Visual Perception Flashcards
cornea
outer layer of eye
pupil
opening at center of the iris
When does the pupil dilate?
When dark, opens to increase amount of light into the eye
When does the pupil constrict?
When bright, shrinks to decrease amount of light in the eye
What is the function of the iris?
adjust size of pupil to control amount of light
Parasympathetic component is when
pupils dilate with nervousness
What is the lens?
Helps focus light via changing shape
What are binocular cues?
Use of both eyes/convergence
How many layers of the retina are there?
10
What is the action potential in the eye?
transduction
What is the macula responsible for?
specific details such as
* text on page
* differences between faces
* tiny movements
* specific colors
When macula function is lost, what happens?
Blurriness
Describe the fovea.
Place of highest visual acuity level, cones are concentrated here, center of gaze. No rods here.
Where is the fovea located?
small pit inside of macula, .35mm
Why do we move our head and eyes to see?
Placing objects in front of the fovea to line it up
Movement of stimuli sequence…
- Light hits photoreceptors
- Interacts molecule - photo pigment
- Initiates chain events - prorogates the visual signal
- Bipolar Cells – receive action potential from cones & rods, in turn will activate ganglion cells,
- Ganglion cells leave eye in large cluster - Optic Disc
Describe the optic disc?
-contains no photoreceptors
-cannot process any visual information
-natural blind spot, do not notice because surrounding photoreceptors & info from the other eye to fill in (closure)
Ganglion cells become _____ when they leave the retina
optic nerve
Function of optic nerve?
carries visual info to brain to be processed
Photoreceptors induce graded potential in response to light to dark and vice versa causing ____?
Increase/decrease of glutamate
Starting at retina, there is coding for what 3 things?
color
shape
movement
2 areas that cross at the optic chiasm?
nasal and temporal
Which area is in the nasal portion of optic chiasm?
refers to the portion of the eye closest to the nose
Which area is the temporal portion of optic chiasm?
refers to the portion of the eye closest to temple
After optic chiasm visual fibers are no longer called optic nerve they now known as _______
_________
optic tract
Where does most of the optic tract travel to?
thalamus, but not smell!
What is the thalamus?
relay system that send the signal outward to appropriate location.
Direction of the optic tract?
1.enters thalamus at lateral geniculate nucleus (LGN) –
2. sends signal to primary visual cortex (within occipital lobe)
–where interpretation of signal occurs
What is another name for optic radiations?
Geniculocalcarine Tract
Info about optic radiations…?
Bilateral in brain
Leave LGN and extend toward back brain as bundles of fibers known as optic radiation
Optic radiations travel to primary visual cortex
Primary visual cortex makes a visual image from stimuli received, neurons activated preferentially base on features i.e. movement, orientation
What is the primary visual cortex?
the tissue that surrounds calcarine sulcus
From the optic tract to which 5 locations?
- Geniculocalcarine - from LGN to primary visual cortex
- Tectopulvinar (aka retinotectal) - detection and orientation to stimuli
send neuronal signals to - superior colliculus in tectum
- vestibulo-cerebellar system – body in space
- hypothalamus – circadian rhythm
Where do 1% of ganglion cells travel to?
pretectal area
synapse CN III & Edinger-Westphal nucli (accessory CN III) responsible for accommodation, Pupillary light reflexes (PEERLA) & saccadic responses of eyes
What is the dorsal bundle?
Baum’s loop, info from lower visual field
What is the ventral bundle?
Meyer’s loop - info from upper visual field
What 2 areas does the optic radiation divide into?
dorsal bundle
ventral bundle
What is V1?
primary visual cortex
What helps with color?
photoreceptors
What controls shape?
via Parvocellular cells, boundaries object, (in LGN in Thalamus)
↑ spatial resolution
↓ temporal resolution
What controls motion?
via Magnocellular cells (in LGN in Thalamus)
↑ temporal resolution
↓ spatial resolution
Parvo cells need ______ objects to process movement
stationary
What is parallel processing?
Brains ability to simultaneously process color , shape and motion
What are fixations in eye movement?
When eyes re stopped on an object, not completely steady during a fixation, show small, involuntary tremors
What are saccades?
rapid movement/scans toward visual, auditory, and tactile stimuli
What are smooth pursuits?
when eyes track a moving object, not considered a saccade
What are dwell times?
How long the eyes dwell on object, may consist of several fixations, time affected by difficulty of information extraction.
What makes visual information useful?
- Retinal Acuity- how clearly you can see
- Cortical Magnification-where brain focuses on features, magnifies useful information
- Attention-
Useful field of Vision (UFOV) – attentional window on the world (how long you can stay focused)
UFOV middle of visual field
Width determined by ease of image extraction and other factors such as impact aging
What connects attentional windows?
Saccades
What are visual fields?
Defined as the total area in space perceived when the eyes are in fixed, static position looking straight ahead.
What degree is temporal?
100
what degree is nasally?
60
what degree is superiorly?
60
what degree is inferiorly?
70
what degree is the blind spot at?
15 temporally where optic nerve leaves the eye
What are the 12 eye diseases?
- Macular degeneration
- Diabetic retinopathy
- cataract
- glaucoma
- amblyopia
- strabismus
- drusen
- floaters/spots
Refractive Errors
9. myopia
10. hyperopia
11. astigmatism
12. presbyopia
What are the Visual Processing Disorders
- visual discrimination
- visual figure ground discrimination
- visual sequencing
- visual-motor processing issues
- long/short term memory
- visual spatial issues
- visual closure issues
- letter and symbol reversal issues
What is agnosia?
neurological disorder characterized by inability to recognize and identify objects or persons using one or more of the senses.
What causes agnosia?
damage to parietal, temporal or occipital lobes. Areas important for memories of function, importance of objects, sigh
What is appreciative agnosia?
unable to recognize an object, even if they can describe object by size, shape texture.. Impairment is to object perception
What is associative agnosia?
subtype of visual agnosia – perception intact impairment is to the association of the precept with meaning, difficulty understanding the meaning of what they are seeing. Able to draw or copy the object but do not know what it is
What is prosopagnosia?
inability to recognize faces, aka face blindness. Believed to be related to damage to right fusiform gyrus
What is topographic disorientation?
Acquired inability to navigate the environment in daily life. “Memory deficit in visual realm”
Lesion in medial occipitotemporal area
What is pure alexia?
alexia without agraphia – acquired reading disorder, unable to read despite preservation of other aspects of language including spelling and writing. Associated with occlusion distal branches of left posterior cerebral artery.
What does monocular mean?
one eye
Heteronymous Hemianopsia definition?
loss of half of the visual field on different sides in both eyes
Binasal hemianopsia –the loss of fields surrounding the nose
Homonymous Hemianopsia definition?
loss on the same side of the visual field in both eyes
Spatial representations….describe
concept of left/right
spatial rotation
acalculia - “borrowing”
palindrome - tap vs. pat
Sequence of Light?
-Light passes through cornea which shaped like dome and bends the light to help eye focus
-Light enters eye through pupil while iris (colored part eye) how much light the pupil lets in
-Light passes through lens (clear inner part of the eye)
-Lens works with cornea to focus light correctly on retina
What is transduction
Neural components of the eye, where light converts to electricity
What are rods?
dim light, no perception of color, rather black/white
Rods out number cones through most of visual system
Concentrated on peripheral vision
What are cones?
under daylight, allow for color perception, visual acuity.
Concentrated around fovea
sensitive to wavelengths of red, blue, yellow
