The purpose of the experiment was to study how humans react to the presence of smooth, curved contours versus their reaction to sharp-angled contours. The hypothesis was that the reaction to objects or patterns with sharp contours would be more negative than the reaction to objects or patterns with curved contours.
There were sixteen participants, eight males and eight females; all were healthy with normal vision. None were aware of the purpose of the study. In addition to hypothesizing that the participants would like the sharply contoured images less than the smoothly contoured images, the researchers also hypothesized that the amygdala would be activated when making this snap decision. They used an fMRI to test their hypothesis.
140 pairs of real objects (Part A in Figure 1), like a chair, a plant, or a shirt, and 140 pairs of novel, meaningless designs (Part B in Figure 1) were collected. The meaningless designs were created by the researchers and were simply patterns. All of the pairs were presented on a computer screen in grayscale. One item in each pair was with curved contours, and one item had sharp-angled contours. There were also 80 control images that had an approximately equal amount of sharp angles and smooth contours. (Part C in Figure 1)
The results of the study showed that the overall, the participants liked the curved images more than the control images, and they liked the control images more than the sharp-angled images. This showed that the participants liked the curved images more than the sharp-angled images.
The fMRI results showed that there was considerably more activity in the amygdala when the participant was observing an image with sharp contours.
This was consistent for both the real objects and the patterns. The researchers think this may be because the sharp angled objects present more of a threat.
A second experiment was done to rule out the possibility of the results merely reflecting whether the participants liked or disliked the images. The researchers wanted to see if the sharp-contoured images were actually more threatening. To do this, a similar experiment was performed, in which the participants had to respond by saying whether the images were threatening or non-threatening, as opposed to whether they like or dislike the image. In this study, the participants called the sharp-angled objects threatening much more than the curved objects.
The amygdala is the part of the brain that is activated when there is danger. It makes sense that it would activate in response to a perceived threat. LeDoux discusses an experiment in which a rat is subjected to a warning signal, and then to a mild electrical shock. The rat’s response to danger is to freeze. The next time around, the rat will remember that the electrical shock follows the warning signal, and will freeze when it hears the sound. This is called the Pavlovian Response. However, damage to the amygdala deletes this process; the rat will no longer have this awareness. The amygdala is responsible for controlling this type of reactive behavior. In the same way, the amygdala is activated when a human sees a sharply contoured image.