Lecture 4 The Visual Sense of Motion

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Question Answer
Where was the middle temporal area (MT) first identified and where is the human equivalent?at the posterior end of the middle temporal gyrus in owl monkeys; In humans the equivalent area is the ascending limb of the inferior temporal sulcus, part of MT+ which contains multiple regions, each specialized in different aspects of motion perception
Without MT, with What streamautomatic perception of motion is lost and visual motion becomes a series of stills. Judgement of an object's speed and direction becomes difficult
MT+ receptive field size, acuity, colourlarge receptive fields, poor acuity, sees only in black & white, good at determining direction the object is moving, cannot identify object (function of what stream)
With MT, without What streampoor acuity, black & white, cannot identify objects, can determine motion
Parvocellular LGN feeds layer 4c which in turn feeds1. cells in the blobs which analyze colour, 2. orientation sensitive cells which extract edges/form & orientation sensitive binocular cells in between; both have high visual acuity
The motion system gets its input frommagnocellular LGN, low acuity. Cells in layer 4C project to cells in layer 4B (orientation sensitive like simple and complex cells above and below layer 4, motion sensitive in particular directions, signal stereopsis b/c get binocular input, send their signal directly to MT and indirectly via V2 and V3); provides MT a signal that is binocular, orientation sensitive, motion sensitive
Neural circuit used to detect motion When the light moves to the right, APs all arrive at the output neurons at the same time and it fires (synchronous activation) - neurons activated first are those connected to longest axons. When light moves to left, APs arrive at output neurons asynchronously and output neuron does not reach threshold. Thus this circuit is sensitive to motion but only in 1 direction. This circuit is found in the eye of birds and a modified form is in V1 of primates
Explain the aperture problemmotion of line is ambiguous if we cannot see where the ends of lines are. Simple and complex cells in layer 4B of V1 sense motion of line. Complex cells are maximally activated by lines moving perpendicular to the line's orientation (synchronous activation).
Does area MT or V1 perceive motion?MT is activated by perceived motion and not by the actual motion. V1 is activated by the actual motion and not perceived.
AttentionMT neuron receptive field activated by a upward motion. When attention is focused on the blue dot, MT cell becomes insensitive to upward motion of the unattended green dot. Attention is selective tuning - tuned to particular dot AND dot's motion is in neuron's preferred direction
What is area MT+ composed of?middle temporal area (area MT), area MST (MSTd and MSTl)
MT is organized intocolumns (like V1, IT, MSTd). 1 particular column receives input from 1 patch of retina. Columns divided into mini-columns each sensitive for a particular direction and depth. Neighboring mini-columns prefer slightly different directions of motion and depth. Different cells prefer different speeds. Thus the most active cell within the mini-column signal perceived direction, speed, depth from 1 patch of retina
MSTlsenses when a small object moves (activating small part of retina). Involved in generating pursuit eye movement
MSTdsenses the visual motion produced when you move. Movement of the background produces an optical flow pattern on the entire retina. Have large receptive field so bilateral, neurons receive input from the ipsilateral MT + contralateral MT via corpus callosum. Different MSTd neurons are wired to recognize these different patterns of optic flow.
Which have contralateral receptive fields?MT, MSTl, V1, LOC
Which have bilateral receptive fields?MSTd, FFA (IT)
MSTd organized intocolumns. Each column is tuned to a particular pattern of optical flow
Motion parallaxperception of depth, independent of binocular cells, it compares one eye's view over time. Near objects sweep quickly across the retina, far objects sweep more slowly.
Motion parallax during pursuit eye movementsPursuit of a near target causes retina slip of the far target. Pursuit of far target causes retina slip of near target. Need motion of the eye to decode the optic flow pattern correctly.
If the image moves on the retina (retinal slip) + eye is stillcorollary discharge is 0, motion on retina must be due to the object
If the image moves to the right of the retina (retinal slip) + eye is moving leftcorollary discharge is -, motion on retina due to eye motion, object is still
If the image moves on the retina (retinal slip) + forward movement corollary discharge, motion on retina due to movement, object is still
Why does motion after-effect happen?Effect produced in part by changes in MT. Velocity scale becomes recalibrated. Different velocities are coded by populations of neurons. Neurons that represent velocities around that constant velocity become fine tuned and pulls the scale, giving other velocities a coarser representation. The neuron that encodes a slow velocity in the opposite direction gets pulled to 0 velocity range.
Motion after-effect misinterpretationeffect occurs b/c of neuron fatigue. 2 Good functional reason for this effect - adaptation & rebound and velocity scale becoming recalibrated
How does MT assist LOC and vice versa?motion is used to bind the line elements and separate them from the background. MT sends info to LOC that analyse form. Areas in what stream send info to the where stream which produces a sense of motion
Biological motionperception of something living. Motion helps extract the form, and the relative motion of the form's parts; another example is motion of lips as you talk
Where does the analysis for biological motion occur?superior temporal sulcus (STS). Gets 1) input from the object's form from the LOC, 2) motion input from MT. STS can determine from few fragments things from motion
MT is sometimes called the what streamwhen stream