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The current study investigated the development of online reach control. Six- and 11-month-old infants reached for a toy while their hand position was tracked. The toy either remained stationary (baseline trials) or unexpectedly displaced left- or rightward during the reach (perturbation trials). To obtain a measure of online reach correction, we compared reaches in the perturbation trials to reaches in baseline trials using autoregression analysis. Infants of both age groups adjusted their reach trajectories in the direction of the displacement. Moreover, we divided the reaching movements into movement units, defined as the submovements of a reach between local minima in hand speed. Eleven-month-old infants adjusted their reach within the span of a single movement unit; corrections in 6-month-olds spanned multiple movement units. These results suggest that the reach control system has a rudimentary replanning capacity by 6months of age, which, with age, further develops to a more sophisticated online control mechanism for ongoing reaches.

Recent work shows that 18-month old infants understand that counting is numerically relevant-infants who see objects counted are more likely to represent the approximate number of objects in the array than infants who see the objects labeled but not counted. Which aspects of counting signal infants to attend to numerosity in this way? Here we asked whether infants rely on familiarity with the count words in their native language, or on procedures instantiated by the counting routine, independent of specific tokens. In three experiments (N=48), we found that 18-month old infants from English-speaking households successfully distinguished four hidden objects from two when the objects were counted correctly, regardless of their familiarity with the count words (i.e., when objects were counted in familiar English and in unfamiliar German). However, when the objects were counted using familiar English count words in ways that violated basic counting principles, infants no longer represented the arrays, failing to distinguish four hidden objects from two. Together with previous findings, these results suggest that children may link the procedure of counting with numerosity years before they learn the meanings of the count words.

Infants by 6months recognize that speech communicates information between third parties. We investigated whether 6-month-olds always expect speech to communicate or whether they also consider social features of communication, like how interlocutors engage with one another. A small sample of infants watched an actor (the Speaker) choose one of two objects to play with (the target). When the Speaker could no longer reach her target object, she turned to a new actor (the Listener) and said a nonsense word. During speech, the actors were either face-to-face, the Speaker was facing away from the Listener, or the reverse. When the actors had been face-to-face, infants looked longer when the Listener selected the non-target object compared to the target. Infants looked equally regardless of what the Listener chose when either actor had been disengaged. Area-of-interest gaze coding suggests that infants were similarly interested in the interaction across conditions, but their pattern of attention to Speaker and Listener differed when the Listener was disengaged during speech. Although these experiments should be replicated with a larger sample, the findings provide initial evidence that 6-month-olds do not expect speech alone to communicate, but also attend to the social context in which speech is produced.

Previous studies found an onset of holistic face processing in the age range between 0-4 and 7months of age. To validate these studies, the present study investigated infants 4 and 7months of age with a different experimental approach. In a habituation-dishabituation experiment, the infants were tested with stereoscopic stimuli in which stripes floated above a face, thereby occluding some parts of the face (amodal completion condition), and stereoscopic stimuli in which the same face parts floated above stripes (modal completion condition). Research with adults indicates that faces are processed holistically, that is as global wholes, in the amodal, but as independent parts in the modal completion condition, resulting in superior face recognition when the occluding bars are in front of than when they are behind the visible face parts. The present study found that infants regardless of whether they are 4 or 7months old reliably recognized and differentiated the faces in the amodal but not in the modal completion condition. Moreover, the difference between the experimental conditions was statistically significant. These findings show that approximately at the age of 4-7months of life, infants begin to holistically unify disjoint face parts into a coherent whole.

Most research with the mobile paradigm has the underlying assumption that young infants can selectively move the limb causing the contingent feedback from the mobile while avoiding irrelevant motor responses. Contrary to this long-held belief, others have argued that such differentiation ability is not fully developed early in life. In the current study, we revisited the traditional mobile paradigm with a contemporary research approach (using high-precision motion capture techniques, a yoked-control design, and a large sample size) to investigate whether response differentiation ability emerges before 5months of age. The data collected from 76 infants (aged between 115 and 159days) revealed that infants can learn sensorimotor contingencies by increasing the movement of the connected leg relative to their baseline level. However, they did not differentially increase the movement of the leg causing an effect in the environment compared with that of other limbs. Our results illustrate that response differentiation ability emerges later than previously suggested.