Wednesday, March 24, 2010

The Psychology of User Interface Responsiveness

aka The Psychology of Time Perception in Software
Steven Seow, Microsoft

What is objective is not necessarily what is perceived by users. Many layers to consider when talking about performance and responsiveness.

WYSMNBWYG: What you see may not be what you get.

Central course for attention. When you pay attention to non-temporal events, you lose information about time. When you pay attention to time, you lose information about details. Attenuation hypothesis.

Perception,  what the brain does with the information it receives from the senses. Couple of layers before it hits the brain. Something that's objectively described can mean different things to different people in different contexts.

Anything we can do to reduce perceived duration is a good thing.

No specific spot in the brain to perceive time. No need to question if perception is reality. A clock tells time, a metric tells a number. No judgment involved.

Tolerance, the maximum degree of something we are willing to experience to attain something.

"The download took 5 minutes."

Yesterday, it took 3 minutes: too slow.

File only 1MB: too slow.

Used to take more than an hour: download is great!

Maister's first law of service: satisfaction is a function of discomfirmation, or the difference between what was perceived and what was expected.

Responsiveness: the ability of a system to respond to user input and process internal operations without undue delay. 

Responsiveness relative to interaction in question, subjectively perceived & interpreted, non-exclusive (users aren't carrying stopwatches).

Relate a metric not to an interaction, but to a user expectancy. When you get a new interaction, relate it to the user expectancy, not the metric.

Classes of responsiveness:
  • Instantaneous (< 0.1 - 0.2 sec.)
  • Immediate (< 0.5 1 sec.)
  • Continuous (< 2 - 5 sec.)
  • Captive (< 7 - 10 sec.)
Continuous is about flow. Applicable to UA in areas of error messages. If too much text, too much to read, users will scan. Aim for 2-5 seconds, at 5-6 words per seconds, and aim for that size in error messages.

Not a mathematical model, but a psychological, empirical model, based on what users expect.

Time is a precious commodity. Users shell out not only money, but time, and have an expectation for their experience.

Uncertainty is the biggest poison. Information is a powerful antidote. The right amount of content at the right time.

Check out the book, "Designing and Engineering Time"

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