Description of dataset The dataset presents the results of the investigation of the early lexical-semantic knowledge organization capabilities of 18- and 24-month-old toddlers. We were interested in the maturational differences in age and language proficiency. We included full-term (FT) and late preterm (PT) Hungarian-speaking infants. The PT and FT groups were matched according to their maturational ages. We conducted an infant-adapted target-absent Visual World Paradigm for eye-tracker presenting a Target Word verbally. It was followed by a visual panel with four pictures (aphonological distractor, a categorical distractor, and two unrelated images). We also tested children with the Hungarian version of the MacArthur-Bates Communicative Development Inventory (CDI). The dataset includes descriptive data of the participants, the CDI results (word count per category and the total sentence length), and fixation duration and count data registered by the eye-tracker for the presented stimuli. We provide the raw fixation data and the calculated variables per stimulus picture categories.

Article abstract An organized mental lexicon determines new information acquisition by orienting attention during language processing. Adult-like lexical-semantic knowledge organization has already been demonstrated in 24-month-olds. However, the outcomes of earlier studies have been contradictory in terms of the organizational capacities of 18-month-olds, thus our aim was to examine lexical-semantic organization in this younger age group. In prematurely born infants, audiovisual integration deficits have been found alongside disruptions in language perception. By including late preterm infants with corrected ages in our study, we aimed to test whether maturational differences influence lexical-semantic organization when vocabulary is growing rapidly. We tested 47 late preterm and full-term 18- and 24-month-old infants by means of an infant-adapted target-absent task using a slightly modified version of the original visual world paradigm for eye tracker. We found a longer fixation duration for the lexical and semantic distractors compared to the neutral pictures. Neither language proficiency nor age affected the looking time results. We found a dissociation by age between taxonomic and associative semantic relations. Maturational differences were detectable in the initial processing of taxonomic relations, as processing in the preterm group was slightly delayed and qualitatively different in the first half of the looking time. The size and composition of the expressive vocabulary differed only by age. In general, our study demonstrated a stable lexical-semantic organization between 18 and 24 months of age, regardless of maturational differences.

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