Biopsychology Week 5-3 PDF

Biopsychology PSY-303 Week 5-3 Retina: Rods and Cones Blood vessels Optic Nerve Horizontal cell Amacrine cell Axons from ganglion cells Ganglion cells Bip...

Biopsychology PSY-303 Week 5-3 Retina: Rods and Cones Blood vessels Optic Nerve Horizontal cell Amacrine cell Axons from ganglion cells Ganglion cells Bipolar cells Receptors  Retina: Rods and Cones Rods Most abundant in periphery Respond to faint light (120 million per retina) Cones Most abundant in and near fovea (6 million per retina) More useful in bright light Essential for color vision Provide about 90% of the brain’s input Retina: Rods and Cones Convergence of Input  Retina: Fovea vs. Periphery Characteristic Foveal vision Peripheral vision Receptors Cones Proportion of rods increases toward periphery Convergence Each ganglion cell excited by a single cone Each ganglion cell excited by many rods of Input Brightness Distinguishes among bright lights Responds well to dim light sensitivity Responds poorly to dim light Poor to distinguish among bright lights Sensitivity Good detail vision because each cone’s own Poor detail vision because many rods converge to detail ganglion cell sends a message to the brain their input onto a given ganglion cell Color Vision Good (many cones) Poor (few cones) Question Do lights have color? NO! Lights have wavelengths. We perceive wavelengths as color!  Color Vision Wavelength Visible light is a portion of electromagnetic spectrum Color vision depends on the wavelength of light Humans perceive wavelengths between 400 and 700 nanometers (nm)  Color Vision Trichromatic theory Opponent-process theory Retinex theory  Color Vision Trichromatic theory (Young-Helmholtz theory) Three types of cones; each cone responds to a broad range of wavelengths S-cones: sensitive to short wavelength M-cones: sensitive to medium-wavelength L-cones: sensitive to long-wavelength  Color Vision Trichromatic theory (Young-Helmholtz theory) Ratio of activity across the three types of cones determines the color  Color Vision Trichromatic theory (Young-Helmholtz theory) Even distribution of S-cones across retina Random distributions of M-cones and L-cones Vary across individuals  Color Vision Opponent-process theory Perceive color in terms of paired opposites Red vs. Green Yellow vs. Blue White vs. Black A possible mechanism for the theory Bipolar cells are excited by one set of wavelengths and inhibited by its opposite Once they become fatigue, inhibition from the opposite set of wavelengths decreases, which means excitation by the opposite set  Color Vision Retinex theory Retina + Cortex Cortex compares information from various parts of the retina to determine the brightness and color for each area  Color Vision Trichromatic theory Ratio of activity of the 3 types of cones Opponent-process theory Negative afterimage Retinex theory Illusions Question Which of the following is true? Check all that apply. A. Humans perceive wavelengths between 1400 and 1700 nanometers B. Short wavelength is perceived as blue, and long wavelength is perceived as green C. Seeing a color relies only on the one type of cones associated with that wavelength D. The retinex theory explains the phenomenon of negative afterimage (LGN)