Methylphenidate-induced information processing dysfunction in nonschizophrenic patients.

To examine the relationship of aminergic overactivity to information processing, we gave methylphenidate hydrochloride, oxazepam, or placebo to 12 nonpsychotic patients in one-week blocks in a double-blind, randomized design. Methylphenidate induced a pattern of information processing dysfunction similar to that seen in schizophrenic patients, strengthening the linkage of the schizophrenia-information processing dysfunction-aminergic overactivity relationship. Further, the time course of the observed deficits in both schizophrenic and methylphenidate-induced states is strikingly compatible with the temporal mapping pattern of monoaminergic neuronal systems. More research is needed to identify definitively the aminergic influences on attentional functioning. A psychophysical task-pharmacologic probe strategy should prove useful.

Impaired speed of visual information processing in marijuana intoxication.

The authors conducted a double-blind crossover study to investigate the effects of marijuana on visual information processing. The authors used a tachistoscopic paradigm, and the results show no marijuana effect on the critical stimulus duration, a measure of stimulus intake. The visual backward masking data are compatible with a marijuana-induced slowness of information processing from labile unconscious iconic memory to more permanent memory processes. These results are discussed in relation to reports of marijuana's effects on perception and early information processing.

Investigations into the nature of the association between threshold microstructure and otoacoustic emissions.

Three studies are described which investigate the nature of the association between threshold microstructure and otoacoustic emissions. In the first study, threshold dips (similar in shape to those seen in threshold microstructure) are produced by introducing a low-level masker. Threshold microstructure is not abolished when tonal probes are replaced by narrowband-noise probes, while dips induced by external tonal maskers are eliminated. These findings rule out a simple interpretation of the microstructure dips as an instance of masking by otoacoustic emissions. In the second study, ear-canal measurements of the interactions of external tones with spontaneous emissions indicate that, although beating is often detected near threshold maxima, stimuli close to threshold minima are perceived as tonal because the emission is frequency locked by the external tone. The last study shows that reduction of the levels of otoacoustic emissions by aspirin consumption is associated with an initial reduction of thresholds in regions of threshold microstructure, with the greatest reduction occurring at threshold maxima. This suggests that threshold maxima may be due, at least in part, to interference or masking by the nearby otoacoustic emissions. A simple analog (driven Van der Pol oscillator) of an external tone interacting with a spontaneous emission is used to interpret ear-canal pressure waveforms and associated psychophysical percepts (including threshold detection), for tones close in frequency to emissions.

[Strengthening interhemispheric interferential inhibition in man with diazepam]. / Usilenie diazepamom mezhpolusharnogo interferentsionnogo tormozheniia u cheloveka.

The influence of oral diazepam administration (10 mg) on interhemispheric proactive and retroactive interferential inhibition during detection of test verbal signals was tachistoscopally studied in eight healthy right-handed subjects, in conditions of forward and backward contralateral masking according to the scheme of double blind investigations. Strengthening of effects of forward and backward contralateral masking was revealed which is considered as a testimony to participation of GABA-ergic inhibitory systems in the mechanisms of interhemispheric proactive and retroactive interferential inhibition.