<span style="text-decoration:underline; color:#000000;"><span style="background-color:#ffff00;"></span>The Visible Spectrum</span> <span style="color:#0000ff;"><span><span style="color:#000000;">the<span style="background-color:#ffff99;"> adequate stimulus</span> of visible light makes up <span style="color:#ff0000;">1/70th of the electromagnetic spectrum </span> light is a form of energy that travels in oscillating waves, like sound. the unit of measurement is the nanometer </span></span></span><span><span style="color:#3366ff;">(billionth of a meter) </span> the </span><span>wavelength of light determines the color we see</span> <span style="text-decoration:underline; color:#000000;"><span style="text-decoration:underline;">Light and the Visual Apparatus</span></span> the eye contains <span style="color:#ff0000;">126 million light receptors</span>, plus a complex network of cells between the receptors and the optic nerves <span style="text-decoration:underline; color:#000000;">The Eye and its Receptors</span> rods and cones are found in the <span style="color:#ff0000;">retina</span>- the photoreceptors of light: rods are in periphery<span style="color:#3366ff;"> (>20 degrees from center)</span> of retina, detect variations in light but not color, work in low level light and are very sensitive to movement cones are most concentrated in the <span style="text-decoration:underline; color:#ff0000;">fovea</span>, the area of greatest visual acuity, require bright, and differentiate among different wavelengths of light <span style="color:#3366ff;">(red, green, blue)</span> <span style="text-decoration:underline; color:#000000;">Pathways to the Brain</span> where the optic nerve exits the eye there are no receptors; this is known <span style="color:#ff0000;">as the blind spot</span> The optic nerves from each eye join at the <span style="color:#ff0000;">optic chiasm</span> then separate; neurons from the nasal side of the retina cross to the contralateral side, resulting in information from each side of the visual field going to the opposite hemisphere; information transmitted to <span style="color:#ff0000;">lateral geniculate</span> <span style="color:#ff0000;">nucleus</span> of the thalamus, then the occipital lobe <span style="text-decoration:underline; color:#ff0000;"><span style="text-decoration:underline;">retinal disparity</span></span> is the discrepancy in the location of an image on the two retinas <span style="color:#3366ff;">(due to the 6cm separation of the eyes)</span>, providing one of the depth cues <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">retinal disparity</span></span> is the discrepancy in the location of an image on the two retinas<span style="color:#3366ff;"> (due </span><span style="color:#3366ff;">to the 6cm separation of the eyes)</span>, providing one of the depth cues The <span style="color:#ff0000;">visual field</span> is the part of the environment that is being registered on the retina. –Information from the right half of each eye will be transmitted to the right hemisphere. –An image in the right visual field will similarly be projected to the left hemisphere. <span style="color:#000000;">retina</span> the light- sensitive structure at the rear of the eye, is made up of two main types of light- sensitive receptor cells, called <span style="color:#ff0000;">rods and cones</span>, and the neural cells that are connected to them <span style="color:#000000;">light- sensitive chemicals called?</span> photopigments <span style="color:#000000;">rod photopigment is called?</span> rhodopsin <span style="color:#000000;">Rhodopsin</span> is more sensitive to light than is cone photopigment <span style="color:#000000;">Iodopsin</span> the cone photopigment <span style="color:#000000;">Rod System</span> function: best in dim light, detail vision is poor, does not distinguish with colors location: mostly in periphery of retina receptive field: large, due to convergence on ganglion cells, contributes to light sensitivity <span style="color:#000000;">Cone System</span> function: best in bright light, detail vision is good, distinguishes among colors location: mostly in fovea and surrounding area receptive field: small, with one or a few cones converging on a single ganglion cell; contributes to details vision <span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">Color Vision</span></span> Color refers to a person’s experience rather than the true nature of an object <span style="text-decoration:underline; color:#000000;">Trichromatic Theory</span> Young and Helmholtz proposed that only 3 types of color receptors <span style="color:#3366ff;">(red, green, blue)</span> detect every visible color Television operates on this principle <span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">Opponent Process Theory</span> </span> Ewald Hering recognized that yellow is also one of the primary colors, but proposed the eye has only 2 color receptors<span style="color:#3366ff;"> (one for red and green, one for blue and yellow)</span> Red and green are complements, as are blue and yellow. <span style="color:#ff0000;">Complementary colors</span> combine to a neutral gray or white; overstimulation of the eye with one color makes it quite sensitive to its complement <span style="color:#3366ff;">(negative color <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">aftereffect</span></span>)</span> <span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">A Combined Theory</span></span> Hurvich and Jameson proposed 3 types of color receptors (red, green, and blue) connected in an opponent-process fashion to produce yellow This theory requires three color processes at the receptors and four at the ganglion cells Red cones excite R/G and Y/B ganglia, green cones inhibit R/G and excite Y/B. Blue cones inhibit both ganglia. <span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">Color Blindness</span></span> <span style="color:#3366ff;">(color vision deficiency)</span> ·Usually dichromatic, due to a defect in one of the cone systems. Two major types: Red-green color blind, deficient in either the red (protanopia) or green (deuteranopia) cone or photochemical Blue color blind (tritanopia, rarest) ·Diagnostic tests include Ishihara (1917), <span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">Form Vision</span></span> There is a <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">retinotopic map</span></span> in the visual cortex <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">Form vision</span></span> is the detection of an object’s boundaries and features <span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">The Perception of Objects,</span></span><span style="text-decoration:underline;"><span style="color:#000000; text-decoration:underline;">Color, and Movement: </span></span><span style="color:#000000;">Processing</span> <span style="text-decoration:underline;">Modular Processing:</span> Each component of processing is segregated into separate locations <span style="text-decoration:underline;">Hierarchial Processing:</span> information is processed by ascending through increasingly complex levels of the nervous system Visual functions are<span style="text-decoration:underline; color:#ff0000;"> distributed</span> across a wide area of the brain <span style="color:#000000;"><span style="text-decoration:underline;">The Perception of Objects, Color, and Movement:</span> The Two Pathways of Visual Analysis</span> 1.The <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">ventral stream</span></span> handles the “what” of processing ·Flows from the visual cortex to the temporal lobes and is dominated by the parvocellular system ·People with damage in the ventral stream have trouble identifying objects visually but walk around them or reach for them 2.The <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">dorsal stream</span></span> handles the “where” of processing ·Flows from the visual cortex to the parietal lobes and is dominated by the magnocellular system ·Patients with damage to this area can identify objects visually but have trouble orienting toward them, reaching for them, and shaping the hand to grasp them. <span style="color:#000000;"><span style="text-decoration:underline;">The Perception of Objects, Color, and Movement:</span> Disorders of Visual Perception</span> 1.<span style="text-decoration:underline;">Object and Face Agnosia</span> ·Damage to the inferior temporal cortex <span style="color:#3366ff;">(ventral stream)</span> ·<span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">Object Agnosia</span></span> is the impaired ability to recognize objects ·<span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">Prosopagnosia</span></span> is the impaired ability to recognize familiar faces 2. <span style="text-decoration:underline;">Face Blindness and Blindsight</span> ·Damage to V1 causes blindness, but information from superior colliculus to striate areas allows people with <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">blindsight</span></span> to react to unseen objects unconsciously. ·The <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">visual word form area (VWFA)</span></span> of the inferior temporal cortex responds to whole written words. 3. <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">Color Agnosia</span> is the inability to perceive color due to brain damage</span> 4. <span style="text-decoration:underline;"><span style="color:#ff0000; text-decoration:underline;">Movement Agnosia</span> is the inability to perceive movement</span> 5.<span style="text-decoration:underline;">Neglect and the Role of Attention in Vision</span> ·<span style="color:#ff0000;">Neglect refers to the patient ignoring visual, touch, and auditory stimulation on the side contralateral to the injury.</span> ·Due to a deficit in <span style="background-color:#ffff99;">attention</span> resulting from injury to the posterior parietal cortex, not a lack of sensation or visual processing.