Article No :754 | October 27, 2011 | by Andrew Turrell

If you’ve been involved in usability tests, you’ve witnessed this scenario: a test subject is looking for a specific interface element, and even though he is looking directly at it, he can’t seem to see it. This idea of looking but not seeing is a well-known concept in psychology called inattentional blindness, or selective attention. The below video documents a study by Daniel Simons and Christopher Chabris that’s a great demonstration of this phenomenon.

In their research, Simons and Chabris found that only 50% of viewers saw the gorilla, even though this unexpected, strange figure was plainly visible for several seconds. Participants missed it because they focused their attention on the white shirts and the ball being passed. Selective attention made the test subjects unable to see the gorilla, and it’s the same phenomenon that contributes to usability test subjects’ inability to see certain interface elements.

Psychological research abounds in this area (I reference a couple great books at the end of this article), but there are several points related to selective attention that are particularly relevant to UX design:

  1. Human visual perception is much more incomplete and inaccurate than most people realize. Our eyes are not able to process everything that comes into their field of view. Our minds simply do not have enough cognitive resources. Emily Balcetis and David Dunning discuss this in their article, Wishful Seeing: Motivational Influences on Visual Perception in a Physical Environment:
    The naive assumption among most laypeople is that the eye functions like a camera, in that the visual system captures everything in the environment in all its detail. However the assumption of comprehensive vision is wrong… Perception is not the cold, calculated processing of light, but is instead a result of concurrent interactions among experienced sensations, memory and thinking, and social influences.
  2. More focus in one area means less attention elsewhere. Attention is a zero-sum game. If we pay more attention to one object, we consequently pay less attention to others. Difficult or important tasks require a great deal of attention, which leaves less cognitive processes left for gorilla-noticing, or observing whatever else happens to be in one’s field of view.
  3. Expectations manipulate our perceptions. Because we have limited visual intake, we use our biases, expectations, and memories to fill in the gaps. As a result, what we process are highly subjective interpretations of what’s actually there—interpretations that vary drastically from person to person.
  4. Motivations manipulate our perceptions. When we take an action, we do so with intent. We have some task or goal in mind and we want to take steps that bring us closer to achieving that goal or accomplishing that task. Balcetis and Dunning use the term “wishful seeing,” which means that we interpret things in a way that fits with our goals—in other words, we see what we wish to see. Again, these interpretations are highly subjective and vary drastically from person to person.

These quirks and limitations of human visual perception have some specific ramifications for UX:

  1. Don’t be surprised when different users perceive your product in radically different ways, or overlook and misinterpret elements of your interface. This is simply the way that our visual perception works. Expect users to be unpredictable and inconsistent. Assume they’ll make errors and misinterpretations. Assume that different users will interact with and react to your product in very different ways. Consequently, don’t overlook the importance of effective and helpful error handling, and design your product to be clear and straight-forward, reducing the likelihood of misinterpretation or error.
  2. Know users’ motivations and goals, and reinforce them using information scents. Users are goal-oriented, and will ignore anything that does not help them achieve their goals. Giving off a strong information scent means presenting words and actions that reassure users that they’re on the right track. This requires understanding your users and their motivations, and using the specific words and interactive elements that reinforce them.
  3. Make your interface predictable. Your users have limited perceptive capabilities, and will fill in the cracks with their memories and expectations. So, align your product’s interface with those expectations by following accepted design conventions and mental models. Again, understanding your user base is crucial, and by meeting their expectations, they will more easily accomplish their goals.
  4. Practice “right place, right time” design. Your users focus their attention on the task at hand and see little else, particularly if their task is difficult or important (such as an e-commerce flow, where you’re spending real money and it’s difficult to undo). Avoid cluttering your product’s interface with all possible options, just in case a slim minority of users might want them. Instead, only give users access to tasks at the right place and right time. One easy way to determine the right place and right time to include an interface element is by using analytics. It’s an invaluable tool to determine what is and isn’t being used in your interface. Be aggressive about removing elements that are infrequently used.

Most people are unaware of how limited, imperfect, and subjective human visual perception really is. Understanding these limitations is very helpful in predicting how your users will interact with your product. You can counteract these limitations with good, basic design principles:

  • Have a solid understanding of your users
  • Design interfaces that have focus and clarity
  • Meet your users’ expectations
  • Use information scent to reassure to users that they are progressing toward their goals
  • Practice “right place, right time” design

If you’re interested in reading more about selective attention, here are a couple of great books:

Social Psychology of Visual Perception, Emily Balcetis and G. Daniel Lassiter

The Invisible Gorilla: How Our Intuitions Deceive Us, Christopher Chabris and Daniel Simons