Spatial attention in Ponzo-like patterns.

A variant of Ponzo's pattern was devised by drawing converging oblique lines at the ends of each of two horizontal lines that were located directly one above the other. Pairs of converging or diverging fins (either between or outside the horizontal shafts) were systematically removed. The results showed that, as predicted by integrative field theory, oblique lines between the shafts produced more distortion than did oblique lines outside the shafts. Also, it was shown that the attentive field construct in integrative field theory was crucial for predicting patterns of means and variances in this experiment. The modified Ponzo effect was shown to have much in common with the classical Müller-Lyer illusion. The subtle differences between the two were explained by proposing that the size of the optimum attentive field was larger in the Ponzo tasks than in the Müller-Lyer tasks because expansion fins are found on both shafts in the Ponzo-like figure.

Attentive fields are related to focal and contextual features: a study of Müller-Lyer distortions.

The mathematical model associated with integrative field theory was used to infer the size of attentive fields in a task involving judgments of size. A compounded Müller-Lyer task was employed in which fins between or outside the standard shafts were systematically removed. Performance on this task was simulated by a computer that generated families of theoretical functions varying in the parameter of attentive field size. Individual theoretical functions were then correlated with an empirical function obtained from real observers. The value of attentive field size that provided the best fit between functions was then selected. The results showed that, in almost all cases, the optimum size of the attentive field was smaller for the shrinkage form than for the expansion form of the Müller-Lyer pattern, that the attentive field changed more dramatically with changes in stimulus variables in the expansion form than in the shrinkage form, and that changes in viewing distance had little effect on the optimum size of the attentive field. It was concluded that the attention was involved both in figure-ground segregation and in maintaining object constancy. The similarity of these results to data obtained in recognition and detection tasks was noted.

In defense of the assimilation theory of visual illusions.

It is argued that, contrary to Schiano's view (1986), assimilation theory does explain the nonmonotonic relationship between degree of distortion and size of context.

Contrast and assimilation in the Baldwin illusion.

Four experiments were conducted to investigate the role of "large" squares on the occurrence of assimilation and contrast in the Baldwin illusion. In Exps. 1 and 2, in which subjects reproduced the length of the test line, large squares induced illusions of assimilation. In Exp. 3, reproduction of the entire length of the test line also resulted in illusions of assimilation but bisection of the test line and reproduction of one-half the length of the test line resulted in contrast. Exp. 4 replicated the findings involving judgments of one-half the length of the test line. Over-all, the results indicate that judgments of one-half the length of the test line result in contrast, whereas judgments of the entire extent result in assimilation.

Psychophysical methods and life-span changes in visual illusions.

Research designed to establish the relationship between chronological age and visual distortion has produced reliable but contradictory findings. It is proposed that the contradictions cannot be resolved by better experimental techniques; that laws do not exist in nature independently of the observer, and that psychological scientists must include the observer and the measuring device as integral components of their enterprise.

Evidence for the role of attentive fields in masking.

A masking task was employed to determine whether predictions derived from the attentive-field postulate of assimilation theory could be verified. The distance between masking and test lines was varied both towards and away from the center of the attentive field. As predicted, masking was greater when the mask was near the center of attention than when it was located at the periphery of the field. A variation of the mathematical formula developed previously to predict visual illusions was employed to fit the individual and group functions found in this study.

Are black circles attentive fields? A reply to Bross, Blair, and Longtin.

It is argued that the experiment carried out by Bross et al is not a valid test of assimilation theory because they confuse a graphic representation of a constant with the construct itself and assume that changing the former will alter the latter.

Effects of gap size between shaft and fins and of angle of fins on the Müller--Lyer illusion.

Assimilation theory was employed to generate quantitative predictions relating the ingoing Müller--Lyer illusion to both angle of fin and gap between shaft and fin. Gap sizes were varied from zero to 18 mm in steps of 2 mm, and angles of fins were varied from 30 degrees to 180 degrees in steps of 30 degrees. Five subjects adjusted the length of a comparison line to match the apparent length of the shaft at each combination of gap size and angle of fin. It was predicted that the gap necessary for a reversed illusion to occur, and the gap at which the maximal reversed effect occurred, would be inversely related to angle of fins. Empirical functions verified the predictions.