1. Salk Institute for Biological Studies, La Jolla, California 92037, USA
2. Present address: Henry Wellcome Building for Neuroecology, University of Newcastle upon Tyne, NE2 4HH, UK.

Correspondence to: Gene Stoner¹ Correspondence and requests for materials should be addressed to G.S. (e-mail: Email: gene@salk.edu).

Natural visual scenes are cluttered with multiple objects whose individual features must somehow be selectively linked (or 'bound') if perception is to coincide with reality. Recent neurophysiological evidence^{1, 2} supports a 'binding-by-synchrony' hypothesis³: neurons excited by features of the same object fire synchronously, while neurons excited by features of different objects do not. Moving plaid patterns offer a straightforward means to test this idea. By appropriate manipulations of apparent transparency, the component gratings of a plaid pattern can be seen as parts of a single coherently moving surface or as two non-coherently moving surfaces. We examined directional tuning and synchrony of area-MT neurons in awake, fixating primates in response to perceptually coherent and non-coherent plaid patterns. Here we show that directional tuning correlated highly with perceptual coherence, which is consistent with an earlier study⁴. Although we found stimulus-dependent synchrony, coherent plaids elicited significantly less synchrony than did non-coherent plaids. Our data therefore do not support the binding-by-synchrony hypothesis as applied to this class of motion stimuli in area MT.