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CHAPTER 4: THE VISUAL CORTEX AND
BEYOND
1. The Visual Pathways
2. Visual Cortex of the Cat
3. Simple Cells in the Cortex
4. Complex Cells in the Cortex
5. Contrast Sensitivity
6. Orientation Aftereffect
7. Size Aftereffect
8. Development in the Visual Cortex
9. Retinopy: Ring
10. Retinotopy: Wedge
11. What and Where Streams
Chapter 4: The Visual Cortex and Beyond
1. The Visual Pathways
Drag and drop the structure that corresponds to each location in the visual pathway. If you are
wrong, your answer won’t stick. After you have finished, click on the dot under the left visual
field to see how information from one visual field travels along the visual pathway to the brain.
Pay special attention to the spatial relations of input from the left and right visual fields.
Clicking on audio or script will present an explanation of this pathway.
RESULTS & DISCUSSION
1. Identify, in order, the major structures in the neural pathway for vision.
2. How does the original location of a stimulus in the environment relate to where the stimulus
(a) is imaged on the retina, and (b) causes activity in the cortex?
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2. Visual Cortex of the Cat
In this classic 1972 film, vision researcher Colin Blakemore describes his pioneering
experiments measuring response properties of neurons in the cortex of the cat. He demonstrates
the mapping of receptive fields of neurons in the visual cortex of the cat. The three main types
of visual cortical neurons are isolated and their activity in response to visual stimuli is recorded
using a microelectrode. He also demonstrates visual neurons arranged in columns within the
visual cortex. Courtesy of Colin Blakemore.
RESULTS & DISCUSSION
1. Describe how Blakemore used a patterned card to determine the response properties of
neurons in the visual cortex.
2. What is the significance of the noise heard when Blakemore moves the patterned card?
3. Do cortical neurons respond to changes in general illumination (turning the room lights off
and on)?
4. Describe the preferred stimulus of the simple cell shown in the film. How did Blakemore
demonstrate this?
5. Describe the preferred stimulus of the complex cell shown in the film. How did Blakemore
demonstrate this?
6. Describe the preferred stimulus of the hypercomplex cell shown in the film (Note that
hypercomplex cells are also known as end-stopped cells). How did Blakemore demonstrate
this?
7. What characteristics of cell firing are observed when a microelectrode penetrates the cortex
perpendicular to the surface? When the penetration is at an angle to the surface?
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Chapter 4: The Visual Cortex and Beyond
3. Simple Cells in the Cortex
The receptive fields for simple cortical cells have elongated side-by-side arrangement of
excitatory and inhibitory areas. As a result, these cells respond best to oriented lines. This
demonstration illustrates how a simple cortical cell responds to different stimulus orientations.
RESULTS & DISCUSSION
1. Enter the cell’s response to different orientations.
Vertical:
Slanted left:
Horizontal:
Slanted right:
2. Why does firing rate decrease for the slanted and horizontal lines?
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Chapter 4: The Visual Cortex and Beyond
4. Complex Cells in the Cortex
Complex cortical cells are selective not only for line orientation, but also for the direction of
motion. For each orientation, click on the arrows to move the bar.
RESULTS & DISCUSSION
1. Which orientation and direction of movement resulted in the greatest response?
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5. Contrast Sensitivity
The contrast threshold is the minimum intensity difference between two adjacent areas that can
just be detected. Contrast sensitivity is the reciprocal of contrast threshold, so low threshold
represents high sensitivity. Contrast threshold can be measured by determining the lowest
contrast between bars of a grating stimulus that is barely detectible. This experiment allows you
to determine the relationship between contrast sensitivity and the width of the grating bars
(which is related to a measure called spatial frequency that depends on the width of the bars and
the observer’s viewing distance). You can use either the method of adjustment or the method of
limits. Be sure to read the instructions and do some practice trials before beginning the actual
experiment, and be patient because there are 78 trials for each condition.
RESULTS & DISCUSSION
1. Present your data from each psychophysical method.
2. Did your contrast sensitivity vary with spatial frequency? Which spatial frequencies have the
highest contrast thresholds?
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6. Orientation Aftereffect
In this demonstration you view two gratings that differ in orientation. Look at the white bar that
is located between the two gratings. After the adaptation period has ended, the tilted gratings
will be replaced by two vertical gratings. Keep looking at the white bar, while noting the
orientations of the upper and lower gratings.
RESULTS & DISCUSSION
1. Did the vertical gratings look vertical, or did they appear tilted? How did any tilt relate to the
tilt of the corresponding adaptation stimulus?
2. How could this result be explained by the adaptation of orientation-selective neurons in the
cortex?
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7. Size Aftereffect
In this demonstration you will see two gratings, one above and one below a small white bar.
Look at the white bar during the adaptation period. When adaptation ends, the wide and narrow
gratings will be replaced by two identical gratings of an intermediate bar-width. Keep looking at
the white bar, but compare the two gratings, and take note of differences in the sizes of the bars.
RESULTS & DISCUSSION
1. Describe your perception of the gratings you viewed after the end of adaptation.
2. If you saw a difference between the gratings you viewed after adaptation, what does this
result indicate about the adaptation of neurons that respond best to wide bars and to narrow
bars? (Note: This is not covered in the Goldstein text.)
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Chapter 4: The Visual Cortex and Beyond
8. Development in the Visual Cortex
In this classic 1973 film, vision researcher Colin Blakemore describes his experiments measuring
response properties of neurons in the kitten’s cortex. Blakemore discusses the role that the
environment has in shaping the response properties of visual neurons. Courtesy of Colin
Blakemore.
RESULTS & DISCUSSION
1. What proportion of neurons in the newborn kitten and adult cat has connections to both eyes?
2. What happens to the connections to the left and right eyes when one eye is covered early in
life?
3. What is the “sensitive period”?
4. Describe the environment in which Blakemore’s kittens were reared in his selective rearing
experiment.
5. How do the cats behave when first exposed to a normal environment? What does Blakemore
think causes their abnormal behavior? Was this initial abnormal behavior permanent?
6. What are the permanent behavioral effects of selective rearing? Describe how the kitten
responds to verticals and horizontals.
7. What is the neural mechanism that is responsible for the kittens’ abnormal response to
oriented lines?
8. What do the results of Blakemore’s experiments suggest about the role of acquired vs. innate
properties in visual perception?
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9. Retinotopy: Ring
Retinotopy is a term that refers to the mapping of the areas of the retina to which different brain
regions respond. Not until recent advances were made in the field of functional magnetic
resonance imaging (fMRI) have we been able to obtain detailed retinopic maps of visual cortex
in humans.
In fMRI studies, blood flow response to different regions of the brain is measured and is thought
to reflect activity related to the processing of a stimulus. Structural anatomical images are
obtained for each individual tested using fMRI and are graphically flattened in order to plot the
blood flow data in a way that allows us to visualize activity within each bump and groove of the
cortex clearly. This movie shows the response measured by fMRI in the visual cortex of a
human who was viewing a stimulus. The stimulus shown is a flickering ring with a
checkerboard pattern that slowly expanded, moving from the center of vision (the foveal region)
to the periphery.
Notice that the left and right hemispheres are shown separately and increases in activity are
shown in white for three areas within each hemisphere: V1 in the center (red), V2 (green), and
V3 (blue). The red ring represents the checkerboard ring stimulus presented in the experiment.
Play the movie several times, noting the relationship between changes in the stimulus and
changes in brain activity.
Courtesy of Geoffrey Boynton.
RESULTS & DISCUSSION
1. Describe how brain activity changes as stimulation moves from the fovea towards the
periphery.
2. How does this demonstration illustrate the concept of the “retinotopic map” in visual cortex?
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10. Retinotopy: Wedge
This movie is similar to the “Ring” movie, but illustrates how the cortex is activated by a moving
wedge stimulus.
Courtesy of Geoffrey Boynton.
RESULTS & DISCUSSION
1. Describe activation of the left and right hemispheres that occurs when the wedge is in the left
visual field (at 9:00 o’clock) and in the right visual field (at 3:00 o’clock).
2. What does this result indicate about how an object present in one visual field activates the
cortex?
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11. What and Where Streams
In this exercise you can drag and drop each label to its appropriate location. Drag and drop the
structure that corresponds to each location. If you are wrong, your answer won’t stick.
RESULTS & DISCUSSION
1. Where do both pathways originate? To which cortical area does the dorsal pathway go? The
ventral pathway?
2. Why does it make sense that the dorsal pathway is the “action” pathway?
3. Different aspects of processing occur in different pathways, and yet we normally have a
unified perception. In order to account for this, what other kinds of pathways must exist?
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