Simplifying Visual Search for Presentations

Tim Brock / Monday, November 2, 2015


When giving presentations it's very tempting to try and squeeze as much information as possible into a short time slot of perhaps only ten or fifteen minutes. Practice certainly helps when it comes to matching the talk to the time slot, but we really should also consider whether the audience is likely to have had enough to time to absorb all the information we've thrown at them.

One of the difficulties is that this is quite a hard thing to measure. It's relatively easy to determine the speed of a moving vehicle, the speed of sound in air or the speed of light in vacuum. But measuring the speed of comprehension or the speed of thought is a quite different task. Nevertheless, when it comes to chart presentation, we can still help out our audience by making visual search — literally the task of identifying a specific object in a visual environment that contains other distracting objects — easier.

The basic principle is simple: make the thing you want the audience to focus on stand out. The easiest way to do this (at least without resorting to big "LOOK HERE" arrows) is through judicious use of color.

First an example without any color variation. See how quickly you can find the one square in the field of circles and triangles.

The chart below is the same except the square is now colored red and "pops out" at a glance:

Simple, right? And you probably already know to highlight things of interest with more vibrant colors than the less interesting "distractors". But maybe it's not just the square data point that is of interest. Maybe you want to discuss all three point types at different times in the presentation. If the data were being presented in a book or newspaper you could just use three different colors of similar salience and, with the aid of a legend, the reader can take the time to work things out for themselves:

This is space-efficient. But specific points no longer pop out and the observer may have to switch from data area to legend and back several times, an inefficient visual search strategy. When you're more bothered about effective use of time than space it can make more sense to use multiple charts that all share the same basic structure but that highlight different aspects of the data. When talking about the square data point the visible slide should have a chart like the one above with only the square data point colored. When you move on to discuss the circles, switch to a slide with those colored instead and with them moved to the front.

And do the same thing for the triangles too:

Creating multiple charts will obviously make the presentation preparation process a little more laborious but it's worth the effort if it helps your audience understand what you're actually saying. It also adds more structure to the talk so some of the additional time in creation of graphics may be offset by reduced time spent on memorizing the spoken part.

You can use the same simple "trick" with line charts too. The chart below shows some fictitious time-series data.

This graphic is perhaps acceptable for a printed page or website. But on a slide deck we can probably do better by matching the visuals to the audio again. If we're really only concerned with sales of apples (the other lines only providing context), give that line color and make the others thin and gray.

As with the scatter plot, it may be that we're interested in all categories but still focusing on one at a time. We can fade those of less interest (at some moment) by making them semi-transparent and thus bring focus to the category of interest, like apples (again)...

... or pears...

And so on. We can also compare two at a time with subtler distractions (though I think this is somewhat less effective):

You can (and sometimes should) use the simple techniques above with your printed charts too, of course. But when your main constraint becomes temporal rather than spatial, like with a short presentation, it becomes more important. Match the focus of your chart to the focus of your speech at that time and make your audience's task of following along that bit easier. Don't just assume the chart you designed for the website or a printed article will "do" for a presentation. Take the time to adapt for the situation at hand.

The one (major?) drawback here is that audience viewing conditions for your presentation will likely not be as great as yours when you're sat in front of your monitor. Because of this, you probably don't want to reduce the opacity in faded lines (and labels) quite as much as you can get away with when viewing on your own screen. If at all possible, test your slides out in advance in similar conditions to those in which you will give your presentation. 


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