LECTURE 21: PERCEPTION (CHAPTER 7)
•Sensation refers to the raw energy- bottom raw processing.
•Perception can be one way or another. It all depends on your memory, past, culture, etc..helps
you perceive different objects in different ways.
•Primary visual cortex is made up of a large number of “modules” which contain a large
number of nerve cells that all respond to different aspects of the same part of the retina …
termed the visual field of those nerve cells.
•The retina is not evenly represented but, instead, more primary cor tex is devoted to images at
or near the fovea.
•Some nerve cells in a module respond only to lines of certain orientations, others respond only
to motion, others to colour, etc.
•Thus, pr imary cortex codes the basic features of the image it receives. Primary cor tex begins
the building process.
•Secondary visual cortex regions (i.e., association cor tex) is responsible for higher level visual
processes as revealed by various types of brain injur y:
•Damage to primary visual cor tex - often results in “blind spots” but no problems with object
recognition. Part of your visual scene you can’t see…
•Damage to one part of association cortex can lead to an inability to see colour altogether, a
problem termed achromatopsia. Association cortex helps you see color. Association cortex=
past and memor y
•Damage to a slightly different part of visual association cortex can result in an inability to
perceive motion. They see stuff and know it is out there, but they don’t get the sense of f luid
motion-they see things in snap shots.
•Perhaps the most interesting deficits occur when the parietal region of visual association
cor tex is damaged.
•Sometimes damage here leads to an inability to identify objects despite “normal” visual
acuity - visual agnosia.
•Other times, the damage results in an inability to recognize faces, even those of very familiar
people - prosopagnosia.