Impoverished second-order input to global linking in human vision

Recent evidence points to the importance of global operations across spatia l regions larger than individual cortical receptive fields. Studies of cont our integration and motion trajectory detection suggest that network operat ions between local detectors underlie the encoding of extended contours in space and extended trajectories in motion. Here we ask whether such network operations also occur between second-order-detectors known to exist in vis ual cortex. We compared performance for stimuli composed of either first-or der or second-order elements equated for visibility, and we show that unlik e the first-order case, there is little or no linking interaction between l ocal second-order detectors. Near chance performance was found for elements defined by second-order attributes when observers had to identify either a n elongated spatial contour or an extended motion trajectory embedded in no ise elements. This implies that the network operations thought to underlie these two global tasks receive, at best, an impoverished input from local d etectors that encode second-order image attributes. (C) 2000 Published by E lsevier Science Ltd. All rights reserved.