Neuropsychology: Chapter 13

V1->V2->V3

dynamic form (shape of objects in motion). we use color to see things moving

in humans, how do we study vision?

with lesion studies-study people's brains who went color blind and have issues. study their brain after they died. can also use FMRI

quadrantanopia or hemianopia

-complete loss of vision in one quarter of the fovea or in one-half of the fovea, respectively -results from a lesion to the occipital lobe

summary of the visual processing hierarchy:

info going to V1 originates in your retina (either ipsilateral or contralateral (optic chiasm)) area of V1 seems to be for sorting info on to the next step (info can go to V2, V3, etc..) form and color of something tells us what it is form and motion tells us what we need to do very complex. (look at slide pic)

parietal occipital sulcus

lots of info moves that direction and as it needs to be processed such as motion

lesion study

(look at picture on slide) -not great data, but best we can do -problem w/ graphic: all on one side but not really in reality. -facial recognition (red circles) process in ventral temporal lobe

Visual pathways beyond the occipital lobe: STS stream

-characterized by polysensory neurons (neurons are responsive to both auditory and visual input or both visual and somatosensory input. they take info from multiple sensory systems) -neurons can take in multiple sensory info (synesthesia-neurons can accidentally hear something you hear or vice versa. our neurons may get confused. -originates from structures in the parietal and temporal cortex -interaction between dorsal and the ventral streams -largely an elaboration of ventral stream (provides perceptual representation of biological motion)

nasal hemianopia

-affects 1 side -loss of vision of one nasal field -results from lesion of the lateral chasim. -lesion in one side

Color vision

-amount of color processing certainly varies across occipital regions -color vision primary job of V4, but distributed throughout occipital cortex -plays a role in detections of movement, depth, and position.

homonymous hemianopia

-blindness of one entire visual field -results from a complete cut of the optic tract, LGN, or area V1.

disorder of visual pathways (continued)

-brain=map of visual world -when you see: left vis. field-see w/ both eyes-info all goes to right brain. left crosses and right stays. -each side of brain processes info from both sides -damage in one eye: close one eye and things are normal-something wrong w/ eye not brain (monocular problem).

Visual streaming

-connections-very complex! primary visual cortex (v1) -input from LGN -output to all other occipital levels secondary visual cortex (v2) -output to all other occipital levels -After V2: 3 distinct parallel pathways -output to the parietal lobe-dorsal stream -output to the inferior temporal lobe -multimodal output to the superior temporal sulcus (STS) (just know that dorsal stream is still intact for ppl w/ V1 lesions) Dorsal stream: motor and visual guidance of movements. -ventral streams to temporal lobe

macular sparing

-homonymous hemianopia with macular sparing -process in large surface area-big lesion but still enough brain power to process. -damage after optic chiasm-in optic tract, thalamus (LGN). -left side: messed up-info stays and crosses. (use symptoms to see where lesion is.) -differentiates between lesions of the optic tract or thalamus from cortical lesions b/c macular sparing happens only after (usually large) unilateral lesions to the visual cortex.

monocular blindness

-loss of sight in one eye -problem w/ eye -results from destruction of the retina or optic nerve that eye.

bitemporal hemianopia

-loss of vision from both temporal fields -both sides affected -results from lesion to the optic chasm severing crossing fibers -symptoms in both eyes -Ex. tumor in pituitary gland (pituitary gland is ventral to chiasm)sitting medially to chasm-produces loss of lateral vision (due to problem w/ eye or between optic nerve and chiasm) pituitary tumor could push on chiasm and you could lose crossing abilities. -often b/c of optic chiasm

subdivisions of the occipital cortex

-map based on monkey occipital cortex -monkey brains are not exactly like human's visual system but for humans, we can use: 1)Functional Magnetic Resonance Imaging (FMRI)-measure amount of glucose, non-invasive, can see areas of brain involved in certain activities but less specific than electrode method but more ethical. (less specific. for example:when you are watching a car, doing many things at same time). 2) look at people's brains -precise location of the human homologues (beyond V1-V4) are still being settled.

Visual functions beyond the occipital lobe

-more cortex is devoted to vision than to any other function in the primate brain. -multiple visual regions in the temporal, parietal and frontal lobes -vision: not unitary, composed of many specific forms of processing (5 categories/ways that vision is processed)

Theories of Occipital Lobe Function/damage to different areas

-selective lesions up in the hierarchy produce specific visual defects. -V4 damage: loss of color cognition, cannot see, imagine, or recall color--can't understand color but can receive it, couldn't remember what it was like to experience color. -V5 damage: erases the ability to perceive objects in motion, can only see objects at rest. able to perceive objects but as soon as it moves, is disappears from their vision and don't see it until it is stationary. -V1 damage: people with lesion to V1 are cortically blind-on Josh and Kyle's test w/. the arrows, they would be guessing with eyes open and would have no perception or cognition of vision. not consciously seeing things but still receiving visual input.

Milner and Goodale's discovery to the Dorsal and Ventral Stream

-the dorsal stream is a set of systems for visual control action and can unconsciously see location, size, shape. -Ventral Stream: object recognition, shapes hand appropriately for grasping. -they proved that there are unconscious streams EVIDENCE: -visual neurons in the posterior parietal cortex are active only when the brain acts on visual information -3 distinct pathways run from V1 to the parietal cortex, must be functionally dissociable. V1->V5->parietal cortex v1->V3a->parietal cortex v1->V2->parietal cortex -visual impairments after parietal lesions can be characterized as visuomotor or orientational.

1st category of vision

-vision for action -required to direct specific movements. ex. grasping -must be sensitive to target's movement -a function of parietal visual areas in dorsal stream. -dorsal stream is processed in parietal lobe and processed by motor cortex. -using vision for action-ppl good at this have fast reaction time (baseball).

scotomas

-visual field defect -small blind spots in visual field. sometimes don't even realize you have scotoma. (nystagmus--eyes move to cover missing spot). -scotoma is a resulta of small lesions to the occipital lobe. -we all have blind spot but brain covers it up--this is bad! you may not know you have a blindspot/tumor until it is too late! -nystagmus: constant involuntary eye movements, fills in field so blind spots not not noted.

Dorsal Stream

-visual guidance of movements for grasping -output to the parietal lobe -some neurons may take part in converting visual info into coordinates for action

3rd category of vision

-visual recognition-actually knowing what you are seeing. -object recognition -specialized areas in temporal lobe for biologically significant info such as faces, hands, objects, places. -inferior ventral stream.

object agnosia

1) apperceptive agnosia: failure in object recognition but basic visual functions (acuity, color, motion) preserved. can't identify what lines/color of things make together. -simultagnosia common symptom -unable to perceive more than one object a time -results from gross bilateral damage to the lateral parts of the occipital lobes, usually from carbon monoxide poisoning. 2) associative agnosia -inability to recognize an object despite its apparent perception -can copy a drawing accurately but cannot identify it -results from lesions higher in the processing hierarchy, such as the anterior temporal lobe. -can name objects but don't know how to interact w/ them-see book and don't know how to open it but would know what to do w/ it by feel.

disorder of visual pathways

1) the left half of each retina sends its projection to the right side of the brain -representation of each side of the visual world seen by each eye is sent to the same place in the brain. -damage to V1 affects vision in both eyes -if visual disturbance restricted to one eye, damage must be outside the brain 2) diff parts of the visual field are topographically represented in diff parts of V1 -injury to specific region of V1 produces a loss of vision in a specific part of the visual world.

2nd category of vision

Action for vision -move eyes in order to see better (ex. involuntarily eye movement) -most ppl have shapes/face recognition on r. hemisphere so see left side -moving eyes in order to see -we see more on the left -top down processing to focus on specific features (conscious/decide where to look) -visual scanning involves many eye movements -eye movements not random, selective focus -when scanning a face, focus is on eyes and mouths, in the left visual field (not found in scanning any other objects) -when asked about objects' appearances or rotation of it, eye movements usually made to the left. -eye movement of normal subjects concentrate on the shapes of the objects. -agnosic subject: not able to make correct eye movements or control what they see, random eye movement.

Vision begins in _____ and _____

V1 and V2 (primary visual cortex or striate cortex), which are heterogeneous(diverse in their function) and then travels to more specialized cortical zones. -After V1/V2-things get specific and are specialized, V1 and V2 direct info to specialized cortical zones -blobs-certain areas of V1 and V4

4th Category of vision

Visual space: using vision to understand space -parietal and temporal lobes -superior vental stram -spatial location: -location of an object relative to person (egocentric space) -vision for action -location of an object relative to another (allocentric space) -visual recognition -how things are related to each other in space-use touch and hearing (can do it egocentrically-in relation to me) or allocentrically (in relation to others).

names of visual systems

change all the time, nothing is for certain in the brain

why is our color vision so good?

fruits have a different color than leaves. foods area good source of energy and selected for and so we adapted to use color vision.

ventral stream

output to the inferior temporal lobe, multimodal output to the superior temporal sulcus (STS). -ventral streams to temporal lobe: inferior: down lower, object perception goes down inferiorly to temporal lobe close to fusiform face area. Superior side:high temporal lobe, visuospatial. -IT inferior temporal cortex (object perception) -STS-visuospatial functions (where things are/you are in relation to others. often use auditory and visual systems at same time in superior.)

other types of agnosias

prosopagnosia: face blindness Alexia: pure word blindness-can see everything except words, cannot learn to read dyslexia: labored reading dyscalculia (completely dif part of brain from alexia and dyslexia)-hard to put simple math into longterm memory acalculia: (completely dif part of brain from alexia and dyslexia) --can read but can't understand it

blob areas of V1 and V4

responsive to color. some responsive to color and form

fuisifrom gyrus

runs on ventral side of temporal lobe, used for specific object recognition facial or body

V1->V2->V5

to detect movement

5th category of vision

visual attention -how long should I look at each thing? -selective attention for specific aspects of visual input -parietal lobes: independent mechanisms for guiding movements -Temporal lobe: independent mechanisms for object recognition Facebook uses this-application to advertising-maybe b/c we read Left to right or b/c of convention. can measure where ppl are looking and put ads there.

how do we test V4 in monkeys?

we put electrodes under brain to measure electricity of brain. we put them in v4 and monkeys sense tons of electrical signals--tells us V4 is for color.