APROXIMACIONES AL CONCEPTO DE LITERATURA INFANTIL

The second set of analyses entailed a comparison of the groups of children and adults with WS with three groups o f TD children representing a cross-section of the typical

developmental trajectory. Interestingly, in the analysis o f overall differences in reaction

time, children with WS turned out to be slower than all the other groups. These findings

suggest that for children with WS, the task of magnitude comparison required particular

effort. On the basis of initial visual inspection o f the results, it was decided that the difference between WS children and adults needed to be contrasted with the difference

between the groups of 4-5 and 9-10 year old TD children. This analysis revealed that all

groups exhibited an effect of distance and that this did not interact with group or

development. However, a small 3-way interaction effect of the three independent variables (group, development and distance) on reaction time was found. Post-hoc

analyses revealed that the locus of this interaction was a difference in the effect of

development on the distance effect in the two groups. While in the two groups of TD

children there was a clear decrease in the effect of distance on reaction time, no such

difference was found between the groups of children and adults with WS. The data from

both groups of WS participants were highly noisy with response time distributions overlapping between the groups.

One might interpret this three-way interaction as an indication that, unlike for typically developing children, development does not involve significant changes in the effect of

distance on reaction time in WS. This suggests an atypical developmental trajectory of non-verbal magnitude representations in WS compared with typical development for

reaction time data. It also suggests that the differentiation between mental magnitudes that appears to characterize the typical developmental trajectory seems to be arrested in

WS (Sekuler & Mierkiewicz, 1977). From the perspective o f the neural coding o f relative numerical magnitude, it may be the case, that the kind of neurons in the prefrontal cortex,

recently discovered by (Nieder et al., 2002), have highly undifferentiated response properties and have broad tuning filters in individuals with WS, making them respond to

a larger number of numerical magnitudes than is true of typically developing individuals, which could explain why magnitude comparisons are so slow and effortful for individuals

with WS.

In a similar way as for the findings from the comparison of the WS groups with their individually matched controls, the results obtained for accuracy differed slightly from the

reaction time data. Here, no significant differences were found in terms o f total number

of errors between children with WS and 4-5 year olds, nor between adults with WS and

the group of 9-10 year old TD children. Furthermore, while a significant main effect of

o f distance on accuracy did not differ significantly between groups. In addition, the

significant development X distance interaction suggests that in both groups the effect of

distance decreased as a function o f development. These findings imply that, at least in terms o f accuracy, the developmental trajectory in WS, while delayed, appears to follow

the developmental trajectory observed among TD children.

However, the difference in the results of the reaction time and accuracy data points to the

possibility that the mechanisms underlying developmental change in WS may differ from

those underlying typical developmental changes. The reaction time data showed that the decrease in the effect of distance on reaction time in WS was not as strong as in the case

o f TD children. This result may indicate that, for individuals with WS, the noise in the

underlying representations does not change substantially over developmental time. In light of this interpretation, the changes observed for the accuracy data suggest that

individuals with WS develop strategies to discriminate successfully between their noisy

representations o f magnitudes, thereby yielding increases in accuracy over developmental time that are similar to those observed between the groups of 4-5 and 9-10 year old TD children.

It should be noted, however, that alternative interpretations are also possible. It might be

that the accuracy data are more reliable indices of the quality and developmental changes o f the underlying representation o f numerical magnitude, because the reaction time data

in the groups of children and adults with WS are highly noisy. This interpretation is supported by the inspection o f individuals’ data (presented in Appendix B) where it is

clear that for both control and WS groups the accuracy data are less variable (in terms of

the direction o f the distance effect) and therefore may be construed as a more reliable

measure.

From the current data, it cannot be clearly stated which o f the above interpretations is

correct. However, it is interesting to note that the difference between reaction time data

and accuracy data is only apparent for the groups o f individuals with WS and not for the

observed in the groups o f young TD children (matched controls and 4-5 year olds). This

suggests that this difference in WS does indeed have a functional role and is indicative of

a developmental deviance in this clinical group.

Taken together, the present findings suggest that the developmental trajectory of

magnitude comparison abilities in WS differs in subtle ways from the developmental

trajectory observed among TD children. However, the findings raise a number of

questions that cannot be answered by the current results. A number of potential future studies, arising from this work are addressed below.

5 .5 .3 Individually m atched control analysis and comparison o f