Why Your Students Forgot Everything On Your PowerPoint Slides

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Don’t fret, we’ve all been there: You’re up late the night before Thursday and you have to teach a lesson at 8 AM the next day. So, what do you do? Throw some text on a PowerPoint and get ready to talk through your points. Couldn’t hurt, right? You might not always read straight off of the slides—they’ll just help keep your lecture on track, and if you lose your place, the text is right there for you.

Unfortunately, whether you’re discussing Columbus with 4th graders or quantum physics with college freshmen, you may be hurting your students’ learning more than helping them.

Let’s explore why instructional design doesn’t typically work with students, or anyone’s learning for that matter, when you teach with PowerPoint—as well as how you can avoid it. It all begins with a little concept called “cognitive load.”

Too Much for the Student to Process

Imagine your student’s brain as a container. When you start tossing rocks into the container, it gets heavier and heavier—and more difficult for the student to carry or sort through. Essentially, that’s cognitive load. Cognitive load describes the capacity of our brain’s working memory (or WM) to hold and process new pieces of information. We’ve all got a limited amount of working memory, so when we have to handle information in more than one way, our load gets heavier, and progressively more challenging to manage.

In a classroom, a student’s cognitive load is greatly affected by the “extraneous” nature of information—in other words, the manner by which information is presented to them (Sweller, 2010). Every teacher instinctively knows there are better—and worse—ways to present information. The reason for these, research shows, is that when you lighten the load, it’s easier for students’ brains to take information in and transform it into memory.

Teaching with text-based PowerPoint slides while also reading them aloud, unfortunately, amounts to throwing too many rocks into the student container—and potentially causing students to regress.

The Redundancy Effect

Simultaneous auditory (spoken) and visual presentation of text, often done through PowerPoint presentations, is an all-too-common occurrence in classrooms nowadays. Think about it: How many times have you walked into a classroom or lecture hall and heard a teacher reading out the text on slides displayed on the front board?

A study in Australia in the late 1990s (the 1999 Kalyuga study) compared the learning achievement of a group of college students who watched an educator’s presentation involving a visual text element and an audio text element (meaning there were words on a screen while the teacher also talked) with those who only listened to a lecture, minus the pesky PowerPoint slides. The researchers concluded that utilizing visual stimuli involving words while a separate auditory presentation is delivered increases the cognitive load, rather than lessening it.

It’s called the the redundancy effect. Verbal redundancy “arises from the concurrent presentation of text and verbatim speech,” increasing the risk of overloading working memory capacity—and so may have a negative effect on learning.

Consider, for instance, a science lesson on food chains. A teacher may start by lecturing on the difference between herbivores and carnivores. Up comes a slide with definitions of each term. The teacher starts reading directly from the slide. The duplicated pieces of information—spoken and written—don’t positively reinforce one another; instead, the two flood students’ abilities to handle the information.

Researchers including John Sweller and Kimberly Leslie contend that it would be easier for students to learn the differences between herbivores and carnivores by closing their eyes and only listening to the teacher. But students who close their eyes during a lecture are likely to to called out for “failing to paying attention.”

How to Lighten the Load

So, then, what do you do? How do you ensure that your kids learn from your lectures rather than wind up with brains that feel like oversoaked sponges? (And keep in mind, entrepreneurs—this could apply to your product pitches as well.)

Richard Mayer, a brain scientist at UC Santa Barbara and author of the book Multimedia Learning, offers the following prescription: Eliminate textual elements from presentations and instead talk through points, sharing images or graphs with students. This video illustrates exactly what he means:

This approach, he suggests, is particularly appropriate for those subjects where geometric graphs and visual imagery are crucial for understanding key concepts, like food chains, the water cycle or calculating surface area.

Other studies, such as a separate Australian investigation by Leslie et al. (2012), suggest that mixing visual cues with auditory explanations (in math and science classrooms, in particular) are essential and effective. In the Leslie study, a group of 4th grade students who knew nothing about magnetism and light learned significantly more when presented with both images and a teacher’s explanation than a separate group which received only auditory explanation.

Are you a science teacher? Throw up a picture of a lion’s tooth and a zebra’s tooth onto the screen while explaining the differences between carnivores and herbivores. Teach social studies? Surround the number “1776” with painted images of the founding fathers signing the Declaration of Independence, rather than including straight facts on your presentation.

And if you find it difficult to eliminate words entirely from your PowerPoint presentations, especially when you want students to get those key vocabulary words down, here are some additional hints:

  • Limit yourself to one word per slide. If you’re defining words, try putting up the vocabulary word and an associated set of images—then challenge students to deduce the definition.
  • Honor the “personalization principle,” which essentially says that engaging learners by delivering content in a conversational tone will increase learning. For example, Richard Mayer suggests using lots of “I’s” and “you’s” in your text, as students typically relate better to more informal language.

Have a favorite theory-backed practice that works for your students? Leave your comments below—I’m all ears. And eyes.

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