4. Motion Perception Flashcards
What is motion from the perspective of the visual system?
Perceptual inference where there is sometimes real motion; an object changes position over time.
What is the difference between the following?
Simple smooth motion, apparent motion, and optic flow.
Smooth motion is an object actually moving.
Apparent motions is where there is the illusion of movement (sequence of lights turning on and off).
Optic flow is the perception of movement based on the difference in movement speed of the observer and a scene.
What is the natural importance of motion perception?
(4 points)
- Navigation/optic flow
- Hazard avoidance (tend to dodge to the right)
- Peripheral vision is particularly sensitive to motion information
- Segmentation of objects
What part of vision is particularly sensitive to motion information?
Peripheral vision.
What is the role of V1 in motion perception and where does it receive its input from?
V1 has many cells which show direction selectivity in their response and the different layers of V1 have different proportion of direction selection cells to other cell types.
Receives input from the M-LGN.
What is the role of MT/V5 in motion perception and what happens when there is a lesion here? Where does MT/V5 receive its input from?
It has large receptive fields which integrates the motion information from V1 in to global motion outputs. Perception of motion can be altered by direction stimulation to area MT cells. Lesions here lead to impaired motion perception which can be recoverable as surrounding areas can help out.
Receives input from V1.
What is the role of MST in motion perception and how does it differ from MT?
It’s adjacent to MT and is specifically great for recognising optic flow. It also has large receptive fields (as MT).
Is there cross-talk between the dorsal and ventral streams?
The M and P-systems don’t follow 100% separate pathways. The orientation information from the ventral stream is important in perception of motion.
What is akinetopsia?
Visual motion blindness, individuals with this condition cannot perceive the movement of an object.
Is there another motion perception pathway in the human system? If yes, what is it and does it result in?
Yes, the retina -> superior colliculus -> V5 (the colliculo-cortical pathway). It results in ‘blindsight’; residual sensitivity to stimuli in a blind hemifield.
