The effect of false size cues on distance perception in total darkness

Katie Williams, Melissa Bobier, and Ann Isbell
02cawill@alma.edu, 02mlbobi@alma.edu, 02amisbe@alma.edu
Alma College

Emmert's law emphasizes the relationship between size and distance. It states that you use distance to estimate size and vice versa. But the size of the object is not the only cue that helps determine its distance. One of these cues is binocular disparity. This occurs because the eye gives off two different views of the world, and we are able to estimate the distance of the object by the difference in the views.

In our experiment we investigated the relationship between size cues and estimates of distance. We wanted to see if subjects were given false size cues of an object, if it had any impact on their estimate of distance. We also wanted to investigate if darkness had negative effects on the distance estimates.

Methods:

Subjects
There were a total of twenty participants; ten of whom participated in the control and ten of who were in the experimental group. The twenty student volunteers were undergraduates from Alma College.

Apparatus and Materials:
Two wooden frames were used, one box was 1x1 square feet and the other was 2x2 square feet. Each box was covered by glow-in-the-dark paint, which is a rather weak illumination, so there is no excess light to leak out and reflect off other objects in a pitch black room which allowed no light in.

Procedure:
Each subject was seated in a pitch-black room and shown the box that was one foot squared adn the box that was two feet squared. The boxes were placed at varying distances between six and twelve feet. Each distance was randomly assigned. The subjects viewed the box minocularly (with one eye) and binocularly (with two eyes). Each box was shown for .25 seconds. Each subject was asked to estimate the distance of the box from them minocularly and binocularly; they were told the size of the box before it was illuminated.

For the control group, the ten subjects were told the correct size of the box and asked to estimate the distance, first with one eye and then with both. With a patch covering one eye each subject was shown the two boxes at random distances. Then the eye patch was taken off and the subjects were again asked to estimate the distance of the two boxes.

The experimental group was given false size cues. They were told the boxes were larger and smaller than they really were. First they performed the experiment with one eye. At a random distance, they were told the box was bigger than it actually is and then told it was smaller than it actually was. The subjects then viewed the boxes binocularly and were again given false size cues.

Results:

Our restults indicate that when the subjects were told false sizes of the boxes, their error in distance estimation increased. That is to say that there was a larger difference between what the distance actually was and what the subjects thought it was. When the experimental subjects were told that the 1x1 square foot box was smaller than it actually was, they thought the box was closer than it was. Subjects were again told false size cues, they were told that the 2x2 square foot box was larger than it actually was, subjects also estimated this box to be closer than its actual distance. After running the factorial anova we found that there was a probability of 0.0016. So, the datum indicates that the false size cues influenced our subjects distance estimates. Also, our experiment showed that viewing the stimulus binocularly made it a little easier to estimate the distance accurately. The difference was not significant.

Discussion:

Our results show that there is a relationship between size and distance estimate. This can be seen through the increased error in distance estimations with out experimental group as compared to our control group. Although, there was a surprise because the results show that when subjects were told a box was bigger than it actually was, they estimated that it was closer. Logically, the box should have appeared farther away to the subjects. Perhaps this oddity is due to their distance estimations making the box appear closer. Either way, our experiment shows that size and distance estimation are related.
Figure 1. Error in distance estimation of correct and false size cues

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