Rodney Chang, 1972

Chicago, Illinois




It is generally accepted that color perception is the result of physical energy stimuli triggering biochemical reactions within the retina. Different colors (hues) seen are the visual manifestations of different sized light wavelengths. It is theorized that specific cones of the retina selectively react biochemically when stimulated by their respective hue wavlength. After a certain span of time of continuous fixed hue stimulation, it is believed that the cones functional for that particular hue fatigue and cones specfiic for the corresponding complementary hue begin to trigger as a compensation reaction. This results in the so called "afterimage". Thus if one continues to gaze at a red spot, upon looking away after a certain minimum time interval he will perceive green (i.e., the color wheel or spectral complement of red).




The purpose of this study was to test the theory that hue afterimages are the results of biochemical-physical reactions of the retina. The investigator tested to see if complementary afterimages could be created by inducing imaginary hues in the cerebrum while in a hypnotic trance. He also investigated if learning associations between non-complementary hue pairs through conditioning under hypnosis could influence later visual-mental responses to true physical chromatic light stimuli upon the retina (colored paper rectanlges were used).




Four female college students volunteered for the hynotic afterimage sessions consisting of four sessions spread a week apart from each other. Three girls claimed no formal art background whereas one was currently enrolled in a color theory course. All were able to open their eyes and still remain in the hypnotic trance state, therefore indicating that they were acceptable hypnotic subjects. Subjects were placed in the trance state and tested on an individual basis rather than employed group hypnosis for

1) Better operator control of the test situation

2) Maximum operator-subject repoire under the condition of limited acquaintances

3) Responses not influenced by other subjects' responses

The series of test were done in three parts. The first part consisted of three different trance sessions in which the subject, with closed eyes, was suggested to imagine particular hues for twenty seconds and then momentarily open her eyes and look at a white board upon her lap. It was suggested that she would see a color on this board (which could also be the same hue she was seeing "in her mind"). Upon seeing the hue, she would verbally relay her visual response and the close her eyes (to insure maintainence of the trance state). In the fourth and final session the subject was run through the previous trails once again but this time told to remember the responses she gave to the particular imagined hues (i.e., an attempt to produce associative learning).



(more detail and "Results and Discussion" left out here online, rather lengthy...)





The results of this experiment support the idea that visual afterimages are indeed the result of physical-biochemical changes in cones of the retina. Hypnotic suggested mental hue images did not produce complementary afterimages (on the white cardboard background). Instead, "seen" noncomplementary hue responses were probably subjective hallucinations. Hue hallucinations tended to be in the blues and greens and not in oranges or purples.

No "brain-washing", non-complementary learned hue associations during hypnosis affected the usual retinal hue-complementary afterimage relationship. For example, in the hypnotic trance, subject were told they would see orange on the white board after previously opening the eyes to view a red spot. In the trance, when opening the eyes once again they would state that yes, they saw an orange spot. However, in subsequent non-hypnotic ("awake" or conscious state) session, once again looking at the red spot would result in later "seeing" the usual green afterimage complementary match for red.

Further investigation is needed to demonstrate whether or not learned color theory (introduction of the "color wheel" and "complementary colors" to students) adds a biasing factor in the otherwise phsical-optical nature of retinal color perception.