Carpe Noctem: Is it Time for Chronolinguistics?

Williams, S. E., & Horst, J. S. (2014). Goodnight book: Sleep consolidation improves word learning via storybooks. Frontiers in psychology5. (open access)

A few months ago, I read a wonderfully-written and informative book called Rest by Alex Pang. Pang reviews recent research on the benefits of taking breaks, napping, and sleeping on learning, creativity, and productivity.

So when Jessica Horst (whose work on storybook reading I discussed here) sent me a fine paper she and her colleague did on sleep and vocabulary acquisition, I finally had an excuse to look more closely at the “sleep literature” as it relates to language acquisition.

Williams and Horst studied the effects of a napping and sleep on word acquisition by a group of three-year-olds. In previous studies, Horst and colleagues had determined that young children (three-year-olds) acquire more novel words when the words appear in stories that are re-read to them than when they appear in different stories.

In other words, young children acquire more words when their parents do precisely what they request them to do: read the same story over and over again.

The researchers extended this work to see whether napping soon after storybook reading would improve recall and retention of novel words. Forty-four three-year-old children in nurseries and pre-schools were assigned to one of four different conditions:

  1. Listen to the same story three times + take a nap
  2. Listen to the same story three times + no nap
  3. Listen to three different stories + take a nap
  4. Listen to three different stories + no nap

All the stories contained the same novel words, and the nap/no nap condition was based on the child’s current preferences – that is, kids who had stopped taking naps were assigned to the “no nap” group, and the kids who still regularly napped were put in the “nap” group. The novel words (pseudo-words) were not explained to the children explicitly. The children were tested immediately after they heard the stories and then again at intervals of 2.5 hours, 24 hours, and seven days.

As had been found in their previous studies, hearing the same stories read three times resulted in more vocabulary gains than hearing three different stories (.73 versus .38; chance = .25). But the big news is the effect of the nap: napping increased retention for both the same-story and different-stories groups.

The same-story group’s scores increased from .67 to .92, and the different-stories group from .38 to .71. These gains were maintained (or slightly increased) at 24 hours and seven days.

Both no-nap groups got worse at the 2.5 hour mark, but the kids who were read three different stories never recovered, scoring just .25 at the seven-day post-test. The no-nap same-story group managed to hold on to gains, though their scores also declined from the 24-hour to seven-day post-tests (from .87 to .625) (all from Table 2, p. 6).

The differences between napping and not napping after the storybook sessions were dramatic, especially in the retention scores. Does this mean we should all start brushing up on our French right before we nod off at night?

There have been several studies of older children and adults on word learning (both pseudo-words and bilingual lists) and sleep, and all of them have found improvements in retention after napping (Lahl et al., 2008) and sleep (Brown et al., 2012; Dumay & Gaskell, 2012; Gais et al, 2006; see also Walker, 2005). The drawback of these studies is that the word learning is all intentional: subjects are asked to memorize a set of novel words and then are tested after napping or sleeping.

What makes Williams and Horst’s results so intriguing is that they have shown that retention is better for incidentally acquired words as well, at least for young children. Since most of our vocabulary is acquired incidentally, this is an important advance in our knowledge – more so than I think the researchers themselves realize, as they don’t seem to distinguish between incidental and intentional word acquisition in their discussion.

For second language acquirers, we know that words learned intentionally through bilingual word lists or classroom instruction are forgotten more quickly than words acquired through incidental exposure (see McQuillan, 2016, for a brief review of some these studies). As such, a better test of the napping/sleeping effect for adults would be do to “read-and-test” design, with acquirers reading a text with novel words, having a (surprise) vocabulary test on the words, and then being re-tested seven days later. One class could be a night class, the other an early morning class.

We already have a body of research in “chronomedicine” and “chronobiology.” Perhaps the time has come for chronolingustics?

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