PSYCH 1XX3 Lecture Notes - Visual Acuity, Double Star, Cortical Blindness
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February 12, 2013
Coding and interpreting energy from the world
Sensation converts energy into nerve impulses
Perception interprets nerve impulses
o You don’t really think about it, it just happens
o Unconscious inference about the world
Two rows of circles
o Spheres or Indents??
o Your brain assumes that there is a single light source
o Brain assumes that light comes from above
Even if your head is upside down, your brain continues to assume that the sun is
coming from above, and therefore
o Brain assumes that like objects are grouped together
Sensation: Stimuli to nerve impulses
o Image on the back of the retina is upside down initially
o Changed the angle of the image focused on the retina (to the right)
o The brain makes adjustments with time
o The image will then seem normal
o Basically: The brain has pretty awesome adaptive abilities
Visual Acuity vs. hyperacuity:
o Hyperacuity is not physically limited by photoreceptors
o The best example of the distinction between acuity and hyperacuity comes from vision.
The first stage is the optical imaging of the outside world on the retina. Light impinges
on the mosaic of receptor sense cells, rods and cones, which covers the retinal surface
without gaps or overlap, just like the detecting pixels in the film plane of digital cameras.
Each receptor accepts all the light reaching it but acts as a unit, representing a single
location in visual space. This compartmentalization sets a limit to the decision whether
an image came from a single or a double star (resolution). For a percept of separately
articulated stars to emerge, the images of the two must be wide enough apart to leave
at least one intervening pixel relatively unstimulated between them. This defines the
resolution limit and the basis of visual acuity.
Information is compressed as the information travels to the visual cortex
Processing input in the Primary Visual Cortex
o VERY ORGANIZED
o V1 Organization: shaped by input
Blindsight is the ability of people who are cortically blind due to lesions in their striate cortex, also known as primary
visual cortex or V1, to respond to visual stimuli that they do not consciously see. The majority of studies on
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