Tectopulvinar pathway Damage causes visual ataxia- loss of "where"; inability to track visual information Includes projections to the pretectum (pupillary reflexes) and the superior colliculus (visually guided eye movements- saccades when reading)
Geniculosriate pathway The perception pathway Visu...
Psych 115 Quiz 5 Questions and Correct
Answers
Tectopulvinar pathway ✅Damage causes visual ataxia- loss of "where"; inability to
track visual information
Includes projections to the pretectum (pupillary reflexes) and the superior colliculus
(visually guided eye movements- saccades when reading)
Geniculosriate pathway ✅The perception pathway
Visual perception is lost without this pathway
-loss of "what"
Information from the right visual field goes to left lateral geniculate nuclei (LGN) and
vice versa
-Optic nerves terminate in the LGN of the thalamus
Functional classes of retinal ganglion cells ✅Small "P" ganglion cells project to the
parvocellular layer of the LGN and can discriminate cells
-lesions to these layers produce inpairments in color contrast sensitivity- complete loss
of color vision
Large "M" ganglion cells project to the magnocellular layer of the LGN which can not
discriminate color
-important for vision requiring low spatial and high temporal resolution (movement)
LGN Receptive Fields ✅Similar to retinal ganglion cells
Each geniculate neuron receives its main input from only a few ganglion cells
Ex: Lateral geniculate cell with concentric field; on-center/off-surround
1. Response to light in center of cell's field: increased firing of action potentials
2. Response to light in periphery of cell's field: opposite
Organization of LGN ✅90% of retinal axons terminate here
Layers 1 and 2 are part of the magnocellular pathway
-large cell bodies, large receptive fields (good for tracking movement across space)
-involved in movement detection
Layers 3-6 are part of the parvocellular pathway
-small cell bodies, small receptive fields
-color, acuity and stationary or slow moving objects
Layers receive information in order "left eye, right eye, left eye, etc."
LGN send projections to the primary visual cortex
Primary Visual Cortex ✅Axons from neurons of the LGN terminate in the primary visual
cortex (V1) or "striate cortex" of the occipital lobe- the region where most information
first arrives
Cortical Regions in general:
, -The cortex consists of 6 layers of cells
-Each layer consists of different cell types
-Some layers receive information and process it
-Other layers send information following processing
-In most cortex, the cells responding to a certain type of information are arranged in
columns
The visual cortex: The more light, the more cones the visual cortex devotes to that part
of the retina (i.e. the fovea has the largest representation/number of cells in the visual
cortex)
Most of the topographic/retinotopic projection of visual space is devoted to the foveal
region.
Retinotopic Map ✅Anesthetized monkey viewed flickering bullseye pattern and
received radioactively labeled glucose.
V1 dissected, flattened and exposed to film.
2 major types of neurons in V1 ✅Distinguished based on how they respond to stimuli
v1 neurons transform information so that they are orientation selective and direction
selective
-start to have cells responding to particular aspects rather than just light
1) simple cortical cells- also called bar or edge detectors- respond best to an edge or
bar of a particular width, orientation, and location in the visual field
Ex: cortical cell sensitive to orientation, responds strongly only when stimulus is a
vertical shape
-action potentials when vertical, opposite when horizontal
2) Complex cortical cells also respond to a bar of a particular width and orientation but
may be located within a larger area of the visual field.
Ex: cortical cell sensitive to motion, responds strongly when stimulus moves up and
down. Repsonds weakly to upward motion and does not respond at all to sideways
motion
-action potentials when it goes down, and opposite when moving sideways
Simple cortical neurons ✅Each cortical neuron has access to information from a small
part of the contralateral visual field - a location.
Simple cortical neurons will respond to bars and edges present in that location
-orientation matters (orientation selectivity)
On-center receptive fields (retinal ganglion and LGN) can combine to produce rod-
shaped receptive fields.
V1 Organization and Receptive Fields ✅V1 has representation for four parts of a visual
stimulus:
-location in the visual field
-ocular dominance (whether stimulus is more or less responsive to a particular eye)
-orientation
-color
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