Lecture 23 Visual Feedback to control voluntary motor actions Flashcards
Take home message
The dorsal visual stream is important for controlling actions, the ventral visual stream is important for perceptual judgments
Sensory information we receive from the world around us
Visual, Auditoary, Smell
Exteroception: sensory information that tells us about the state of our body in relation to surroundings
Visual information in the most dominant source of exteroception feedback for motor control
Receptors in our eyes respond to light and provide information about world around us
Mammal eyes contain specialized cells called photoreceptors. They absorb photons, triggering change in the cells membrane potential
Rods: Human retina (eye) contains ~90-129 million rod cells. They are in peripheral portions of retina
Cones: Human retina contains ~4.5 million cone cells, concentrated in central portion of retina (fovea). High spitial resolution and colour vision
More rods to ganglion cells (mu) then cones to ganglion cells
Receptive fields in retina
receptive fields grow with distance from the fovea (centre of retina)
fovea= where vision is focused
Rods are concentrated in the periphery, low visual focus, sensitive to motion
Cones are concentrated in fovea, high visual focus, colour vision (higher spatial resolution)
Dorsal stream
where pathway, uses vision for action guidance. where next step should be
connected is venture-dorsal: important for grasping and interpreting the actions of others
Rapid, unconscious processing of visual information
in the dorsal stream, visual feedback is processed and used to correct ongoing actions
Ventral stream
What pathway, uses vision for perception. ties meaning to objects and people
object identification and recognition. stimulus identification phase
slow conscious processing of visual information
Form Agnosia from Ventral stream damage
when you can see the parts of an object but can’t recognize the object itself
does not matter where from
ex: Give person photo of pig
can draw pig but doesn’t know what it is
ventral stream image can cause selective impairments in conscious object perception
Optic Ataxia from dorsal stream damage
lack of coordination between visual input and hand movements
inability identify where and use vision to correct movements
damage to dorsal stream can cause optic ataxia which leads to inability to use vision to guide movements
ex; can see pig and recognize but cannot draw
optic flow
When the object is closer to the eye, the size of the image on the retina
changes at a faster rate
closer = the faster
ship in distance vs punch coming at you
Information provided by optic flow:
- Time to contact- how larger is it getting how quickly (perception)
- Direction of movement relative to objects in environment
- Movement of objects in the environment (objects moving or am I?)
- Stability and Balance - eyes closed less balance
- Velocity of movement through the environment
rate of expansion increases as time to contact does
vision helps improve accuracy of slow deliberate movements
Use of visual feedback to control and correct movements
The dorsal visual (where) stream enables fast, stimulus dependent control of visual feedback.
-where, visual info for guiding movement, where change is
The ventral visual (what) stream enables (somewhat) slower, task-dependent control of visual feedback
-what, position, processing, stimulus identification
