Motion Perception Flashcards
what is the where? how? pathway called
dorsal
which area is involved with depth vision
V3A/V7
which area is involved with motion vision
V5/MT
which area is involved with hand actions
superior parietal lobule & inferior parietal sulcus
what does damage to area V3A/V7 result in
stereo loss
what does damage to V5/MT result in
akinetopsia
what does damage to the SPL & IPS result in
optic ataxia
what is the what? pathway called
ventral
which area is involved with colour vision
V4
which area is involved with object vision
lateral occipital cortex LOC
which area is involved with recognising faces
inferior temporal IT/fusiform gyrus
what does damage to V4 result in
achromatopsia
what does damage to the LOC result in
form agnosia
what does damage to the IT/fusiform gyrus result in
prosopagnosia
list the areas which are involved in the where? how? pathway
- V3A/V7 - depth
- V5/MT - motion
- SPL & IPS - hand actions
list the areas which are involved in the what? pathway
- V4 - colour
- LOC - object
- IT/fusiform gyrus - recognising faces
where does the where? how? dorsal pathway run through
through V5/MT, to medial superior temporal (MST) to the posterior parietal (PP) cortex
what does the where? and how? stand for in the dorsal pathway
where = objects are how = to interact with them
where does the what? ventral pathway run through
from V1/V2, travels down to area V4 to inferior occipital temporal & into inferior temporal cortex
which RGC is the dorsal pathway mainly associated with
magno
which RGC is the ventral pathway mainly associated with
parvo
what does MT stand for in V5/MT
middle temporal (where it is located)
which is the general all purpose motion processor
area V5/MT
which are the more specialised motion processors
- V5A/MST medial superior temporal area
- STS superior temporal sulcus area
- Occipital area V3 & superior parietal area V6A
where does area V5A/MST sit
next to area V5
where does area STS superior temporal sulcus sit
above V5A
which area sits at the more posterior areas
superior parietal area V6A
which areas are involved in more aspects of particular motion processing
occipital area V3 & superior parietal area V6A
what is there an increase of cells for in the extra striate cortex, compared to area v1
increase in the % of cells selective for a specific object property or attribute e.g. more cells interested in colour processing in area V4 than in V1
what type of organisation of a particular property is there in the extra striate cortex compared to v1
columnar organisation of a specific property
what attributes do the cells RFs have in the extra striate cortex compared to area v1
- increased RF sizes at all eccentricities
& - increased RF complexity, responses increasingly resemble perception of object attributes
what significance does an increased RF sizes at all eccentricities in the extra striate cortex have
analysing a bigger area of field than v1
what is the increased RF complexity of in the extra striate cortex
of what we really see & whats out there in the world
what type of VF representations does the extra striate cortex have
biased VF representations, with the highest areas lacking retinotopic or even hemi-field organisations
i.e. much larger representation of peripheral part of visual field than there is for central, visa versa for area v1
how many v1 cells are direction selective
25%
what are the 25% of v1 direction selective cells for only
only orientated stimuli
which part are the oriented stimuli, direction selective cells in area v1 mainly in
layer 4B
what do the direction selective cells in area v1 layer 4B respond best to
respond best to movement of the oriented stimulus in one direction = bar is same direction to the long axis of the contour/opposite (orthogonal) direction to the stimulus, but does not respond when bar is in the opposite direction to the long contour/opposite direction to same stimulus
what do v1 cells tend to be broadly tuned for
movement speed
what speeds does v1 prefer
slow speeds 1-20 deg/s
what speeds do v1 cells rarely respond to
fast speeds >100 deg/s
how many cells of V5/MT are direction selective
80-90% (compared to 25% in v1)
how much larger are the RF sizes of V5/MT compared to v1
5x so they analyse motion over a wider range of visual field
what are the direction preferences of area V5/MT independent of
the moving object’s other properties e.g. its colour, size, shape, orientation, contrast
what do V5/MT cells only care about
direction
what do V5/MT cells respond weakly to if at all
flashed, stationary stimuli so are pure motion detectors and velocity tuning (speed of stimulus)
when do V5/MT cells only get excited
when an object is moving in the right direction and at which speed, doesn’t matter which stimulus is provided
from a complete range of velocities from slow 2 to fast 256 deg/s, what do the majority of V5/MT cells prefer
moderate velocity of 20-50 deg/s
higher than v1
what do cells of direction columns running through grey matter of V5/MT in adjoining/vertical columns interested in
the same direction of motion, but different to the column before
how do the preferred direction of motion change between adjoining direction-selective cells recorded tangentially across the layers in direction columns of grey matter of V5/MT
changes systematically
= columnar orientation of direction preferences in that particular area
what does the recording from left cortex V5/MT represent
right hemifield = whats recorded of right visual space
which visual quadrant of V5/MT is over represented
lower visual quadrant (compared to upper visual quadrant)
which field representation in V5/MT show general bias and what for
in the more peripheral field representation
for fast speeds and for direction of motion away from the centre of gaze
what does lower visual field and direction biases suggest about area V5/MT
area V5/MT may also be involved in the initial stages of processing the specific directions of ‘retinal image motion’ associated with computing ‘optic flow’ patterns that typically occur during forward self-motion/navigation through the environment
e.g. when we drive down an open road and when we look into the distance, there is no movement of the image as you’re fixing on a stationary point in the FOV. but objects which are close & at ground level or trees near by in the periphery appear to whiz by us quickly, which is called optic flow. most things we navigate through are at lower part of visual field, as they’re at ground level & fast motion is out at the periphery & biased of V5/MT is at lower quadrant which indicates single cells at V5/MT represent optic flow.
which complex type of visual motion and role does the dorsal sub-division of MST (dMST) have
- wide field
- expansion/contraction
- rotary & apparent (phi) motion + 3D motion in depth + optic flow
which complex type of visual motion and role does the ventral sub-division of MST (vMST) & STS have
‘structure-from-motion’ & ‘biological’ motion
which complex type of visual motion and role does the occipital area V3 & superior parietal area V6A have
also optic flow & or motion in depth
like dorsal sub division of dMST
what is the pattern between RF sizes and eccentricity in V5/MT & V1
linear relationship of RF from 0-50 degrees eccentricity
RF sizes increase with eccentricity at all locations & 5x wider than V1
what is the pattern between RF sizes and eccentricity in MST
increase of RF sizes with eccentricity, some single cells with 100% RF sizes (cells seeing motion in almost the entire VF), but the mean RF size in MST is 40 degrees
give examples of more complex wide-field (RF sizes = 100x100 degrees, so the semi-field where single cells are able to report motion in the opposite semi-field anywhere as their RF’s are huge) moving stimuli to which different, highly specialised direction-selective dMST, but not V5/MT cells respond
- cells which prefer objects which move in one direction and another cell which prefers object moving in the opposite direction (vertically and horizontally)
- another cell likes rotary of clockwise spinning but hates spinning of objects in opposite direction, where as another cell prefers the opposite
give an example of a dMST cell’s opposite responses to looming & receding optic flow
this cell is excited by the textured random-dot display moving towards it (at walking pace of 0.2m/s) & is inhibited by the same display moving away
where in the human brain is area V5/MT located
middle temporal MT cortex is located, at the junction of the inferior occipital sulcus (ios) & the superior temporal sulcus (sts) at left and right hemispheres, and is at back end of middle temporal gyrus
what are the ventral part of MST & superior temporal sulcus interested in
structure from motion & biological motion = something we do all the time
what is structure from motion
showing somebody dots which are moving in a direction & what they will see is a cylinder rotating on the screen, there is not actually a cylinder but a series of dots which indicate an object is moving in 3D space. so get to see structure of object through component of motion
what is intact in a classic case of akinetopsia
- visual fields
- VA stereo acuity
- colours
- objects = stationary
= unconscious aspects of motion processing spared
what does a px complain of with akietopsia
visual motion made them feel tired & unwell with
- pouring tea ‘frozen glacier’
- crossing the street ‘vehicle approaching from their sound’
- crowded room ‘people suddenly appearing’
= conscious aspect of motion messed up
what damage to brain can result in akinetopsia
a venous infarct/stroke which took out hV5/MT+, V5/MT on both sides of the brain & MST entered on brodmann areas 19 & 37
what other motion perception and other deficits are experienced in a case of akinetopsia
- no simple or complex objects moving faster than 10-15 deg/s (did have perception of objects moving slowly as v1&v2 are intact in her brain, but disappear above 10-15 deg/s)
- reduced temporal frequency selectivity
- no or reduced 3D, apparent or structure-from-motion vision
- no smooth pursuit/tracking eye movements to targets >10 deg/s
what are a patient with akinetopsia contrast sensitivity functions like
- acuity/CS functions for stationary gratings is similar to that of control subjects ~30cpd = 6/6
however - it is significantly reduced for drifting (moving) gratings at all spatial & temporal frequencies
what are a patient with akinetopsia temporal frequency like
non existent as she can’t see flicker more than 10x per sec
same for peak spatial frequency at 5cpd & for lower 1cpd, & control can see flicker at 40-50x per sec which is behind magno processing for motion selectivity
what is a patient with akientopsia spatial frequency like
- high spatial frequency same as control
- reduction at low spatial frequency
what underlies the sparing of navigation (i.e. based on optic flow) & some catching abilities (if moving slowly) in a px with akinetopsia (bilateral area hV5/MT+ lesions, veneer stroke centred on brodmann areas 19 & 37)
another prallel magno & motion/spatial vision pathway via v1 & v2 to areas v3 & v6A
two parallel pathways that come out of v1 & v2 that are involved in motion processing, one goes from/through V5/MT, other goes through V3 into area V6A
is area V5/MT selectively activated between optic flow vs random directions
no, as both stimuli equally activate area V5/MT
which area is selectively activated between optic flow vs random directions
V3 & V6A is activated by optic flow stimuli and NOT by random directions
so lets us navigate through environments
