Saturday, January 14, 2012
Most students, at one time or another, have crammed for an examination. Researchers refer to this as massed trials, where objects of learning are studied all at the same time in one session. Students may be forced to cram because they have procrastinated or did not have a regular, organized, and disciplined approach to study. Non-students may cram too, as in lawyers briefing a case, speakers rehearsing a speech, professors preparing a lecture, salesmen practicing a pitch, and so on.
In most situations research has made it abundantly clear that spacing the learning over many shorter sessions is much more effective than trying to do it all in one big session. Surprisingly, longer intervals between learning sessions are more effective than shorter intervals. For example, one study of students learning foreign-language words found that recall was highest at 56-day intervals as opposed to 28-day or 14-day intervals. The total amount of study time was cut in half: 13 sessions spaced 56 days apart produced comparable recall as 26 sessions with a 14-day interval.
Unfortunately, most academic courses are not designed to support longer study intervals (perhaps educators need to re-think how things are done). Not enough studies have been performed to examine which spacing protocol works best for certain kinds of learning tasks, but it is clear that massed trials are not efficient.
Why spacing makes such a big difference is not understood either, but it does have to do with basic biology. A recent study on seal snails, of all things, showed that the gene expression underlying long-term memory was affected by how five training shocks were spread out over time. Compared with a control test where snails got five shocks at 20-minute intervals, the most effective pattern (developed by computer model) was to give three shocks at 10-minute intervals, followed by a fourth at five minutes later and the fifth shock 30-minutes later.
There is no reason to think this protocol is optimal for humans learning a variety of tasks. But it does help make the point that spaced learning is more effective and perhaps irregular intervals might be better than evenly spaced ones.
Why does spacing work? Two ideas prevail. One is that in massed trials, there is not much time for each presentation to be processed in context. In spaced trials, each learning presentation occurs in a slightly different context, thus providing many more implicit cues that can be unconsciously accessed during retrieval attempts.
Finally, a host of recently reported studies show that each time you are re-exposed to a learning object, the memory is re-consolidated. Successive consolidation events reinforce each other. Multiple consolidations do not occur in massed trials because consolidation takes many minutes or even hours.
Given what I have explained elsewhere on the benefits of self-testing, I suspect that spaced learning would be optimized if the learner self-tested first during each rehearsal session and then checked the recall against the original learning material.
Bahrick, H. P. et al. (1993). Maintenance of foreign language vocabulary and the spacing effect. Psychological Science. 4 (5): 316-321.
Zhang, Y. et al. (2011). Computational design of enhanced learning protocols. Nature Neuroscience. Published online Dec. 28, doi: 10.1038/nn.2990