Ignacio Serrano-Pedraza¹ (), Raul Luna¹, Marcos Padilla-Ruiz¹, Milagros Tirado-Perez¹, Omar Bachtoula¹; ¹Universidad Complutense de Madrid

There are two well-known inhibitory mechanisms in motion perception. The first is surround suppression, where duration thresholds for motion discrimination are higher for large, high-contrast stimuli compared to smaller ones. The second is the cross-scale interaction, in which the duration threshold for detecting motion of a high spatial frequency pattern increases when a static low-frequency component is added. Previous work has suggested a link between surround suppression and motion-segregation efficiency, but it remains unclear whether motion segregation is linked to cross-scale interactions. To investigate this, we performed three motion-discrimination experiments. In Experiment 1, we measured duration thresholds using binary noise windowed by raised-cosine apertures of 5deg and 0.75deg. In Experiment 2, we measured duration thresholds for discriminating motion of a 3cpd drifting Gabor (4 deg diameter), presented either alone or combined with a static anisotropic noise centred at 1cpd. In Experiment 3, we measured motion-segregation duration thresholds for an oriented ellipse drifting at 4.94deg/s, composed of binary-noise and surrounded by binary noise moving in the opposite direction at the same speed; participants reported the orientation of the ellipse. From Experiments 1 and 2 we computed two indexes: a suppression index (SI), defined as the log-threshold difference between the large and small stimuli; and an interaction index (II), defined as the log-threshold difference between the compound and simple stimuli. SI did not correlate with II and did not correlate with motion-segregation thresholds. In contrast, II showed a significant and positive correlation with motion-segregation thresholds. These findings suggest that surround suppression and motion segregation are independent processes, whereas, for the first time, we show a strong relationship between cross-scale interaction and motion segregation. Therefore, motion segregation does not appear to depend on how strongly observers suppress large stimuli, but rather on how the visual system integrates motion information across spatial scales.

Acknowledgements: Supported by grant PID2024-155243NB-I00 from Ministerio de Ciencia, Innovación y Universidades (Spain) to ISP.