Tolerance For Local And Global Differences In The Integration Of Shape Information
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1
University of Western Australia, Psychology, Australia
Some shapes are processed as global units. This study extends our understanding of the critical features required for shape integration and evaluates some leading hypotheses. The work examines the specific hypotheses that contour curvature coding is influential in local shape coding and that radial-frequency decomposition is involved in the processes leading to global integration of contour information in human vision.
Thresholds for shape deformation in radial frequency (RF) targets (circle distorted by periodic modulation of the radius) are determined using Two-interval Forced-Choice (2IFC) psychophysics. Three conditions are compared (sinusoidal, negative-, and positive- rectification of the modulator). These manipulations significantly vary local curvature cues.
2x2IFC methodology is then used to compare the threshold for modulation detection to that required to identify different patterns. Identical thresholds imply separate labelled lines for the shapes. Conditions: 1) detection and identification of the modulator type, 2) detection and identification of modulators of different periodicity.
Observers (n=4) show that modulator rectification supports global contour integration but not identification at that threshold. Detection and identification thresholds can be identical for RF patterns varying in modulator frequency.
From these results we conclude that modulator rectification in RF contours changes curvature but not the results: curvature continuity isn't essential for integration. The polar angle between two points of maximum curvature was sufficient to allow identification at detection threshold: patterns could be labelled for this measure but the results are not consistent with a decomposition of contours into radial frequency components.
Keywords:
Psychophysics,
Visual Perception,
Shape Perception,
global processing,
shape channels
Conference:
XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014.
Presentation Type:
Poster
Topic:
Sensation and Perception
Citation:
Badcock
D,
Dickinson
J,
Bell
J and
Cribb
S
(2015). Tolerance For Local And Global Differences In The Integration Of Shape Information.
Conference Abstract:
XII International Conference on Cognitive Neuroscience (ICON-XII).
doi: 10.3389/conf.fnhum.2015.217.00071
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Received:
19 Feb 2015;
Published Online:
24 Apr 2015.
*
Correspondence:
Prof. David Badcock, University of Western Australia, Psychology, Perth, Australia, david.badcock@uwa.edu.au