Report

Opponent-process theory is a hypothesis of color vision, suggested by Ewald Hering in 1878, in which there are two types of cells in the visual system: one for recording color, and the other for recording brightness. This theory explains the phenomenon known as retinal, or complementary afterimages.

Stanley Smith Stevens, a contributor of psychoacoustics and the field of experimental psychology, is known for the Power Law, which is the most straightforward method of determining perceived intensity of a stimulus. According to this law, S=kI^a, where S=perceived sensation magnitude, k=constant, I=stimulus intensity, and a=power exponent dependent on modality.

According to Stevens' Power Law, the perceived magnitude of a stimulus is a factor of the stimulus intensity raised to a constant power. In this case, the value of a is 0.5.

During my research of Stevens' Power Law, I wondered if there was a similar formula regarding perceived magnitude of a stimulus based on a different factor such as time. I wanted to find out if there was a way to calculate the relationship between time and perceived magnitude of a retinal afterimage.

For the study, I used a sample of ten subjects. My subject pools was comprised of a variety of genders and races. Each subject was shown an image and asked to focus on the cross in the center of the image. Then, after the image disappeared, he or she was asked to rate the perceived intensity of the afterimage on a scale from 1 to 10 (1-weakest, 10-strongest).

Conclusion

The findings were weak. Further research and modification of the study would be required. In a future study, more subjects would be necessary. In addition, the original 1-10 scale used for rating the perceived intensity of the afterimage should be expanded to a 1-100 scale. This would allow the subjects more freedom to convey the varioation between similar scores and extreme scores.

I also noticed that some subjects thought that the afterimages closer to the end of the experiment were stronger than the ones at the beginning, even if some of the images towards the end were shown for less time than the ones in the beginning. To counteract this in a future experiment, I would use only one image throughout the experiment, but allow the subjects enough time between viewings to clear their vision of the afterimage.