Psychomotor, subjective and neuroendocrine effects of acute tryptophan depletion in the healthy volunteer

SummaryThe effects of acute tryptophan depletion were investigated in 20 healthy volunteers. Ten of them received a balanced amino acid solution and 10 a tryptophan-free solution. The fall in tryptophan levels induced by the oral administration of a mixture tryptophan-free of L-amino acids was - 77% for free tryptophan and - 81% for total tryptophan. Before treatment, there were intergroup differences affecting alertness parameters (critical flicker threshold, recognition reaction time), plasma levels of prolactin and baseline performance in the proofreading correction test. In the tryptophan-depleted group, the number of errors reported during the unpleasant sound signal was increased (+ 48%) after treatment, whereas the number of errors fell (— 15%) in the group receiving the tryptophan supplement. Conversely the levels of prolactin were correlated with those of serum tryptophan. Few subjective effects were reported.

Time to Recognise Tones: Memory Scanning or Memory Strength?

Three experiments measured the time to decide whether a probe tone was a member of a set of one to four remembered tones. Reaction time increased with the size of the remembered set, and in one experiment the functions were similar to functions that have been reported for recognition of verbal items. Positive reaction time was largely determined by recency of presentation of the probed item. Variables thought to influence memory strength of tones (interpolated noise, delay, and tone duration) proved to affect recognition reaction time. However, the positive relation found between error rate and error reaction time disconfirmed a prediction of memory strength models based upon the theory of signal detection. Possible memory strength and memory scanning theories were considered.

Does Post-Exposural Directional Scanning Offer a Sufficient Explanation for Lateral Differences in Tachistoscopic Recognition?

White's recent criticisms of experiments by McKeever and Huling are discussed. The points are made that, contrary to White's claim, McKeever and Huling never attributed all obtainable lateral recognition differences to effects of cerebral dominance and that White's criticisms in no way establish a directional scanning hypothesis as compatible with the results obtained under the conditions of the McKeever and Huling experiments. That the scanning hypothesis also fails to account for many other results obtained in recognition and recognition reaction time studies is indicated.