Stimulus localisation and processing of motion Flashcards
How are processing of motion and stimulus localisation interlinked?
By identifying the direction of motion - can predict where the stimulus will be in the next moment of time
What are 4 examples of object localisation in the visual system? What are these?
1) Orienting reflex (Orientation of head so that the eyes can focus important stimulus on the fovea)
2) Smooth pursuit (Following a moving object)
3) Prediction of motion during prey capture (motion anticipation)
4) Saccadic movement of the eye (eyes flicker)
What does the orienting reflex happen independently of?
The stimulus
What happens when a stimulus appears in the visual field?
Why?
Orienting reflex:
Move head and eyes so this part of the visual field is focused on the fovea - highest visual acuity
When motion anticipation needed?
Why?
When something is moving fast:
- Speed at which the brain processes information doesn’t allow to follow the stimulus at any moment in time
- Phototransduction cascade takes time
Describe saccadic eye movements during object inspection?
- They are not random
- Some parts are inspected more than others
What does ablation of the optic tectum/superior colliculus result in?
Disappearance of the orienting reflex
What is the optic tectum/superior colliculus?
Optic tectum is the lower vertebrate homologue of the superior colliculus (mammals)
What are the important areas in the brain involved in motion processing?
- Retina - M-type ganglion cells
- Dorsal stream in the visual cortex
- Superior and inferior colliculus
Where does the superior colliculus receive inputs from?
What is the role of the superior colliculus?
ALL different sensory modalities (smell, taste, hear, see, touch)
Role: to INTEGRATE the information from different sensory modalities, in order to make decisions on where to move, issue motor commands
What is the MAIN function of the superior colliculus? (regulate…)
Regulates saccadic eye movements
Orienting reflex
What do lesions in the superior colliculus result in?
Disappearance of the orienting reflex
How are different brain areas organised?
Describe this organisation
Retinotopically:
- Neighbouring cells in the retina feed information to neighbouring places in the target structure
What changes the activity in the brain and why?
Position of the stimulus - activity of the brain is different
Firing in the TECTUM is not random
Where are retinotopic maps present in the brain?
- Retina
- Superior colliculus
- LGN
- Early visual cortex
What do ‘command’ neurons regulate?
Eye saccades
What do command neurons do?
Spike before saccadic movements, in order to regulate them
Where are command neurons present?
In the deeper layers of the superior colliculus
How are the command neurons organised?
What is this similar to?
In maps
Similar to retinotopic maps
Where do command neurons send their projections to?
What does this result in?
Different layers, to stimulate SPECIFIC neurons
Stimulation of a specific neuron leads to the eye shifting to a specific angle
How can processing in the superior colliculus happen, where motor commands are issued?
Describe the processing
Retinotopic map (visual map) is aligned with a deeper motor map:
- Stimulus in the visual field - stimulation of specific visual neurons in the superior colliculus
- If the activation of this neuron is large enough - leads to activation of the lower neurons (in the motor map) which are responsible for moving the eye in that direction
- This activation is via COMMAND NEURONS (send projections from visual map to motor map)
Along the dorsal stream, what neurons become present?
Neurons that respond to moving objects (motion)
Along the dorsal stream, what does movement of a stimulus in different directions cause?
Different responses of the specific neurons
What is the direction of movement that causes the maximum response in a specific neuron?
Preferred direction
