Unit 2 Visual Disorders

Deuteranopia

(M) cones deficit that causes Red-Green Colorblindness

Tritanomaly

Blue weakness

Perception

The process of recognizing, organizing, and interpreting sensory information

Monochromacy

a form of congenital achromatopsia (color blindness) arising from problems in the retina. only see one color

Retinal colorblindness

an inability to correctly see colors due to mutations in photoreceptors (e.g., medium-length cones mutated to respond like long-length cones)

Deuteranomaly

green weakness

Associative (amnesic) type

problems with recognizing familiar faces (can tell it's a face, but not whose face it is)

Cornea

the transparent dome-shaped anterior portion of the outer covering of the eye

Perception for recognition

ventral visual stream this portion determines "what is it"

hemifield

'half the visual field,' typically refers to left and right halves only (not top/bottom)

quarterfield

'one quarter or quadrant of the visual field,' defined by the quadrant created by the vertical and horizontal meridian lines

Protanopia

(L) cones deficit that causes Red-Green Colorblindness

Tritanopia

(S) cones deficit that causes Blue-Yellow Colorblindness

Melanopsin-containing retinal ganglion cells (ipRGCs)

(also called intrinsically photosensitive retinal ganglion cells) are a recently discovered type of retinal ganglion cell that can directly absorb light. They contain the photopigment melanopsin (related to melanin), which allows them to function like the photoreceptors that transduce light for the rod and cone retinal ganglion cells. These ganglion cells have a very large dendritic tree, which contributes to the role of these cells in signaling gross changes in light intensity. This information is sent to subcortical structures and is thought to be used in circadian rhythms and pupil constriction. -respond relatively sluggishly - signal the presence of light over long term -regulate circadian rhythms and melatonin release -may play a conscious vision role

Photoreceptor proteins

- light-sensitive protein molecules involved in the sensing and response to light in a variety of organisms by undergoing a structural change when they absorb light. This structural change opens ion channels, which causes a change in the graded potential (ion flow) of the photoreceptor (in other words, causes the photoreceptor cell to signal that light has been detected).

Ishihara plates

38 colored plates used to test those with red-green color blindness

Fusiform face area

A bilateral visual processing area that is thought to be specialized for face processing (with some controversy--some authors argue that it is specialized for detailed visuospatial processing, not necessarily just face processing). Damage to this region can cause face perception deficits. -identified as the brain area that responds more when people view images of faces than common objects

Apperceptive visual agnosia

A disorder characterized by the inability to name, copy or recognize visually presented objects. Shape perception and figure-ground segregation is impaired, but basic visual functions (color discrimination luminance discrimination, visual acuity), and object identification based on nonvisual cues are preserved. Abnormal Visual Perception: -inabilitu to name, copy or recognize visually present objects -problems with basic shape perception and figure ground segregation preserved(more or less): -basic visual functions (color discrimination, luminance discrimination,visual acuity) -object identification based on non-visual cues are preserved

Prosopagnosia

A disorder in which faces cannot be recognized (damage to the fusiform face area), but other forms of object recognition are unimpaired. -visual processing of faces is an important specialization of human vision

Visual agnosia

A disorder in which the patient suffers from the inability to recognize and identify objects, features of objects or scenes, faces or persons despite having knowledge of the characteristics of the objects, scenes, faces or persons. This condition can be loosely divided into two types that differ by severity: apperceptive and associative

Visual object agnosia

A disorder in which visual object recognition is impaired (e.g. naming of visually presented objects, categorization, matching by function), but elementary visual perception is more or less preserved, e.g., matching and copying of visually presented forms and objects, drawing objects from memory, and non-visual object recognition.

Associative visual agnosia

A disorder in which visual object recognition is impaired (e.g. naming of visually presented objects, categorization, matching by function), but elementary visual perception is more or less preserved. This is how object agnosia is typically described, as this is the more common type. Normal Visual Percept is stripped of its meaning: -visual object recognition is impaired ex: naming of visually presented objects preserved(more or less): -elementary visual perception ex: matching and copying of visually presented forms and objects -drawing objects from memory -non visual object recognition

Red-green colorblindness

A form of retinal colorblindness where either the green cones are missing completely or respond like red cones. It is much more common in males than females. it is sex linked affecting males more

Blue-yellow colorblindness

A form of retinal colorblindness where people confuse blue with green and yellow with violet. It is very rare (roughly 1/10,000) and not sexlinked.

Thalamus

A part of the brain involved in relaying sensory information from sensory organs to processing areas of the cerebral cortex

lateral geniculate nucleus (LGN)

A part of the thalamus where the visual processing streams pass through on their way to the optic radiations and primary visual cortex

Blindsight

A phenomenon where people who are perceptually blind demonstrate some response to visual stimuli (because only part of their visual system is impaired, other parts - parts involved in motion perception - may still function)

magnocellular pathway

A visual processing stream of large cells that pools over many receptors, whose retinal ganglion cells (parasol retinal ganglion cells) fire in bursts and are useful for detecting motion

parvocellular pathway

A visual processing stream of the small cells that pools over fewer receptors. The cells involved (midget retinal ganglion cells) have a sustained response and are involved in processing color, fine details, textures, and depth processing.

Koniocellular pathway

A visual processing stream that gets S-cone input only (from small bistratified cells), processing low acuity visual information, and innervating V1 and extrastriate cortex

Scotoma

An area of impaired or lost vision in the visual field. A scotoma can arise from from damage anywhere along the visual pathway from the retina to primary visual cortex (V1). Beyond V1, more specialized types of visual disorders arise (e.g., visual object agnosia). The following terms describe different extents of a scotoma that can occur due to very specific locations of damage

Photoreceptor cells

Cells that line the back of the retina and have parts that change shape when they are hit with a photon, allowing them to detect light in a certain part of the visual field. The overall function of the photoreceptor cell is to convert the light energy of the photon into a form of energy communicable to the nervous system and readily usable to the organism: This conversion is called signal transduction. Humans have two main types, rods and cones, and there are three different subtypes of cones.

anomalous trichromacy

Color blindness due to a partial loss of each cone type. they all don't function normally. may come from retinal or cortical damage. most common, deuteranomaly is the most common type

Hemiachromatopsia

Loss of color vision is restricted to one half of the visual field. The rest of the visual field has normal color vision. (Color vision can even be lost for just one quarter of the visual field.)

Dorsal visual pathway

Made up of multiple visual areas, it is one of two main visual processing streams after primary visual cortex. This pathway is involved in perception for action.

Ventral visual pathway

Made up of multiple visual areas, it is one of two main visual processing streams after primary visual cortex. This pathway is involved in perception for recognition.

optic radiation

Nerve pathway along the visual processing stream from the LGN to primary visual cortex.

cones

Photoreceptor cells that are concentrated in the fovea, but also more sparsely extend into the periphery. They are responsible for high acuity vision, but take more photons of light to activate (good for daytime - photopic - vision). There are three types, each most responsive to different wavelengths of light (long (L), middle (M) and short (S) -wavelength cones, corresponding to maximal absorption of red, green, and blue light, respectively). The combination of inputs from different cone types though opponent processing (see below) produces for color vision.

Rods

Photoreceptor cells that are located outside the fovea. They are highly sensitive to light and thus are responsible for low-light (scotopic) vision, like under starlight. Rods also contribute to visual motion detection, but have poor visual acuity. They also do not differentiate between colors.

Protanomaly

Red-weakness, looks dull not as bright.

lens

Situated behind the iris of the eye, it focuses light entering the eye onto the retina

Capgras syndrome

The delusional belief that an acquaintance has been replaced by an identical-looking imposter. -It is one of the delusional misidentification syndromes more commonly seen in schizophrenia, dementia, and brain trauma. -May arise from an abnormal emotional response to faces -> disconnect between temporal and limbic cortex; possible example of a really high-order face processing issue

Fregoli syndrome

The delusional belief that different people are in fact a single person who changes appearance or is in disguise, generally viewed with paranoia (that the "shapeshifting" person is out to get them). -This is another rare delusional misidentification syndrome. -Appears to arise from damage to left frontal and right temporoparietal regions, possibly due to a disconnection between hemispheres, that affects high-order face processing. - A person with the Fregoli delusion may also inaccurately recall places, objects, and events, leading to the theory that associations among stored memories may be messed up - with the image of one face (or place/object/event) ending up being improperly associated with another one.

primary visual cortex

The first area in the brain where visual information is processed at a low level. Visual information flows into here from the retina and flows to higher levels of visual processing (V2, V3, etc.) that do increasingly complex visual processing. V1 is also called striate cortex due to the visible stripe of inputs from retina to layer 4 of V1

Sensation

The first stage in the functioning of the senses, starting with information at the peripheral sensory receptors

optic chiasm

Where the optic nerves cross in the brain, allowing information from the left visual field (from both eyes) and right visual field (from both eyes) to be separated and directed to the appropriate contralateral hemisphere.

Dorsal simultagnosia

a deficit in scene perception where the patient can only perceive one stimulus at a time (more severe than ventral type) -from bilateral lesions at the parietal-occipital junction -can perceive one object but nothing else may appear blind

Ventral simultagnosia

a deficit in scene perception where the patient can see multiple objects, but cannot recognize them (can navigate and count, but cannot read) -from damage to left inferior occipitotemporal junction -can navigate and count but can NOT read

Simultagnosia

a deficit in scene perception, -with a normal visual fields and -normal lower-level (elementary) visual perception. -problem with scene perception -dorsal and ventral subtypes -may arise from problems with attention,visuospatial mapping, and/or pattern analysis

opsins

a type of photosensitive pigment proteins found in photoreceptors: e.g., rhodopsin in rods and photopsin in cones (3 types are in cones, making up the L,M, and S cone types), and melanopsin in the melanopsin-containing retinal ganglion cells (also called intrinsically photosensitive retinal ganglion cells. once an opsin absorbs light, it takes time to regenerate back to functional state.

Central/Cerebral achromatopsia (Cortical color blindness)

an impairment of color vision in the entire visual field that arises from cortical lesions on the ventral surface of the temporal-occipital lobes. -lesions caused by cortical lesions such as: stroke,trauma,dementia -bilateral V1/V4 -rare -Loss of color vision in the full visual field is rare, as lesions would need to affect color processing in both hemispheres. Subtypes: -hemi achrommatopsia (loss of color in one half of visual field,quarterfield losses are also possible) -transient achromotopsia (temporary loss of colors which lasts hours,ischemia- transient ischemic attack)

cataract

an opacity in the lens that blocks light from reaching the retina; often occurs in older age due to sunlight (UV) exposure

Hemianopsia

blindness in one half of the visual field in one or both eyes

Binasal hemianopsia

blindness in the middle halves of the visual field in both eyes, due to damage to uncrossed fibers (often due to calcification of carotid arteries; also associated with hydrocephalus) -damage to uncrossed fibers -calcification of carotid arteries -associated with hydrocephalus

Bitemporal hemianopsia

blindness in the outer halves of the visual field in both eyes, due to damage to the optic chiasm (tumors are often the culprit). -normally caused by tumor

Homonymous hemianopsia

blindness in the same hemisphere of the visual field in both eyes, due to -damage to the opposite hemisphere of cortex (often from -stroke or trauma). 'Right homonymous hemianopsia' refers to the loss of the right hemifield of vision in each eye from damage to left V1.

retinal ganglion cells

cells in the retina that receive input from modulatory neurons (which get input from photoreceptor cells) and transmit the information down the optic nerve to the brain. Primary types of retinal ganglion cells are the midget cells (smaller in size, and smaller = higher visual acuity) (parvocellular pathway), parasol cells (magnocellular pathway), and small bi-stratified cells (koniocellular pathway). An additional light-absorbing type is the melanopsin-containing retinal ganglion cells. closer to fovea = smaller which has higher acuity. they are classified by: shape, size, light responses, turning for color,form,motion. sustained *constant) response vs phasic (motion/bursting) response

Dichromacy

color vision disorder in which one type of cone is absent or nonfunctioning. they lack one type of cone

opponent-processing color vision theory

color vision theory that color is processed in 3 different opponency channels created by specific wiring together of cone photoreceptors and retinal ganglion cells: o red (L cone) vs. green (M cone) o blue (S cone) vs. yellow (L+M cone), o dark vs. bright (red/L+green/M+blue/S) => comparison produces luminance

optic nerve

composed of the axons of the retinal ganglion cells that leave the retina and head back towards the optic chiasm in the brain, taking with them visual information. This nerve is the reason humans have a blind spot, because no photoreceptive cells exist where the optic nerve exits the eye.

perception for action

dorsal visual stream this portion determines "where is it?'

Cortical magnification

is a property of sensory and motor systems in which one part of a topographical representation is relatively larger than the rest, producing a region with higher acuity (better sensitivity) in the magnified region. In the visual system, cortical magnification describes how many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size, as a function of visual field location. In the center of the visual field, corresponding to the center of the fovea of the retina, a very large number of neurons process information from a small region of the visual field. If the same stimulus is seen in the periphery of the visual field (i.e. away from the center), it would be processed by a much smaller number of neurons. The increased number of neurons devoted to processing central vision helps make our central vision more sensitive than our peripheral vision. The magnification of central (e.g., foveal) is achieved in several steps along the visual pathway, starting in the fovea with densely packed cones and the midget retinal ganglion cells of the parvocellular pathway and continuing to the large region of cortex that receives information from the central vision. Other examples of cortical magnification include the expansion of the face and hand representations in the somatosensory and motor cortical regions. These body parts have sensitive touch and excellent motor control

Unilateral field loss

loss of an entire eye's vision due to tumor or trauma that results from the disconnection of the optic nerve

L/M - Cone monochromacy

only rods and L or M cones are functional -like blue-cone colorblindness,except is still functional -only single case studies reported

Blue cone monochromacy

only rods and blue cones are functional. -fully color blind in daylight -dichromatic vision at twilight when rods are active -can see ~100 colors vs. ~10 million =sex linked inheritance like red-green colorblindness

Cone monochromacy

patient has one functioning cone type. Color vision is restricted to about 100 colors (rather than our normal ~10 million). Blue-cone monochromacy is rare, but slightly more common than L/M-cone monochromacy.

V1

primary visual cortex, first binocular cells are created in V1. -receive inputs from a single eye or from both eyes -respond best to oriented lines -increase response with contrast -have a preferred spatial frequency -can have a preferred direction and depth

Apperceptive type

problems with recognizing a face vs. other objects (can't tell by vision alone whether something is a face or not)

primary sensory cortex

refers to the first location in cortex that receives inputs from the peripheral sensory receptors - in this case, the retina

Rod monochromacy

rod monochromats are people whose cone photoreceptors are present in the retina but are completely non-functional. The cones cannot absorb light, and therefore the patient relies only on rod vision (sees in black and white with low visual acuity). -complete color blindness -day blindness, photophobia -low visual acuity and lack of functional fovea -involuntary eye movements (nystagmus)

Transient achromatopsia

temporary loss of color vision in any part of the visual field, usually from a TIA (transient ischemic attack)

retina

the back of the eyeball, considered a part of the brain, where light hits the photoreceptive cells and visual information begins being processed.

Iris

the colored portion of the eye, a muscular diaphragm that controls the size of the pupil, which in turn controls the amount of light that enters the eye

visual field

the entire area or field of view that can be seen when an eye is fixed straight at a point on space. Descriptions of the visual field include: vertical meridian - line dividing the field of view into left/right halves; horizontal meridian - line dividing field of view into top and bottom halves

pupil

the hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye

Akinetopsia

the inability to perceive motion that arises from damage to V5/MT - the area of cortex responsible for visual motion; patients experience a strobe-light effect of vision. It can be caused by damage such as stroke, trauma and rarely from some antidepressants.

fovea

the part of the retina, where vision is most acute and color vision is best. Cone photoreceptors are most prevalent here and contains only cone photoreceptors. output to the brain: retinal ganglion cells. only L and M cones

Blind spot

the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the axons of the retinal ganglion cells exit the retina and form the optic nerve. Because there are no photoreceptor cells to detect light on the optic disc, the corresponding part of the field of vision is invisible. Some process in our brains "fills-in" the blind spot with estimates of expected visual info based on surrounding detail and information from the other eye, so we do not normally perceive the blind spot.

Sclera

the white part of the eye that, with the cornea, forms the protective outer covering of the eye

trichromatic color vision

three types of cones: (S)short, (M)medium and (L)long that each preferentially respond to a prefered range of wavelengths

Tetrachromats

women who have 4 types of cones, which likely allows them to see about 100 million colors (rather than our normal ~10 million). The 4th type of cone occurs when one woman inherits two different L-cone alleles (gene subtype), each of which codes for an L-cone photopigment with a small mutation that makes it absorb a slightly different wavelength of light than the other allele. Due to a process called X-chromosome inactivation (in every female cell, one of the X chromosomes is randomly inactivated), each retinal L-cone cell may randomly express one L-cone allele or the other. Fascinatingly, the opponency system of our color vision can incorporate the two slightly different L-cones as individual photoreceptor types. I would have assumed that our brain would not be able to change to accommodate the new input type, that the two L-cone types would just be grouped together as L-cone info. Instead, our brains can instead make a more complex opponency system that allows tetrachromats to see more colors, as Lcone type 1 now can be compared to L-cone type 2, and so on, just like L-cone vs. Mcone comparisons in trichromats (normal human vision).