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Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 13, Iss. 12 — Dec. 1, 1996
  • pp: 2305–2318

Contrast gain control in first- and second-order motion perception

Zhong-Lin Lu and George Sperling  »View Author Affiliations


JOSA A, Vol. 13, Issue 12, pp. 2305-2318 (1996)
http://dx.doi.org/10.1364/JOSAA.13.002305


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Abstract

A novel pedestal-plus-test paradigm is used to determine the nonlinear gain-control properties of the first-order (luminance) and the second-order (texture-contrast) motion systems, that is, how these systems’ responses to motion stimuli are reduced by pedestals and other masking stimuli. Motion-direction thresholds were measured for test stimuli consisting of drifting luminance and texture-contrast-modulation stimuli superimposed on pedestals of various amplitudes. (A pedestal is a static sine-wave grating of the same type and same spatial frequency as the moving test grating.) It was found that first-order motion-direction thresholds are unaffected by small pedestals, but at pedestal contrasts above 1−2% (5−10× pedestal threshold), motion thresholds increase proportionally to pedestal amplitude (a Weber law). For first-order stimuli, pedestal masking is specific to the spatial frequency of the test. On the other hand, motion-direction thresholds for texture-contrast stimuli are independent of pedestal amplitude (no gain control whatever) throughout the accessible pedestal amplitude range (from 0 to 40%). However, when baseline carrier contrast increases (with constant pedestal modulation amplitude), motion thresholds increase, showing that gain control in second-order motion is determined not by the modulator (as in first-order motion) but by the carrier. Note that baseline contrast of the carrier is inherently independent of spatial frequency of the modulator. The drastically different gain-control properties of the two motion systems and prior observations of motion masking and motion saturation are all encompassed in a functional theory. The stimulus inputs to both first- and second-order motion process are normalized by feed forward, shunting gain control. The different properties arise because the modulator is used to control the first-order gain and the carrier is used to control the second-order gain.

© 1996 Optical Society of America

History
Original Manuscript: October 23, 1995
Revised Manuscript: July 9, 1996
Manuscript Accepted: July 11, 1996
Published: December 1, 1996

Citation
Zhong-Lin Lu and George Sperling, "Contrast gain control in first- and second-order motion perception," J. Opt. Soc. Am. A 13, 2305-2318 (1996)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-13-12-2305

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