Chapter 6

• light can be thought of in two different ways: as a wave and as a particle called photons
• light are waves of electromagnetic energy between 380 and 760 nanometers
• rattlesnakes can see infrared waves
• wavelength plays an important role in the perception of color, while intensity plays an important role in the perception of brightness.
• light enters the eye through the pupil
• sensitivity - the ability to detect the presence of dimly lit objects
• acuity - the ability to see the details of objects
• behind each pupil is a lens, which focuses light onto the retina
• accomodation - a process of adjusting the lens to focus on near or distant objects
• binocular disparity - the difference in the position of the two eyes when looking at the same object
• the retina converts light to neural signals
• the retina is composed of five different neurons: receptors, horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells
• amacrine and horizontal cells are specialized for lateral communication
• lateral communication - communication across the major channels of sensory input
• blind spot - a gap in the receptor layer, necessary for the bundle of retinal ganglion cell axons to leave the eye.
• fovea - an indentation, about 0.33 centimeters in diameter, at the center of the retina
• fovea - the area of the retina that is specialized of high-acuity vision
• surface interpolation - a completion process by which we perceive surfaces; the visual system extracts information about edges and from it, infers the appearance of large surfaces
• duplexity theory - the theory that cones and rods mediate different kinds of vision
• photopic vision - also called cone-mediated vision predominates in good lighting and provides high-acuity colored perceptions of the world.
• Scotopic vision - predominates in dim illumination
• scotopic vision - also known as rod-mediated vision, provides low acuity black-and-white perception of the world
• spectral sensitivity curve - a graph of relative brightness of lights of the same intensity presented in different wavelengths
• there are three different kinds of involuntary fixational eye movements: tremor, drifts, and saccades
• Transduction - conversion of one form of energy to another
• Visual transduction - conversion of light to neural signals by visual receptors
• rhodopsin - a G-protein-coupled receptor that responds to light rather than to neurotransmitter molecules
• the largest and most thoroughly studied visual pathways are the retina-geniculate-striate pathways.
• retina-geniculate-striate pathways - conduct signals from each retina to the primary visual cortex (also know as striate cortex) via the lateral geniculate nuclei of the thalamus.
• about 90 percent of axons of retinal ganglion cells become part of the retina-geniculate-striate pathways
• all signals from the left visual field reach the right primary visual cortex, either ipsilaterally from the temporal hemiretina of the right eye, or contralaterally (via optic chiasm) from the nasal hemiretina of the left eye
• the retina-geniculate-striate system is retinotopic; each level of the system is organized like a map of the retina.
• parvocellular layers - composed of neurons with small cell bodies, these layers are the top 4 layers where one channel of communication in the lateral geniculate nucleus flows through
• magnocellular layers - composed of neurons with large cell bodies, the bottom two layers where the other channel (in the lateral geniculate nucleus) runs through
• parvocellular neurons - neurons (in layers) that are particularly responsive to color, fine pattern details, and stationary or slowly moving objects
• magnocellular neurons - are neurons (in layers) that are particularly responsive to movement
• about 25 percent of the primary visual cortex is dedicated to analyzing the input from the fovea
• depending on how close or far away an object is, the lens is adjusted using the ciliary muscles
• visual edge - it is merely the place where two different areas of a visual image meet
• receptive field -