Motion detection with movement detectors. It is a non-linear device: response to velocity a and...
-
date post
22-Dec-2015 -
Category
Documents
-
view
215 -
download
0
Transcript of Motion detection with movement detectors. It is a non-linear device: response to velocity a and...
• It is a non-linear device: response to velocity a and velocity b is not equal to velocity a+b
• movement detection may be asymmetric (response to velocity a is not opposite to response to velocity -a) or symmetric
Requirements on movement detectors
a
b
a+b
Movement detector
V = Δx/Δt
Note:• the same velocity v is detected for
various Δx and Δt as long as
Δx/Δt = constant
Relation between temporal and spatial gradients
vt
x
xtxIttxI
t
txI
t
x
x
txI
dt
txdIx
txItxxI
x
txIt
txIttxI
t
txI
),(
),(
),(),(),(0
),(),(),(
),(),(),(
Δx
Δx
Movement detector in fly visual system
Response to spatial sinewave pattern with wavelength 16o and τ = 50 ms.
The aperture problem
A single cell cannot solve the aperture problem; only an ensemble of cells can under the assumption of a rigid body
Responses of neurons in VIP to various optic-flow patterns
Be aware : position of receptive field relative to stimulus !