psychology 100:12 chapter 5 sensation & perception part iii

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