Chapter 3- Visual Perception Flashcards
Akinetopsia:
• Inability to perceive motion even though other aspects of vision seem normal
Can see difference in position (object that was here is now over there), but doesn’t see the object moving
Retina
○ Light sensitive tissue lining back of eyeball
Fovea (center of retina)
Cornea and lens
○ Focus incoming light
○ Muscle around lens tightens to bulge lens to focus nearby objects
Muscle around lens relaxes to flatten lens to focus far away objects
Rods
Sensitive to low levels of light
Can distinguish different intensities of light
Can’t distinguish colour
More rods than cons farther away from fovea
Cones
Less sensitive than rods
Need more incoming light to operate
Sensitive to colour differences
3 different types, each respond to different wavelengths
Important for acuity
§ Ability to see detail
In fovea, cons far out number rods (no rods at all in center of fovea)
Bipolar cells
Intermediate cells that are stimulated by photoreceptors which then excite ganglion cells
Ganglion cells
Spread uniformly across retina, but axons converge to form optic nerve
Lateral Geniculate Nucleus (LGN)
Info from optic nerve sent here first, then transmitted to occipital lobe
Located in thalamus
Lateral Inhibition
Once stimulated, cells inhibit activity of neighbouring cells
Edge Enhancement
Lateral inhibition highlights a surfaces edge because cells in the middle will be inhibited more than cells at the edge
Single Cell Recording:
• Animal is immobilized and has electrodes placed outside optic nerve or brain
• Various patterns on a computer flashed in front of animals eyes
Used to define a cell’s receptive field (size and shape of area in visual that the cell responds to)
Centre Surround Cells
○ Center has one response, surrounding ring has opposite response
If both center and surrounding are stimulated, they cancel each other out
Edge detectors
Fire at maximum only when a stimulus has an edge in a specific orientation (i.e. horizontal, vertical)
Will still fire when they detect a stimulus orientated in a different way, but not as strongly
Area V1
○ Site on occipital lobe where axons from LGN first reach cortex
Contains cells to detect every kind of stimulus (horizontal, vertical…etc)
Area MT
Neurons are acutely sensitive to direction and speed of movement
Optic Nerve
Composed of P and M cells
P Cells
§ Provide main input for LGN’s parvocellular cells
Specialized for spatial analysis and detailed analysis of form
M Cells
§ Provide input for LGN’s magnocellular cells
Specialized for detection of motion and perception of depth
Ventral Stream:
What System
Occipital lobe-> temporal lobe
Crucial for identification of visual objects
Damage can cause visual agnosia
Inability to recognize objects in visual field
Dorsal Stream
Where System
Occipital lobe-> parietal lobe
Crucial for locating object in space
Damage can result in difficulty reaching out for objects
Binding Problem:
Task of reuniting various elements of a scene that are initially addressed by different systems in different parts of the brain
Spatial Position:
Various brain areas all keep track of where an object is
i.e. where a circle is, where the blueness is, where motion was detected, where things were still
Neural Synchrony:
If neurons detecting 2 different attributes are firing together, then they must be detecting the same object
i.e. vertical line moving down stimulates neurons detecting orientation, and neurons detecting movement, therefore the are detecting the same object
Neural Synchrony:
If neurons detecting 2 different attributes are firing together, then they must be detecting the same object
i.e. vertical line moving down stimulates neurons detecting orientation, and neurons detecting movement, therefore the are detecting the same object
