Judgments of proportions.

This study investigated the processes that underlie estimates of relative frequency. Ss performed 4 tasks using the same stimuli (squares containing black and white dots); they judged "percentages" of white dots, "percentages" of black dots, "ratios" of black dots to white dots, and "differences" between the number of black and white dots. Results were consistent with the theory that Ss used the instructed operations with the same scale values in all tasks. Despite the use of the correct operation, Ss consistently overestimated small proportions and underestimated large proportions. Variations in the distributions of actual proportions affected the extent to which Ss overestimated small proportions and underestimated large proportions in the direction predicted by range-frequency theory. Results suggest that proportion judgments, and by analogy probability judgments, should not be taken at face value.

Some effects of an ACTH 4-9 analog (Org 2766) on human performance.

The effects (on human beings) of the ACTH analog Org 2766 were investigated for a range of performance tests: complicated serial reaction task, running memory span, verbal learning and non-verbal mental ability tests (closure flexibility and non-verbal abstraction). Subjective ratings on feelings were taken and heart rate was measured. Only the 30-min reaction task produced significant drug effects. In this task performance tends to deteriorate as a function of time on task. During the test period there is a gradual increase in the number of lapses in performance due to moments of inattention. This deterioration is counteracted by the ACTH 4-9 analog, a result also found in previous study using ACTH 4-10 (Org OI63). Thus ACTH fragments which are devoid of endocrine effects seem to have a beneficial effect on goal-directed motivation oriented on the requirements of the task.

Attention effects on auditory EPs as a function of inter-stimulus interval.

The present study focuses on the effect of the duration of the inter-stimulus interval (ISI) on the 'processing negativity', the endogeneous negative brain potential elicited by attended stimuli in various selective-attention paradigms. Three constant ISIs are used, 250 msec. 800 msec, and 2000 msec, in a selective dichotic-listening situation in which the subject's task is to detect occasional slight pitch changes in the input to a designated ear. Frontal (Fz), vertex (Cz), and parietal (Pz) evoked potentials (EP) are recorded. The processing negativity is observed in each condition, even in that involving the 2 sec ISI, which is in contrast with the commonly held view that this attention effect is only obtained with very short ISIs. The processing negativity was observed to have two components: (1) an early, central component of small amplitude which appears to be independent of the ISI: (2) a later, frontal component of large amplitude and long duration which is certainly elicited with long ISIs such as the 800 msec and 2000 msec ISIs used here, but also appears to be present even in the short-ISI condition overlapping the central component. This suggests that it is the frontal component which is sensitive to the ISI.

EP components, visual processing stages, and the effect of a barbiturate.

In a 2 x 2 x 2 factorial experiment, ten subjects carried out a visual choice reaction task. In addition to RT measurement, evoked potentials (EPs) were recorded from the central (Cz) and occipital (Oz) derivations. Independent variables were drug treatment (barbiturate versus placebo), visual stimulus intensity and visual stimulus degradation. The reaction time data showed that visual intensity and degradation had additive effects, which indicates that these variables affect independent stages, i.e. stimulus preprocessing and stimulus encoding. The effect of barbiturate on RT was additive with intensity but appeared to interact with degradation. This suggests a selective effect of that drug on the encoding state. EP components also showed selective effects of intensity, degradation and drug treatment. It was suggested that these components may be related to stages in the reaction process.