Chapter 3: The Visual Brain Flashcards
Functional Specialization
specialization of different neural pathways and different areas of brain for representing different kinds of information
Retinotopic Mapping
signals from RGC with receptive fields are next to each other on retina travel to neurons that are next to each other in visual area of brain
Optic Chiasm
location where optic nerve from two eyes split half and half axons from each eye crosses over to other hemisphere
Optic Tract
continuation of optic nerve past optic chiasm
Contralateral Organization
opposite- side organization
Right hemisphere- looks at left visual field
Left hemisphere- looks at right visual field
Primary pathways from RGC to area V1
Geniculostriate pathway:
- looks at detail and color
- 80-90% of all visual info goes through this pathway
Tectopulvinar pathway:
- bypasses LGN
- info about motion
- optic tectum in midbrain to pulvinar nucleus in thalamus
Suprachiasmatic Nucleus (SCN): - structure in hypothalamus that deals with circadian rhythm
Lateral Geniculate Nucleus
part of thalamus
- receives visual signals via axons of RGCs
Magnocellular cells: layer 1 and 2
Parvocellular cells: layers 3-6
Kiniocellular layers: thin layers in between all the other layers
Ipsilateral: layers 2, 3, 5
Contralateral: layers 1, 4, 6
Magnocellular Layer
responds best to info about motion from parasol RGC
large cells bodies
responds to rods and cones
Parvocellular Layers
responds best to static properties (color, texture, form, and depth) information from midget cells
small cell bodies
high acuity and cones
Koniocellular Layers
respond best to color information from bistratified cells
very very small
in response to size of perceptive field
Superior Colliculus (SC)
one each SC in each hemisphere of the brain form tectum (roof) of midbrain together with inferior colliculi
- helps control eye movement
- can respond to any visual stimulus
- also receives signals from auditory and somatosensory systems
site of multisensory integration - sends signals to areas beyond V1 without going through V1, creating blind spot
Multisensory Integration
function of brain areas in which signals from different sensory systems are combined
Primary Visual Cortex (Area V1)
part of occipital lobe where signals flows from LGN
- highly organized, with columns for ocular dominance and orientation
- organized retinotopically and shows cortical magnification
Cells in V1: simple , complex, and end-stopped cells
Cortical Magnification
nonuniform representation of visual space in cortex
more cortical space dedicated to certain place
amount or cortical territory devoted to the central part of the visual field is much greater than the amount devoted to the periphery
many more V1 neurons have receptive fields in the fovea than in areas in the periphery of the retina (reason why acuity is power in periphery)
End-Stopped Cells
response increases as length of edge increases (up to point) and then weakens
Simple Cells
responds best to stimulus with particular orientation in location of receptive fields
- looks at light on dark background
Preferred Orientation
stimulus orientation that produces strongest response
Orientation Timing Curve
curve on graph that shows average response of orientation-tuned neuron
Population Code
consistent difference in patterning of relative responses of population of differently tuned neurons
Complex Cells
include neurons in area V1 that respond best to a stimulus with a particular orientation
- differ from simple cells in the variety and location of stimuli that generate a response
- responds to dark on light and light on dark
Organization of V1
Cortical Columns- small volume of neural tissue running through layers if cortex perpendicular to its surface
- consists of neurons that respond to similar types of stimuli type that have highly overlapping receptive fields
- gives spatial info
Ocular Dominance Columns- cortical columns consisting of neurons that receive signals mainly from left eye or mainly from right eye
Orientation Columns- cortical columns consisting of neurons with same (or similar ) orientation tuning
Hypercolumns
organizes info like orientation and dominance
Functional Specialization
functional specialization is starts with the neurons that transduce light into neural signals, the rods and cones –>
specialization continues in the different functions of midget, parasol, and bistratified RGCs, which send signals to neurons in the parvocellular, magnocellular, and koniocellular layers if the LGN –> signals from the layers of the LGN then travel to separate layers of area V1, where populations of neurons encode edge orientation and other visual features
Functional Areas and Pathways
- areas differ according to the types and distributions of neurons within them
- areas differ according to the other areas in the brain from which they receive signals or ton which they send signals
- areas differ according to the properties to which their constituent neurons are tuned
- each visual area contains a retinotopic map of the visual field
*when two brain areas are connected, the connection is always reciprocal
Dorsal Pathway
V1 and V2 –> MT –> parietal cortex
- is responsible for representing properties related to object’s motion or location; info also used to guide action
- the “where” pathway and/or the “how” pathway
Ventral Pathway
V1 and V2 –> V4 –> inferotemporal cortex
- is responsible for representing properties related to object’s identity, such as its color and shape
- the “what” pathway
Optic Ataxia
deficit in ability to guide movements visually
Area V4
color and curvature
- ventral pathway
- can look at orientations and fine tunes there
- area in occipital lobe consisting of neurons that respond selectively to color of stimuli and to curvature of edges
- includes lateral occipital cortex and inferotemporal cortex (specialized for responding to complex shapes)
Damage to V4 and other attached areas is called achromatopsia
Achromatopsia
cortical color blindness
- inability to perceive colors despite having normal array of cones in retina
Lateral Occipital Cortex
- ventral pathway
- object-selective region
- responds strongly when person views pictures of faces, animals, buildings, tools, appliances, or other objects but don’t respond well to random texture viewing
Fusiform face area (FFA)
Parahippocampal place area
Fusiform face area (FFA)
faces
fusiform gyrus of IT cortex
Parahippocampal place area
large-scaled spatial layouts
parahippocampal gyrus of IT cortex
Inferotemporal Cortex (IT)
cortex in bottom part of temporal lobe
- object- selective regions of visual system
Area MT (V5) neurons
- dorsal pathway
- medial temporal area
- respond selectivity to direction and speed of motion of stimuli
Visual Neuroprosthetic Devices
designed to help the blind see
- use neural stimulators implanted in area V1 to activate the visual system on the bases of signals received from and external camera
- relay signals from camera/ photocells to implanted stimulators that activate visual systems
Prosopragnosia
damage to FFA leading to impairment of ability to recognize faces
