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Psychology 100:12
Chapter 5
Sensation &
Perception
Part III
Outline• Basic Sensory Processes
• Vision• Transduction• Colour • Receptive fields• Feature detectors
Study Question:
• Compare and contrast the trichromatic theory of colour vision with the opponent process theory of colour. Relate these theories to the Law of Complimentary and the Three Primaries Law.
• Vision: The Physical Stimulus
Vision Vision
Sensation
• The Eye
Vision
Sensation• Vision: The Retina
Vision
Sensation• Rod and cone vision
– Cones> Specialized for colour and acuity> concentrated in fovea
– Rods> Specialized for sensitivity in dim light> concentrated in periphery
– Both contain a photochemical that reacts to light (in the rods: rhodopsin)
– Two reasons why rods are more sensitive to light1. Rhodopsin is more sensitive to light
2. Density of cones in the fovea
Vision
Sensation• Colour Vision
– The colour of objects is determined by pigments
– Subtractive colour mixing
> Colour perception is created by absorption of wavelengths of light
Vision
Vision
• Additive Colour Mixing– When coloured lights are mixed, two laws apply:
> Three Primaries Law> Law of Complimentarity
Vision
Vision
• Two Theories of colour vision– Trichromatic theory
> -> the three types of receptors are sufficient for colour perception
• Opponent Process theory
– Trichromatic theory does not account for complimentary colours.
– Colour vision is mediated by cells that can be excited or inhibited
– Blue- Yellow, Red - Green, & brightness
Vision
Vision
Contrast
• Coding of Contrast and Contour– Three examples of exaggerated contrast
Contrast
• Coding of Contrast and Contour– Three examples of exaggerated contrast
Contrast
• Coding of Contrast and Contour– Three examples of exaggerated contrast
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• Contrast heightening
Contrast
• Coding of Contrast and Contour – Receptive fields and on-off areas
Hermann - Hering grid
Coding of Contrast and
Contour
Contrast
• Receptive fields and the Hermann-Hering illusion
Coding of Contrast and
Contour
Contrast
Feature detectors
• Feature detectors– Hubel and Weisel
> Simple cells - edge detectors
> Complex cells - edges at particular angles
> Hypercomplex cells - angles and length
– Higher level feature detectors: Motion detectors
Vision
Feature detectors
• More From Ramachandrin
Vision
