Eye tracking technology received new attention recently due to its inclusion in the Samsung Galaxy IV phone, where it can (with mixed results, according to reviewers) let users scroll the screen with their eyes or dim the screen when they look away. Clearly this is a technology that has the potential for a lot of clever applications. But what are the privacy implications?

Eye tracking for research was used for over a century before computers (see the quick history outlined in this article). The earliest research, in the 19th century, actually involved direct mechanical contact with the cornea. Already by 1898, researchers were discovering some really cool phenomena of the human brain. Motion pictures were applied to the problem as early as 1905, and the first head-mounted eye-tracker was developed in 1948, which freed study subjects from having to keep their heads still. In the mid-1970s the first remote trackers were developed that were truly unobtrusive to the subject. By then, research and writing based on eye tracking was booming, not only on the part of psychologists but also the military.

In recent years much eye-tracking research seems to have been focused on “human-computer interaction”—measuring how the human brain processes various user interfaces, web pages, graphics in layouts, marketing approaches, etc., and how best to optimize those things. By tracking the eyes of someone sitting in front of a computer viewing a scene, researchers can measure “scanpaths”—the order in which somebody looks at an image or scene—or create “fixation maps,” in which the time that the eye lingers at various points in an image (“gaze durations”) is measured. Take a look at this presentation to get a taste of the complexity of the science in this area. Here is an analysis of users’ gazes at Facebook pages (of keen interest to advertisers and marketers).

UCLA electrical engineering professor John Villasenor has written about the privacy implications of eye tracking on the Samsung phone and in other uses. The technology is still not “quite ready for mass-market adoption,” he notes, but:

Once the technology for eye-tracking is in place, it will glean information conveying not only what we read online, but also how we read it. Did our eyes linger for a few seconds on an advertisement that, in the end, we decided not to click on? How do our eyes move as they take in the contents of a page? Are there certain words, phrases, or topics that we appear to prefer or avoid? In the future, will we be served online ads based not only on what we’ve shopped for, but also on the thoughts reflected in our eye movements?

Those are the kinds of things that much eye tracking research has focused on to date, in the context of a human sitting at a computer, and are certainly where the near-term privacy threats lie. But it’s possible that the privacy threat from this technology could reach far beyond one’s computer or smartphone screen. It’s not hard to imagine that eye tracking could get good enough to be targeted at a person in public, at a distance—perhaps even someone walking down a sidewalk. Already studies have been done comparing how shoppers scan different stores’ window displays. Those studies used photographs, but the incentive to develop live tracking is obvious.

Meanwhile, progress is likely to continue on another front: research on what we can learn about people by tracking their gaze. As one eye tracking expert puts it, “eye movement data provide an unobtrusive, online measure of visual and cognitive information processing.” Combine the two, and we could see the technology become a standard part of an analytics toolbox plugged in to every surveillance camera fixed on the public.

Among the things that eye tracking has or could be used to try to discover about us:

Cognitive disorders. Research has already suggested that autism, attention deficit disorder, dyslexia, and speech disorders could be diagnosed using eye tracking.

Research has already suggested that autism, attention deficit disorder, dyslexia, and speech disorders could be diagnosed using eye tracking. Drug and alcohol use. Alcohol and drug use has been shown to have effects on eye movements, as does fatigue.

Alcohol and drug use has been shown to have effects on eye movements, as does fatigue. Mental and psychological illness. Schizophrenia is another disorder that research already suggests eye tracking may be able to detect. Alzheimer’s is yet another. Eye tracking has also been suggested as a way to detect post-traumatic stress disorder and eating disorders.

Schizophrenia is another disorder that research already suggests eye tracking may be able to detect. Alzheimer’s is yet another. Eye tracking has also been suggested as a way to detect post-traumatic stress disorder and eating disorders. HIV/AIDS. Individuals infected with HIV sometimes contract a disorder called AIDS Dementia Complex, which can be detected with eye tracking.

Individuals infected with HIV sometimes contract a disorder called AIDS Dementia Complex, which can be detected with eye tracking. Lie detection. Lie detection is a notorious sinkhole of pseudoscience—the link between high-level mental states such as “truthfulness” and low-level, involuntary external behavior is just too ambiguous and unreliable—but the quest for lie detection continues, and claims are being made about the usefulness of eye tracking for this.

Intelligence. A significant amount of eye tracking research appears to have been focused on reading and how humans scan various texts. It’s not hard to imagine that the technology could reveal insights into how different people think, analyze, and process information. I guarantee it wouldn’t be long before someone starts searching for, or claiming, a correlation with criminality, as we have seen in the area of genetic research.

Sexuality. In a quick search I found some research tracking “visual attentional capture” in the viewing of erotic images, and comparing men and women. I would think that by putting a sexualized image containing both an attractive man and an attractive woman, one could probably tell a lot about who is gay and who is straight from the scanpaths and fixation points of people walking by. (Or more precisely, how attracted to men and how attracted to women each subject is.) One study did find changes in pupil size could reveal gender attraction.

The application of eye-tracking technology on the general public via video cameras is, at the present time, science fiction—but clearly not far-future sci-fi. And regardless of how much of the above ever comes to pass, it’s yet another reminder of the huge wave of privacy-invading technology that is headed our way, and of our need to get ready for that.