LARGE RECEPTIVE-FIELDS FOR OPTIC FLOW DETECTION IN HUMANS

We used a psychophysical summation technique to study the propel-ties of detectors tuned to radial, circular and translational motion, and t o determine the spatial extent of their receptive fields. Signal-to-no ise motion thresholds were measured for patterns curtailed spatially i n various ways. Sensitivity for radial, circular and translational mot ion increased with stimulus area at a rate predicted by an ideal integ rator. When sectors of noise were added to the stimulus; sensitivity d ecreased at a rate consistent with an ideal integrator. Summation was tested for large annular stimuli, and shown to hold up to 70 degrees i n some cases, suggesting very large receptive fields for this type of motion (consistent with the physiology of neurones in the dorsal regio n of the medial superior temporal area (MSTd)). This is a far greater area than observed for summation of contrast sensitivity to gratings ( Anderson SJ and Burr DC, Vis Res 1987;29:621-635, and to this type of stimuli (Morrone MC, Burr DC and Vaina LM, Nature 1995;376:507-509, co nsistent with the suggestion that the two techniques examine different levels of motion analysis. (C) 1998 Elsevier Science Ltd. All rights reserved.