The Aperture Problem
 
 
 
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Glossary

Chapter 7. The Aperture Problem

Demonstration 7.3
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The Aperture Problem

Interact with animated displays to explore the aperture problem.

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Parts of objects seen through small openings - like the white object in this photo - are often ambiguous. Our visual system must solve this problem in order to correctly perceive motion.
Photo: © Keith Levit / Alamy.

What Is the Aperture Problem, and How Does the Visual System Solve It?

V1 neurons have small receptive fields, which means that any one V1 neuron monitors just a small part of the retinal image. All that a V1 neuron "sees" is what's happening within its receptive field. This is called the aperture problem, because a V1 neuron, in effect, views the world through a small aperture and has no way of "knowing" what's going on elsewhere in the retinal image. Because of the aperture problem, any given direction-tuned V1 neuron will often fail to produce an accurate representation of the direction of motion of an object with a retinal image larger than the neuron's receptive field.

To solve the aperture problem, the visual system needs to combine the information contained in the signals from multiple V1 neurons in order to assess motion over a larger area of the retina than that seen by individual V1 neurons. This is a process that neurons in area MT are well suited to carry out. Neurons in MT have much larger receptive fields than those in V1, which means they receive signals from multiple V1 neurons. An MT neuron that could combine the information in the signals from multiple V1 neurons could unambiguously indicate an object's direction of motion based on the different patterns of responses by the V1 neurons.
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What Is the Aperture Problem?
Clearly, these objects are moving in different directions. But would that still be clear
if you viewed the objects through small apertures? Click SHOW APERTURES to see.

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How Does the Visual System Solve the Aperture Problem?

Four V1 neurons are tuned for the direction fo the motion indicated by the arrows. Click on the directions of motion of the object. Note which neurons are activated by each direction of motion. To understand why a neuron is activated or not, look at the direction of motion of the edge of the object within the aperture of the neuron's receptive field, and compare that direction of motion with the neuron's direction tuning. Click HIDE OBJECT to hide the object outside the apertures.

Is there a unique pattern of activation associated with each direction of motion?

Click WHAT'S GOING ON? for the answer.

explain_text

What Is the Aperture Problem, and How Does the Visual System Solve It?

V1 neurons have small receptive fields, which means that any one V1 neuron monitors just a small part of the retinal image. All that a V1 neuron "sees" is what's happening within its receptive field. This is called the aperture problem, because a V1 neuron, in effect, views the world through a small aperture and has no way of "knowing" what's going on elsewhere in the retinal image. Because of the aperture problem, any given direction-tuned V1 neuron will often fail to produce an accurate representation of the direction of motion of an object with a retinal image larger than the neuron's receptive field.

To solve the aperture problem, the visual system needs to combine the information contained in the signals from multiple V1 neurons in order to assess motion over a larger area of the retina than that seen by individual V1 neurons. This is a process that neurons in area MT are well suited to carry out. Neurons in MT have much larger receptive fields than those in V1, which means they receive signals from multiple V1 neurons. An MT neuron that could combine the information in the signals from multiple V1 neurons could unambiguously indicate an object's direction of motion based on the different patterns of responses by the V1 neurons.

You must select an answer and then click SUBMIT before you can click proceed to the next screen.
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Select your answer to the question below. Then click SUBMIT.

The following statements are all true. Which one relates to the aperture problem?

A.
Not all V1 neurons are tuned for direction of motion.
B.
Area MT is a "motion center" in the brain.
C.
Disruption of area MT impairs motion perception.
D.
The receptive field of a direction-tuned V1 neuron covers just a small part of the retinal image.
Correct! Click EXPLAIN if you want to review this topic.
Incorrect.
The correct answer is D.
Click EXPLAIN if you want to review this topic.
You must select an answer and then click SUBMIT before you can click proceed to the next screen.
test_single_choice

Select your answer to the question below. Then click SUBMIT.

Which of the following statements explains why the aperture problem is a problem?

A.
Any given direction-tuned V1 neuron will often fail to produce an accurate representation of the direction of motion of
an object.
B.
Neurons in MT have much larger receptive fields than those in V1.
C.
Neurons in MT receive signals from multiple V1 neurons.
D.
Any direction-tuned V1 neuron doesn't respond to the motion of an object with a retinal image larger than the neuron's receptive field.
Correct! Click EXPLAIN if you want to review this topic.
Incorrect.
The correct answer is A.
Click EXPLAIN if you want to review this topic.
You must select an answer and then click SUBMIT before you can click proceed to the next screen.
test_single_choice

Select your answer to the question below. Then click SUBMIT.

How does the visual system solve the aperture problem?

A.
The visual system automatically adjusts the size of direction-tuned V1 neurons' receptive fields to encompass the entire retinal image of a moving object.
B.
When the retinal image of a moving object is larger than the receptive field of direction-tuned V1 neurons, MT neurons take over the function of those V1 neurons.
C.
Neurons in MT receive signals from multiple direction-tuned V1 neurons and combine the information in those signals to produce an unambiguous representation of an object's direction of motion.
D.
The visual system cannot really solve the aperture problem. Instead, it uses other cues in the retinal image to assess an object's true direction of motion.
Correct! Click EXPLAIN if you want to review this topic.
Incorrect.
The correct answer is C.
Click EXPLAIN if you want to review this topic.
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The Aperture Problem.
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