Compositional number concepts in children: The role of base-5 numeral structures in Sign language

Language exposure and the structure of cardinal numbers play significant roles in shaping children's numerical cognition. Deaf children often experience delays in language acquisition, which can lead to delays in developing number concepts and arithmetic skills. This study examines the impact of the compositional structure of Colombian Sign Language (LSC), which employs an additive base-5 system, on arithmetic performance in deaf children compared to their hearing peers who use spoken Spanish. Two experimental studies were conducted. In Study 1, 15 first-grade Spanish-speaking children completed a symbolic addition task and a dot quantification task. Each task included problems within two numerical ranges (5-9 and 11-15) and trials that either included or excluded the number 5. The results indicated that hearing children performed better on simpler problems and in dot quantification tasks, with no significant advantage observed from the presence of the number 5. Study 2 replicated the same design with 34 deaf children who are native users of LSC. Their performance in both tasks was significantly influenced by the presence of the number 5, especially in more complex problems (within the 11-15 numerical range). These effects remained significant even after controlling children's school grade and their counting skills. The analysis suggests that the additive structure of LSC may provide cognitive scaffolding, making the number 5 a functional anchor for deaf children's arithmetic reasoning. The morphological encoding of the number 5 in LSC may enhance arithmetic performance by emphasizing compositional number structures, thereby supporting language-dependent models of numerical cognition.