Sunday, May 25, 2008

Child care quality matters

Love et al. (August 2003). Child care quality matters: how conclusions may vary with context. Child Development, 74, 4, 1021-1033.

A report from the NICHD concluded that more time spent in a variety of nonmaternal care arrangements leads to more externalizing behavior problems, regardless of child care quality. Authors were skeptical and tested the generalizability of these findings with 3 other studies. These new findings suggest that quality of child care is an important factor influencing children's development, and that quality may be an important moderator of the amount of time in care.

Friday, May 9, 2008

Cultural variation in infant's sleeping arrangements

Morelli, G.A., Rogoff, B., Oppenheim, D., & Goldsmith, D. (1992). Cultural variation in infant's sleeping arrangements: Questions of Independence. Developmental Psychology, Vol. 28, No. 4, 604-613.

Cultural practices differentiate infant sleep arrangements. In the middle-class US population, a common goal is to have infants sleep in their own rooms as soon as possible, consonant with the culture's importance on independence. In the Mayan population, it is not uncommon for children to sleep with their parents or other siblings well on into childhood, reflecting their culture's value on interpersonal relations. Changes are not prescribed by the authors; instead, broader cultural perspective is offered for American readers.

Wednesday, May 7, 2008

Seasonal changes of hippocampus volume in parasitic cowbirds

Clayton, N.S., Reboreda, J.C., & Kacelnik, A. (1997). Seasonal changes of hippocampus volume in parasitic cowbirds. Behavioral Processes, 41, 237-243.

This study compared a set of phylogenetically closely related species with striking differences in natural behavior, offering the opportunity for seeking neural differences in association with these behavioral changes. Notable differences exist in these South American cowbirds of the genus Molothrus related to parasitic nesting. In one species, the birds are especially active during the breeding season, searching and locating potential hosts' nests. In another two species, only females are active during the breeding season in locating potential hosts' nests (sexual dimorphism). A fourth species is non-parasitic and no sexual differences are known with respect to spatial memory use in either season. Results show that the first species shows significantly larger relative hippocampal volume in the breeding season. The sexual dimorphic species show significantly larger relative hippocampal volume in the breeding season, but only in females. The evidence suggests seasonal variation in neuroanatomy associated with specific changes in behavior, namely spatial memory demands, as opposed to purely seasonal fluctuations per se.

Continuous flash suppression reduces negative afterimages

Tsuchiya, N. & Koch, C. (August 2005). Continuous flash suppression reduces negative afterimages. Nature Neuroscience, Vol. 8, No. 8, 1096-1101.

Continuous flash suppression (CFS) is a tool that can be used to reliably suppress vivid images from conscious awareness for long periods of time. Here, different patterned images ("Mondrians") are flashed rapidly into one eye while input to the corresponding location in the other eye remains fixed, the latter typically remaining unseen often for durations greater than ten times what can be achieved with binocular rivalry or other masking methods, even though the image remains present on the retina for several minutes. Interestingly, researchers discovered that negative afterimages or "photogenes", effects lingering in view after termination of the visual stimulus, also seem to be diminished with exposure to CFS. Though it is widely believed that afterimages originate among retinal neurons, this evidence supports the conclusion that the weakened afterimage must be due to interference from sites at or beyond binocular convergence, such as the lateral geniculate nucleus (LGN) or cortex. Specifically, it must be an area which receives input from both eyes but does not correspond directly to the neuronal correlates of perceptual awareness. The results hint at differences between concepts of attention and awareness.

Tuesday, May 6, 2008

Sign Language in the Brain

Hickok, G., Bellugi, U. & Klima, E.S. (June 2001). Sign Language in the Brain. Scientific American.

Because sign language relies heavily upon visual-spatial contrast, one might expect sign language to be supported by systems in the right hemisphere rather than the traditional left hemisphere language systems. However, this does not appear to be the case. A deaf signer with damage to Wernicke's area is likely to have comprehension difficulties and one with damage to Broca's area may have difficulty producing signs, just like normal speakers. And signers with right hemisphere damage continued to be fluent and accurate in their production of signs, used normal grammar, and comprehended signs with ease. One exception of the left hemisphere's monopoly on language production is creation of a coherent discourse, where right hemisphere damage may lead to rambling as it tends to be involved in more global-level processes. Generally speaking, sign language abilities of lifelong signers appear to be independent of their nonlinguistic spatial skills. Thus, it is likely that signers maintain unique early stages of processing compared to regular speakers, but thereafter neural organization is quite similar, being translated into a format optimized for linguistic processing and being routed to central linguistic systems.

Monday, May 5, 2008

Marijuana use as a coping response

Preston, P. (2006). Marijuana use as a coping response to psychological strain: racial, ethnic, and gender differences among young adults. Deviant Behavior, 27, 397-420.

Besides tobacco and alcohol, marijuana is the most frequently used and abused substance. This study used data taken from the National Household Survey of Drug Abuse (from all 50 states), and examined 4601 subjects between the ages of 18-25 who used marijuana within the past year. Their dependent variable was marijuana use frequency, defined as either recreational or chronic, with chronic being greater than 12 times per month. Independent variables measured included strain, economic strain, norms favorable to drug use, number of friends who use drugs, and attitudes towards risky behavior. Results were also examined through the lenses of gender, ethnicity, marital status, employment status, and education.

Results indicate that social learning factors have the strongest effect on chronic marijuana use, operationalized as the number of friends who use drugs and a personal approval of drug use. Strain (operationalized as social nervousness) had the next strongest effect. Self control had a weak effect overall. High school dropouts and the unmarried were found to be particularly at risk for becoming chronic users. Strain appeared to have a stronger effect on minority groups, possibly suggesting fewer alternative coping strategies in this population. Minority women experience a "double-whammy", more likely than their nonminority counterparts to be chronic users and also more likely to be affected by social learning and self control variables.

Love in Infant Monkeys

Harlow, H.F. (June 1959). "Love in Infant Monkeys", Scientific American.

Harlow used baby rhesus monkeys to yield insights into the origin of the infant's love for its mother and concluded that bodily contact comfort is a decisive variable in this relationship. For example, newborn monkeys preferred a surrogate "cloth" mother to a "wire" mother, and sought out the cloth mother in times of emotional stress. Other variables were also explored. A mother's rocking motion appeared to enhance affection, but less so than simple contact. Heat of the mother did not appear to be an important variable. Other visual, auditory, and olfactory stimulation may also play a role. Additionally, a critical period to attachment formation seems to be evident.