The rub is that working memory has very limited capacity - maybe 3 or 4 chunks at a time. That feeding tube of information from our mouths to our learners' long-term memory has to be threaded through the eye of working memory's needle.
Since Alan Paivio's work in the 1970s, it has become widely accepted brain science that we receive and process new visual and verbal information through 2 separate but related channels:
- The visual channel and
- The verbal channel.
So, PowerPoint is great, right? It works the visual channel while we talk and work the verbal channel. Not really. Text on a screen is visual but working memory quickly verbalizes written words and sends them through the verbal channel. As you are reading this you are undoubtedly hearing the words in your head.
That means text on a PowerPoint slide competes with and distracts from what you're saying. But, you say, if I'm simply reading the text aloud, there's no competition. Maybe not, but if all you're going to do is read your PowerPoint slides aloud save everyone time and just email the presentation to your learners. There's also the redundancy effect problem.
The redundancy effect
We process verbal information at a different speed than visual. Working memory converts visual text into verbal information, but it's being processed at a different speed than the speaker's voice reading the text. Ever watch a movie where the sound was out of sync with the video? It's distracting and harder to follow. That's what happens when presenters read their PowerPoint slides. Learners may not be aware of why they're frustrated like they would be if the movie was out of sync, but they're frustrated and out of kilter just the same.
Richard Mayer (web link below) conducted an experiment well-known in the brain science world that investigated the redundancy effect. One audience viewed a multi-media presentation in which the same material was both narrated and appeared as text on a screen. The second audience heard the same narration but the redundant text was removed.
Contrary to conventional wisdom and practice, removing the text improved learning. The second audience retained 28% more information and was able to apply 79% more creative solutions using the information than the first audience.
First kill all the PowerPoint
To paraphrase gun advocates,
Presenters kill learning.
PowerPoint can help listeners learn, retain and apply information - if it is used with the science of how we learn in mind.