Usability research discovers the value of blind trials

The gold standard of evidence in psychiatry and other healthcare
research is the double blind randomised controlled trial. It has been
the mainstay of evidence-based medicine since it dispelled the myth of
the insulin-induced coma as a treatment for schizophrenia.

Usability engineers seem to be noting the value of blind trials. They
may not yet have discovered the value of double and even triple blind
trials.
http://eyetrackingupdate.com/2010/11/07/eye-tracking-alter-user-behavior/
Does Eye Tracking Alter User Behavior?

"
We all know eye tracking can be informative in showing what someone pays
attention to during various tasks. But we haven't read too many studies
in which researchers have taken into account the behavioral changes
subjects undergo when they know that they are being observed. People act
one way when they know they are alone, but a lot changes when they know
or think someone is watching them.

Previous studies have shown that individuals are more likely to donate
money to someone or some cause when they know they are being watched.
But interestingly enough, there need not be another person present to
influence behavior.

Researchers at the University of British Columbia and Arizona State
University recently published a paper in which they tested individuals'
attention both with and without an eye tracker. Using a hidden camera
embedded in a swimsuit calendar hanging from a wall, they were able to
observe how a subject's behavior changed when they were sitting at the
computer and performing tasks with an eye tracker and what they did
without an eye tracker.

Twenty-four undergraduate students were offered course credit to partake
in the study. Participants were seated in front of a computer with
instructions to carry out a set of tasks for about six minutes. Upon
completion, they were asked to don an eye tracking device manufactured
by Applied Science Laboratories known as MobileEye, a head mounted eye
tracking system equipped with glasses that connected to a digital video
recorder that monitors data from the eye and the scene. Subjects
performed tasks for another minute while researchers monitored from the
hidden camera in the calender. After the study, the subjects were told
about the hidden camera and asked for their consent to use the recorded
material.

The researchers and participants completed a few more similar
experiments, and results showed that an implied social presence had
quite an influence on the looking behavior of the subjects. The results
made for a novel look at social influence as well as a methodological
challenge to those designing, engineering, and testing with eye tracking
devices.
"

Link to the research at the bottom of the page.