How much information can a user reasonably process from a UI?

Question

As an example, say there's an interface that contains a table/grid of information that is periodically updated. The table is meant to represent an event that has happened, perhaps the date and time of a stock price change . The acutal frequency of these events could be dozens of events per second. This is obviously too much information for a user to process/understand, so I'm trying to find out how much information a user COULD process in a given amount of time so that we can throttle the data and come up with an alternate display. I know some studies have been done on this, but I can't seem to find an authorative source.

Answer 1

There is research into this topic but it will give you a complex answer. You can increase how much a person can take in from a UI if you use different sensory modalities rather than just one. For example using sights and sounds you may be able to pump more information into a user than using just sight or just sound. There are also findings that suggest that if your user has to really process or think about the inputs there are more significant bottlenecks that are more difficult to avoid even if you cross sensory modalities. Training helps. Expert users can process more but in the typical cases you will run into limits.

But to get down to your question of how fast you can change the display in particular table: You can look into the Psychology literature on the topic of "Attentional Blink" and "Psychological Refractory Period (PRP)" but the general advice that I can give you from that is don't push faster than changes every 500ms for a single watched location. Typical users can need that much time to process even simple single location changing input. If you're doing it continuously 500ms is a speedy but perhaps roughly workable rate. You may be able to push down to 250ms but this will depend on what percentage of your users you're willing to put off. Also if your users are having to scan multiple locations for possible changes you may have to slow down even from a 500ms change rate. This doesn't necessarily mean 1000ms if you have two locations. It's not a linear relationship but the answer for that is going to be more complex and depend a lot more on what your UI looks like exactly.

Wikipedia: Attentional Blink

Answer 2

Most people can only hold about seven distinct pieces of information in the brain at once. If using a UI requires more than thinking about, remembering and manipulating more than at once it's too busy. I think you can display more than that, but try and group them in separate "islands" that keep related elements down to about a 1/2 dozen or so.

http://www.codinghorror.com/blog/2006/08/the-magical-number-seven-plus-or-minus-two.html

Answer 3

This depends on a lot of factors:

• Is the table as a whole updating (eg, every row changes), or is it just one row at a time?
• If it's a row at a time, is it an arbitrary row that a user has to jump their eyes to, or is it always a new row at the top? The former would require more spacing between updates than the latter.
• How much data is on each row?
• Is most of it unimportant, and only the outliers are important to the user (in which case they're probably skimming the data, so you can put it out a lot faster)? Or does all the data need to be read and mentally processed.

My (admittedly minimal- a couple college classes worth) experience with calculating user experience metrics (like data processed per second) has lead me to believe that the field is pretty immature, and that you're better off doing empirical measurement. If you really want to try to optimize a specific UI, nothing beats usability testing.

Answer 4

Doesn't this depend a lot of the specific application and the users is targetting?

You can find a number of updates for stocks, say, but that depends on whether user is a typical Google finance junkie or a investment guy working in a Bloomberg propietary app I guess.

Therefore, you may want to get some feedback from potential users.

Answer 5

By user, do you mean the web surfer or the one "using"? Either way, this page comes to mind.

Answer 6

It is generally understood that most people can store about 7, plus or minus 2, pieces of information in their head at once. You can use chunking to increase the amount of data someone can store. For example 12/8/1987 is a lot easier to remember than 7, 8, 1, 1, 2 9, 8 (even though it is the same numbers). A lot of people think they can break this barrier, or think that many people will fall under the norm, but the most fascinating thing about this "rule" is how often it holds true.