Biological Psychology-Lecture Slides 06-Psychology-Andrew Weeks, Slides of Biological Psychology

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Topics

6.1 Light Enters the Eye and Reaches the Retina

6.2 The Retina and Translation of Light into Neural Signals

6.3 From Retina to Primary Visual Cortex

6.4 Seeing Edges

6.5 Seeing Color

6.6 Cortical Mechanisms of Vision and Conscious Awareness

Light Enters the Eye and Reaches the Retina

• No species can see in the dark, but some are

capable of seeing when there is little light

• Light can be thought of as:

1. Particles of energy (photons)

2. Waves of electromagnetic radiation

• Humans see light between 380-

nanometers

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Experiments

FIGURE 6.2: The electromagnetic spectrum and the colors associated with the wavelengths that are visible to humans

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The Pupil and the Lens

FIGURE 6.3: The Human Eye

Eye Position and Binocular Disparity

• Convergence – eyes must

turn slightly inward when

objects are close

• Binocular disparity –

difference between the

images on the two retinas

• Both are greater when

objects are close – provides

brain with a 3-D image and

distance information

The Retina and Translation of Light into Neural Signals

FIGURE 6.5:

The Retina and Translation of Light into Neural Signals

 Blind spot: no receptors where

information exits the eye

 The visual system uses

information from cells around

the blind spot for

“completion,” filling in the

blind spot

 Fovea: high acuity area at center

of retina

 Thinning of the ganglion cell

layer reduces distortion due to

cells between the pupil and the

retina

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Cone and Rod Vision

Cones:

Photopic (daytime)

vision

• High-acuity color information in good lighting
• Only cones are found at the fovea

Rods:

Scotopic (nighttime

vision)

• High-sensitivity, allowing for low-acuity vision in dim light, but lacks detail and color information
• More convergence than the cone system, increasing sensitivity while decreasing acuity

Duplexity theory of vision – cones and rods mediate different kinds of vision

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Cone and Rod Vision

FIGURE 6.8: A schematic representation of the convergence of cones and rods on retinal ganglion cells.

Spectral Sensitivity

 Lights of the same intensity but

different wavelengths may not all

look as bright

 A spectral sensitivity curve

shows the relationship between

wavelength and brightness

 There are different spectral

sensitivity curves for photopic

(cone) vision and scotopic (rod)

vision

Spectral Sensitivity

FIGURE 6.10: Human photopic (cone) and scotopic (rod) spectral sensitivity curves.

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Universe

Visual Transduction: The Conversion of

Light to Neural Signals

• Transduction – conversion of one form of energy to another
• Visual transduction – conversion of light to neural signals by visual receptors
• Pigments absorb light
• Absorption spectrum describes spectral sensitivity

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Visual Transduction

Figure 6.

The

inhibitory

response of

rods to light