EFFECTS OF INTERSTIMULUS INTERVAL AND PREDICTABILITY OF EVENT STRUCTURE ON SERIAL REACTION TIME

A mean interstimulus interval (ISI) of 10 sec. resulted in significantly-shorter RTs to a single light stimulus than a 30 sec. average ISI. During a second workperiod the groups performing under each of the two ISI conditions were divided into four subgroups given 0, 25, 50 or 75% interspersion of an additional stimulus (sound). With short ISIs the condition of maximum predictability of event structure (light stimulus only) gave the shortest average RTs. With lessened predictability (increased proportion of the sound stimulus) there was a slight monotonous increase in RT. With long ISIs the same relationship was curvilinear, i.e. 25% interspersion of sound stimulus was most effective in preserving vigilance.     

ABILITIES OF TWINS

The investigation concerns two main problems: (1) the distribution of ability test scores among twins in comparison with single-borns; and (2) intra-pair similarity among the various twin categories. More than 1000 individual twins were compared with 2700 single-borns on 21 test variables covering Swedish, Mathematics and English. The twin group consistently showed a lower average than the single-borns due to a displacement of the test score distribution as a whole among twins. The intra-pair similarities, expressed as intra-class correlations, run between 0.85 and 0.90 for identical pairs, whereas like-sex fraternals showed coefficients about 0.60. The unlike-sex fraternals had coefficients ten to twenty hundredths lower than those of the like-sex pairs.     

Rational understanding: toward a probabilistic epistemology of acceptability

Synthese - To understand something involves some sort of commitment to a set of propositions comprising an account of the understood phenomenon. Some take this commitment to be a species of belief;...