Foreground and background in dynamic spatial orientation

The dependency of visually induced self-motion sensation upon the density of moving contrasts as well as upon additional stationary contrasts in the foreground or background was investigated. Using two different optokinetic stimuli, a disk rotating in the frontoparallel plane, and the projection of horizontally moving stripes onto a cylindrical screen, it was found that: (1) visually induced self-motion depends upon the density of moving contrasts randomly distributed within the visual field and, with a single contrast area of 1/4 %, is saturated when about 30% of the visual field is moving; (2) additional stationary contrasts inhibit visually induced serf-motion, proportional to their density; and (3) the location in depth of the stationary contrasts has a significant effect upon this inhibition. Their effect is considerable when located in the background of the moving stimuli but weak when appearing in the foreground. It is concluded that dynamic visual spatial orientation relies mainly on information from the seen periphery, both retinal and depth.     

Tactile roughness of grooved surfaces: A model and the effect of friction

Previous experimental data on the roughness of grooved aluminum tiles provide a data base against which to test theories of roughness perception. A model based on the static deformation of the skin touching the stimulus tile is developed, and 11 parameters of the deformation are individually compared with the experimental data. All parameters were tested first in an approximate way, and then the better parameters were recalculated in a more exact manner. Three parameters, the depth to which the finger penetrates the groove, the cross-sectional area of the finger within the groove, and the cross-sectional area of the deviation of the skin from its resting position, all predict the roughness well as a function of finger force and groove width. The last of the three predicts roughness best as a function of land width, and is tentatively preferred as “the stimulus for roughness.” All predictions from the static model indicate that variation of the coefficient of friction between skin and tile should have little or no effect. This counterintuitive prediction was confirmed by an experiment.     

Range estimates of distant visual stimuli

Os made magnitude estimations of the range of visual targets located at physical distances from a few hundred yards or less to more than 5 miles. The targets were at different elevations in different experiments so that O’s gaze varied from 0 to 90 deg. The targets were presented against the empty sky or against water. The Os were stationary in most experiments, but were in motion in one. Results show that the psychophysical functions are power functions whose exponents range from ca. 1.25 to 0.8, depending on the angle of the target above the horizontal. Background texture or O motion had no effect.     

Individual commitment to risky and conservative choices as a determinant of shifts in group decisions1

The consistently positive relationship between initial riskiness and perceived influence obtained in past work led us to speculate that (1) the deliberative effort involved in making a choice increases with its riskiness, as a result (2) individuals who select a risky course of action will be more committed to their choice than conservative individuals, and (3) the former will be more influential in group decisions. The following support was obtained for these conjectures When individuals had to select a reaction time interval to beat, those who were risky, that is, who selected a short interval, were more confident in having chosen wisely, were less likely to feel they might change their choice given the opportunity, and took longer to make their choice than those who were conservative, that is, who selected a long interval The first two of these measures were assumed to reflect commitment to the choice, and the third was taken as a rough indication of the amount of effort involved in choosing A group decision was also made regarding the reaction time interval It tended to be riskier than that preferred by the average individual prior to the decision if the riskiest member was more committed and/or expended more effort in choosing than his partners, on the other hand, it tended to be more conservative than the average prior preference if the most conservative member was more committed and or expended more effort