Chapter 6 Vision Flashcards
Bipolar cells
Neurons that receive messages from visual receptors
Located closer to the center of the eye
Send messages to ganglion cells
Amacrine cells
Control the ability of the ganglion cells to respond to shapes, movements, or other specific aspects of visual stimuli
Macula
The center of the human retina
Fovea
Allows for acute and detailed vision
Packed tight with receptors
Nearly free of ganglion axons and blood vessels
Midget ganglion cell
A single bipolar cell and a single ganglion cell with an attached receptor in the fovea
The vertebrate retina consists of two kind of receptors?
Rods
Cones
Rods
Most abundant in the periphery of the eye and respond to faint light
Good during green+ yellow light because is easier to detect in the dark
120 million per retina
Cones
Most abundant in and around the fovea
Essential for color vision and more useful in bright light
6 million per retina
Photopigments
Chemicals contained by both rods and cones that release energy when struck by light
The perception of color is dependent upon?
The wavelength if the light
Shortest: 400 nm violet
Longest: 700 no ( red)
Colors have three things?
Hue
Intensity
Value
There is a lot of overlap between colors
Discrimination among colors depend upon?
The combination of responses by different neurons
Two major interpretations of color visions include?
Trichromatic theory/ Young-Helmholtz
Opponent process theory
Trichromatic theory
Color perception occurs through the relative rates of response by three kinds of cones
Short, medium, long wavelength
Each cone is maximally sensitive to a different set of wavelengths
Opponent process theory
We perceive color in terms of paired opposites
A mechanism that perceives color on a continuum from red to green and another from yellow to blue
Horizontal cells
Cells in the eye that make inhibitory contact onto bipolar cells
Lateral geniculate nucleus
Part of the thalamus specialized for visual perception
Destination for most ganglion cell axons
Sends axons to other parts of the thalamus and to the visual areas of the occipital cortex
Cortex and thalamus feed information back and forth to each other
Lateral inhibition
The reduction of activity in one neuron by activity in neighboring neurons
The retinas way responsible of sharpening contrasts to emphasize the borders of objects
Receptive field
Refers to the part of the visual field that either excites or inhibits a cell in the visual system of the brain
The point in space from which light strikes it
Ganglion cells of primates generally fall into three categories?
Parvocellular neurons
Magnocellular neurons
Konicellular neurons
Parvocellular neurons
Highly sensitive to detect color and visual detail/ details of shape
Have smaller cell bodies and small receptive fields
Located in or near the fovea
Connect only to the lateral geniculate nucleus
Magnocellular neurons
Highly sensitive to large overall pattern and movement
Throughout the retina
Larger cell bodies and visual fields
Connect to the lateral geniculate nucleus and visual areas of the thalamus
Konicellular neurons
Small cell bodies
Found throughout the retina
Connect to the lateral geniculate nucleus, parts of the thalamus, and the superior colliculus
Primary visual cortex (area V1)
Receives information from the lateral geniculate nucleus and is the area responsible for the first stage of visual processing
Blindsight
An ability to respond to visual stimuli that they report not seeing
Ventral stream
The most magnocellular visual paths in the temporal cortex
Specialized for identifying and recognizing objects
Dorsal stream
Helps the motor system to find objects and move towards them
The visual path in the parietal cortex
Complex cells
Responds to pattern of light in a particular orientation and most strongly to a stimulus perpendicular to its access
Large receptive fields that can not be mapped into fixed excitatory or inhibitory zones
Located v1 or v2
End stopped or hyper complex cells
Respond to a bar shaped pattern of light anywhere in its large receptive field, provided the bar does not extend beyond a certain point
Feature detectors
Neurons whose response indicate the presence of a particular feature/ stimuli
Inferior temporal cortex
Contains cells that respond selectively to complex shapes but are insensitive to distinctions that are critical to other cells
Visual agnosia
The inability to recognize objects despite satisfactory vision
Caused by damage to the pattern pathway usually in the temporal cortex
Prosopagnosia
Inability to recognize faces
Occurs after damage to the fusiform gyrus
Saccades
A decrease in the activity of the visual cortex during quick eye movements
Preventing confusion and blurring of images
Strabismus
A condition in which the eyes do not point in the same direction
Lazy eye
Astigmatism
A blurring of vision for lines in one direction caused by an asymmetric curvature of the eyes
