Why do infants imitate selectively? Neural correlates of infants’ action understanding in the head-touch paradigm

Imitation is an important social learning mechanism for young infants exploring the world. Interestingly, infants do not imitate every action they observe – they rather do so selectively. Fourteen-month-olds predominantly imitated an unusual and inefficient action (turning on a lamp with one’s forehead) when the model’s hands were free compared to when the model’s hands were occupied (Gergely et al., 2002). Behavioral scientists have proposed contrasting explanatory accounts, differing with regard to the assumed level of infants’ cognitive abilities. Rational-imitation accounts suggest that infants selectively imitate unusual actions because they are surprised by the inefficiency of the action (Gergely & Csibra, 2003). In contrast, non-rational imitation accounts propose that selective imitation depends on more basic factors such as motor abilities (Paulus et al., 2011a,b). The integrative model by Zmyj and Buttelmann (2014) represents the first attempt to put together these opposing theories. Both accounts may operate on different processing levels. Bottom-up processes are related to non-rational imitation accounts, whereas top-down processing is based on the assumptions of the rational-imitation accounts. Despite the large body of behavioral research on selective imitation, the question of what are the neural mechanisms underlying these processes remains unanswered. In my dissertation, I aimed to uncover the underlying cognitive processes during the observation of head-touch actions by recording infants’ neurophysiological responses in three empirical studies. To test the assumptions of the top-down processes linked to the rational-imitation accounts, I examined neural markers associated with violation of expectation (VOE) in an adaptation of the head-touch paradigm. Overall, results suggest that 12- to 14-month-old infants, but not 9-month-old infants, display VOE when observing a person performing an inefficient head touch. This VOE response is context-dependent and is elicited when the model’s hands are free but not when the hands are restrained. In Study 1, VOE has been linked to a reduction in mu power in response to the unexpected head touch. In Study 2, this finding was extended such that when 12- to 14-month-old infants observed an unexpected head touch, their brains responded with increased attentional engagement (enhanced Nc amplitude) and a detection of a semantic violation (N400 component). Finally, in Study 3, in the absence of contextual information, 1-year-olds discriminated between hand- and head-touch outcomes on the Nc component only. Thus, infants require information of the action context to detect semantic violations within the head-touch paradigm. To conclude, the studies presented in my dissertation have paved the way to further our understanding of infants’ action perception and observational learning. Understanding the neural mechanisms of infants’ action perception in more depth, will help us to adequately foster the ideal observational learning conditions of novel actions. The results of this dissertation suggest that presenting infants with surprising action means puts them in an optimal receptive state for knowledge acquisition

Corrigendum: Reduced mu power in response to unusual actions is context-dependent in 1-year-olds

During social interactions infants predict and evaluate other people’s actions. Previous behavioral research found that infants’ imitation of others’ actions depends on these evaluations and is context-dependent: 1-year-olds predominantly imitated an unusual action (turning on a lamp with one’s forehead) when the model’s hands were free compared to when the model’s hands were occupied or restrained. In the present study, we adapted this behavioral paradigm to a neurophysiological study measuring infants’ brain activity while observing usual and unusual actions via electroencephalography. In particular, we measured differences in mu power (6 – 8 Hz) associated with motor activation. In a between-subjects design, 12- to 14-month-old infants watched videos of adult models demonstrating that their hands were either free or restrained. Subsequent test frames showed the models turning on a lamp or a soundbox by using their head or their hand. Results in the hands-free condition revealed that 12- to 14-month-olds displayed a reduction of mu power in frontal regions in response to unusual and thus unexpected actions (head touch) compared to usual and expected actions (hand touch). This may be explained by increased motor activation required for updating prior action predictions in response to unusual actions though alternative explanations in terms of general attention or cognitive control processes may also be considered. In the hands-restrained condition, responses in mu frequency band did not differ between action outcomes. This implies that unusual head-touch actions compared to hand-touch actions do not necessarily evoke a reduction of mu power. Thus, we conclude that reduction of mu frequency power is context-dependent during infants’ action perception. Our results are interpreted in terms of motor system activity measured via changes in mu frequency band as being one important neural mechanism involved in action prediction and evaluation from early on

Investigação da atividade abortiva e/ou infertilizante de Stryphnodendron adstringens (Mart. Coville)

Stryphnodendron adstringens (barbatimão) é uma árvore natural dos Estados do Pará ao Mato Grosso do Sul e São Paulo (Brasil). O objetivo deste estudo foi determinar a toxicidade dos extratos das vagens desta espécie e verificar efeitos sobre a gestação de ratas. As vagens foram coletadas na região de Cuiabá (MT, Brasil) e separadas em cascas e sementes. Foram feitos extratos brutos hidroalcoólicos (2:1), a frio e depois levados à secura (máximo 55°C). Ratas fêmeas virgens foram acasaladas e receberam extratos (0,5 ml/100 g de peso, 100 g/l) ou água na mesma proporção (controle) por gavagem do 1° ao 7° dia de gestação. No 7° dia, foram feitas laparatomias para contagem do número de implantes uterinos. As ratas foram sacrificadas no 21° dia de gestação. Os extratos das sementes reduziram o peso do útero e o número de fetos vivos em relação ao grupo controle. A dose média letal (DL50) calculada para o extrato das sementes foi de 4.992,8 mg/kg. A DL50 do extrato das vagens foi maior que 5.000 mg/kg. Pode-se concluir que o extrato das sementes de S. adstringens interfere na gestação de ratas, sendo que esta ingestão pode prejudicar animais herbívoros.Stryphnodendron adstringens (barbatiman) is a tree found from Pará to Mato Grosso do Sul and São Paulo States (Brazil). The aim of this study was to determine the toxicity of the extracts of the broad beans of this species and to verify if they have some effect on the pregnancy of rats. The broad beans were collected in the region of Cuiabá (MT, Brazil) and separated in husks and seeds. The crude hydroalcoholic (2:1) extracts were prepared at room temperature and dried at a maximum of 55ºC. Female virgin rats were mated and received the extracts (0.5 ml/100 g weight, 100 g/l) or water in the same proportion (control) by gavage from day 1 to day 7 of gestation. Laparatomies were made at day 7 to count the number of uterine implants and the rats were sacrificed on the 21st day of gestation. The seed extracts reduced the weight of the uterus and the number of live fetuses compared to the control group. The mean lethal dose (LD50) calculated for this extract was 4,992.8 mg/kg and the LD50 of the extract of the husk was higher than 5,000 mg/kg. We may conclude that the extract of S. adstringens seeds impaired the gestation of rats, and its ingestion could be harmful to herbivorous animals

Interpersonal neural synchrony when predicting others’ actions during a game of rock-paper-scissors

As members of a social species, we spend most of our time interacting with others. In interactions, we tend to mutually align our behavior and brain responses to communicate more effectively. In a semi-computerized version of the Rock-Paper-Scissors game, we investigated whether people show enhanced interpersonal neural synchronization when making explicit predictions about others’ actions. Across four experimental conditions, we measured the dynamic brain activity using the functional near-infrared spectroscopy (fNIRS) hyperscanning method. Results showed that interpersonal neural synchrony was enhanced when participants played the game together as they would do in real life in comparison to when they played the game on their own. We found no evidence of increased neural synchrony when participants made explicit predictions about others’ actions. Hence, neural synchrony may depend on mutual natural interaction rather than an explicit prediction strategy. This study is important, as it examines one of the presumed functions of neural synchronization namely facilitating predictions

Visually entrained theta oscillations increase for unexpected events in the infant brain

Infants form basic expectations about their physical and social environment, as indicated by their attention toward events that violate their expectations. Yet little is known about the neuronal processing of unexpected events in the infant brain. Here, we used rhythmic visual brain stimulation in 9-month-olds (N = 38) to elicit oscillations of the theta (4 Hz) and the alpha (6 Hz) rhythms while presenting events with unexpected or expected outcomes. We found that visually entrained theta oscillations sharply increased for unexpected outcomes, in contrast to expected outcomes, in the scalp-recorded electroencephalogram. Visually entrained alpha oscillations did not differ between conditions. The processing of unexpected events at the theta rhythm may reflect learning processes such as the refinement of infants’ basic representations. Visual brain-stimulation techniques provide new ways to investigate the functional relevance of neuronal oscillatory dynamics in early brain development