Hearing

    • Properties of sound
      • 1) Wavelength or frequency
        • Pitch
      • 2) Wave amplitude
        • Quality of loudness
      • 3) Wave purity or mixture
        • Timbre or complexity of sound wave
    • Stimulus for the auditory system is sound
    • Sensory processing
      • 1) Outer ear
        • Sound is conducted by vibration of air molecules
          • Pinna
            • Sound collecting cone which funnels sound waves into the auditory canal and then to the eardrum
          • Eardrum : a taut membrane that vibrates in response to sound waves
      • 2) Middle ear
        • Sound is conducted by vibration of movable bones
          • Ossicles
            • Smallest bones in body : Hammer, Anvil, Stirrup
              • Lever system and amplify tiny changes in pressure
      • 3) Inner ear
        • Sound is conducted by waves in a fluid which are then converted into neural signals and sent to the brain
          • Cochlea
            • snail like structure with neural tissue
          • Basilar Membrane
            • runs the length of the cochlea and holds the auditory receptors call hair cells
          • Hair Cells
            • Stimulated by waves of fluid.
              • Neural signals are routed though the thalamus to the auditory cortex in the temporal lobe which has a feature detectors of sound

12. Smell

    • Physical stimuli are chemical senses dissolved in the mucous in the nose
      • Receptors for smells are called olfactory colia, hairlike structures in the upper portion of the nasal passages.
      • Pheromones are chemical messages that can be sent by one member of a species to another and usually linked to sexual attraction

13. Touch

    • Nerve endings in our skin can sense pressure, pain, and temperature
      • Tactile stimulation :(sensing pressure) we can sense where a feather has touched us
        • Parts of the skin have receptive fields with a centre surround arrangement like the eye has with an excitatory centre and inhibitory surround or vice versa
      • Sensing Pain
        • Messages are sent to the brain through two different pathways and through two different parts of the thalamus
          • Fast pathway uses myelinated neurons and registers localized pain in a fraction of a second
          • Slow pathway uses unmyelinated neurons and lets us know about less localized, longer lasting aches and burning pain that comes later
        • One may feel less pain after being distracted, or receiving a placebo. This shows that cognitive and emotional processes in the higher brain centres must be able to block signals from the skin receptors

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