I focus here on concepts that are not part of core knowledge – the ability to treat people as social agents with shareable mental states. Spelke proposes that learning language from another might account for the development of these concepts. I suggest that homesigners, who create language rather than learn it, may be a potential counterexample to this hypothesis.

Adults display cross-linguistic variability in their speech in how they package and order semantic elements of a motion event. These differences can also be found in speakers’ co-speech gestures (gesturing with speech), but not in their silent gestures (gesturing without speech). Here, we examine when in development children show the differences between co-speech gesture and silent gesture found in adults. We studied speech and gestures produced by 100 children learning English or Turkish (n = 50/language) – equally divided into 5 age-groups: 3–4, 5–6, 7–8, 9–10, and 11–12 years. Children were asked to describe three-dimensional spatial event scenes (e.g., a figure crawling across carpet) first with speech and then without speech using their hands. We focused on physical motion events that elicit, in adults, cross-linguistic differences in co-speech gesture and cross-linguistic similarities in silent gesture. We found the adult pattern even in the youngest children: (1) Language shaped co-speech gesture beginning at age 3 years, showing an early effect of language on thinking for speaking (as measured by gestures that occur during the speech act). (2) Language did not affect silent gesture at any age, highlighting early limits on the effects language has on thinking and revealing a language of gesture that shows similarities across languages.

The commentaries have led us to entertain expansions of our paradigm to include new theoretical questions, new criteria for what counts as a gesture, and new data and populations to study. The expansions further reinforce the approach we took in the target article: namely, that linguistic and gestural components are two distinct yet integral sides of communication, which need to be studied together.

How does sign language compare with gesture, on the one hand, and spoken language on the other? Sign was once viewed as nothing more than a system of pictorial gestures without linguistic structure. More recently, researchers have argued that sign is no different from spoken language, with all of the same linguistic structures. The pendulum is currently swinging back toward the view that sign is gestural, or at least has gestural components. The goal of this review is to elucidate the relationships among sign language, gesture, and spoken language. We do so by taking a close look not only at how sign has been studied over the past 50 years, but also at how the spontaneous gestures that accompany speech have been studied. We conclude that signers gesture just as speakers do. Both produce imagistic gestures along with more categorical signs or words. Because at present it is difficult to tell where sign stops and gesture begins, we suggest that sign should not be compared with speech alone but should be compared with speech-plus-gesture. Although it might be easier (and, in some cases, preferable) to blur the distinction between sign and gesture, we argue that distinguishing between sign (or speech) and gesture is essential to predict certain types of learning and allows us to understand the conditions under which gesture takes on properties of sign, and speech takes on properties of gesture. We end by calling for new technology that may help us better calibrate the borders between sign and gesture.

We designed a parent-directed home-visiting intervention targeting socioeconomic status (SES) disparities in children's early language environments. A randomized controlled trial was used to evaluate whether the intervention improved parents' knowledge of child language development and increased the amount and diversity of parent talk. Twenty-three mother–child dyads (12 experimental, 11 control, aged 1;5–3;0) participated in eight weekly hour-long home-visits. In the experimental group, but not the control group, parent knowledge of language development increased significantly one week and four months after the intervention. In lab-based observations, parent word types and tokens and child word types increased significantly one week, but not four months, post-intervention. In home-based observations, adult word tokens, conversational turn counts, and child vocalization counts increased significantly during the intervention, but not post-intervention. The results demonstrate the malleability of child-directed language behaviors and knowledge of child language development among low-SES parents.

Speakers of all ages spontaneously gesture as they talk. These gestures predict children's milestones in vocabulary and sentence structure. We ask whether gesture serves a similar role in the development of narrative skill. Children were asked to retell a story conveyed in a wordless cartoon at age five and then again at six, seven, and eight. Children's narrative structure in speech improved across these ages. At age five, many of the children expressed a character's viewpoint in gesture, and these children were more likely to tell better-structured stories at the later ages than children who did not produce character-viewpoint gestures at age five. In contrast, framing narratives from a character's perspective in speech at age five did not predict later narrative structure in speech. Gesture thus continues to act as a harbinger of change even as it assumes new roles in relation to discourse.

Young children are skilled language learners. They apply their skills to the language input they receive from their parents and, in this way, derive patterns that are statistically related to their input. But being an excellent statistical learner does not explain why children who are not exposed to usable linguistic input nevertheless communicate using systems containing the fundamental properties of language. Nor does it explain why learners sometimes alter the linguistic input to which they are exposed (input from either a natural or an artificial language). These observations suggest that children are prepared to learn language. Our task now, as it was in 1974, is to figure out what they are prepared with – to identify properties of language that are relatively easy to learn, the resilient properties, as well as properties of language that are more difficult to learn, the fragile properties. The new tools and paradigms for describing and explaining language learning that have been introduced into the field since 1974 offer great promise for accomplishing this task.

Languages typically express semantic components of motion events such as manner (roll) and path (down) in separate lexical items. We explore how these combinatorial possibilities of language arise by focusing on (i) gestures produced by deaf children who lack access to input from a conventional language (homesign); (ii) gestures produced by hearing adults and children while speaking; and (iii) gestures used by hearing adults without speech when asked to do so in elicited descriptions of motion events with simultaneous manner and path. Homesigners tended to conflate manner and path in one gesture, but also used a mixed form, adding a manner and/or path gesture to the conflated form sequentially. Hearing speakers, with or without speech, used the conflated form, gestured manner, or path, but rarely used the mixed form. Mixed form may serve as an intermediate structure on the way to the discrete and sequenced forms found in natural languages.

Speakers move their hands when they talk—they gesture. These gestures can signal whether the speaker is ready to learn a particular task and, in this sense, provide a window onto the speaker's knowledge. But gesture can do more than reflect knowledge. It can play a role in changing knowledge in at least two ways: indirectly through its effects on communication with the learner, and directly through its effects on the learner's cognition. Gesturing is, however, not limited to learners. Speakers who are proficient in a task also gesture. Their gestures have a different relation to speech than the gestures that novices produce, and seem to support cognition rather than change it. Gesturing can thus serve as a tool for thinking and for learning.

Children produce a deictic gesture for a particular object (point at dog) approximately 3 months before they produce the verbal label for that object (“dog”; Iverson & Goldin-Meadow, 2005). Gesture thus paves the way for children's early nouns. We ask here whether the same pattern of gesture preceding and predicting speech holds for iconic gestures. In other words, do gestures that depict actions precede and predict early verbs? We observed spontaneous speech and gestures produced by 40 children (22 girls, 18 boys) from age 14 to 34 months. Children produced their first iconic gestures 6 months later than they produced their first verbs. Thus, unlike the onset of deictic gestures, the onset of iconic gestures conveying action meanings followed, rather than preceded, children's first verbs. However, iconic gestures increased in frequency at the same time as verbs did and, at that time, began to convey meanings not yet expressed in speech. Our findings suggest that children can use gesture to expand their repertoire of action meanings, but only after they have begun to acquire the verb system underlying their language.

Children with pre/perinatal unilateral brain lesions (PL) show remarkable plasticity for language development. Is this plasticity characterized by the same developmental trajectory that characterizes typically developing (TD) children, with gesture leading the way into speech? We explored this question, comparing eleven children with PL – matched to thirty TD children on expressive vocabulary – in the second year of life. Children with PL showed similarities to TD children for simple but not complex sentence types. Children with PL produced simple sentences across gesture and speech several months before producing them entirely in speech, exhibiting parallel delays in both gesture + speech and speech-alone. However, unlike TD children, children with PL produced complex sentence types first in speech-alone. Overall, the gesture–speech system appears to be a robust feature of language learning for simple – but not complex – sentence constructions, acting as a harbinger of change in language development even when that language is developing in an injured brain.

The talk children hear from their primary caregivers predicts the size of their vocabularies. But children who spend time with multiple individuals also hear talk that others direct to them, as well as talk not directed to them at all. We investigated the effect of linguistic input on vocabulary acquisition in children who routinely spent time with one vs. multiple individuals. For all children, the number of words primary caregivers directed to them at age 2 ; 6 predicted vocabulary size at age 3 ; 6. For children who spent time with multiple individuals, child-directed words from all household members also predicted later vocabulary and accounted for more variance in vocabulary than words from primary caregivers alone. Interestingly, overheard words added no predictive value to the model. These findings suggest that speech directed to children is important for early word learning, even in households where a sizable proportion of input comes from overheard speech.