The locus of maximum weighting within attentive fields: an empirical investigation

Effects of method, orientation, and size of angle on the Ponzo illusion

The Ponzo figure was used to test predictions based upon Pressey's 1971 concept of attentive fields. Subjects made judgements using either the method of successive reproduction (n = 18) or the method of reproduction (n = 17). Size of the acute angle between the oblique and test lines (30 degrees, 45 degrees, and 60 degrees) and orientation of test figures (apex pointed up, left, right, and down) were varied. It was predicted with the method of successive reproduction that illusions of shrinkage would occur and that the variable of orientation would not affect size of illusion. With the method of reproduction the prediction was made that illusions of expansion would occur when the apex pointed up and that illusions of shrinkage would occur when the apex pointed down. Analysis showed that with the method of successive reproduction illusions of shrinkage occurred when the apex was pointed either up or down. When the apex pointed either to the right or left nonsignificant illusions were found. With the method of reproduction the classical illusion of expansion occurred when the apex pointed up but changed to one of shrinkage when the apex pointed down. Size of expansion illusion diminished as the acute angle formed between the oblique and standard lines decreased. In general, some of the results were consistent with Pressey's concept of attentive fields.

Assessment of apparent length and angle explanations of the Poggendorff effect

Explanations of the Poggendorff effect were assessed by comparing the degree of angular distortion induced by modified and traditional configurations. Assimilation theory predicted that the traditional effect would be reversed in modified configurations. Analysis showed that the effect, although reduced in magnitude, was not reversed. Comparison of the degree of the effect induced by modified and traditional configurations indicated that a substantial portion of the Poggendorff effect was due to processing of areas between the long vertical lines of the display. This finding is not consistent with theories based on subjective distortion of angles. It was concluded that a theory of the Poggendorff effect must include processing of internal areas of the configuration.

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.