Put simply, the illusion of truth is that we (by which I mean people!) have a tendency to belief/trust those things which are familiar. It doesn’t have to be true for that to work, we just have to remember it. For example, I often say (and hear other people say even more!) “I can’t remember where I heard this, but…” and then out comes some half-remembered fact that may or may not be true.
In fact, we might be remembering it particularly because it was such tosh that it’s stuck in our heads – but we’ve not necessarily remembered that context.
Publishing in the Journal of Experimental psychology, Ozubko and Fugelsang carried out a series of ingenious experiments to find out what people remembered and trusted, compared to how many times they’d heard the fact before. The experiments are a bit too complicated to describe here, but the results are pretty straight-forward. We trust what’s familiar. What’s more, it turns out that we don’t even have to hear something several times to trust it – we can be convinced by something that we’ve only heard once, but have had to recall from memory a few times!
What that means in terms of how you can design your presentations is obvious.
- Repeat yourself – not to the point of boring your audience of course, but enough to give them a sense of familiarity with the material
- Provide an overview slide or handout at the start, so that the audience recognises the ‘chapters’ of your presentation when they get to them… even if it’s just the name!
- Pre-teach – provide some introduction material before the presentation, so that some key concepts are familiar to the audience before you start your presentation. There’s some research evidence that something as simple as providing a glossary of acronyms and jargon is helpful in your presentations
- Build on others – find ways of linking what you’re saying to other presentations the audience might have just heard (where it’s relevant, obviously!)
- Refer back to things – and even flash back in your slides to previous materials. You might not want to jump around your slides (that’s easy, by the way!) but there’s no reason to not have a copy of a slide later in your presentation. Or what about a slide with several previous slides stuck on them as though they were pictures?
- Ask questions – these might be interactive or rhetorical, but they should be designed to make the audience think back to something you’ve said earlier in your presentation and make the effort to recall it. “Do you remember a few minutes ago that I mentioned…?”
It’s not rocket science, is it, but the impact can be fantastic.