According to researchers from Massachusetts General Hospital, sounds, sights and smell can subtly alter an individual's response to medical treatment, similar to the placebo effect.

The American Cancer Society defines the placebo effect as a treatment that is not real. It can be in the form of a "sugar pill," but a placebo can also be an injection, a liquid, a procedure, or any other type of therapy that doesn't directly affect the illness being treated. Health experts believe when individuals are receiving treatment they tend to feel better, however new research suggests subliminal cues can trigger an experience similar to the placebo effect.

For the study, lead researcher Karin Jensen showed two different images on a computer screen to 40 volunteers. During the first image, the participants received a painful heat pulse and during the second image the participants received a milder heat pulse. Following each pulse, participants were instructed to rate their pain from none to unbearable.

In the next trial, involving 20 subjects, researchers instructed the participants to expect different levels of pain for each image. However, researchers applied the same level of pain for both images. The subjects continued to rate the "high pain" images as more severe than the "low pain" image despite there being no difference.

In the last trial, 20 subjects viewed the images again. The same levels of heat were used for both photos. This time researchers only displayed the images for 12 milliseconds, so the subjects would not consciously detect what images they were observing. Nevertheless, the subjects were able to subconsciously associate the "high pain" image with more severe pain.

According to Jensen the results demonstrate subliminal cues can assist patients in their recovery. He believes cues as simple as background smells or a firm, reassuring handshake from a doctor, may improve recovery and should be incorporated in clinical practice. In addition, doctors can conversely reduce exposure to cues that can obstruct recovery.

The study was published in the Proceedings in the National Academy of Sciences.