Children's first handwriting productions show a rhythmic structure

Abstract

Although much research has been concerned with the development of kinematic aspects of handwriting, little is known about the development along with age of two principles that govern its rhythmic organization: Homothety and Isochrony. Homothety states that the ratio between the durations of the single motor events composing a motor act remains invariant and independent from the total duration of the movement. Isochrony refers to the proportional relationship between the speed of movement execution and the length of its trajectory. The current study shows that children comply with both principles since their first grade of primary school. The precocious adherence to these principles suggests that an internal representation of the rhythm of handwriting is available before the age in which handwriting is performed automatically. Overall, these findings suggest that despite being a cultural acquisition, handwriting appears to be shaped by more general constraints on the timing planning of the movements.

Figure 1

Homothety. The Condition (Spontaneous, Big, Fast) x Letter (b, u, r, l, e) (all-capital block script: Panel a; cursive: Panel c) and Group (G1, G2, G3, G4, G5) x Letter (b, u, r, l, e) (all-capital block script: Panel b; cursive: Panel d) interactions are shown for the percent duration taken to write each letter. Vertical error bars represent 95% confidence interval.

Figure 2

Isochrony. Panel a reports the log-log plot (natural logarithm) of the word duration (sec) as a function of its length(cm). Panel b reports the log-log plot (natural logarithm) of the mean velocity (cm/sec) as a function of its length. Subpanels on the left represent all-capital block script data, subpanels on the right depict cursive data. All log-log plots were computed on the entire dataset, thus including the five groups of participants all together and the conditions Spontaneous, Big, and Fast.

Figure 3

Isochrony is invariant across school grades. The log-log plot (natural logarithm) of length (cm) against mean velocity (cm/sec) is reported for each group of children - when writing in block and cursive scripts. Each data point represents the word burle written in one of the experimental conditions (Spontaneous, Big, and Fast) by each individual participant. In line with Isochrony, the mean velocity presents a strong positive correlation with the linear extent of the corresponding trajectory for each group of children.