Chapter 10 Visual Perception Receptive field area of the retina from which a ganglion cell receives input Convergence peripheral vision multiple photoreceptors per bipolar cell multiple bipolar cells per ganglion cell Fovea detail periphery makes ganglion cells more capable of detecting any light because of summation effect huge radar disk anything that moves or flickers sets off reflexive movement to identify movement Retino Cortical Pathway Visual field part of the environment that is registered on the retina left and right visual field overlap almost completely because our eyes are so close to each other binocular field Binocular field allows us to perceive depth by looking at slight differences from two eyes depth perception essential to predators Closer to center nasal side Closer to outside temporal side Optic Chiasm half of the optic nerve nasal side cross the midline while the temporal side stays with its previous side Object that was on the non overlapping side of the eye can go to the opposite side of the brain work together If it s in the overlapping part of the visual field then information goes to both sides of the brain Optic Tract past the optic chiasm have to change the name from optic nerve to optic tract because it leaves the peripheral nervous system Lateral Geniculate Nuclei LGN of Thalamus Primary Visual Cortex V1 of occipital lobe Older pathway retinal tectal pathway goes to tectum in the midbrain instead Pre mammalian system No conscious experience of sight There mostly to coordinate our eye movements Blind sight issues with retino cortical pathway occipital damage retinas not working etc cortical blindness ask them to guess where a random dot is on the screen their answers are better than the guess rate if part of retinal tectal pathway is intact it will give info and affect how the person acts even without their awareness of it Retinal disparity discrepancy in the location of an object s image on the two retinas as a function of the object s distance detected by the visual cortex depth perception Color Vision Color is a construct of our minds not a physical property of light waves are a physical property model of the world which can change Can spot food better with color than those without color vision evolutionary advantage Perception of color depends on which niche the species has evolved in cats don t need color vision because they re carnivores we re omnivores that are active during the day so it s advantageous Theories of Color Vision Trichromatic Theory von Helmholtz Young All colors are the results of the processing of three pure colors red green and blue each one detected by a specific receptor Correct up to a certain point can achieve any color hue by mixing these three color of lights not paint short wavelengths blue medium green long red have red green and blue cones in the eyes Problem yellow also appears to observers as pure color innate phenomenon across cultures Opponent Process Theory Hering Explains color vision in terms of opposing neural processes in two specific receptors Receptor for red and green responds to red in one way and green in another way photochemical shine red light on it and then it degrades it shine green light on it and it catalyzes it or works to build it up Receptor for blue and yellow photochemical yellow breaks it down blue helps its synthesis Doesn t matter which is degraded built up just understand the concept Explains complementary colors and negative color aftereffect 3 color receptors trichromatic theory opponent process new theory Opponent process happens at the level of the ganglion cells not the receptors 2 types of ganglion cells Respond to green in one way excitatory inhibitory and red in another inhibitory excitatory Respond to yellow in one way excitatory inhibitory and blue in another inhibitory excitatory Combined Theory Hurvich Jameson