Spatial suppression of motion and motion segmentation in peripheral vision

This study examined motion segmentation and spatial suppression of motion in central versus peripheral vision, their relationship, and whether scaling peripheral stimuli to match larger middle temporal receptive fields reduces eccentricity effects. Ten adults (mean 27.5 years) completed motion segmentation and motion discrimination tasks across five contrast levels (12%-92%), three eccentricities (0°, 10°, 20°), and two stimulus conditions (scaled, unscaled). In the segmentation task, participants identified the tilt of a motion-defined ellipse within an oppositely moving background; segmentation thresholds were minimum stimulus exposure duration required for accurate tilt discrimination. Participants also judged motion direction of the ellipse in isolation. Segmentation efficiency was the log10 threshold difference between ellipse motion and segmentation thresholds. The motion discrimination task involved identifying the motion direction of the moving background patch in isolation, with a suppression index calculated as the log10 threshold difference between highest and lowest contrasts. In the unscaled condition, eccentricity reduced segmentation efficiency (p < 0.01) and suppression index (p = 0.003), with a significant interaction among suppression, segmentation, and eccentricity (p < 0.001). Correlations between segmentation efficiency and suppression index weakened with eccentricity (Pearson's r = 0.81, p = 0.003 at 0°, r = 0.69, p = 0.26 at 10°, r = 0.48, p = 0.16). Scaling improved segmentation efficiency (p = 0.003) and suppression index (p = 0.043) but did not remove eccentricity effects. Thus our ability to segment moving foreground objects declines with eccentricity, even when accounting for receptive field scaling.