Higher visual functions 2: Perception of objects motion and depth Flashcards
How does MT play role in motion detection?
MT neurons have Large receptive fields
that are Sensitive to moving stimuli, and show motion adaptation. so MT is capable of integrating, different local queues
into a global perception of motion.MT.
Is sensitive to this type of coherent motion, and it has a rather low threshold for detecting coherent motion.
How is info transferred to MT?
detection of motion and perception of motion relies on magnocellular pathway, and it starts in the retina. And then, magnocellular layers of LGN and that MT gets its, input from from V1 from the layers that are especially directional selective in V1 .
What is MST and its involvement in motion?
Medial superior temporal area has larger receptive fields. Is very highly sensitive to compelx motion such as expansion, constriction, rotation. More sensitive than MT for all types of motion esp complex. However, MT is about the same for other non-compelx motions.
Akinetopsia
Inability to percieve motion.
human blindsight
Loss of conscious vision
Motion in blindsight
can be detected via 2 alternative pathways by passing V1. Other than M-LGN → V1 → MT pathway there is
- Geniculo-extrastriate pathway: MT receives
direct koniocellular projections from the LGN;
motion detection in human blindsight
- Colliculo-cortical pathway: retina → superior
colliculus/pulvinar → MT; mediating residual
vision in blindsight
Motion detection in unconscious vision?
Patient just knows what the motion is but can’t tell why. No conscious visual registering within V1.
Why is motion detection imp?
We need to percieve hazards flying in our direction before we even percieve them visually. This allows us to avoid and detect them faster. As neurotransmission pathways are really fast.
What do frontal eyes allow?
Stereopsis, allows binocular representation hence depth perception.
What do side eyes prevent?
Depth perception bioncular representation. but have greater peripheral vision.
How are things percieved closer?
Due to retinal disparity. The bigger the disparity the closer the object is. The points at which The images of points located farther or closer than
the horopter do not fall at corresponding retinal locations so there is disparity.
What is a horopter?
circle of points that have zero disparity, they are projected at the corresponding points of the
two retinas.
How is disparity detected?
cells in v1 and v2 as well as other areas of dorsal stream that are tuned to different disparities either beyond or in fron of horopter.m
How does disparity change through the dorsal stream?
It increases. Percentage increases.
V1/V2 40-60%
V3/VP 80%
MT 70%
MST 93% and most tuned to near
or far (non-zero disparity) mostly sensitive to near and far than 0 zero disparity. Receptive fields increases along dorsal stream from v1 to mst ss sensitivity decreases to disparity.
What else do we use in addition to disparity?
Monocular cues.
