Abstract

Languages have a rhythmic structure, have (morpho)syntax and the two are somehow related. Why? In this paper, we attempt to provide an answer to this question based on experimental evidence from language impaired individuals and controls. Briefly, our answer is that rhythm and syntax allow humans to generate predictions concerning the incoming input. In turn, this ability reduces memory load through the pre-activation of the sensory system and allows one to anticipate abstract representations.

In Pagliarini et al. (2015), we showed that children with Developmental Dyslexia (DD) fail to comply with two rhythmic principles of the handwriting: (1) The principle of isochrony (Binet & Courtier, 1893; Stetson & McDill, 1923; Viviani & Terzuolo, 1982) which states “that the speed of movement execution is proportionally related to the length of its trajectory in order to keep the movement duration approximately constant” and (2) “The principle of homothety (Lashley, 1951; Viviani & Terzuolo, 1982), which guarantees the invariance of the relative duration of a movement’s components under a number of possible variations in the duration of the very same movement. While typically developing (TD) children were able to maintain the same global and relative duration constant across conditions, children with DD varied,as shown in figure 1.

We also found that the ability to satisfy the two rhythmic principles of handwriting is correlated with reading measures, non-word repetition. In Pagliarini et al. (2017), we showed that TD children from grade 1 are able to comply with the two rhythmic principles of handwriting. This suggests that their acquisition does not require a lot of training. This fact also allow us to discard the hypothesis that the weakness of children with DD is not due to lack of practice, as younger children with little practice have no problem. The two studies together suggest that children with DD have problems with the temporal organization of events, with rhythm. Rhythm is useful to predict future events. Then, we expect that children and adults with DD have problems in anticipating future events. To test this hypothesis, we carried out an experimentwith 18 adults with DD along with 20 controls. We engaged participants in a task requiring entrainment to a given rhythm and tapping in synchrony with a beat. We found a significant group difference in the predictable condition. Controls were synchronous or anticipate the beat, whereas participants with DD display a tendency of tapping after the occurrence of the beat. In the unpredictable condition, Group was not significant, as participants from both groups responded in response to the beat (i.e. reaction time). Interestingly, participants with good predictive skills were also faster in reading. These results are in line with another finding from the literature provided by Huetting & Brouwer (2015). These authors engaged adults Dutch individuals with DD in an eye-tracking experiment measuring whether they were able to predict an object based on morphosyntactic features of the article. Shorter latency were observed in controls than in adults with DD. Persici & Arosio (in prep) replicated this finding with Italian children with DD. In conclusion, languages display a rhythmic structure that allows individuals to predict incoming linguistic events; similar, morphosyntactic features are used to anticipate the incoming structure and generate an abstract representation used to accommodate the input. Individuals with DD have problems in predicting or in extracting regularities.