T. R. Girill
Technical Literacy Project
trgirill@acm.org

Introduction

Those giving professional technical talks usually accompany their oral presentation with slides--plastic or projected text/image combinations that reinforce and support their spoken words. Effective slide design addresses the same usability issues with the same empirically grounded communication principles as does any report. But since talks involve coping with special constraints (as explained in "Teacher Analysis of Technical Talk Tips"), good slides meet the extra design criteria listed on the "Simple Tips" chart. This commentary gives instructional background on each of those extra, slide-specific communication techniques.

Commentary on Each Slide Tip

Title Sentence

Begin each slide with a headline sentence, not just a topic phrase. Examples: Drosophila [bad; too vague] Drosophila Hmx gene [bad; so what?] Drosophila Hmx gene directs mouse inner-ear development. [good; asserts an interesting claim]

Most people label their slides only with a word or phrase title, such as

Drosophila, or
Drosophila Hmx Gene

Drosophila Hmx gene directs mouse inner-ear development

Beginners often find that coming up with a verb, a full sentence for every slide, is very annoying. But it is a great usability check: if you can't say in a simple sentence what point your slide makes, perhaps it doesn't really make any point (or maybe it makes several points, which should be split among separate slides for clarity). Doing this homework before giving a talk forces a speaker to thoroughly understand just what claims they are trying to advance. For example, this slide probably meant something to its author but this alternative version, with a sentence title, unambiguously reveals the message to every viewer.

Sentence titles can be preceded by milestone cues (such as "Procedures:" or "Second Problem:") to further signal topic transitions to the audience. Also, sometimes splitting a long title-sentence across several consecutive slides ("The three causes are (1)...(2)...(3)") can visually tie their related content together.

Easy Reading

Use large fonts and simple layout for easy reading. Rules of thumb: Use no more than 8 words/line, 8 lines/slide maximum. Can you read it easily if you stand over it on the floor?

A striking and historically important example of these visibility rules is the slide that influenced the decision to launch the ill-fated 1986 Space Shuttle Challenger when the temperature was only 26°F. (This image is freely available from NASA's own archive at http://history.nasa.gov/rogersrep/v4p664.htm) This data-rich slide is almost impossible to interpret effectively because it has:

1. Too many words.
   Most lines on the NASA slide have 11 or 12 words, 50% more than the easy-reading limit of 8.
2. Too many lines.
   Even ignoring the many footnotes, this slide has 14 lines, 75% more than the easy-reading limit of 8.
3. Font too small.
   Students can quickly confirm that no one can read this slide by standing over it and viewing it on the floor at one's feet.

Even with a much bigger font (and hence many fewer words), the Challenger slide would still conceal crucial relationships and trends. The date (and hence the temperature) of each launch (each row in the table) is only handwritten along the left edge of the original, adding to the poor visibility and conceptual confusion.

How can one possibly display so much data on one slide given the severe constraints imposed by these visibility rules of thumb? Forget using (mostly) text and instead try a thoughtful, relationship-revealing graph. Edward Tufte, for example, developed a clever scatter plot to do this (p. 45 in his Visual Explanations, also freely mimicked online in many places including here; but note that it too lacks a sentence title). "Like magicians," Tufte explains, "chartmakers reveal what they choose to reveal" (p. 43). His plot meets audience needs (to "see" the key relationship between launch temperature and o-ring damage) in a way that the original text-heavy version never could. This example thus leads directly to the next cluster of slide tips.

Revealing Images

Choose images carefully not to decorate but to reveal complex details, comparisons, examples.

With slides as with illustrations inside written technical reports, integrating explanatory text with relevant images can help the audience understand the technical content if:

1. The images are "working visuals" chosen for their own explanatory, not decorative, value.
2. The speaker applies the same usability standards to the images as to the text. Irrelevant or confusing diagrams too small to see (or with fake perspective) will not improve any slide's effectiveness.

Students should especially look for (or create) slide images that

• show complex details rather than just describe them in words (for instance, the skeleton picture on the previous (bad) example slide could helpfully show trabecular bone locations, if the relevant bones were clearly labeled),
• reveal comparisons, contrasts, or relationships (for instance, the difference between young and old trabecular structure within large bones), and
• offer visible examples of new (to the audience) technical terms, procedures, distinctions, or results (for instance, an illustration of the cortical/trabecular definitions).

Sequencing

Consider progressive disclosure when sequence is important (sticky notes can help here).

In some technical talks, carefully managing the order (or rate) at which the audience sees new information (even within one slide) greatly contributes to their focused attention or participation. Milestone cues ("first...second...") are a step in this direction. Layering slide content goes even further by

• covering parts of a slide with large (3-by-3-inch or 4-by-6-inch) sticky notes, so that the audience sees some material at once but other content (examples, comparisons) appears only later, when the speaker removes the cover, or
• placing parts of the content on different transparencies and then (gradually) stacking the literal layers to build up a composite view of all the text and pictures (good for revealing a table row by row, for example), or
• using slide-management software (such as Powerpoint) to simulate either of the above techniques with (perhaps time-delayed) sequences of electronic images.

Tufte's Software Warning

Slide-management software, such as Microsoft Powerpoint, is widely used. Careless design with it, however, can promote intellectual confusion or even audience deception. Some students will find Edward Tufte's famous short article claiming that "Powerpoint is Evil" a helpful alert about thoughtful software use. In science, Tufte's conclusion is certainly true: "presentations largely stand or fall on the quality, relevance, and integrity of the content."