Sensation

1
Sensation

• How do we know what is real?
• Locke and the empiricists Is sensation where
  knowledge begins?
• The fear of the Lord is the beginning of
  wisdom. (Proverbs 17)

2
Sensation and bottom-up processing

• How do we know what is real? Empiricism and
  epistemology
• Experience is traditionally divided into two
  parts
• Sensation
• Perception
• But they are intimately connected.

3
The psychology of sensation

• Psychophysics What is the relationship between
  the physical characteristics of a stimulus and
  the psychological experience of it?
• Sensory physiology How do sense organs, receptor
  cells, and neural circuits respond to physical
  stimuli?
• Transduction and coding
• Place or anatomical coding
• Temporal coding Rate and pattern

4
Psychophysics and thresholds Scaling.

• The absolute threshold (Reiz Limen) in classical
  psychophysics serves as the zero point.

5
More measures of Absolute Threshold
6
Signal detection and relative thresholds

• Subliminal stimulation Priming emotions
• Difference thresholds Weber, Fechner, and the
  jnd
• Which is louder?

7
Sensory adaptation

• Receptor fatigue
• Habituation
• The Troxler effect

8
Habituation

• Saccadic movement
• Stabilizing the retinal image

Mounting an LED or a miniature projector on a
contact lens produces a fixed retinal image.
9
The physics of light

• Light energy characteristics
• Waves and particles
• Frequency
• The visible spectrum 380nm to 760 nm

• Ultraviolet and infrared
• Amplitude or intensity
• Purity

10
The structure of the eye and the physics of light
11
Physics of light and the visual system

• Sensitivity and reliability
• Retinal cells
• Rods and cones
• The fovea
• Accommodation
• Binocular disparity

12
Color vision

• Young Helmholtzs trichromatic theory
  Different colors are sensed by cones containing
  different photopigments
• Green photopigment, in 50 of cells
• Red photopigment, in 45 of cell
• Blue photopigment, in 5 of cells
• Sensed color depends on which combinations of
  cones are absorbing light in their photopigments.

13
Opponent process theory

• Herings theory of ganglion cells
• Red/Green cells
• Yellow/ Blue cells
• Sensed color is coded by rate of firing Faster
  for red and yellow slower for green and blue.
• Habituation of ganglion cells produces negative
  afterimages.

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Negative afterimages
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Color Blindness

• Sex-linked conditions Genes on X chromosome, so
  more common in men.
• Protanopia, missing red photopigment
• Deuteranopia, missing green photopigment
• Non-sex-linked condition
• Tritanopia, missing blue photopigment or blue
  cones

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18
What do you see?