Motion detection with movement detectors

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

Asymmetric movement detector V = Δx/Δt

Movement detector V = Δx/Δt Note: the same velocity v is detected for various Δx and Δt as long as Δx/Δt = constant

Velocity dependence of movement detector v v response

Relation between temporal and spatial gradients Δx

Movement detector Step-like response functions are not very likely

Movement detector responsie Δt

Movement detector

Movement detector in fly visual system Response to spatial sinewave pattern with wavelength 16 o and τ = 50 ms.

The aperture problem

Receptive field of movement detector Δx

The aperture problem

Identical responses for v=v 0 /cosα α v0v0

The aperture problem A single cell cannot solve the aperture problem; only an ensemble of cells can under the assumption of a rigid body

Example 1

Example 2

Various types of cells End-stop cell

Example 3

Hypothetical solution

Optic/flow detectors

Divergence operator

Rotation operator

Deformation operator

Schematic overview of monkey brain

Responses of neurons in VIP to various optic-flow patterns

Be aware : position of receptive field relative to stimulus !

Retinal motion Due to object motion due to eye movements

Schematic overview of monkey brain

Responses of MST neurons to active vs passive optic flow

Perceptual responses to moving stimuli

Movement detector V = Δx/Δt Detectors have all orientations

Transparent motion Percept ?

Movement detector V = Δx/Δt Variation in v is achieved by both: larger Δx smaller Δt

Transparent motion Percept : two different separately moving patterns

References