There will be an exam on the Thursday, March 3, right after you return from Reading Week. Here are the text readings from Goldstein (8th edition)
pp 34 39 (end of Chapter 2)
pp 6168 (end of Chapter 3)
Chapter 4 (Visual cortex and Beyond)
Chapter 9 (Colour)
Chapter 10 (Depth) up to page 235 (ends before Bincolar Depth Information)
Notice that some things are in the lecture that are not in the text (such as spatial frequency) and those were coverd in lecture but they are not covered in
depth in the text. (Well... there is a TINY bit on spatial frequency on pages 383384 as it relates to infants.)
*The exam will have the same format as the last one. There will be 30 multiple choice and a 2 part shortessay section that is worth 10 marks. Note that
the exam is *NOT* cumulative, but you cannot afford to forget what thresholds are, how neurons work, how to interpret a neural circuit, etc. As always,
when trying to figure out how to study, information in both the text and lecture has highest probability, closely followed by information in the lecture only.
The lowest probability question will be ones solely based on the text, but there will be some questions like that (as there were in the last exam). Don't
forget you have a study aid (the Optional Worksheet) to help you prepare.
Optional Worksheet 2
Principles of Sensation and Perception
Second exam period (Exam on Mar 3/ worksheet quiz Mar 10)
1. How the retina works.
a). What is a receptive field? Describe the difference between the receptive fields for photoreceptors and
retinal ganglion cells. A receptive field is the area on the retina that a specific neuron responds to. Each neuron responds to one particular receptive field.
The receptive fields for photoreceptors are a lot simpler to look at than the ganglion cells because of the larger amount of rods and
cones present in the photoreceptors. Receptive fields of ganglion cells are characteristically circular and have either oncenter cells
(light in center causes an on response (increase in ap/sec) and light in periphery causes an off response (decrease in ap/sec)) or off
center cells (light in center causes an off response and light in periphery causes an on response). There are 2 types of retinal ganglion
cells which are called parvo and magno. Parvo ganglion retinal cells make up the majority of cells in the retina and transfer
information slowly with fine detail including colour. These cells also continue to respond most of the time. Magno ganglion cells can
transfer information more quickly due to thick axon and help us to see motion and important things in our periphery. Magno cells
have a transient response meaning they respond to change and stop working after habituation is achieved. They also only exist with
rods, meaning that this information is mostly black and white.
b). What is lateral inhibition? Why is it useful to have both in the visual system? How do lateral
summation and inhibition work in the retina?
Lateral inhibition is inhibition that is transmitted across the retina which allows our eyes to highlight edges so one can see where
they are going and not walk into things. Lateral summation occurs by adding together information and allows us to see in lower
lighting conditions. Lateral summation occurs by multiple excitatory or inhibitory neurotransmitters all connecting to a specific
neurotransmitter while lateral inhibition occurs when an inhibitory neurotransmitter is connected to a different neurotransmitter.
c). Describe 2 illusions that are caused by lateral inhibition, and explain what happens at the level of the
retina to cause the illusion.
1) Hermann grid: the illusion (when there is a black and white grid with the squares filled in black) of the grey spots at every white
corridor intersection in the grid. This occurs because the receptor in the eye that responds to the corridor between the black squares has
a stronger response than the receptor that responds to the intersection of the white lines.
2) Mach Bands: The illusion of the lighter and darker shading on a shadow which allows us to see borders more easily. This illusion
occurs because some receptor cells inhibit light stronger than others and therefore create the illusion of shading.
d). A given retinal ganglion cell has a circular surround, oncentre, offsurround receptive field. If this
neuron has inhibitory and excitatory areas that were equal in size, and had a spontaneous activity level of
30 action potentials per second, how would this cell react if ….
i. a small white dot illuminated the centre of the receptive field and the rest of the area (the outer areas of
the receptive field) was black.
The cell would become excitatory and increase ap/sec. (max ap/sec)
ii. a white light illuminated the entire receptive field
The cell would decrease ap/ sec.
iii. a small black dot illuminated the centre of the receptive field but outside that area (on the receptive
field) it was white.
The cell would decrease ap/sec.
iv. black covered the entire receptive field
The cell would have the min ap/sec.
2. Neuropsychology and Vision a). In class, we did a demonstration where you stared at black and white pattern for some period of time,
and then when the pattern was removed you saw the opposite of what the pattern was floating in front of
your eyes (even though the screen was white). Thus, the parts that were black in the pattern appeared white,
and vice versa. What caused this afterimage?
This after image is caused by the fact that the neurons in charge of allowing you to see the white parts of the pattern become
overworked so when a white background is presented the neurons that were already working to produce white and keep up ap/sec
now produce black because they need time to rest while the receptors working hard to produce black are easily able to produce white
b). Work through the visual system from the optic system to the extrastriate cortex describing each area
involved in vision and what it does.
1. Optic nerve: axons going out of retinal ganglion cells, axons are give myelin
2. Optic chiasm: where the right and left optic nerves “cross”, only some nerves cross but not all of them; nasal side crosses over and
temporal side goes back, nasal side of left side (center) crosses over but temporal (periphery) goes straight back. (suprachiasmatic
nucleus: responsive to light information, lively in some parts of the day but sleepy in others, produces melatonin, lighting conditions
affect how much melatonin is released (melatonin makes us sleepy); jet lag can be helped by going out in the day vs. library and
3. Branch point 1) Tectopulvinar system optic tectum (in animals) superior colliculus (in humans), 2 on both sides of brain, does
not respond to colour, gets fibers from magno ganglion cells, fixation cells (which are ignited when you stare at something), build up
cells (come active before eye movement), burst cells (come active when you