Asymmetric detection of relative speed during motion-based figure-ground segregation

Slower-than-background targets require larger relative-speed differences than faster-than-background targets for detection in human observers, with the strongest asymmetry at low background speeds and reduced coherence.

• Why it matters: Motion-based figure-ground segregation depends on detecting speed differences, but it is unclear whether faster and slower targets are sensed equally and how background speed and motion reliability shape any bias.
• What they did: Four observers performed an eight-alternative forced-choice localization task with a moving random-dot patch at 10-degree eccentricity, using adaptive staircases across five background speeds (2.5–30 deg/s) at 100% and 60% motion coherence.
• The result: Relative-speed thresholds show an increment-decrement asymmetry: slower targets are harder, coherence reduction elevates thresholds overall while disproportionately impairing slower detection, and Weber-like scaling differs between 100% and reduced coherence.

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