Neurophysiological evidence for visual perceptual categorization of words and faces within 150 ms

The nature and early time course of the initial processing differences between visually matched linguistic and nonlinguistic images were studied with event-related potentials (ERPs). The first effect began at 90 ms when ERPs to written words diverged from other objects, including faces. By 125 ms, ERPs to words and faces were more positive than those to other objects, effects identified with the P150. The amplitude and scalp distribution of P150s to words and faces were similar. The P150 seemed to be elicited selectively by images resembling any well-learned category of visual patterns. We propose that (a) visual perceptual categorization based on long-term experience begins by 125 ms, (b) P150 amplitude varies with the cumulative experience people have discriminating among instances of specific categories of visual objects (e.g., words, faces), and (c) the P150 is a scalp reflection of letterstring and face intracranial ERPs in posterior fusiform gyrus.     

Categorization of infant-directed speech: development from 4 to 6 months

To extend a previous finding that 6-month-old infants categorized low-pass filtered infant-directed (ID) utterances, we examined a) 6-month-old infants' categorization of more naturalistic, unfiltered ID utterances and b) the developmental progression of ID-speech categorization. In Experiment 1, 6-month-olds heard seven different unfiltered tokens from one class of ID utterance (approving or comforting), followed by a novel token from either the same or an unfamiliar category. Infants recovered, responding only to the unfamiliar category token, suggesting that they categorized naturalistic ID utterances. Four-month-olds' categorization of filtered and unfiltered versions of the ID utterances was assessed in Experiments 2 and 4. Four-month-olds did not recover, responding to a test token from an unfamiliar class, suggesting that they did not categorize either filtered or unfiltered ID utterances. Experiment 3 demonstrated that 4-month-old infants' failure to categorize did not result from their inability to complete the procedure. These results suggest that infants' processing of ID speech changes from 4 to 6 months of age.     

The International Society for Developmental Psychobiology annual meeting symposium: Impact of early life experiences on brain and behavioral development

Decades of research in the area of developmental psychobiology have shown that early life experience alters behavioral and brain development, which canalizes development to suit different environments. Recent methodological advances have begun to identify the mechanisms by which early life experiences cause these diverse adult outcomes. Here we present four different research programs that demonstrate the intricacies of early environmental influences on behavioral and brain development in both pathological and normal development. First, an animal model of schizophrenia is presented that suggests prenatal immune stimulation influences the postpubertal emergence of psychosis-related behavior in mice. Second, we describe a research program on infant rats that demonstrates how early odor learning has unique characteristics due to the unique functioning of the infant limbic system. Third, we present work on the rodent Octodon degus, which shows that early paternal and/or maternal deprivation alters development of limbic system synaptic density that corresponds to heightened emotionality. Fourth, a juvenile model of stress is presented that suggests this developmental period is important in determining adulthood emotional well being. The approach of each research program is strikingly different, yet all succeed in delineating a specific aspect of early development and its effects on infant and adult outcome that expands our understanding of the developmental impact of infant experiences on emotional and limbic system development. Together, these research programs suggest that the developing organism's developmental trajectory is influenced by environmental factors beginning in the fetus and extending through adolescence, although the specific timing and nature of the environmental influence has unique impact on adult mental health.