The spatial properties of opponent-motion normalization.

Full Abstract

The final stage of the Adelson-Bergen model [J. Opt. Soc. Am. A 2 (1985) 284] computes net motion as the difference between directionally opposite energies E(L) and E(R). However, Georgeson and Scott-Samuel [Vis. Res. 39 (1999) 4393] found that human direction discrimination is better described by motion contrast (C(m))--a metric where opponent energy (E(L)-E(R)) is divided by flicker energy (E(L)+E(R)). In the present paper, we used a lateral masking paradigm to investigate the spatial properties of flicker energy involved in the normalization of opponent energy. Observers discriminated between left and right motion while viewing a checkerboard in which half of the checks contained a drifting sinusoid and the other half contained flicker (i.e. a counterphasing sinusoid). The relative luminance contrasts of flicker and motion checks determined the checkerboard's overall motion contrast C(m). We obtained selectivity functions for opponent-motion normalization by measuring C(m) thresholds whilst varying the orientation, spatial frequency, or size of flicker checks. In all conditions, performance (percent correct) decayed lawfully as we decreased motion contrast, validating the C(m) metric for our stimuli. Thresholds decreased with check size and also improved as we increased either the orientation or spatial-frequency difference between motion and flicker checks. Our data are inconsistent with Heeger-type normalization models [Vis. Neurosci. 9 (1992) 181] in which excitatory inputs are normalized by a non-selective pooling of inhibitory inputs, but data are consistent with the implicit assumption in Georgeson and Scott-Samuel's model that flicker normalization is localized in orientation, scale, and space. However, our lateral masking paradigm leaves open the possibility that the spatial properties of flicker normalization would be different if opponent and flicker energies spatially overlapped. Further characterization of motion contrast will require models of the spatial, temporal, and joint space-time properties of mechanisms mediating opponent-motion and flicker normalization.

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Author information

Author/s: Rainville, Stéphane J M (SJ); Scott-Samuel, Nicholas E (NE); Makous, Walter L (WL);

Affiliation: Center for Visual Science, Meliora 274, University of Rochester, Rochester, NY 14627, USA. rainville@hpl.crestech.ca

Grants: EY-1319 (Agency:United States NEI) ; EY-4885 (Agency:United States NEI)

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.

Journal: Vision research (Vision Res), published in England. (Language: eng)

Reference: 2002-Jun; vol 42 (issue 14) : pp 1727-38

Dates: Created 2002/07/19; Completed 2002/09/30; Revised 2007/11/14;

PMID: 12127106, status: MEDLINE (last retrieval date: 11/6/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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