Psychology 210 Lecture 4 Kevin R Smith

Vision Sensory System –The eye –Exactly what we sense from our environment Perceptual System –The brain –How we put together what we sense into a visual picture

The brain constructs our environment

Multiple experiences of an item lead to different interpretations

The Visual Sensory System Light is made of waves Wavelength –Different colors have different wavelengths Amplitude –Different amplitudes lead to differences in brightness Visible spectrum –400nm to 750nm –ROY G BIV –Short wavelengths are near blue and violet –Long wavelengths are near red and orange

Properties of Light and Waves The color of an object is determined by its abilities across two dimensions –Absorption –Reflection Colors that are reflected are the colors that we see –A red sweater is red because it reflects wavelengths that we perceive as red Other wavelengths would be absorbed and NOT visible as a color for this sweater

Properties of Light and Waves Black is a color that absorbs all other colors –ie. It is the absence of reflected color White is a color that reflects all other colors –ie. It is the presence of all colors prisms White object

Properties of Light and Waves Refraction –The change of direction of the waves Occurs in water Different substances refract light differently

The eye Sclera –Outer covering that protects the eye and gives it shape Cornea –Protective covering for the eye –Begins to bend the light waves and focus them Aqueous humor –Fluid filled area behind the cornea –Provides nutrients to the cornea and lens

Parts of the eye Pupil –Area in the center of the eye –Controls the amount of light that enters –Iris The muscle that controls the widening or narrowing of the pupil Lens –Bend to focus light onto the retina –Accommodation The process of the bending of the lens to properly focus the image on our retina Vitreous humor –Gives the eye its shape –Does not regenerate The vitreous humor your born with is what you still have –Floaters Debris that gathers in the vitreous humor and casts shadows onto the retina

Retina Translates light waves into an electrical signal our brain can process Concave –Object on retina is translated upside-down Photoreceptors –Rods and cones Optic Disk/ Optic Nerve –Area in the retina where nerves and blood vessels exit the eye –Forms a blind spot Fovea –Area in center of retina

Layers of the Retina Four main types of visual processing neurons –Ganglion cell layer –Amacrine and bipolar cell layer –Horizontal cells Visual Sensory Neurons –Photoreceptors RodsCones

Rods and Cones Where a sensory signal (light waves) gets changed into electrical energy –Process called transduction Rods –Sensitive to black and white –Most of them in periphery Cones –Sensitive to color –Most of them in fovea

Rods Contain rhodopsin 120 million in a human eye Responsible for night vision Very sensitive to light Very poor clarity

Cones 6 million in the human eye Responsible for vision in bright light Excellent clarity 3 different types with different pigments

Cones Three different types –Blue, short –Green, medium –Red, long

Horizontal Cells Integrate information from the photoreceptors Transfer that information to bipolar cells

Bipolar cells Receive input from horizontal cells and photoreceptors Transmit information to amacrine cells Contain receptive fields –Antagonistic center- surround organization photoreceptors Horizontal cells Bipolar cells Amacrine Cells

Respond to changes in the visual environment Connect bipolar cells, ganglion cells, and other amacrine cells

Ganglion cells Receive input from bipolar and amacrine cells Same center-surround receptive fields found in bipolar cells On-center bipolar fields connect to on- center ganglion cells Off-center bipolar fields connect to off- center ganglion cells

What do receptive fields do? On-center and off-center fields provide for greater acuity Large unchanged surfaces don’t activate the neurons as well as changing surfaces with lines, cracks, and ends