It may not seem intuitive, but including words on slides has a bigger detrimental effect on the quality of a talk than any other issue I will address.
The slides in most science talks contain many words. This simple fact has many consequences, none positive. Most obviously, words on slides impel listeners to read the words on the slide. If you are talking while they are reading, then you generate cognitive dissonance that makes it difficult for the audience to understand either your spoken words or your written words. So, if you want your audience to read the words on a slide, then, presumably, you should shut up. But, I don’t recommend that. Instead, just cut all the words form your slides.
This recommendation applies also to the dreaded “Title” slide. Title slides are a symptom of treating a talk like a paper (which I discuss further here). What, exactly, are you trying to communicate with a title slide? Who you are? They know that. What you will talk about? They very likely know that. Where you are from? Maybe that is unique information, but it is definitely not information that is pertinent to the science you are going to present. There is no information on any title slide that I have ever seen that improved communication. Instead, title slides often contain gratuitous images and information that distracts the audience from your critical first few sentences. So, with a title slide, you have very quickly ceded the first battle. You have let the audience not focus on your words and let their gaze wander over words (and sometimes images) that communicate very little information. Delete the title slide.
Now, onto the words on the remaining slides. These fall into two main categories. First, many talks include slides with bullet lists, or multiple full sentences. Sometimes these slides summarize the talk structure or sum up the conclusions. I have heard all the arguments about how these slides help guide the audience through the structure of your talk and clearly present the conclusions. There are at least two problems with these slides, however. The first is that speakers often read the lists or sentences. I believe this causes everyone’s comprehension of the subject to slow down. We read quickly, but we speak slowly. You therefore generate a conflict in the minds of the audience members by asking them to do both. Instead of asking them to think about an important issue, you are forcing them to artificially slow down their reading so that your words match their perception of the written words. So, not only have you probably not communicated your point to the majority of the audience, but you have insulted their intelligence to boot (they know how to read!). The second problem is that a well-organized talk really doesn’t require written signposts. These summaries are a crutch that contributes to making science talks clunky and boring.
In the second category of problematic-words-on-slides are titles for each slide. Many instructional materials on "how to give a good science talk" promote the use of titles on slides. The vast majority of science talks currently include slide titles. It seems that slide titles are currently the "industry standard" and accepted as an excellent way to communicate relevant information about the real information (the data) in the slide. We are all victims of this training—I was too, until recently—and I strongly encourage you to break the habit. Slide titles are a poor replacement for clearly stating the point with words. Often, titles purport to “describe” the content of the slide. About half the time these titles are cryptic, however, and simply describe the topic of the material presented in the slide. Since you are presumably talking about this topic, the title is redundant and the audience may have read the title and ignored you while you were speaking. The other half of the time, titles state the conclusion of the experiments presented in the slide. Some will read this conclusion and ignore what you say about the experiments, or worse, they will allow the title to color their interpretation of the data you present in the slide. Never write what you think the conclusion is. It is far better to guide the audience through the data—engage them with the material—and lead them to the conclusion. I explore this topic in further detail in Principle 3: Show Your Data. For now, just delete the titles.
Some words on slides are useful. Citations to previously published work are efficient ways to point the audience to some of the relevant literature. Keep it short, though. Usually the first author, date and journal title are sufficient to allow the audience to track down the reference. Other useful words include labels on figure axes and labels of graphical items. Avoid abbreviations. Use fully spelled out words whenever possible to simplify audience comprehension.
I commonly hear two reasons in support of putting words on slides, including titles and bullet lists. First, I have heard that many people recommend putting a title on the slide because it helps orient audience members who may have lost track of the thread of the talk. Hmm. Really? You are going to start with the assumption that the audience became distracted and lost your meaning? So, a title is really your confession that you are giving a boring talk and people are losing track? We can’t accept this assumption. Since we are going to help you give a non-boring talk, let’s start with the opposite assumption. People will be riveted by what you are saying. Nobody will lose track. And titles are therefore both redundant and distracting.
The second reason I hear is that words on slides help the speaker to remember what they intended to say. This excuse relates to many principles that I will discuss in the future. But let’s start with the basic issue of remembering what you want to say. All Powerpoint-like systems provide Presenter Notes that you can use to provide notes to yourself about what you want to say. This way, you can read what you want to say, but the audience has the impression that you are talking directly to them and not reading from your slides. This is an extremely helpful crutch as you learn to give better talks. Also, it is perfectly fine to write key words or sentences on index cards or a sheet of paper and look at your notes to remind yourself what you intended to say. Eventually, you will find you need these notes less and less. Later, we will discuss some of the other principles that are related to this same issue, like Practice, Practice, Practice and Don't Tell The Audience Everything. We will get to these principles in good time. For now, delete the words from your slides and put them in the Presenter Notes or write them down. You will discover that your audience will immediately start paying more attention to you, since they won’t spend any time reading your slides, which is exactly what we want them to do.
I can think of only one exception to the Don’t Put Words on Slides principle. The only time I have seen this done with any success was when an extremely engaging speaker read a quote from a book that was printed on the screen. We read along with him (silently) and it felt like a game. Even though we could have read ahead, we all read together as if we were a silent chorus. Like all successful exceptions, however, this works only when it is an exception! It breaks the rhythm of the presentation and invites the audience to participate as a community.
So, if you can’t put words on slides, what are the slides for? Now we are getting somewhere! We will revisit the content of slides later. But, for now, just put information that is communicated better with images than with the spoken word. This is really the underlying reason for the Don't Put Words On Slides principle. In other words, use your speech to explain things that can be explained most clearly and efficiently with speech and use your slides to communicate things that cannot be explained efficiently with words. You could try to explain the Mona Lisa to someone with words, or you could just show them a picture. In contrast, when first introducing what you do, just say it. And when you say it, make absolutely sure that there is nothing visible that will distract the audience from your words. Then, they will understand you perfectly.
Some readers may have noticed that the Don't Put Words On Slides principle hews closely to principles espoused by Edward Tufte. See, for example, his take on the problems with PowerPoint. Also see Peter Norvig's brilliant parody of Abraham Lincoln's Gettysburg Address employing PowerPoint.
That’s it for Principle 1. As I have intimated, we will return to the words on slides issue later. All of these principles are related, so I will often refer back to earlier principles and forward to principles that we have not yet discussed.