Speakers tend to assign more linguistic material to less predictable elements. This tendency is typically explained by a bias for an efficient trade-off between production effort and understandability and is claimed to shape linguistic structures across languages. Recent work suggests this trade-off enters the linguistic system through learning processes with learners deviating from their input by increasing marking for less predictable elements. However, no study to date has tested whether child learners also show such predictability-based marking, an important gap seeing that children are the primary learners in real-life language acquisition. A recent study showed that adults increase predictability-based marking of an optional-plural marker, in line with communicative efficiency. Here, we ask if children show a similar pattern. Results show that children, unlike adults, do not show an efficient trade-off in their productions. We discuss implications for the role of different language learners on language change.

Agreement, a systematic formal mapping between linguistic elements, adds redundancy to languages (e.g., in ‘she writes’ the -s adds no information), and yet is crosslinguistically prevalent. Here, we suggest that agreement may be functionally advantageous by providing additional cues for language learning. We conducted an artificial language learning experiment to test whether agreement, and especially, alliterative agreement – where the agreement is expressed by repetition of the same form, can facilitate learning of noun classes (e.g., ‘masculine’/’feminine’). To this end, we compared the learnability of noun class systems in three input conditions: no agreement, alliterative agreement, and non-alliterative agreement. We found that participants who learned the non-alliterative agreement were better at generalizing the noun class system to novel nouns with the relevant semantic features. There was no difference between the alliterative and the no-agreement conditions, suggesting that the possible learnability advantage of agreement marking lies in having distinct forms as cues.

Agreement, a systematic formal mapping between linguistic elements, adds redundant complexity to languages (e.g., in ‘she writes' the -s adds no information), and yet is crosslinguistically prevalent. A prominent hypothesis argues that the ubiquity of agreement may be due to a functional advantage it confers for child learners. Here, we test this using an artificial language learning experiment with 56 English-speaking children (mean age 5;11). We investigate whether agreement can facilitate learning of noun classes (e.g., ‘masculine'/'feminine'). In one condition, agreement appeared as a redundant cue to noun classes, whereas in the other condition there was no agreement. Following exposure, we tested children on noun classification for both nouns they were trained on and novel nouns. Results reveal that children classified nouns equally well in both conditions. However, novel nouns were classified better in the agreement condition compared to the no-agreement condition, suggesting agreement can facilitate generalization for child learners.

If speakers communicate efficiently, they should produce more linguistic material when comprehension difficulty increases. Comprehension difficulty can be impacted by the message itself (studied extensively) or by properties of the listener (studied less). Here we investigate the impact of listeners’ estimated proficiency on speakers’ productions, using referential choice as a case study. Compared to full noun phrases (fNPs, ‘the woman’), pronouns (‘she’) can convey similar content with less linguistic material: accordingly, speakers use more fNPs when the message is unpredictable (Tily & Piantadosi, 2009) and when listeners lack relevant information (Bard & Aylett, 2004). If referential choice is also impacted by listeners’ estimated proficiency, then speakers should use more fNPs when conversing with language learners. To test this, we compared participants' descriptions of the same picture book to learners and proficient speakers. Indeed, participants used more fNPs when their interlocutors were child- or adult-learners, illustrating efficient adaptation to listener type.

Languages seem to be designed for efficient communication. For example, shorter forms are used for more predictable meanings, a tendency argued to stem from speakers’ efficient language use. However, no study to date has systematically tested whether communicative efficiency shapes children’s language use. Investigating whether such a pressure is already present in children will shed light on the development of children’s’ communicative behaviour and the respective roles of adults and children in shaping language structure. Here, we investigate the development of communicative efficiency using a novel experimental paradigm with children ages 4-10. Results show that communicative efficiency is attested already in young children and becomes more adult-like with age: as children grow, they are more likely to shorten messages (minimize effort) when a short message is sufficient for accurate communication. We discuss the implications of our results for cognitive development and for theories of language evolution and change.