How Our Brain Decides How Long We Look at Something

In this week, I’ve talked about how our attention focusing mechanism moves the spotlight of foveal attention around different environments: a Where’s Waldo picture, a webpage, a website with advertising and a search engine results page. I want to wrap up the week by looking at another study that looked at the role of brain waves in regulating how we shift the spotlight of attention from one subject to another.

Eye Spy

eyetrackingsaccadesIf you do eye tracking research, you soon learn to distinguish fixations and saccades. Fixations occur when we let our foveal attention linger on an element, even for a fraction of a second. Saccades are the movements our eyes make from one fixation to the next. These movements take mere milliseconds. Below I show an example of a single session “gaze plot” – the recording of how one individual’s eyes took in an ad (the image is from Tobii, the maker of the eye tracking equipment we use). The dots represent fixations, as measured in milliseconds. The bigger the dot the longer the eye stayed here. The lines connecting the dots are saccades.

When you look at a scene like the one shown here, the question becomes, how do you consciously move from one element to another. It’s not like you think “okay, I’ve spent enough time looking at the logo, perhaps it’s time to move to the headline of the ad, or the rather attractive bosom in the upper right corner (I suspect the participant was male)” The movements happen subconsciously. Your eyes move to digest the content of the picture on their own accord, based on what appears to be interesting based on your overall scan of the picture and your attention focusing mechanisms.

Keeping Our Eyes Running on Time

Knowing that the eye tends to move from spot to spot subconsciously, Dr. Earl Miller at MIT decided to look closer at the timing of these shifts of attention and what might cause them. He found that our brains appear to have a built in timer that moves our eyes around a scene. Our foveal focus shifts about 25 times a second and this shift seems to be regulated by our brain waves. Our brain cycles between high activity phases and low activity phases, the activity recorded through EEG scanning. Neurologists have known that these waves seem to be involved in the focusing of attention and the functions of working memory, but Miller’s study showed a conclusive link between these wave cycles and the refocusing of visual attention. It appears our brains have a built in metronome that dictates how we engage with visual stimuli. The faster the cycles, the faster we “think.”

But, it’s not as if we let our eyes dash around the page every 1/25 of a second. Our eyes linger in certain spots and jump quickly over others. Somewhere, something is dictating how long the eye stays in one spot. As our brain waves tick out the measures of attention, something in our brains decide where to invest those measures and how many should be invested.

The Information Scent Clock is Ticking

Here, I take a huge philosophical leap and tie together two empirical bodies of knowledge with nothing scientifically concrete to connect them that I’m aware of. Let’s imagine for a second that Miller’s timing of eye movements might play some role in Eric Charnov’s Marginal Value Theorem, which in turn plays a part in Peter Pirolli’s Information Foraging Theory.

Eric Charnov discovered that animals seem to have an innate and highly accurate sense of when to leave one source of food and move on to another, based on a calculation of the energy that would have to be expended versus the calories that would be gained in return. Obviously, organisms that are highly efficient at surviving would flourish in nature, passing on their genes and less efficient candidates would die out. Charnov’s marginal value calculation would be a relatively complex one if we sat down to work it out on paper (Charnov did exactly that, with some impressive charts and formulas) but I’m guessing the birds Charnov was studying didn’t take this approach. The calculations required are done by instinct, not differential calculus.

So, if birds can do it, how do humans fare? Well, we do pretty well when it comes to food. In fact, we’re so good at seeking high calorie foods, it’s coming back to bite us. We have highly evolved tastes for high fat, high sugar calorie rich foods. In the 20th Century, this built in market preference caused food manufacturers to pump out these foods by the truck load. Now, well over 1/3 of the population is considered obese. Evolution sometimes plays nasty tricks on us, but I digress.

Pirolli took Charnov’s marginal value theorem and applied it to how we gather information in an online environment. Do we use the same instinctive calculations to determine how long to spend on a website looking for the information we’re seeking? Is our brain doing subconscious calculations the entire time we’re browsing online, telling us to either click deeper on a site or give up and go back to Google? I suspect the answer is yes. And, if that’s the case, are our brain waves that dictate how and where we spend our attention part of this calculation, a mental hourglass that somehow factors into Charnov’s theorem? If so, it behooves us to ensure our websites instill a sense of information scent as soon as possible. The second someone lands on our site, the clock is already ticking. Each tick that goes by without them finding something relevant devalues our patch according to Charnov’s theorem.

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