Distinguishing Reality from Illusion

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Distinguishing Reality from Illusion

• Visual sensation and perception A model for the
  other sensory systems

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Common Properties of the Senses

• Gather and amplify stimulus energy
• The distal stimulus (anything outside the body)
• The proximal stimulus (receptors inside the body)
  
• Transduction
• Receptors transform physical stimulus energy into
  electrical signals
• Sensory coding
• Translation of stimulus information into
  dimensions of sensation and perception (e.g.,
  intensity less vs. more bitter quality sweet
  vs. sour)
• Interaction between sensory system and other
  parts of the system (e.g., adaptation of taste),
  in time (past vs. present) and/or space (one
  region vs. another)

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Sensation and Perception The Distinction

• Sensation (bottom-up processing)
• Stimulation of sense organs
• Perception (top-down processing)
• Selection, organization, and interpretation of
  sensory input

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VisionThe StimulusGathering in

• Light electromagnetic radiation
• Amplitude Amplificationinteraction the
  perception of brightness
• Wavelength perception of color
• Purity mix of wavelengths
• perception of saturation, or richness of colors

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• (Based on Figure 4.2, Weiten)

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The Eye A Living Optical Instrumentwhere
Transduction begins
Sizes Pupil
Pupil
Regulates light
Focuses
Light enters
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The Retina The Brains Envoy in the Eye

• Retina Transduction
• Optic disk
• Receptor cells
• Transduction
• Rods
• Cones
• Adaptation
• Interaction

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Interaction
Cones are more sensitive here
Rods are more sensitive here

• Figure 4.5, Weiten

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Light
1 rods cones

• Bipolar, ganglion cells

3. Optic nerve
4. Optic chiasm
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Theories of Color Vision

• Trichromatic theory Young and Helmholtz
• Opponent Process theory Hering
• antagonistic colors red/green, blue/yellow,
  black/white
• Current perspective both theories necessary

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• Figure 4.15, Weiten

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Perceiving Forms, Patterns, and Objects

• Feature analysis
• Reversible figures and
• perceptual sets
• (Top-down)
• Gestalt psychologists
• the whole is different
• from the sum of its parts

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Bottom-up processing

• Figure 4.17, Weiten

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• Bottom-up processing 1960s Hubel and Wiesel
• Primary visual cortex of cats Major cell types,
  visual cortex Feature Detectors

• Figure 4.8, Weiten

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Gestalt Principles of Visual Organization

• Figure-ground, proximity, similarity, continuity,
  closure, and simplicity
• Perceptual hypotheses
• Context an example
• Induced Motion

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Closure
Poggendorf Illusion Example
The images are exactly the same except for the
thick black area in the right image (an example
of the Poggendorf illusion (1860)). In the figure
on the right, there appear to be two continuous
diagonal lines a red and a blue line. What
occurs in your visual system that could account
for the appearance of the continuous diagonal
lines?
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Closure leads to subjective contours
Kaniza Figures
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Figure/ground (explains reversible figures)
Escher
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• Figure 4.24, Weiten

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Perceiving Depth and Distance

• Binocular cues clues from both eyes together
• retinal disparity
• convergence
• Monocular cues clues from a single eye
• accommodation
• pictorial depth cues

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Perceiving Depth and Distance

• Binocular cues clues from both eyes together
• retinal disparity
• convergence
• Monocular cues clues from a single eye
• accommodation
• pictorial depth cues
• Thus an interaction of physiological and
  experience

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Perceptual Constancies in Vision

• Perceptual constancies stable perceptions with
  changing stimuli
• Size
• Shape
• Brightness
• Hue
• Location in space

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The Power of Misleading Cues Optical Illusions

• Optical Illusions discrepancy between visual
  appearance and physical reality.
• Famous optical illusions Muller-Lyer Illusion,
  Ponzo Illusion, impossible figures, and the moon
  illusion.

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• Figure 4.27
• The Müller-Lyer illusion. Go ahead, measure them
  the two vertical lines are of equal length.

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• Figure 4.28, Weiten