Chapter 1. Size Constancy

1.1 Introduction

Cognitive Tool Kit
true
true

Size Constancy

As an object gets farther away from us, the size of the image of that object on the retina shrinks. Take a look at the figure below.

The two arrows at the top of the figure are exactly the same size, but the more distant arrow will cast a smaller image on the retina, as indicated by the two arrows at the bottom of the figure (drawn to the relative sizes of their images on the retina).

If we saw the world in a way that depended upon the retinal image size, your friends would shrink rapidly as they walked away from you. Their height would halve with each doubling of distance. At 4 feet, they would appear to be half the size or 2 feet. Take a look at the following photograph.

Fortunately, this photograph does not illustrate the way we view the world. We have size constancy, which is the perception that objects stay about the same size despite their different distances from us and the different retinal images they cast. Our depth perception plays a critical role in size constancy and this experiment will illustrate that.

References:

Boring, E. G. (1964). Size constancy in a picture. The American Journal of Psychology, 77(3), 494-498.

Holway, A. H., & Boring, E. G. (1941). Determinants of apparent visual size with distance variant. The American Journal of Psychology, 54, 21-37.

 

1.2 Experiment Setup

Figure 1.1
 

1.3 Instructions

Instructions

You will be asked to adjust the size of the figure on the right so that it appears to be exactly the same size as the figure on the left. When the figures look to be the same size, press the Match button to move to the next trial.

Keyboard Responses

Key What Response Means
+ or = Increase the size of the left figure
- (minus sign) Decrease the size of the right figure
 

1.4 Experiment

Begin Experiment

Start Experiment
Figure 1.2
 

1.5 Results

Results

Figure 1.3
 

1.6 Quiz

Quiz

Question 1.1

One of the independent variables for this experiment is:

A.
B.
C.
D.

1
Correct.
Incorrect.
The independent variable is the value that is changed by the experimenter. In this case, the number of depth cues present was manipulated.

Question 1.2

The dependent variable in this experiment is:

A.
B.
C.
D.

1
Correct.
Incorrect.
The dependent variable is the value that the experimenter collects to indicate how you performed in the experiment. In this case, we recorded the size of the left-hand figure when you pressed the match button. So, the correct answer is the size of the left-hand figure.

Question 1.3

This phenomenon in which two objects of the same size appear to be the same size when one is farther away and casts a smaller retinal image is called:

A.
B.
C.
D.

1
Correct.
Incorrect.
This experiment examines reasons that we see objects of the same actual size as having the same size despite changes in the size of the retinal image. As a result, this phenomenon is called size constancy.

Question 1.4

How is the presence of depth cues involved in this phenomenon?

A.
B.
C.
D.

1
Correct.
Incorrect.
Generally, the more depth cues, the better our size constancy.

Question 1.5

As an object gets farther from you, what happens to its retinal image size?

A.
B.
C.
D.

1
Correct.
Incorrect.
It gets smaller. As an object gets farther from you, it takes up less area on your retina.