Power Point 12 Flashcards
Level 1. Extraction of basic attributes – _____
retina
Level 2. Detection of organizational rules – ________
LGN and primary visual cortex
Detection of Color and Contrast – Foreground vs. Background -
Level 2. Detection of organizational rules – LGN and primary visual cortex
Object recognition depends on separation of __________
foreground and background
To link the elements of visual scene into a unified perception, the visual system circuits relay on organizational rules for grouping:
- segmentation based on similarity, proximity
- contour detection based on good continuation, contour saliency
- segregation of foreground and background based on color, contrast
Level 3. Visual information converges – __________
association areas of the visual cortex
___________plays a role in what is seen
Expectation
Anatomy of Visual Processing:
Low Level - retina
Intermediate Level - lateral geniculate nucleus in the thalamus,primary visual cortex
High Level - association cortical regions:
ventral pathway = to temporal lobe = what: object identification
dorsal pathway = to parietal lobe = where: guiding movement
_________ = to temporal lobe = what: object identification
ventral pathway
__________ = to parietal lobe = where: guiding movement
dorsal pathway
All visual information comes from the ______
retina
the _____ forms a variable diaphragm, allowing light rays to enter the eye
pupil
the _________ provides refractive optics, projecting small image of the outside world onto the retina lining the back of the eye-ball
cornea
The ________ refracts light further, and by changing shape, focuses images of objects located at different distances from the eye.
lens
Retina Performs what Three Major Functions?
Phototransduction – photoreceptor cells adsorb light and convert light energy into electric signals
Adaptation – photoreceptors can process visual signal at varying light intensities
Preprocessing – neural circuits in the retina preprocess visual information, extracting primary visual features from information presented.
_________ cells modulate information processing
amacrine and horizontal
Information transduction:
photoreceptor (input) – bipolar cell – retinal ganglion cell (output)
_______ corresponds to the center of visual field, performs highest resolution processing – smallest receptive fields, densest receptor packing. The farther from the fovea – the bigger receptive fields are
Fovea
________ is the site where axons of retinal ganglion cells exit the retina forming the optic nerve; it does not contain any photoreceptors, generating blind spot in our vision
Optic Disk
Anatomy of Visual Processing
- visual hemifieldregion seen with one eye
- binocular zoneregion seen with both eyes
- monocular crescentperipheral region seen with only one eye
- nasal hemiretina
- temporal hemiretina
outer segment – __________ – distal (closest to the back of the eye), contains stacks of membranous disks that contain light-absorbing pigments
phototransduction
In response to the pattern of light falling on the retina, photoreceptors in the ______ regions get hyperpolarized, whereas those in the dark regions get _______.
light, depolarized
photoreceptors do not fire action potentials, in the dark they continuously release __________
glutamate
Two major types of bipolar cells: ___ and ___ respond to the glutamate released at the photoreceptor-bipolar synapse through distinct mechanisms:
ON and OFF
OFF bipolar neurons use ionotropic AMPA channels –glutamate depolarizes, fire in ________)
darkness
OFF bipolar neurons use metabotropic G-protein coupled receptors. Activation of these receptors hyperpolarizes the cell – silenced in darkness, fire in _______.
light
Retina performs 3 major functions:
Phototransduction, Adaptation, Preprocessing
Anatomical features of the retina:5 major cell types arranged in layers:
Photoreceptors (Rods, Cones, Opsins, Glutamate)
Bipolar (ON and OFF)
Ganglion (ON, OFF, Transient, Sustained)
Amacrine
Horizontal
Two specialized sites in the retina:
Fovea
Optic Disk
Ganglion cell contribution to low-level processing by enhancing/emphasizing:
Brightening And Dimming,
Contrast,
Movement,
Relative Brightness (deconstructing visual environment into basic attributes)
