Avoid surprises and magic tricks

Pair actions with intuitive outcomes

Avoid “magical” events that appear unrelated to user behavior or prior causes, or violate laws of physics to the point of confusion, as they confound the user’s expectations and trigger Error Neurons.

Avoid surprises and magic tricks

UI design suggestions 

1. Avoid “magic” by tailoring outcomes to match the user’s actions
“Magic” is our term for anything that confuses the intuitive sense of cause and effect that a user should feel when exploring a new interface. A magic wand, for instance, is inherently confusing for two reasons: First, its initial appearance is simply an inanimate stick, which doesn’t bear affordances the user would reasonably associate with a particular task. Second, it’s use could be tied to anything, giving the user no ability to predict the effect of using it: waving the wand is just as likely to cause fireworks to appear as it is to delete files, or do nothing at all. On the other hand, most users will immediately know how to use an eraser, for instance; its use can be understood and its effects predicted with no additional explanation.

2. Use realistic physics to create intuitive object interactions and behavior
Confusion can also arise when objects don’t respond in reasonable ways. For instance, gently pushing a holographic ice cube might cause it to slide across a desk, but it shouldn’t fly across the room at 900 mph. Draw from Newtonian physics consistently and consider mass, volume, and other physical properties when applying forces to objects and the collisions between them. Of course, slight deviations from real world physics can be used to creative, practical, or even ergonomic effect, but only when handled with moderation. Beyond a certain threshold (or abstraction), exaggeration or abstraction becomes confusing.

3. Enforce causality with clear associations between action and effect
A sound triggered by a user’s action should occur immediately in time and emanate from the appropriate location. Likewise, visual feedback such as glowing highlights, shadows or physical deformations should be proportionate and spatially close to the event that triggered them.

The neuroscience behind it

When the brain is exposed to a novel situation, such as a new interface,
it compares that input against its most similar prior experiences to make educated assumptions about the outcome. This process minimizes cognitive burden by reducing the amount of problem-solving required to achieve a task.

When a new experience aligns with our assumptions, we can act quickly and accurately. When it differs from our expectations, however, our error neurons are activated, triggering the additional problem-solving necessary to resolve the unknowns, and resulting in wasted mental energy that could have been used for analysis or learning of the content itself, rather than the UI.

Further Study

Paper: Summerfield C., Egner T. (2009) Expectation (and attention) in visual cognition. Trends in Cognitive Sciences. 13(9):403-9