• perception is learnt, not born with

stimulus

  • a change outside or inside the body
  • may result either in sensation or perception
  • a stimulus of adequate strength is always sensed first
  • not all sensations turn into perceptions
    • i.e.: blood gas levels
      • levels of oxygen in blood
      • imperceivable to human perception
      • changes in such stimulus are sensed

perception

  • a conscious appreciation of stimulus or energy
  • somethings can be perceived even without stimulation
  • eg: phantom limbs
    • limbs are perceived to be there when it isn’t there
  • the biggest challenge for perception is interpretation
    • humans are bad eye witnesses because of biology
    • perception is entirely about interpretation

stimulus magnitude - weber’s law

  • the magnitude of the stimulus is not perceived accurately
    • stimulus itself is a change in something
    • the amount of change is not perceived accurately
    • the magnitude of the stimulus is only perceived in relationship to the background
  • \( \Delta P \propto \frac{\Delta S}{S_0} \)
    • \(\Delta P \): Perceptual Magnitude
    • \(S \): Stimulus Intensity
    • \(S_0 \): Background Stimulus Intensity
screens
  • one backlit screen is not better than the other
    • depends on what the background stimulus is

stimulus set

  • stimulus and perception get mixed up
  • stimulus does not predict perception
    • perception depends on background stimulus as well
  • perception is adapted in each animal to enable biological success
examples
  • wavelength is a stimulus perceived as color
    • light inherently has no color
    • 400 nm - 700 nm: visible electromagnetic radiation

  • noxious/injury is stimulus perceived as pain

  • sugar
    • perception is ‘yum’ when eating 1
    • perception is ‘disgusting’ when eating 13

disconnect and road to perception

  • stimulus is disconnected from perception
  • a long road connects stimulus to perception

out-of-body stimulus

  • stimulus like changes in light, changes in sound waves, changes in mechanical energy, touch etc are out-of-body stimuli
    • is the input to the perception path

  • output is perception which depends on the cerebral cortex (neocortex)

  • the outside energy is modulated to neural energy by modulation via
    • transduction of stimuli
    • transmission in thalamus
      • interpreter for the stimuli
    • cerebral cortex perception
  • modulation happens at every level
    • at transduction: taking warm shower being sun burnt
    • at transmission and perception:
      • different people react differently while being administered an injection
      • any food tastes great when very hungry
      • water tastes great when thirsty

errors in perception

  • two basis places where perception goes wrong
    • transduction
      • for both vision and hearing, this is a big part of where things go wrong
    • transmission
      • for vision, stroke causes perception errors
  • perception is not reality necessarily
    • this is a dire misconception

senses

some types of senses

  • vision
    • modalities
      • lowlight/ motion
      • color
  • hearing
  • smell
  • taste
  • touch
    • modalities include
      • light touch
      • hair-bending
      • vibration
      • cool
      • warm
      • pain, aching, stabbing
      • texture

  • vestibular sense: where we are in sense

  • flavor is a combination of smell (70%), touch (20%) and taste (10%)
    • food can taste and smell good, but have a bad temperature or texture
    • flavor is a compound sensation