The representation of nonuniform motion: induced movement

Induced motion occurs when there is a misallocation of nonuniform motion. Theories of induced motion are reviewed with respect to the model for uniform motion recently proposed by Swanston, Wade, and Day. Theories based on single processes operating at one of the retinocentric, orbitocentric, egocentric, or geocentric levels are not able to account for all aspects of the phenomenon. It is therefore suggested that induced motion is a consequence of combining two different types of motion signals: one provides information by registering the motion with respect to the retina, orbit, and egocentre; the other provides information only on the relational motions between the pattern elements. Simple rules are given for defining a frame of reference for the relational motion process, which can result in a reallocation of the motion signals. It is proposed that the two signals in combination are weighted differentially, with the greater influence coming from the relational signals. Procedures for determining the weighting factors are described, and predictions from the model are examined.     

The perception of continuous curves in dot stimuli

Two categorisation experiments are reported in which the perceptual phenomenon that some simple arrays of discrete dots appear as a continuous curve whereas others are perceived as an angular contour or as consisting of separate groups of dots was investigated. Triplets of dots were presented in the first experiment, and complete or incomplete regular dot polygons (ie dots positioned on the vertices of imaginary regular polygons) in the second. In both experiments the perception of a curve versus an angle was determined mainly by the relative orientations of the dots, ie by the angles between successive virtual lines, whereas the lengths of the virtual lines had relatively little influence. In experiment 2 the number of displayed dots was shown to be a second independent factor for perceiving continuity. These results are in agreement with results from experiments on dipole textures discrimination, and suggest the psychological existence and importance of virtual lines in the visual processing of dot stimuli.     

Remembering left-right orientation of pictures

In a study of recognition memory for pictures, we observed an asymmetry in classifying test items as "same" versus "different" in left-right orientation: Identical copies of previously viewed items were classified more accurately than left-right reversals of those items. Response bias could not explain this asymmetry, and, moreover, correct "same" and "different" classifications were independently manipulable: Whereas repetition of input pictures (one vs. two presentations) affected primarily correct "same" classifications, retention interval (3 hr vs. 1 week) affected primarily correct "different" classifications. In addition, repetition but not retention interval affected judgments that previously seen pictures (both identical and reversed) were "old". These and additional findings supported a dual-process hypothesis that links "same" classifications to high familiarity, and "different" classifications to conscious sampling of images of previously viewed pictures.     

Auditory-visual interaction and the timing of inputs

Summary The objective of this study was to analyze the structural properties of the respective inputs that are conducive to immediate auditory-visual cross-modal bias. The study was designed as an updated and extended replication of one by Thomas (1941). Subjects were presented with either auditory or visual target signals in several positions around the median plane, together with a competing signal, always in the other modality, 15° to the left or to the right of that plane. The task was to indicate whether the target signal came left or right of center. Target and competing signals were delivered according to three temporal configurations: continuously on for 4 s, or periodically interrupted at either a fast or a slow tempo, and all combinations of the three configurations were used. Judgements of the location of the auditory target signal were attracted toward the visual competing signal in all conditions but two, those with a periodic target signal and a continuous competing one. Conditions with the two signals in the same configuration yielded larger biases than those combining different configurations, confirming that synchronization of discordant inputs is a major condition of cross-modal interactions. The occurrence of significant bias in nonsynchronous conditions, on the other hand, suggests that another factor might be the attraction of localization responses by competing signals with salient temporal configurations, and that interruption might be one important source of saliency. Auditory biases of visual localization were, as usual, smaller than visual biases, but nevertheless reached significance in a majority of conditions, and were also influenced by timing in much the same way as the latter.This work was supported in part by the Belgian Fonds de la Recherche Fondamentale Collective (FRFC) under convention 2.4505.80. The first author is Chercheur qualifié of the Fonds National de la Recherche Scientifique (FNRS). The results have already been reported at the Symposium on Perception, Action and Development, Brussels, January 1984