The Eye The Eye: Allowing and Focusing Light In Two jobs of the eye: Houses retina, channels light towards retina Cornea: where light enters the eye; transparent Lens: focuses the light rays on the retina, called accommodation Iris: colored ring of muscle, constricts or dilates via amount of light Pupil: regulates amount of light 54 The Retina: Absorbing and Processing Light Retina: absorbs light, processes images Fovea: in the retina, center of ﬁeld of vision Optic disk: optic nerve connection/blind spot Receptor cells: Rods: black and white/low light vision Cones: color and daylight vision 55 56 57 Receptor Cells Rods •Long •100-125 million •Peripheral vision and night vision (Rods=Raccoons) •Bright light dazzles them •Sensitive to dim light •Outnumber cones in periphery of retina •Density greatest just outside fovea •Contain photochemicals Cones •Short •5-6.4 million •Cones = Color vision and daylight vision •Don’t respond well to dim light •Provide more sharp and detailed vision •Concentrated in center of retina (fovea only cones) •Contain photochemicals 58 Visual Pathway Visual receptors---Bipolar cells---Ganglion cells---optic nerve----brain ● Optic Chiasm- place where the optic nerve ﬁbers cross so that the left side of the brain views the right visual ﬁeld and the right side views the left visual ﬁeld Hubel and Wiesel: Feature Detectors and the Nobel Prize • Early 1960’s: Hubel and Wiesel – Microelectrode recording of axons in primary visual cortex of animals – Discovered feature detectors: neurons that respond selectively to lines, edges, etc. – Groundbreaking research: 1981 Nobel Prize • Later research: cells speciﬁc to faces in the temporal lobes of monkeys and humans 60 61 62 FFA - Fusiform Face Area We are hard-wired to recognize faces. There’s an area of our brain dedicated exclusively to facial pattern recognition. Interferes with bottom-up processing. Larger on right side of brain. 63 64 Prosopagnosia -Face Blindness 65 66 Visual Processing Parallel Processing: Different parts of the brain detect either faces, motion, form, contours, depth, or color. These speciﬁc processes are put together as an understanding of what you are seeing. parallel: happening separately but at the same time series: happening one after the other This can lead to things such as blindsighting where someone cannot “see” something but still know what is in front of them (seen in stroke patients) 67 68 Seeing in Color Wavelength alone gives us 200 colors Longer = red shorter = violet Amplitude affects brightness 3 different types of cones ﬁre at different rates or levels when stimulated by different colors (short, medium, long wavelengths) 70 Theories of Color Vision • Trichromatic theory - Young and Helmholtz – Receptors for red, green, blue –other colors are seen by mixing • Opponent Process theory – Hering – 3 pairs of opposing colors – red/green, blue/yellow, black/white – neurons are turned on by 1 color and turned off by its opponent color – Explains afterimages 71 • Current perspective: both theories necessary Afterimages An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. . 73 Color Blindness Missing Green 1% males .01% females Missing Red 1% males .02% females Missing Blue .002% males .001% females 74