PSY – Chap 6 Notes: Perception
Brain Mechanisms of Visual Perception
• Perception is a rapid, automatic, unconscious process. We recognize the information
provided by our sense organs.
• Module: block of cortical tissue that receives info from the same group of receptor cells;
contains ~150,000 neurons. Primary visual cortex contains about 2500 of these modules
• Visual perception is a hierarchy: neurons analyze certain aspects of information and send
the results to other neurons
• The surface of the retina is “mapped” on the surface of the primary visual cortex.
• Receptive field: neural circuits analyzed various characteristics of their own particular
part of the visual field. Ex. some circuits signal the colour of a line, some signal the
width, or orientation etc.
• Visual info analyzed by the primary visual cortex is further analyzed in the visual
• Visual association cortex has 2 pathways:
o Ventral stream: flow of info ends in the lower temporal lobe. Used to form the
perception of an object’s shape, colour and orientation (the “what” system)
o Dorsal stream: flow of into ends in the parietal lobe. Used to form the perception
of an object’s 3-D location in space and if it is moving (the “where” system)
• Visual agnosia: caused by damage to the visual association cortex- the inability to
recognize the identity of an object
o Prosopagnosia: difficulty in recognizing people’s faces
• Specific regions of the brain:
o Fusiform face area (FFA): contains face recognizing circuits. Also, when car
experts viewed cars, the FFA was activated
o Extrastriate body area (EBA): responds to forms resembling the human body.
o Parahippocampal place area (PPA): activated by visual scenes. Looking at a
picture and being able to identify it as a Beach
• Cerebral achromatopsia: the inability to discriminate among different hues, caused by
damage to the visual association cortex.
• Neurons in the dorsal stream are involved in visual attention and control of eye
movements; the visual control of reaching and pointing; visual control of grasping and
hand movements; perception of depth
• The function of the dorsal stream is not just “where” but also “how”: how to perform the
• Without the ability to perceive the velocity of objects, we could not predict where they
• Akinetopsia: the inability to see motion
• Form-from-motion experiment: men and women were fitted with light on their bodies
and performed movements in a dark room. People who watched the lights were able to
identify what the movements were, and even the sex of the individual performing them.
Visual Perception of Objects • Gestalt psychology: a branch of psychology that asserts that the perception of objects is
produced by particular configurations/arrangements of the elements.
o The whole is more than the sum of its parts. Its not just the constituents (of the
visual scene), its the relationship between them.
• Gestalt laws of perceptual organization:
o Law of proximity: elements located closest to each other are perceived as
belonging to the same figure.
o Law of similarity: similar