Seeing READING ASSIGNMENT Discussion of Gregorys Article on Visual Illusions Tues Feb 17 Available in your course pack What kind of energy does the visual system sense and perceive? The Visual System Light is an oscillation (a wave) in the electromagnetic field Light What are some characteristics of light waves? Properties of light What are some characteristics of light waves? amplitude/intensity - how big of a fluctuation in the field/how many waves frequency - how many fluctuations (waves) pass by a certain point in a given period of time polarization - the orientation of the waves Properties of light What perceptions are associated with those physical properties? Properties of light What perceptions are associated with those physical properties? Intensity is associated (loosely) with brightness Frequency is associated (loosely) with color Polarization isnt sensed by humans (but it is by some insects and birds!) Properties of light Light The spectrum is the range of frequencies of electromagnetic waves The eye curved cornea lens retina fovea optic disk Using Light Light is focused on the retina by the curvature of the cornea and the lens Flat lens (relaxed muscles) focuses distant points Using Light Light is focused on the retina by the curvature of the cornea and the lens Accomodation: Bulged lens (muscles flexed) focuses on near points Using Light Light is focused on the retina by the curvature of the cornea and the lens Constriction of the pupil limits how much light gets in AND reduces the amount of focusing required of the lens Using Light photoreceptors transduce incoming light ganglion cells send signals along to the brain The Retina has layers of cells 2 types of photoreceptors: rods and cones rods are very sensitive - useful in dim light Two kinds of Photoreceptors Rods and cones are distributed differently across the retina The Retina visual acuity (ability to see detail) depends on cones - thus acuity varies across the visual field The Retina Why dont you notice your blind spot? The Retina Why dont you notice your blind spot? Blindspots dont overlap! Your brain fills in the missing information The specific information in the blindspot isnt much more missing than the rest of the periphery! The Retina three types of cones: short, medium, and long different absorptions enable color vision The Retina each ganglion cell integrates information from a particular spot on the retina called its receptive field Neurons collect information Receptive Fields Stimulus is in receptive field Stimulus is near receptive field Stimulus is outside receptive field Action potentials Ganglion cells project to the brain via the optic nerve information is projected to contralateral cortex! Visual Pathways