Motion defined surface segregation in human visual cortex
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1
University of Sydney, School of Psychology, Australia
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2
Australian Research Council Centre of Excellence in Vision Science, Australia
Background
Surface segregation provides an efficient way to distinguish between objects in the world. It is a relatively fast process which can speed feature binding. For example, a stimulus alternating simultaneously between two visual features (eg. colour and motion) at a high frequency appears transparent due to surface segregation. Both sets of features persist simultaneously and the colour-motion pairing can be easily identified. However, at a lower alternation frequency, the representation of multiple surfaces breaks down making binding difficult. Here, we investigated motion defined surface transparency through a psychophysical task and fMRI.
Methods
Two oppositely rotating random dot kinematograms (RDKs) were displayed at several alternation frequencies, presented either sequentially or simultaneously. Sequential presentations displayed one RDK on screen at any time while the simultaneous display contained both RDKs in concentric, alternating strips.
The psychophysical task contained coloured RDKs and was a presentation (sequential, simultaneous) by alternation frequency (1.67, 2.5, 3.33, 5, 7.5 and 15Hz) experiment. Participants reported the colour-motion pairing. The fMRI experiment had a presentation (sequential, simultaneous) by frequency (5, 15Hz) design using grey RDKs.
Results
A significant presentation × frequency interaction was apparent in the psychophysical results. At 15 Hz, sequential and simultaneous displays produced ceiling performance indicative of perceived transparency. However, transparency broke down in the sequential presentation at 5 Hz, generating chance performance, while simultaneous presentations continued to appear transparent independent of frequency.
This was also reflected in univariate as well as multivariate analyses of the fMRI BOLD activity in V1, V2, V3, V3AB, hV4, and V5/MT+. We found significant presentation by frequency interaction effects in most areas, such that changes in BOLD signal between presentation types were significantly different only at 5Hz. Multivariate pattern classification confirmed this result, finding significantly higher than chance decoding between presentation types at 5, but not 15Hz.
Discussion
Perceptual transparency was found to be correlated with neural activity in early visual areas. fMRI data mirrored psychophysical interaction effects in qualitatively similar ways, suggesting surface representations may be associated with activity in early areas of the human visual cortex.
Keywords:
human fMRI,
feature binding,
surface perception,
Psychophysics,
temporal transparency
Conference:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013.
Presentation Type:
Poster
Topic:
Sensation and Perception
Citation:
Vigano
GJ,
Maloney
RT and
Clifford
CW
(2013). Motion defined surface segregation in human visual cortex.
Conference Abstract:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference.
doi: 10.3389/conf.fnhum.2013.212.00118
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Received:
16 Sep 2013;
Published Online:
25 Nov 2013.
*
Correspondence:
Mr. Gabriel J Vigano, University of Sydney, School of Psychology, Sydney, Australia, gvig3764@uni.sydney.edu.au