Infant vocabulary development assessed with a British communicative development inventory

Communicative Development Inventories (CDIs) were collected from 669 British children aged between 1;0 and 2;1. Comprehension and production scores in each age group are calculated. This provides norming data for the British infant population. The influence of socioeconomic group on vocabulary scores is considered and shown not to have a significant effect. The data from British infants is compared to data from American infants (Fenson, Dale, Reznick, Bates, Thal & Pethick, 1994). It is found that British infants have lower scores on both comprehension and production than American infants of the same age

The role of noise in sensorimotor control

Goal-directed arm movements show stereotypical trajectories, despite the infinite possible ways to reach a given end point. This thesis examines the hypothesis that this stereotypy arises because movements are optimised to reduce the consequences of signal-dependent noise on the motor command. Both experimental and modelling studies demonstrate that signal-dependent noise arises from the normal behaviour of the muscle and motor neuron pool, and has a particular distribution across muscles of different sizes. Specifically, noise decreases in a systematic fashion with increasing muscle strength and motor unit number. Simulations of obstacle avoidance performance in the presence of signal-dependent noise demonstrate that the optimal trajectory for reaching the target accurately and without collision matches the observed trajectories. Isometric force generation is also shown to have systematic changes in variability with posture, which can be explained by the presence of signal-dependent noise in the muscles of the arm. These results confirm the tested hypothesis and imply that consideration of the statistics of action is crucial to human movement planning. To investigate the importance of feedback in the motor system, the impact of static position on motor excitability was examined using transcranial magnetic stimulation and systematic changes in motor evoked potentials were observed. Force generated at the wrist following stimulation was analysed in terms of different possible movement representations, and the differences between force fields arising from stimulation over the cervical spinal cord and from stimulation over primary motor cortex are determined. These results demonstrate the structured influence of proprioceptive feedback on the human motor system. All the experiments are discussed in relation to current theories describing the control of human movements and the impact of noise in the motor system

The Social Modulation of Imitation Fidelity in School-Age Children

Children copy the actions of others with high fidelity, even when they are not causally relevant. This copying of visibly unnecessary actions is termed overimitation. Many competing theories propose mechanisms for overimitation behaviour. The present study examines these theories by studying the social factors that lead children to overimitate actions. Ninety-four children aged 5- to 8-years each completed five trials of an overimitation task. Each trial provided the opportunity to overimitate an action on familiar objects with minimal causal reasoning demands. Social cues (live or video demonstration) and eye contact from the demonstrator were manipulated. After the imitation, children's ratings of action rationality were collected. Substantial overimitation was seen which increased with age. In older children, overimitation was higher when watching a live demonstrator and when eye contact was absent. Actions rated as irrational were more likely to be imitated than those rated as rational. Children overimitated actions on familiar objects even when they rated those actions as irrational, suggesting that failure of causal reasoning cannot be driving overimitation. Our data support social explanations of overimitation and show that the influence of social factors increases with age over the 5- to 8-year-old age range

The role of anticipated regret in choosing for others

In everyday life, people sometimes find themselves making decisions on behalf of others, taking risks on another's behalf, accepting the responsibility for these choices and possibly suffering regret for what they could have done differently. Previous research has extensively studied how people deal with risk when making decisions for others or when being observed by others. Here, we asked whether making decisions for present others is affected by regret avoidance. We studied value-based decision making under uncertainty, manipulating both whether decisions benefited the participant or a partner (beneficiary effect) and whether the partner watched the participant's choices (audience effect) and their factual and counterfactual outcomes. Computational behavioural analysis revealed that participants were less mindful of regret (and more strongly driven by bigger risks) when choosing for others vs for themselves. Conversely, they chose more conservatively (regarding both regret and risk) when being watched vs alone. The effects of beneficiary and audience on anticipated regret counteracted each other, suggesting that participants' financial and reputational interests impacted the feeling of regret independently

Face2face: advancing the science of social interaction

Face-to-face interaction is core to human sociality and its evolution, and provides the environment in which most of human communication occurs. Research into the full complexities that define face-to-face interaction requires a multi-disciplinary, multi-level approach, illuminating from different perspectives how we and other species interact. This special issue showcases a wide range of approaches, bringing together detailed studies of naturalistic social-interactional behaviour with larger scale analyses for generalization, and investigations of socially contextualized cognitive and neural processes that underpin the behaviour we observe. We suggest that this integrative approach will allow us to propel forwards the science of face-to-face interaction by leading us to new paradigms and novel, more ecologically grounded and comprehensive insights into how we interact with one another and with artificial agents, how differences in psychological profiles might affect interaction, and how the capacity to socially interact develops and has evolved in the human and other species. This theme issue makes a first step into this direction, with the aim to break down disciplinary boundaries and emphasizing the value of illuminating the many facets of face-to-face interaction. This article is part of a discussion meeting issue 'Face2face: advancing the science of social interaction'

Social top-down response modulation (STORM): a model of the control of mimicry in social interaction

As a distinct feature of human social interactions, spontaneous mimicry has been widely investigated in the past decade. Research suggests that mimicry is a subtle and flexible social behavior which plays an important role for communication and affiliation. However, fundamental questions like why and how people mimic still remain unclear. In this paper, we evaluate past theories of why people mimic and the brain systems that implement mimicry in social psychology and cognitive neuroscience. By reviewing recent behavioral and neuroimaging studies on the control of mimicry by social signals, we conclude that the subtlety and sophistication of mimicry in social contexts reflect a social top-down response modulation (STORM) which increases one's social advantage and this mechanism is most likely implemented by medial prefrontal cortex (mPFC). We suggest that this STORM account of mimicry is important for our understanding of social behavior and social cognition, and provides implications for future research in autism

Action understanding requires the left inferior frontal cortex.

Numerous studies have established that inferior frontal cortex is active when hand actions are planned, imagined, remembered, imitated, and even observed. Furthermore, it has been proposed that these activations reflect a process of simulating the observed action to allow it to be understood and thus fully perceived. However, direct evidence for a perceptual role for left inferior frontal cortex is rare, and linguistic or motor contributions to the reported activations have not been ruled out. We used repetitive transcranial magnetic stimulation (rTMS) over inferior frontal gyrus during a perceptual weight-judgement task to test the hypothesis that this region contributes to action understanding. rTMS at this site impaired judgments of the weight of a box lifted by a person, but not judgements of the weight of a bouncing ball or of stimulus duration, and rTMS at control sites had no impact. This demonstrates that the integrity of left inferior frontal gyrus is necessary to make accurate perceptual judgments about other people's actions

Social anxiety is more likely to influence reputation management decisions than autistic traits

People manage their social reputation by selectively sharing achievements, thereby shaping the way others think about them. Autistic traits and social anxiety may have opposing impacts on reputation management. This study aimed to identify the influence of autistic traits and social anxiety on reputation management behavior, independently and in co-occurrence with one another. Seventy-seven adults with varying levels of autistic and social anxiety traits completed a novel self-disclosure task that required them to complete a computerized game and decide whether to disclose their scores to another participant. This design provided a safe social environment for sharing performance outcomes and allowed us to manipulate performance outcomes for participants and set a perceived ‘norm’ of high self-disclosure. Results showed that participants were more likely to disclose their high than low scores to the other player. Social anxiety reliably predicted the likelihood of disclosing their scores while high autistic traits predicted the likelihood of disclosure only in combination with high social anxiety. Additionally, establishing the norm of high disclosure facilitated self-disclosure in all the participants. This study shows that social anxiety may influence reputation management via selective self-disclosure more when co-occurring with high autistic traits. People with varying levels of autistic traits may not behave differently to maintain a social reputation

Social seeking declines in young adolescents

The desire to engage with others is an important motivational force throughout our lifespan. It is known that social behaviour and preferences change from childhood to adulthood, but whether this change is linked with any changes in social motivation is not known. We evaluated 255 typically developing participants from ages 4–20 years on a behavioural paradigm ‘Choose a Movie’ (CAM). On every trial, participants had a choice between viewing social or non-social movies presented with different levels of effort (key presses/screen touch required). Hence, participants chose not only the movie they would watch but also how much effort they would make. The difference between the effort levels of the chosen and not chosen stimuli helps in quantifying the motivation to seek it. This task could be used with all the age groups with minimal adaptations, allowing comparison between the groups. Results showed that children (4–8 years), older adolescents (12–16 years) and young adults (17–20 years) made more effort to look at social movies. Counterintuitively, this preference was not seen in young adolescents (around 9–12 years), giving a U-shaped developmental trajectory over the population. We present the first evidence for non-monotonic developmental change in social motivation in typical participants