PSYB65 – Lecture 5
Sensory Motor Systems
Visual system organization
• Anatomically and functionally
Visual field – What the person can actually see.
=> Is divided into 2 half fields (right half field and left half field)
Optic nerves – Two separate nerves leaving your eyes.
• Come together at one point called the optic chiasm.
• Separate again at the optic tract. [Inside CNS = tract, outside CNS = nerve]
− Your eyes grow out of your brain as you develop.
Each retina has a temporal (half closest to your temples) portion and a nasal (half closest to your nose)
Nerves from the temporal portion remain on the same side and go up to the cortex.
But the nerve from the nasal portion crosses over at the optic chiasm.
=> Information from the left visual field enters into the left eye's nasal portion and the right eye's
• Temporal nerve goes in straight to the right side, while the nasal nerve crosses over from the left
side to the right side at the chiasm.
• Therefore all the information from the left visual field ends up on the right side.
=> Information from the right visual field enters into the right eye's nasal portion and the left eye's
• Temporal nerve goes in straight to the left side, while the nasal nerve crosses over from the right
side to the left side at the optic chiasm.
• Therefore all the information from the right visual field ends up on the left side.
Damage to the visual field is not the same thing as damage to the retina.
• Refer to chart on internet with all the different types of damage to the visual field.
The more central the neuron (more advanced area of the brain), the more complex the image is
that excites it.
In the retina, the neuron responds to light falling in the receptive field.
Brodmann's area 17: That area can decipher lines of light oriented in a specific direction.
Association cortex:Aneuron can respond to a specific face or a specific hand (higher order). • By what the person can and cannot do, you can determine where the location of the lesion is.
Damage to the visual cortex:
Complete damage to the right occipital cortex => Complete blindness in the left hand visual field,
except for a little bit of macular sparing.
Incomplete damage to the right occipital cortex => Partial blindness to the opposite visual field.
• As damage becomes smaller, blindness becomes lessened
Smallest damage => Scotoma: An isolated area of diminished vision.
Everybody has a naturally occurring scotoma, also known as the blindspot. => No rods or cones where
the optic nerve leaves the retina.
Broddmann's Areas 20, 21: Higher order association areas.
=> Problems in perception and complex visual material (faces, patterns).
• More if it is on the right (right is in charge of spatial visual), more language related if damage is
on the left.
Understand by the behaviour, not by where the da