Synapses,Schizophrenia, and Civilization: What Made Homo Sapient?

Progress in technology has allowed dynamic research on the development of the human brain that has revolutionized concepts. Particularly, the notions of plasticity, neuronal selection, and the effects of afferent stimuli have entered into thinking about brain development. Here I focus on development from the age of four years to early adulthood, during which a 30 percent reduction in some brain synapses occurs that is out of proportion to changes in neuronal numbers. This corresponds temporally with changes in normal child behavior from the loose‐associative, almost schizoid, thinking and art of the four‐year‐old to the more trained, or disciplined, or acculturated—and restrained—personality of the young adult. I propose that the synaptic changes can best be thought of as a winnowing process likely subject to environmental influences. Acquisition of language and the ability to link linguistic cognition to the plastic development of the brain provide a potentially powerful means of explaining the evolutionally explosive development of human cognition and culture. Schizophrenia, a disease that can be envisioned as representing a derangement of synaptic maturation, may provide an entry into the search for genes controlling the processes mediating the unprecedented development of Homo sapiens over the past 40,000 to 70,000 years. The recently completed mapping of the genome of the chimpanzee provides a new frame of reference that may speed the search.     

Toward a More Credible Understanding of Post-Traumatic Growth

Traditional research on post-traumatic growth has utilized methodologically flawed cross-sectional designs that involve retrospective assessments of post-traumatic growth. This has resulted in a majority of research in this field suffering from a lack of credibility and reliability. In this special issue, we present nine articles that seek to make innovative conceptual and methodological contributions with the goal of promoting better research practices on post-traumatic growth. In the introduction to this special issue, we provide an overview of these contributions, and discuss the implications of these articles both to improving future scholarship and to encouraging personality scientists to examine this important phenomenon in the years and decades to come.     

Modeling Asymmetry in the Time–Distance Relation of Ordinal Personality Items

In analyzing responses and response times to personality questionnaire items, models have been proposed which include the so-called “inverted-U effect.” These models predict that response times to personality test items decrease as the latent trait value of a given person gets closer to the attractiveness of an item. Initial studies into these models have focused on dichotomous personality items, and more recently, models for Likert-type scale items have been proposed. In all these models, it is assumed that the inverted-U effect is symmetrical around 0, while, as will be explained in this article, there are substantive and statistical reasons to study this assumption. Therefore, in this article, a general inverted-U model is proposed which accommodates two sources of asymmetry between the response times and the attractiveness of the items. The viability of this model is demonstrated in a simulation study, and the model is applied to the responses and response times of the Temperament and Character Inventory–Revised, covering a broad range of personality dimensions.     

Do voices carry valid information about a speaker’s personality?

Research on links between peoples’ personality traits and their voices has primarily focused on other peoples’ personality judgments about a target person based on a target person’s vocal characteristics, particularly voice pitch. However, it remains unclear whether individual differences in voices are linked to actual individual differences in personality traits, and thus whether vocal characteristics are indeed valid cues to personality. Here, we investigate how the personality traits of the Five Factor Model of Personality, sociosexuality, and dominance are related to measured fundamental frequency (voice pitch) and formant frequencies (formant position). For this purpose, we conducted a secondary data analysis of a large sample (2217 participants) from eleven different, independent datasets with a Bayesian approach. Results suggest substantial negative relationships between voice pitch and self-reported sociosexuality, dominance and extraversion in men and women. Thus, personality might at least partly be expressed in people’s voice pitch. Evidence for an association between formant frequencies and self-reported personality traits is not compelling but remains uncertain. We discuss potential underlying biological mechanisms of our effects and suggest a number of implications for future research.     

Factors associated with the socioemotional development of preterm infants

Preterm birth is a risk factor for problems in interactions with others. We compared the difference in socioemotional development between hospital discharge and at six months of corrected age of infants born ≤32 weeks and assessed the impact of maternal and infantile factors on socioemotional development rate within a 6 month’s period. Mother-child dyads (n = 144) were assessed by the Mother-Baby Observation Protocol 0–6 months through a video microanalysis. Multivariate model was built. Neonatal, maternal and child factors were associated with interactive gaze, initiate contact, responsiveness, infantile vocalization, and thus contributed to the socioemocional development of preterm infants with their mothers.     

A time series analysis of the relation between motor skill acquisition and sleep in infancy

To systematically examine the relation between motor milestone onset and disruption of night sleep in infancy, three families kept microgenetic, prospective, daily checklist diaries of their infants’ motor behavior and sleep (197-313 observation days; 19,000 diary entries). Process control and interrupted time series analyses examined whether deviations from the moving average for night wakings and evening sleep duration were temporally linked to motor skill onset and tested for meaningful differences in individual sleep patterns before and after skill onset. Model assumptions defined skill onset as first day of occurrence or as mastery and moving average windows as 3, 7, or 14 days. Changes in infants’ sleep patterns were associated with changing expertise for motor milestones. The temporal relation varied depending on infant and sleep parameter. Intensive longitudinal data collection may increase our understanding of micro-events in infant development.     

Tapping into the interplay of lexical and number knowledge using fast mapping: A longitudinal eye-tracking study with two-year-olds

Language skills and mathematical competencies are argued to influence each other during development. While a relation between the development of vocabulary size and mathematical skills is already documented in the literature, this study further examines how children’s ability to map a novel word to an unknown object as well as their ability to retain this word from memory may be related to their knowledge of number words. Twenty-five children were tested longitudinally (at 30 and at 36 months of age) using an eye-tracking-based fast mapping task, the Give-a-Number task, and standardized measures of vocabulary. The results reveal that children’s ability to create and retain a mental representation of a novel word was related to number knowledge at 30 months, but not at 36 months while vocabulary size correlated with number knowledge only at 36 months. These results show that even specific mapping processes are initially related to the acquisition of number words and they speak for a parallelism between the development of lexical and number-concept knowledge despite their semantic and syntactic differences.     

The Persistence of Priming: Exploring Long-lasting Syntactic Priming Effects in Children and Adults

The implicit learning account of syntactic priming proposes that the same mechanism underlies syntactic priming and language development, providing a link between a child and adult language processing. The present experiment tested predictions of this account by comparing the persistence of syntactic priming effects in children and adults. Four-year-olds and adults first described transitive events after hearing transitive primes, constituting an exposure phase that established priming effects for passives. The persistence of this priming effect was measured in a test phase as participants described further transitive events but no longer heard primes. Their production of passives was compared to a baseline group who described the same pictures without any exposure to primes. Neither immediate nor long-term priming effects differed between children and adults but both children and adults showed significant immediate and persistent effects of the priming when the test phase occurred immediately after the exposure phase and when a short delay separated the exposure and test phase. The implications of these results for an implicit learning account of syntactic priming are discussed.