The subjects were made to view erotic imagery; "homosexual words," as well as an early form of lie detector to measure perspiration and pulse.
It had previously been determined that the pupils would dilate in relation to the amount of interest in the picture, in a technique termed "the pupillary response test".
[6] One physiological problem with the method was that the researchers failed to take into account the varying sizes of the pupils and the differing distances between the eyes.
Also, the amount of light coming from the photographs changed with each slide, causing the subjects' pupils to dilate in a way that was unrelated to their interest in the picture.
[5] The idea was based on an unrelated study done by an American university professor, which measured the sizes of the subjects' pupils as they walked through the aisles of grocery stores.