Transcript primary visual cortex

Psychology 304:
Brain and Behaviour
Lecture 32
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Exam: December 11, 8:30-11:00 AM, Osborne A
• The exam is worth 25% of your final grade.
• The exam will be scored out of 75 points.
• The exam will include 40 multiple choice questions (1
point each), 5 definitions (2 points each), and short
answer questions (2-8 points each, totaling 25 points).
• The exam will cover Chapters 5, 7, 8 (p. 215-234), 9
and 10 (p. 281-299, 301-314) of the textbook and all
material discussed in class since the midterm exam.
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• Please arrive on time; students who arrive after a
classmate has completed the exam and left the exam
room will not be permitted to write the exam.
• Bring a pencil, eraser, pen, and your student ID to the
exam.
• Electronic devices are not permitted at your desk.
• Due to concerns regarding theft, do not bring valuables
to the exam room.
• Hats (e.g., baseball caps) should not be worn during
the exam.
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Reminder
I will hold additional office hours in preparation for the
December exam:
Friday, December 3: 3:30-4:30
Thursday, December 9: 10:00-12:00, 1:00-3:00
Friday, December 10: 10:00-1:00
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The Visual System
1. What is the structure of the eye and where are the
receptors for light? (continued)
2. How is information about light relayed to the brain?
3. What are the major areas of the brain that are
associated with the perception of light?
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By the end of today’s class, you should be able to:
1. distinguish between cones and rods.
2. explain how an action potential is generated in the
retinal cells of the visual system.
3. review the pathway by which visual information is
transmitted from receptors to the brain.
4. identify the locations and functions of the primary
cortex, secondary cortex, and association areas for
the visual system.
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From last class ….
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Convergence of Cones and Rods on
Retinal Ganglion Cells
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What is the structure of the eye and where are the
receptors for light? (continued)
• The fovea is specialized for high-acuity vision.
• Visual acuity at the fovea is enhanced by:
1. the presence of cones.
2. the “thinning” of the bipolar and ganglion cell layers
in this region.
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The Fovea
Cone vs. Rod Density
at the Fovea
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Retinal Cells at the Fovea
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• When light reaches a receptor, photopigments (e.g.,
rhodopsin) are activated that hyperpolarize the
receptor cell. Reduced neurotransmission by the
receptor cell results in depolarization of the adjacent
bipolar cell (for “on-center” cells only).
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• In turn, depolarization of the bipolar cell results in
depolarization of the adjacent ganglion cell.
• When the ganglion cell is stimulated, an action potential
is triggered that passes down the cell’s axon, along the
optic nerve—cranial nerve II.
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Generation of an Action Potential in the Retina
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How is information about light relayed to the brain?
• Visual information is relayed to the brain via many
pathways. The largest and most studied visual
pathway is the retina-geniculate-striate pathway.
• Within this pathway is the optic chiasm: at this point,
axons from the nasal halves of the retinas “cross over”
and ascend to the dorsal lateral geniculate nucleus
(LGN) of the thalamus. Thus, each hemisphere
receives information from the contralateral visual field.
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Retina-Geniculate-Striate Pathway
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• The LGN contains six layers of neurons. The inner two
layers are called magnocellular layers, and the outer four
layers are called parvocellular layers.
• The magnocellular neurons are most responsive to
movement and receive the bulk of their input from rods.
• The parvocellular neurons are most responsive to color,
fine pattern details, and stationary objects and receive
the bulk of their input from cones.
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Magnocellular
Layers of the LGN
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What are the major areas of the brain that are associated
with the perception of light?
• The thalamic neurons that receive visual information
subsequently project the information to the primary
visual cortex.
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Primary Visual Cortex
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Primary Visual Cortex
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• The retina-geniculate-striate pathway is characterized by
retinotopic organization.
• The primary visual cortex is organized into functional
vertical columns (i.e., ocular dominance slabs,
orientation columns).
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Ocular Dominance Slabs and Orientation Columns
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• Information received by the primary visual cortex is
segregated into distinct pathways that project to areas of
the secondary visual cortex and, then, the association
visual cortex.
• Two main pathways from the primary visual cortex
have been identified: The dorsal stream and the ventral
stream. The dorsal stream is associated with location
and movement; the ventral stream is associated with
identification.
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The Dorsal and Ventral Streams
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VI: Location,
orientation, colour
V2: Form, relays
information
V3: Form
V4: Colour, form,
concentric and radial
stimuli
Inferior temporal
area: Form, pattern
recognition
V5, Medial temporal
area: Motion
perception
Prefrontal cortex:
Facial recognition
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The Visual System
1. What is the structure of the eye and where are the
receptors for light? (continued)
2. How is information about light relayed to the brain?
3. What are the major areas of the brain that are
associated with the perception of light?
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