vision Flashcards
cones
see color and acuity
were do you find the most cones
fovea
Rods
color-blind; better for motion
photoreceptors
rods and cones
Fovea
‘best vision’ for acuity and color
Goal of lens of eye, eye & headmovement, and brain guidance is to getthe light to focus on the fovea… so yousee best! only cones in the fovea
Extra fovea
all cell types includingcones and rods.
more rods then cones
Extra fovea
all cell types includingcones and rods.
more rods then cones
Pathway from retina to visual cortex:
Retina(ganglion cells are theneurons of origin)
Optic nerve
Optic chiasm (crossing of some axons)
Optic tract
Lateral geniculate nucleus (thalamus), LGN
Through the parietal andtemporal cortex as optic radiations
Visual cortex
the visual field
each eye seen 2/3 of the visual field, there is an overlap in the center
Nasal retinal information goes where
crosses at optic chiasm to go to contralateral V1
lateral portions of each visual fields - nearest nose/medial
Temporal retinal information goes where
does not cross at chiasm, continues ipsilaterally to V1
medial portion of each visual field - near temporal bone/lateral
Left visual cortex, receives retinalafferent from where
axons with information about theright (opposite) half of thevisual field ofeach eye
peripheral aspects of the visual field is seen by what
about aquarter of the visual field is seen byone eye only.
Visual context
the visual signal from the background of the scene
Visual experience/learning changes in neural circuits
experience-dependent (e.g.a lifeguard surveys a crowded pool andsees features of the person in trouble; PT in busy gym recognizes thepatient in pre-distress)
Cognitive influences of attention, expectation, task-dependent (even perceptual task):
hockey player skating up theice, finds the potential open path to the goal; person walking dogs inthe pre-dawn attentive to potential harm – wild animal, stranger,vehicles out of control
Neurons in the LGN receptive fields
Neurons in the LGN have centersurround receptive fields
These neurons with surround RF will enhance the light when it on the RF and depress some of the weaker light responses
They depress the weaker unit and support the brighter inputs
Visual cortex (V1) two type of cells
simple cells and complex cells
simple cells in V1
on/off: Neuronshave orientation sensitivity;respond to specific light orientations oflines/edges
They are tuned to light in a very specific orientation
Complexcells in V1
respond to continuousbar of light in a specific orientationanywhere in receptive field; integratesimple cell content to form lines andedges, with contours/textures
V1 - visual cortex preception of what
color and motion
Preconscious path for quick action
‘M’cells, magnocellular visual path
Rapid transmission back to the visual cortex
retina to visual cortex via thelateral geniculate nucleus(LGN).
‘Where & how’ – it over there for better move now
Conscious slower path for integratedperception and thought
P’ cells,parvicellular visual path
‘What’
dorsal stream for action
Visually-guided reaching
‘Visually-informed grasping’
‘Visually-informed grasping’
Translates visual info about object properties into successful grasping
Extrastriate cortex to premotor ventral (PMv) via anterior intra-parietal area
‘Visually-guided reaching’
Extrastriate to dorsal premotor (PMd) via medial dorsal- and medial intra-parietal areas
Translates visual info of object location to reaching direction
ventral stream for
objectrecognition
What is that object, I have seen that face before
Inferior temporal cortex codeswhat
codescomplex, higher order integratedinformation,e.g.faces,hands
he ventral stream has lot of connects with whta?
Has a lot of connection with the prefrontal cortex
Posterior parietal cortex (PP)
Functions in recognition ofself, relativeto world:
Internal representation of body
Perception ofself relativeto theworld: our actions vs their actions
Posterior parietal cortex (PP) neuron RF
complex
Posterior parietal cortex (PP)lesion
Lesions associated withspatiotemporal disorganized reachand grasp; gaze disorders;disorientation; constructionalapraxia (put on a sweater …)
Prefrontal cortex (PF)(+premotor, PM)
Motor planning, judgement
Select appropriate, suppress inappropriate behavior for current conditions
Provides control and flexibility in behavior
depthperception needs what cues
Both binocular andmonocular cues
binocular disparity neuronsare active when
the image inview is focused on slightlydifferent parts of the retinasof eacheye.
Attention
looking for something, expectation, what to attend to a specific stimulus
Top down
attention of your intent
Looking for someone in a red shirt
Bottom or mid- up
what your gaze caught – eye muscleproprioceptors to visual cortex via thalamus …
Two types of eye movements
Gaze stabilization
Direction of gaze
Gaze stabilization
: keeps image stable when our head moves
VOR
Direction of gaze
attend to visual targets:
How do we explore ourenvironment quickly and efficiently?
Direction of gaze two type
saccades
smooth pursuit
saccades
voluntary or reflexive, shift the fovea rapidly to a new visual target
Reading- we do not read left to right, we looking at different parts of the sentence to put it together
Redirects center of sight, allows us toscanenvironmentquickly
smooth pursuit
Following a moving target
Keep target on fovea
Match eye speed to target speed
Much slower speed (maximum 100degrees per second)
what muscle do smooth pursuit and saccades use
But,they both use the six extraocular muscles/agonist –antagonist pairs
Medial and lateral recti move the eye what direcction
horizontally
Superior rectus and inferior oblique move the eye
elevate eye
inferior rectus andsuperior oblique move the eye
depress it
Conjugate gaze
– moving two eyes together
Triggered (reflexive) saccades
something moves in visual field [detect]
Attention (voluntary) saccades:
visual attention to something in visual field [find]
Attention (voluntary) saccades pathway
Input from frontal eye fields, posterior parietal cortex tosuperiorcolliculusto pontine brainstem centers for gaze motor control
basal ganglia role on saccades
input to superior colliculusinhibit superior colliculusand suppress saccades. (consider: performing a well-learned motor skill,not interested in distraction of detect orfind saccade eye movements)
When you are doing a well learned skill the BG stop saccades – stopping distractions
smooth pursiut pathway
Information about object movementfrom visual association cortex > middle temporal cortex >frontaleye fieldsprojected > pontinenuclei > the cerebellum andvestibular nuclei and onto pontinecenters for gaze movement control.
Tau
Time to contact
When a n object is moving close to you it is expanding on the retina
Very powerful predictive information, feedforward
Optical Flow
the visual information that is streaming past us
