By Althea Need Kaminske

After reading a summary of the research on highlighting I became an adamant anti-highlighter (1). I mean, it was worse than re-reading in some cases. Re-reading. The standard control in memory experiments. The literal least you could do to qualify as “engagement” with material. When I present this information to students, however, I usually hedge my bets and state that highlighting is the first step in a series of study habits. It can be useful, for example, if you are highlighting terms that you would like to make flashcards out of so you use retrieval practice. But if highlighting is all you are doing you should expect very little gains in actual learning or understanding.

I was somewhat surprised, then, when students in my Research Methods class wrote a fairly compelling literature review in defense of highlighting. One of the articles they brought to my attention was Yue, Storm, Kornell, & Bjork (2015) (2). While this research isn’t exactly a ringing endorsement for highlighting (even the best performing condition only got 47% correct), it does provide an example of when highlighting can help so I think it’s worthwhile to take a closer look at this experiment.

Before explaining what happened in the experiment, let’s review the potential pros and cons of highlighting. The cons that I am most familiar with center around issues of metacognition. Highlighting draws our attention to the highlighted word, making it easier to read. The concern is that ease of reading can be interpreted as ease of knowing. That instead of thinking, “oh, that was easy to read” we think, “I must really know/understand this concept.” This is referred to as an illusion of knowing (3). This illusion of knowing might then prevent a student from taking appropriate steps to improve their knowledge, i.e. engage in effective study habits, because they think it’s unnecessary to continue studying.

Why might highlighting help students learn? One argument is that the act of choosing what to highlight may cause students to process the text a deeper level than if they had simply read it without highlighting (4). Another argument is that the main benefit of highlighting happens during re-reading of the highlighted text. By making the words stand out in a different way on a repeated, and likely spaced, reading the highlighting could provide some sort of context variability (2). Encountering information repeatedly in slightly different contexts typically improves memory (5).

To better understand when highlighting might help learning, Yue and colleagues compared highlighting vs not highlighting over spaced or unspaced re-readings of a text (2). There were four main experimental groups: highlighting with no spacing, highlighting with spacing, no highlighting with no spacing, and no highlighting with spacing. Students read a text and were instructed to either highlight as they normally would, or not highlight and simply read the text. Students then either re-read the text immediately after (no spacing) or were given another task for 30 minutes then asked to re-read the passage (spacing). Student’s recall of key words in the text was tested one week later.

Somewhat surprisingly, students in the highlighting and no spacing group, recalled the most one week later (about 45% of the key words). Students in the no highlighting and no spacing group recalled the least (about 30% of the key words). Almost equally surprising, there was no difference in recall between highlighters and non-highlighters in the spaced conditions (both were around 35%). The authors pointed out that the research on the spacing effect is very well demonstrated, so it is unlikely that spacing does not improve memory as this result might suggest. Instead, they noted that there is already spacing inherent in a text. A well written text will refer back to ideas previously presented in the text, creating spacing between concepts within the text. The text that students read in this experiment was long enough that a few minutes could pass between spacing of concepts (it was 856 words long and students were allowed 6 minutes to read it). This means that when dealing with longer texts it’s difficult to create a perfectly non-spaced condition.

Again, my strong anti-highlighting stance compels me to point out that 45% is not great. But, it is better than 30%. The authors attributed this boost to memory to the idea that choosing what to highlight led to deeper processing. To further investigate this hypothesis they compared “heavy highlighters” versus “light highlighters” within their sample. They found that light highlighters remembered proportionally more key terms than heavy highlighters (41% vs 39%). Students who were more selective about what they highlighted recalled more than students who over highlighted. This supports the idea that highlighting can lead to deeper processing if it forces students to be selective about what to highlight. This is also supported by research showing that students who receive training in how to highlight (i.e. read the text first, then decide what the key concepts are and highlight on a second pass) perform better than students who do not receive training (6).

So, should you use highlighting while studying? I stand by my advice to never use highlighting as the ONLY means of studying. However, based on this research I can see more utility for using it as the first pass at understanding material. If you are going to use highlighting (even I can admit to a certain amount of joy from purchasing new brightly colored highlighers), then research suggests that there are some highlighting best practices. Namely, be selective about what you highlight. To do this it might be best to hold off on highlighting until you’ve had a chance to read the entire passage or text to better understand what the main ideas are (6).

References

(1) Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students’ learning and comprehension: promising directions from cognitive and educational psychology. Psychological Science in the Public Interest, 14, 4-58.

(2) Yue, C. L., Storm, B. C., Kornell, N., & Bjork, E. L. (2015). Highlighting and its relation to distributed study and students’ metacognitive beliefs.

(3) Bjork, R. A. (1999). Assessing our own competence: heuristics and illusions. In D. Gopher & A. Koriat (Eds.), Attention and performance XVII. Cognitive regulation of performance: interaction of theory and application (pp 435-459). Cambridge: MIT Press.

(4) Nist, S. L., & Hoegrebe, M. C. (1987). The role of underlining and annotating in remembering textual information. Reading Research and Instruction, 27, 12-25.

(5) Smith, S. M., Glenberg, A., & Bjork, R. A. (1978). Enbironmental context and human memory. Memory & Cognition, 6, 342-353.

(6) Leutner, D., Leopold, C., & Den Elzen-Rump, V. (2007). Self-regulated learning with a text-highlighting strategy: a training experiment. Zeitschrift Fur Psychology/Journal of Psychology, 215(3), 174-182.