Elevation and reduction of plasma tryptophan and their effects on aggression and perceptual sensitivity in normal males

Data from experimental animals suggest that 5-hydroxytryptamine (5HT) may have an inhibitory effect on aggression, while clinical studies have found a correlation between pathological aggression and low brain 5HT. To investigate this relationship further we used amino acid mixtures designed to raise or lower the levels of the 5HT precursor, tryptophan. Normal male subjects were given tryptophan-depleted, balanced, or tryptophan-supplemented ammo acid mixtures and tested for aggression 5 hours later. The balanced amino acid mixture served as a control for the tryptophan depletion and supplementation. Testing for aggression was done using the Buss paradigm in which subjects deliver electric shocks to a (nonexistent) partner in response to stimulus tones. Duration and intensity of shock delivered were the measures of aggression, while responsivity to the stimulus tones was the measure of perceptual sensitivity. Neither tryptophan supplementation nor tryptophan depletion had any effect on these measures of aggression or perceptual sensitivity. We conclude that raising or lowering the synthesis of brain 5HT through alterations in tryptophan availability does not influence aggression in normal males as measured by the Buss task.     

Subtyping versus bookkeeping in stereotype learning and change: connectionist simulations and empirical findings

A distributed connectionist network can account for both bookkeeping (M. Rothbart, 1981) and subtyping (M. B. Brewer, V. Dull, & L. Lui, 1981; S. E. Taylor, 1981) effects. The finding traditionally regarded as demonstrating subtyping is that exposure to moderate (compared with extreme) disconfirmers leads to subsequent ratings of the group that are less stereotypic. Despite learning that is incremental and analogous to bookkeeping, the simulations replicate this finding and suggest that the "subtyping" pattern of results will be drastically reduced if disconfirmers are encountered before the stereotype is well-established. This novel prediction holds with human participants and offers a tantalizing suggestion: Although moderate disconfirmers may produce more stereotype change. stereotype development might be discouraged by exposure to either extreme or moderate disconfirmers.     

Differential age effects for case and hue mixing in visual word recognition

The authors compare older adults' lexical-decision data with younger adults' data reported in P. Allen, A. F. Smith, et al. (2002). On the basis of their work, it was proposed that consistent-case wordswould be processed by the faster holistic (magnodominated) stream, but that mixed-case words would be processed by the slower analytic (interblob-dominated or blob-dominated) steams. Hue mixing was predicted to have no effect on consistent-case performance, but mixed-hue/mixed-case words were predicted to be recognized faster than monochrome/mixed-case words. Younger adults showed the predicted results, but older adults did not. These results suggest that holistic central processes are maintained, but that older adults exhibited an analytic decrement     

Inhibition and superconditioning

Superconditioning is said to occur when learning an association between a conditioned stimulus (CS) and unconditioned stimulus (US) is facilitated by pairing the CS with the US in the presence of a previously established conditioned inhibitor. Previous demonstrations of superconditioning have been criticized because their control conditions have allowed alternative interpretations. Using a within–subjects autoshaping procedure, the present study unambiguously demonstrated superconditioning. The results support the view that superconditioning is the symmetric opposite of blocking.     

On boredom and experimentation in humans

This article discusses the ethical and methodological issues associated with boredom experienced by human participants during psychological experiments. Ways are suggested in which informed consent, briefing, and debriefing can be used to prevent or remedy boredom induced during experiments. We address methodological and ethical concerns, and we discuss the advantages of the proposed approach for experimenters' practice and training of undergraduate students. Future directions for much needed research on these topics are also emphasized.