Chapter 1. Orientation Tuning of Simple Cells in V1, and Population Coding
1.1 Title slide
Demonstration 1.2
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Orientation Tuning of Simple Cells in V1, and Population Coding
Control the orientation and contrast of stimuli on the receptive field of a simple cell to measure its orientation tuning curve.
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Color coding in this image of the surface of V1 in a treeshrew reveals columns of neurons with similar orientation tuning.
[From Bosking et al., 1997]
[From Bosking et al., 1997]
How Does the Visual System Use the Responses of Multiple Simple Cells in V1 to Determine the Orientation of Visual Stimuli?
The orientation tuning curve of a simple cell in V1 depends not just on the preferred orientation of the cell but also on the luminance
contrast of the stimulus with the background—that is, how much brighter or darker than the background the stimulus is. Generally, the greater
the contrast, the stronger the response. This means that the responses of an individual simple cell don't give the visual system enough
information to unambiguously determine the orientation of the stimulus. To understand why—and to understand how the visual system gets the
information it needs—consider Figure 1, which shows the orientation tuning curves of a single simple cell in response to a low-contrast bar
and a high-contrast bar.
In this graph, the horizontal dashed line shows that three different stimuli could evoke a response of 40 spikes/sec above baseline from this cell:
Thus, it would be impossible for the visual system to "know" the orientation of the bar based just on a 40 spikes/sec response by this single cell. However, any relatively small area on the retina contains the receptive fields of a population of many simple cells, covering the full range of preferred orientations. Figure 2, which shows the orientation tuning curves of two simple cells (A and B) with receptive fields at the same location on the retina, indicates how the visual system uses this to solve the problem of unambiguously determining orientation.
Consider the responses of cells A and B to low- and high-contrast bars oriented at 75° or 90°, as shown in the following table:
Thus, for a 90° bar the response of cell A is greater than the response of cell B, regardless of contrast. But for a 75° bar, the pattern is reversed: the response of cell B is greater than the response of cell A, regardless of contrast.
This type of patterning of the relative responses of neurons with different orientation tuning curves is called a population code, because the response patterns of a population of differently tuned neurons function as a code that lets the visual system compute the orientation of a bar of light.
In this graph, the horizontal dashed line shows that three different stimuli could evoke a response of 40 spikes/sec above baseline from this cell:
- A high-contrast bar oriented at 67°.
- A low-contrast bar oriented at 90°.
- A high-contrast bar oriented at 111°.
Thus, it would be impossible for the visual system to "know" the orientation of the bar based just on a 40 spikes/sec response by this single cell. However, any relatively small area on the retina contains the receptive fields of a population of many simple cells, covering the full range of preferred orientations. Figure 2, which shows the orientation tuning curves of two simple cells (A and B) with receptive fields at the same location on the retina, indicates how the visual system uses this to solve the problem of unambiguously determining orientation.
Consider the responses of cells A and B to low- and high-contrast bars oriented at 75° or 90°, as shown in the following table:
Thus, for a 90° bar the response of cell A is greater than the response of cell B, regardless of contrast. But for a 75° bar, the pattern is reversed: the response of cell B is greater than the response of cell A, regardless of contrast.
This type of patterning of the relative responses of neurons with different orientation tuning curves is called a population code, because the response patterns of a population of differently tuned neurons function as a code that lets the visual system compute the orientation of a bar of light.
1.2 Explain - Custom activity
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Click on a low-contrast or high-contrast stimulus to project it onto the receptive field of
a simple cell in V1. You'll see the cell's response in the table
and as a plotted point in the graph. Note how the cell's response depends
on both the contrast and the orientation of the stimulus.
Click SHOW TUNING CURVES to see the cell's tuning curves in response to both types
of stimuli.
Click on every stimulus to see how the plotted points define the tuning curves.
1.3 Explain - Custom activity
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In general, the firing rate of any individual simple cell in V1 doesn't provide enough information to let the visual system determine the orientation of a stimulus. To see why, select a firing rate. You'll see that several different stimuli can evoke that response from this typical simple cell.
1.4 Explain - Custom activity
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The responses of multiple simple cells make a pattern that can function as a population code,
giving the visual system the information it needs to determine the orientation of a stimulus. Click a button for a pair of response rates for
Simple Cells A and B. In the graph, you'll see plotted points corresponding to the orientations of stimuli that would produce the selected
response rate for each cell.
Above the graph, you'll see bars with those orientations. Can you figure out the actual orientation of the
stimulus that produced this pair of response rates?
1.5 Explain
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How Does the Visual System Use the Responses of Multiple Simple Cells in V1 to Determine the Orientation of Visual Stimuli?
The orientation tuning curve of a simple cell in V1 depends not just on the preferred orientation of the cell but also on the luminance contrast of the stimulus with the background—that is, how much brighter or darker than the background the stimulus is. Generally, the greater the contrast, the stronger the response. This means that the responses of an individual simple cell don't give the visual system enough information to unambiguously determine the orientation of the stimulus. To understand why—and to understand how the visual system gets the information it needs—consider Figure 1, which shows the orientation tuning curves of a single simple cell in response to a low-contrast bar and a high-contrast bar.
In this graph, the horizontal dashed line shows that three different stimuli could evoke a response of 40 spikes/sec above baseline from this cell:
● A high-contrast bar oriented at 67°.
● A low-contrast bar oriented at 90°.
● A high-contrast bar oriented at 111°.
Thus, it would be impossible for the visual system to "know" the orientation of the bar based just on a 40 spikes/sec response by this single cell. However, any relatively small area on the retina contains the receptive fields of a population of many simple cells, covering the full range of preferred orientations. Figure 2, which shows the orientation tuning curves of two simple cells (A and B) with receptive fields at the same location on the retina, indicates how the visual system uses this to solve the problem of unambiguously determining orientation.
Consider the responses of cells A and B to low- and high-contrast bars oriented at 75° or 90°, as shown in the following table:
Thus, for a 90° bar the response of cell A is greater than the response of cell B, regardless of contrast. But for a 75° bar, the pattern is reversed: the response of cell B is greater than the response of cell A, regardless of contrast.
This type of patterning of the relative responses of neurons with different orientation tuning curves is called a population code, because the response patterns of a population of differently tuned neurons function as a code that lets the visual system compute the orientation of a bar of light.
In this graph, the horizontal dashed line shows that three different stimuli could evoke a response of 40 spikes/sec above baseline from this cell:
● A high-contrast bar oriented at 67°.
● A low-contrast bar oriented at 90°.
● A high-contrast bar oriented at 111°.
Thus, it would be impossible for the visual system to "know" the orientation of the bar based just on a 40 spikes/sec response by this single cell. However, any relatively small area on the retina contains the receptive fields of a population of many simple cells, covering the full range of preferred orientations. Figure 2, which shows the orientation tuning curves of two simple cells (A and B) with receptive fields at the same location on the retina, indicates how the visual system uses this to solve the problem of unambiguously determining orientation.
Consider the responses of cells A and B to low- and high-contrast bars oriented at 75° or 90°, as shown in the following table:
Thus, for a 90° bar the response of cell A is greater than the response of cell B, regardless of contrast. But for a 75° bar, the pattern is reversed: the response of cell B is greater than the response of cell A, regardless of contrast.
This type of patterning of the relative responses of neurons with different orientation tuning curves is called a population code, because the response patterns of a population of differently tuned neurons function as a code that lets the visual system compute the orientation of a bar of light.
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! Click EXPLAIN if you want to review this topic.
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The correct answer is D.
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The correct answer is D.
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! Click EXPLAIN if you want to review this topic.
Incorrect. The correct answer is B.
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! Click EXPLAIN if you want to review this topic.
Incorrect. The correct answer is B.
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