The positive association between age and Transfer Index (ρ = 0.428, p < 0.001), together with the significant between-age-group difference (H = 24.153, p < 0.001) and the rise in median Transfer Index from 86.60% at age 6 to 100.00% by ages 11–12 (Table 3.2), supports the broader developmental literature linking maturation of interhemispheric transfer to age. This pattern is consistent with the classic finding that tasks requiring transfer of tactile, kinesthetic, and motor-pattern information across the hemispheres show clearer age-related gains than purely perceptual transfer tasks, as reported in one of the earliest developmental studies of interhemispheric transfer in children aged five to ten (O'Leary, 1980), where motor-movement and spatial-pattern transfer tasks — but not simple discrimination tasks — showed a developmental increase in transfer efficiency. The present Transfer Index, which similarly indexes motor/tactile inter-manual transfer, aligns with that earlier observation that motor-based transfer tasks are particularly sensitive to age-related callosal change. The finding also converges with studies using the visuomotor crossed-uncrossed difference (CUD) paradigm, in which children aged 5–10 years showed a decreasing CUD with age, interpreted as reflecting increasingly efficient interhemispheric communication during the same developmental window examined here. At the same time, other work using electrophysiological and behavioural interhemispheric transfer time (IHTT) measures in 7-year-olds has found that behavioural CUD estimates can be unreliable over a 6-month retest interval and may fail to detect age effects that electrophysiological measures do detect, suggesting that behavioural transfer measures — including the Transfer Index used here — index a real but sometimes noisy developmental signal, and that convergent evidence from multiple modalities strengthens rather than substitutes for behavioural findings such as those reported in this thesis. Anatomically, this behavioural trajectory is compatible with the well-established observation that the corpus callosum, particularly its body and splenium, continues to myelinate and increase in cross-sectional area well into the second decade of life, with functional maturation broadly paralleling this structural change. The present results should nonetheless be interpreted, as emphasised in Section 3.Y.8, as evidence of an age-related behavioural trend consistent with ongoing interhemispheric maturation, not as a direct structural or physiological measurement of the corpus callosum itself. 4.Y.3 The Gap Score: A More Modest and Less Graded Age Relationship In contrast to the Transfer Index, the Gap Score showed a comparatively weak negative correlation with age (ρ = −0.245, p = 0.007) and no significant difference across the seven age bands (H = 10.604, p = 0.101), despite the descriptive trend toward lower (better) Gap Scores in older children (Table 3.2). This dissociation between a significant continuous correlation and a non-significant categorical (age-group) comparison is not unusual in developmental motor research and is consistent with reports that not all components of a multi-task interhemispheric transfer battery mature at the same rate or show the same developmental pattern; in the four-task battery used by O'Leary (1980), for example, two of the four component tasks showed no clear developmental change even though the battery as a whole was designed to tap the same underlying construct. A plausible explanation is that the Gap Score, which captures inter-manual asymmetry in bimanual tapping rather than transfer accuracy per se, may be more sensitive to trial-by-trial motor variability, attentional fluctuation, and individual differences in motor strategy than to callosal maturation alone, which would attenuate its sensitivity to discrete age-group differences even while a modest linear trend with age remains detectable. This interpretation is consistent with work on bimanual finger-tapping interference in children aged 4–11 years, which found that the percentage of inter-manual interference during a dual bimanual task did not differ significantly across four age groups even though unimanual and bimanual performance both improved with age — indicating that asymmetry/interference indices and raw performance indices do not necessarily mature in lockstep during childhood. 4.Y.4 Bimanual Coordination and Its Developmental Trajectory Bimanual Coordination scores rose steadily with age (ρ = 0.388, p < 0.001; H = 19.660, p = 0.003), from a median of 48.43 at age 6 to 61.75 at age 12. This finding is consistent with a substantial body of literature describing bimanual coordination as a late-maturing motor skill that continues to develop through middle childhood and into adolescence. A recent study using a bimanual circles–lines coupling task in children aged 5–13 years similarly reported a significant developmental improvement in independent bimanual control with age, and interpreted this improvement as reflecting maturation not only of transcallosal motor pathways but also of the fronto-parietal network and prefrontal executive control — a multi-system account that may equally apply to the age-related gains in Bimanual Coordination observed in the present sample. Other work using dual bimanual tapping-and-tracing tasks in children aged 4–11 years has likewise shown that overall bimanual task performance improves with age, even where asymmetry/interference indices (comparable in spirit to the present Gap Score) remain relatively stable — a pattern that mirrors the present study's dissociation between the age-sensitive Bimanual Coordination score and the more modestly age-related Gap Score. This convergence across independent samples and task paradigms strengthens confidence that the Bimanual Coordination measure used in this study is capturing a genuine, replicable developmental process rather than a sample-specific artefact, and supports its inclusion as a core outcome in the interhemispheric connectivity battery proposed by this thesis. 4.Y.5 Absence of Sex Differences No statistically significant sex differences were found for Transfer Index (p = 0.717), Gap Score (p = 0.661), or Bimanual Coordination (p = 0.080). This pattern is broadly consistent with prior fine-motor and finger-tapping literature in children, which has generally reported that sex accounts for little variance in tapping-based motor measures once age is taken into account; a preschool finger-tapping study, for instance, found no significant effect of gender on tapping speed, and a hand-preference study in 4- to 6-year-olds similarly found no significant sex-related differences in a fine motor tapping task. Larger population-based studies using quantitative finger-tapping and grasp-lift paradigms have occasionally detected small sex-related effects on certain sub-components of motor performance, suggesting that sex differences in fine motor and interhemispheric tasks, where present, tend to be small and outcome-specific rather than pervasive. The Bimanual Coordination comparison in the present study (p = 0.080) fell short of the conventional significance threshold but was noticeably closer to it than the other two comparisons. Consistent with the cautious framing already adopted in Section 3.Y.4, this is best treated as a non-significant trend that may warrant re-examination in a larger, adequately powered sample, rather than as either a confirmed sex difference or definitive evidence of no difference — the present study was not powered a priori for sex-stratified comparisons, which were specified as secondary and exploratory. 4.Y.6 Preliminary Age-Specific Reference Values The age-stratified values presented in Table 3.2 extend the descriptive literature on task-based interhemispheric measures by providing indicative benchmarks across the 6–12-year range for a battery that, to the author's knowledge, has not previously been reported in combination in this form for this age range. However, consistent with the terminology adopted throughout this thesis, these values are presented as preliminary reference values rather than validated population norms. Per-age-band sample sizes ranged from n = 10 (age 9) to n = 25 (age 10), which is well below the sample sizes conventionally recommended for the derivation of clinical normative data, and the sample was drawn from a single setting under a right-hand-dominance inclusion criterion, further limiting generalisability. These values should therefore be read as a preliminary developmental map to guide future, adequately powered normative studies rather than as thresholds for individual clinical interpretation. 4.Y.7 Robustness of Findings and Data-Quality Handling As detailed in Section 3.Y.7, a small number of data-quality issues (one out-of-range Transfer Index value and two missing categorical codes) were identified, verified against source records, and corrected prior to analysis. The sensitivity re-analysis excluding the originally affected observations reproduced results consistent in direction, magnitude, and statistical significance with those reported in Tables 3.1–3.3. This consistency suggests that the principal findings — the age-related improvement in Transfer Index and Bimanual Coordination, the weaker age relationship for Gap Score, and the absence of significant sex differences — are not artefacts of a small number of miscoded observations, and can be interpreted with reasonable confidence. conncise to short