Psychology 210

1. Psychology 210 Lecture 4 Kevin R Smith

2. Vision • Sensory System • The eye • Exactly what we sense from our environment • Perceptual System • The brain • How we put together what we sense into a visual picture

3. The brain constructs our environment

4. Multiple experiences of an item lead to different interpretations

7. The Visual Sensory System • Light is made of waves • Wavelength • Different colors have different wavelengths • Amplitude • Different amplitudes lead to differences in brightness • Visible spectrum • 400nm to 750nm • ROY G BIV • Short wavelengths are near blue and violet • Long wavelengths are near red and orange

8. Properties of Light and Waves • The color of an object is determined by its abilities across two dimensions • Absorption • Reflection • Colors that are reflected are the colors that we see • A red sweater is red because it reflects wavelengths that we perceive as red • Other wavelengths would be absorbed and NOT visible as a color for this sweater

9. Properties of Light and Waves • Black is a color that absorbs all other colors • ie. It is the absence of reflected color • White is a color that reflects all other colors • ie. It is the presence of all colors • prisms White object

10. Properties of Light and Waves • Refraction • The change of direction of the waves • Occurs in water • Different substances refract light differently

11. The eye • Sclera • Outer covering that protects the eye and gives it shape • Cornea • Protective covering for the eye • Begins to bend the light waves and focus them • Aqueous humor • Fluid filled area behind the cornea • Provides nutrients to the cornea and lens

12. Parts of the eye • Pupil • Area in the center of the eye • Controls the amount of light that enters • Iris • The muscle that controls the widening or narrowing of the pupil • Lens • Bend to focus light onto the retina • Accommodation • The process of the bending of the lens to properly focus the image on our retina • Vitreous humor • Gives the eye its shape • Does not regenerate • The vitreous humor your born with is what you still have • Floaters • Debris that gathers in the vitreous humor and casts shadows onto the retina

14. Retina • Translates light waves into an electrical signal our brain can process • Concave • Object on retina is translated upside-down • Photoreceptors • Rods and cones • Optic Disk/ Optic Nerve • Area in the retina where nerves and blood vessels exit the eye • Forms a blind spot • Fovea • Area in center of retina

15. Layers of the Retina • Four main types of visual processing neurons • Ganglion cell layer • Amacrine and bipolar cell layer • Horizontal cells • Visual Sensory Neurons • Photoreceptors • Rods • Cones

16. Rods and Cones • Where a sensory signal (light waves) gets changed into electrical energy • Process called transduction • Rods • Sensitive to black and white • Most of them in periphery • Cones • Sensitive to color • Most of them in fovea

17. Rods • Contain rhodopsin • 120 million in a human eye • Responsible for night vision • Very sensitive to light • Very poor clarity

18. Cones • 6 million in the human eye • Responsible for vision in bright light • Excellent clarity • 3 different types with different pigments

19. Cones • Three different types • Blue, short • Green, medium • Red, long

21. Integrate information from the photoreceptors Transfer that information to bipolar cells Horizontal Cells

22. Bipolar cells Amacrine Cells Bipolar cells Horizontal cells • Receive input from horizontal cells and photoreceptors • Transmit information to amacrine cells • Contain receptive fields • Antagonistic center-surround organization photoreceptors

24. Amacrine Cells • Respond to changes in the visual environment • Connect bipolar cells, ganglion cells, and other amacrine cells

25. Ganglion cells • Receive input from bipolar and amacrine cells • Same center-surround receptive fields found in bipolar cells • On-center bipolar fields connect to on-center ganglion cells • Off-center bipolar fields connect to off-center ganglion cells

27. What do receptive fields do? • On-center and off-center fields provide for greater acuity • Large unchanged surfaces don’t activate the neurons as well as changing surfaces with lines, cracks, and ends