Chapter 4: Visual System: The Brain Flashcards
Optic chiasm
the location in the optic tract where the optic nerve from each eye splits in half, with nasal retinae crossing over and temporal retinae staying on the same side of the optic tract
Optic tract
the optic nerve starting at the optic chiasm and continuing into the brain
Contralateral representation of visual space:
the arrangement whereby the left visual world goes to the right side of the brain, and the right visual world goes to the left side of the brain
Ipsilateral organization
same-side organization; in the visual system, the temporal retina projects to the same side of the brain
Contralateral organization
opposite-side organization; in the visual system, the nasal retina projects to the opposite side of the brain
Lateral geniculate nucleus (LGN)
a bilateral structure (one is present in each hemisphere) in the thalamus that relays information from the optic nerve to the visual cortex
Magnocellular layers
layers of the lateral geniculate nucleus with large cells that receive input from M ganglion cells (parasol retinal ganglion cells)
Parvocellular layers
layers of the lateral geniculate nucleus with small cells that receive input from P ganglion cells (midget retinal ganglion cells)
Koniocellular layers
layers of the lateral geniculate nucleus with very small cells that receive input from K ganglion cells (bistratified retinal ganglion cells)
Parasol retinal ganglion cells
(M cells)
retinal ganglion cells that project to the magnocellular layer of the lateral geniculate nucleus; they represent 10% of ganglion cells and possess high sensitivity to light
Midget retinal ganglion cells
(P cells)
retinal ganglion cells that project to the parvocellular layer of the lateral geniculate nucleus; they represent 80% of ganglion cells, possess low sensitivity to light, and are sensitive to wavelength
Bistratified retinal ganglion cells (K cells)
retinal ganglion cells that project to the koniocellular layer of the lateral geniculate nucleus; they represent 10% of ganglion cells, possess low sensitivity to light, and are sensitive to wavelength
Parvocellular pathway
(P pathway)
a pathway characterized by the retinal ganglion cells known as midget retinal ganglion cells
Koniocellular pathway (K pathway)
a pathway that starts with bistratified retinal ganglion cells and projects to the koniocellular layers of the lateral geniculate nucleus
Magnocellular pathway
(M pathway)
a pathway that starts with the parasol retinal ganglion cells and projects to the magnocellular layers of the lateral geniculate nucleus
Superior colliculus
a structure located at the top of the brain stem, just beneath the thalamus, whose main function in mammals (including humans) is the control of eye movements
Smooth-pursuit eye movements
voluntary tracking eye movements
Saccades
the most common and rapid of eye movements; sudden eye movements that are used to look from one object to another
Primary visual cortex (V1)
the area of the cerebral cortex that receives input from the lateral geniculate nucleus, located in the occipital lobe and responsible for early visual processing
Retinotopic map
a point-by-point relation between the retina and V1
Cortical magnification
the allocation of more space in the cortex to some sensory receptors than to others; the fovea has a larger cortical area than the periphery
Simple cells
V1 neurons that respond to stimuli with particular orientations to objects within their receptive field; the preferred orientation of a simple cell is the stimulus orientation that produces the strongest response
Orienting tuning curve
a graph that demonstrates the typical response of a simple cell to stimuli or different orientations
Complex cells
neurons in V1 that respond optimally to stimuli with particular orientations; unlike simple cells, they respond to a variety of stimuli across different locations, particularly to moving stimuli
End-stopped neurons
neurons that respond to stimuli that end within the cell’s receptive field
Ocular dominance column
a column within V1 that is made up of neurons that receive input from only the left eye or only the right eye
Orientation column
a column within V1 that is made up of neurons with similar responses to the orientation of a shape presented to those neurons
Hypercolumn
a 1-mm block of V1 containing both the ocular dominance and orientation columns for a particular region in visual space
Blobs
groups of neurons within Vl that are sensitive to color
Interblobs
groups of neurons that are sensitive to orientation in vision
Extrastriate cortex
(secondary visual cortex)
the collective term for visual areas in the occipital lobe other than V1
V2
the second area in the visual cortex that receives input; often considered the area that starts with visual associations rather than processing the input (sometimes called the prestriate cortex)
Ventral pathway
starts with midget and bistratified retinal ganglion cells and continues through the visual cortex into the inferotemporal cortex in the temporal lobe; often called the
“what” pathway, as it codes for object identification as well as color vision
Dorsal pathway
starts with parasol retinal ganglion cells and continues through the visual cortex into the parietal lobe; often called the “where” pathway, as it codes for the locations of objects and their movement
Object agnosia
an acquired deficit in identifying and recognizing objects even though vision remains intact
Inferotemporal cortex
the region in the temporal lobe that receives input from the ventral visual pathway; one of its functions is object identification
MT (V5)
an area of the occipital lobe in the dorsal pathway, specific to motion detection and perception
Blindsight
the presence of visual abilities even though a person experiences blindness because of damage to V1
Scotoma
an area of partially or completely destroyed cells, resulting in a blind spot in a particular region of the visual field
Internuclear ophthalmoplegia
a conjugate palsy resulting from damage to the brain stem region known as the medial longitudinal fasciculus
What is another name for the primary visual cortex?
area 17
Which of the following is associated with the dorsal pathway?
locations
Each layer of the lateral geniculate nucleus receives input from only one eye. T/F
True
In ______, damage to the brainstem affects the ability of both eyes to train on the same object.
conjugate gaze palsy
The ventral pathway is also known as the ______ pathway.
“what”
The M pathway is also known as the ______ pathway.
dorsal
Hubel and Wiesel discovered that neurons in the brain ______.
respond to only some patterns of stimuli
End-stopped neurons are neurons that respond to stimuli that end outside the cell’s receptive field. T/F
false
Nora sustains damage to part, but not all, of her primary visual cortex. Which disorder is most likely to result from this injury?
scotoma
Why does the fovea take up so much space in the cortex?
The fovea specializes in sending information necessary for acuity-reliant functions, such as object identification.
Why would hte visual system represent visual space – what function does it serve?
The visual system represents visual space as it perceives the location of objects to ensure our safety in different surroundings. This also helps us to be able to coordinate our movements. In continuation it also helps us create a perceive images, and depth of objects to judge distances that we see.
Describe the relation of the retinotopic organization to the representation in the external world.
Retinotopic organization mirrors the external world as retinal ganglion cells from adjacent areas of the retina connects to cells that are in adjacent areas within the LGN.
What are the functions of V3, V4 and V5 (MT)? What might happen if these areas are damaged?
V3 is an area that perceives movement and depth perception, where damage to the area can result to an impairment to these functions.
V4 recognizes shapes, as the neurons are sensitive to binocular disparity, and it also plays a role in color vision since if its damaged color vision will be affected.
V5 neurons are sensitive to the direction and speed of motion. If this area were to be damaged the individual would not be able to perceive motion.
Why would color information be important for the ventral pathway but not the dorsal pathway?
Color information is important for the ventral pathway since it goes through V2 & V4, which are areas that have thin stripes that respond to color, while the dorsal pathway focuses on movement and location of objects.
