CAPTURE OF VISUAL DIRECTION - AN UNEXPECTED PHENOMENON IN BINOCULAR VISION

Binocular perception of visual direction is based on laws which were f ormulated more than 100 years ago. These laws govern the directions in which human beings perceive objects visible to both eyes (binocular o bjects) and objects visible to only one eye (monocular objects). We re port here that the laws do not hold for monocular objects adjacent to binocular objects. The perceived directions of these monocular objects are captured by those of nearby binocular objects. Capture of binocul ar visual direction is an unexpected phenomenon because it refutes the generally accepted notion that a particular retinal location gives ri se to a particular subjective visual direction. The practical conseque nce is that the subjective techniques for measuring eye position which are widely used in fundamental research and clinical practice are unr eliable if they are used in densely structured stimuli. We suggest tha t capture results from a mechanism of lateral interaction between adja cent visual directions. This mechanism ensures that, despite eye movem ents, objects have the same spatial order in monocular and binocular v ision. This conservation of spatial order also explains why retinal bl ind spots are not manifest in binocular vision. (C) 1997 Elsevier Scie nce Ltd.