VISUAL-ATTENTION MODULATES METACONTRAST MASKING

Citation
Vs. Ramachandran et S. Cobb, VISUAL-ATTENTION MODULATES METACONTRAST MASKING, Nature, 373(6509), 1995, pp. 66-68
Citations number
17
Categorie Soggetti
Multidisciplinary Sciences
Journal title
NatureACNP
ISSN journal
00280836
Volume
373
Issue
6509
Year of publication
1995
Pages
66 - 68
Database
ISI
SICI code
0028-0836(1995)373:6509<66:VMMM>2.0.ZU;2-B
Abstract
HOW does the human visual system 'bind' different fragments in the vis ual scene to create enduring representations of objects(1-5)? A visual illusion known as 'metacontrast'(6-9) or backward masking provides co mpelling evidence that perception is not instantaneous and that it occ urs sequentially in distinct stages, If a solid white target square is displayed for 50 ms in a tachistoscope, switched off, and followed by a 50 ms display of two flanking mask squares, remarkably, subjects re port seeing only the two flanking squares: the first square is simply not 'seen'. By plotting the magnitude of masking as a function of the delay between the target and mask (the stimulus onset asynchrony), one can obtain a characteristic 'U'-shaped function(7) with optimum maski ng occurring at about 50 ms, and no masking with synchronous target an d mask presentations or at delays higher than 300 ms. The illusion is also highly sensitive to elementary stimulus dimensions such as colour , orientation and spatial frequency(8), and it has been suggested(10) that it is based on 'low level' autonomous visual mechanisms rather th an cognitive processes, Here we describe a novel visual stimulus that demonstrates that metacontrast can be strongly modulated by 'top down' influences such as voluntary visual attention.