Rarefaction and resolution, stimulus area and detection: an order of priority.

The aim of this research was to establish the priority of different effects between phenomenal variables in acuity tasks. The phenomenon we considered--observed at first by Vicario in 1971--is a good example of links between different percepts. In Exp. 1 the threshold of the resolution distance of square gratings having the same phenomenal frequencies (as observed in a 1985 experiment by Vardabasso and Zanuttini), although different areas, was checked. The distance at which the oblique lines, with the same phenomenal frequencies, are distinguished does not differ significantly for the two squares. In Exp. 2 we checked the effect of two different variables--the physical spacing between the lines and the area of the pattern--on detection thresholds on a task which allowed comparing the distance at which a gap in the diagonal of the squared gratings "small and large", "sparse and dense" was detected.

Regularity, exposure time and perception of numerosity.

Two experiments are described. In Exp. 1, subjects compared the apparent numerosity of two kinds of dot patterns, regular vs irregular, with two different exposures (160 vs 2000 msec.). In Exp. 2, the subjects had to estimate the numerosity of the same patterns, presented one at a time. Analysis showed a relative overestimation of the regular patterns in Exp. 1 but not in Exp. 2. In general an overestimation occurred with an increase in exposure. Such results support our hypothesis of two separate processes as the basis of the two kinds of performance (estimating vs comparison).