Lecture 7
Object movement during self-movement
Whilst you are moving, it potentially causes problems with the real world when
identifying movement.
Identifying object movement in the real world
When stationary:
If motion in the retinal image, there is motion in the world.
The scene is completely stationary, but something starts moving, so detect
motion in the retinal image, therefore something must be moving.
Still stationary but whilst moving your eyes:
Relative motion: if you're perfectly stationary and making a pursuit eye
movement, everything that is stationary in the scene will be moving at the same
velocity, moving at the same direction at the same speed. If there is something
that is moving at a different velocity then it is moving within the scene, there is a
relative motion between the background and itself.
Prior knowledge: know that lamp posts don’t move, so if moving in retinal
image, we know that its probably not moving in the world.
Head centric Motion: if moving your eyes, then everything in the retinal image is
moving, but relative to the head it isn’t. The eyes are rotating but the head isn’t,
but as the eyes are moving you're generating retinal motion because the eyes are
moving. The brain knows that the eyes are moving because extra retinal
information is telling it that the eyes are moving. Can use extra retinal
information to work out what is moving and what is not. The ER information
knows the speed that the eyes are moving at, so therefore we can use this to see
if anything else is moving at a different speed to the retinal motion so therefore
detect its motion.
Extra Retinal Eye Velocity Signals:
If you make an eye movement whilst trying to work out what in the scene is
moving, you can make use of extra retinal information and combine ER and R
information,
1. Compensate for the effect of eye rotation on the image
2. Convert image motion into head-centred motion.
Head Rotation:
Oculo-motor stabilisation: when the head is rotated, basic stabilisation
mechanisms rotate the eyes to compensate for the head. This reduces the motion
in the image. One way of the brain dealing with head rotations.
Moving in Space (translating):
The eyes aren’t rotating, they are moving through space.
Motion is created throughout the retinal image, and motion is not at the same
speed throughout the retinal image.
If you step to one side, the direction is the same but the speeds are different.
Object movement during self-movement
Whilst you are moving, it potentially causes problems with the real world when
identifying movement.
Identifying object movement in the real world
When stationary:
If motion in the retinal image, there is motion in the world.
The scene is completely stationary, but something starts moving, so detect
motion in the retinal image, therefore something must be moving.
Still stationary but whilst moving your eyes:
Relative motion: if you're perfectly stationary and making a pursuit eye
movement, everything that is stationary in the scene will be moving at the same
velocity, moving at the same direction at the same speed. If there is something
that is moving at a different velocity then it is moving within the scene, there is a
relative motion between the background and itself.
Prior knowledge: know that lamp posts don’t move, so if moving in retinal
image, we know that its probably not moving in the world.
Head centric Motion: if moving your eyes, then everything in the retinal image is
moving, but relative to the head it isn’t. The eyes are rotating but the head isn’t,
but as the eyes are moving you're generating retinal motion because the eyes are
moving. The brain knows that the eyes are moving because extra retinal
information is telling it that the eyes are moving. Can use extra retinal
information to work out what is moving and what is not. The ER information
knows the speed that the eyes are moving at, so therefore we can use this to see
if anything else is moving at a different speed to the retinal motion so therefore
detect its motion.
Extra Retinal Eye Velocity Signals:
If you make an eye movement whilst trying to work out what in the scene is
moving, you can make use of extra retinal information and combine ER and R
information,
1. Compensate for the effect of eye rotation on the image
2. Convert image motion into head-centred motion.
Head Rotation:
Oculo-motor stabilisation: when the head is rotated, basic stabilisation
mechanisms rotate the eyes to compensate for the head. This reduces the motion
in the image. One way of the brain dealing with head rotations.
Moving in Space (translating):
The eyes aren’t rotating, they are moving through space.
Motion is created throughout the retinal image, and motion is not at the same
speed throughout the retinal image.
If you step to one side, the direction is the same but the speeds are different.
