Learning to become an expert : reinforcement learning and the acquisition of perceptual expertise

To elucidate the neural mechanisms underlying the development of perceptual expertise, we recorded ERPs while participants performed a categorization task. We found that as participants learned to discriminate computer-generated "blob'' stimuli, feedback modulated the amplitude of the errorrelated negativity (ERN)-an ERP component thought to reflect error evaluation within medial-frontal cortex. As participants improved at the categorization task, we also observed an increase in amplitude of an ERP component associated with object recognition (the N250). The increase in N250 amplitude preceded an increase in amplitude of an ERN component associated with internal error evaluation (the response ERN). Importantly, these electroencephalographic changes were not observed for participants who failed to improve on the categorization task. Our results suggest that the acquisition of perceptual expertise relies on interactions between the posterior perceptual system and the reinforcement learning system involving medial-frontal cortex

Toward a model of multiple paths to language learning: response to commentaries

Language learning, while seemingly effortless for young learners, is a complex process involving many interacting pieces, both within the child and in their language-learning environments, which can result in unique language learning trajectories and outcomes. How does the brain adjust to or accommodate the myriad variations that occur during this developmental process. How does it adapt and change over time? In our review, we proposed that the timing, quantity, and quality of children's early language experiences, particularly during an early sensitive period for the acquisition of phonology, shape the establishment of neural phonological representations that are used to establish and support phonological working memory (PWM). The efficiency of the PWM system in turn, we argued, influences the acquisition and processing of more complex aspects of language. In brief, we proposed that experience modulates later language outcomes through its early effects on PWM. We supported this claim by reviewing research from several unique groups of language learners who experience delayed exposure to language (children with cochlear implants [CI] or internationally adopted [IA] children, and children with either impoverished [signing deaf children with hearing parents)] or enriched [bilingual] early language experiences). By comparing PWM and language outcomes in these groups, we sought to highlight general patterns in language development that emerge based on variation in early language exposure. Moving forward, we also proposed that the language acquisition patterns in these groups, and others, can be used to understand how variability in early language input might affect the neural systems supporting language development and how this might affect language learning itself

The N250 Brain Potential to Personally Familiar and Newly Learned Faces and Objects

Studies employing event-related potentials have shown that when participants are monitoring for a novel target face, the presentation of their own face elicits an enhanced negative brain potential in posterior channels approximately 250 ms after stimulus onset. Here, we investigate whether the own face N250 effect generalizes to other highly familiar objects, specifically, images of the participant’s own dog and own car. In our experiments, participants were asked to monitor for a pre-experimentally unfamiliar target face (Joe), a target dog (Experiment 1: Joe’s Dog) or a target car (Experiment 2: Joe’s Car). The target face and object stimuli were presented with non-target foils that included novel face and object stimuli, the participant’s own face, their own dog (Experiment 1), and their own car (Experiment 2). The consistent findings across the two experiments were the following: (1) the N250 potential differentiated the target faces and objects from the non-target face and object foils and (2) despite being non-targets, the own face and own objects produced an N250 response that was equal in magnitude to the target faces and objects by the end of the experiment. Thus, as indicated by its response to personally familiar and recently familiarized faces and objects, the N250 component is a sensitive index of individuated representations in visual memory

Variations in phonological working memory: linking early language experiences and language learning outcomes

In order to build complex language from perceptual input, children must have access to a powerful information processing system that can analyze, store, and use regularities in the signal to which the child is exposed. In this article, we propose that one of the most important parts of this underlying machinery is the linked set of cognitive and language processing components that comprise the child's developing working memory (WM). To examine this hypothesis, we explore how variations in the timing, quality, and quantity of language input during the earliest stages of development are related to variations in WM, especially phonological WM (PWM), and in turn language learning outcomes. In order to tease apart the relationships between early language experience, WM, and language development, we review research findings from studies of groups of language learners who clearly differ with respect to these aspects of input. Specifically, we consider the development of PWM in children with delayed exposure to language, that is, children born profoundly deaf and exposed to oral language following cochlear implantation and internationally adopted children who have delayed exposed to the adoption language; children who experience impoverished language input, that is, children who experience early bouts of otitis media and signing deaf children born to nonsigning hearing parents; and children with enriched early language input, that is, simultaneous bilinguals and second language learners

8.4GHz VLBI observations of SN2004et in NGC6946

We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20 February 2005 (151 days after explosion). The Very Large Array (VLA) flux density was 1.23$\pm$0.07 mJy, corresponding to an isotropic luminosity at 8.4GHz of (4.45$\pm$0.3)$\times10^{25}$ erg s$^{-1}$ Hz$^{-1}$ and a brightness temperature of (1.3$\pm$0.3)$\times10^{8}$ K. We also provide an improved source position, accurate to about 0.5 mas in each coordinate. The VLBI image shows a clear asymmetry. From model fitting of the size of the radio emission, we estimate a minimum expansion velocity of 15,700$\pm$2,000 km s$^{-1}$. This velocity is more than twice the expected mean expansion velocity estimated from a synchrotron self-absorbed emission model, thus suggesting that synchrotron self-absorption is not relevant for this supernova. With the benefit of an optical spectrum obtained 12 days after explosion, we favor an emission model which consists of two hot spots on an underlying expanding shell of width comparable to that of SN 1993J.Comment: Accepted for publication in A&A (22/05/07

AGN-Host Galaxy Connection: Morphology and Colours of X-ray Selected AGN at z < 2

The connection between AGN and their host galaxies has been widely studied over recent years, showing it to be of great importance for providing answers to some fundamental questions related with AGN fueling mechanisms, their formation and evolution. Using X-ray and one of the deepest broad-band optical data sets, we studied morphology and colours in relationship with X-ray properties for sources at redshifts z < 2.0, using a sample of 262 AGN in the Subaru/XMM-Newton Deep Survey (SXDS). Morphological classification was obtained using the galSVM code, one of the new methods useful especially when dealing with high-redshift sources and low-resolution data. Colour-magnitude diagrams were studied in relationship with redshift, morphology, X-ray obscuration, and X-ray-to-optical flux ratio. Finally, the significance of different regions was analysed on colour-magnitude diagrams, relating the observed properties of AGN populations with some models of their formation and evolution.Comment: 24 pages, 19 figures, accepted for publication in Astronomy&Astrophysic

Exploratory study evaluating the relationships between perinatal adversity, oxidative stress, and infant neurodevelopment across the first year of life.

Early childhood adversity increases risk for negative lifelong impacts on health and wellbeing. Identifying the risk factors and the associated biological adaptations early in life is critical to develop scalable early screening tools and interventions. Currently, there are limited, reliable early childhood adversity measures that can be deployed prospectively, at scale, to assess risk in pediatric settings. The goal of this two-site longitudinal study was to determine if the gold standard measure of oxidative stress, F2-Isoprostanes, is potentially a reliable measure of a physiological response to adversity of the infant and mother. The study evaluated the independent relationships between F2-Isoprostanes, perinatal adversity and infant neurocognitive development. The study included mother-infant dyads born >36 weeks' gestation. Maternal demographic information and mental health assessments were utilized to generate a perinatal cumulative risk score. Infants' development was assessed at 6 and 12 months and both mothers and infants were assayed for F2-isoprostane levels in blood and urine, respectively. Statistical analysis revealed that cumulative risk scores correlated with higher maternal (p = 0.01) and infant (p = 0.05) F2-isoprostane levels at 6 months. Infant F2-isoprostane measures at 2 months were negatively associated with Mullen Scales of Early Learning Composite scores at 12 months (p = 0.04). Lastly, higher cumulative risk scores predicted higher average maternal F2-isoprostane levels across the 1-year study time period (p = 0.04). The relationship between perinatal cumulative risk scores and higher maternal and infant F2-isoprostanes at 6 months may reflect an oxidative stress status that informs a sensitive period in which a biomarker can be utilized prospectively to reveal the physiological impact of early adversity

Perceptual Other-Race Training Reduces Implicit Racial Bias

Background: Implicit racial bias denotes socio-cognitive attitudes towards other-race groups that are exempt from conscious awareness. In parallel, other-race faces are more difficult to differentiate relative to own-race faces – the ‘‘Other-Race Effect.’ ’ To examine the relationship between these two biases, we trained Caucasian subjects to better individuate other-race faces and measured implicit racial bias for those faces both before and after training. Methodology/Principal Findings: Two groups of Caucasian subjects were exposed equally to the same African American faces in a training protocol run over 5 sessions. In the individuation condition, subjects learned to discriminate between African American faces. In the categorization condition, subjects learned to categorize faces as African American or not. For both conditions, both pre- and post-training we measured the Other-Race Effect using old-new recognition and implicit racial biases using a novel implicit social measure – the ‘‘Affective Lexical Priming Score’ ’ (ALPS). Subjects in the individuation condition, but not in the categorization condition, showed improved discrimination of African American faces with training. Concomitantly, subjects in the individuation condition, but not the categorization condition, showed a reduction in their ALPS. Critically, for the individuation condition only, the degree to which an individual subject’s ALPS decreased was significantly correlated with the degree of improvement that subject showed in their ability to differentiate African American faces