Abstract
Although early filters are narrowly tuned in the spatial frequency domain, distant spatial frequencies are not completely independent as cross-frequency interactions can facilitate (improve) or impair contrast sensitivity. For instance, a high-spatial frequency texture at high contrast can impair contrast sensitivity to low spatial frequencies, whereas at low contrast, it can facilitate contrast sensitivity. This surprising facilitation could be caused by late interactions within the visual system (e.g., integration of outputs from simple cells tuned to different spatial frequencies) or early interactions (e.g., cross-frequency lateral inhibition in the LGN). The current study investigated whether the cross-frequency interaction responsible of the facilitation effect occurs at a late stage where form and motion processing are distinct or at an earlier stage before form and motion processing have distinct pathways. If the cross-frequency interaction occurs at a stage at which form and motion processing are distinct, then static noise should have no impact on motion sensitivity. On the other hand, if the cross-frequency interaction occurs at a stage at which form and motion are not distinct, then static noise should have the same impact on contrast and motion sensitivity. We investigated the impact of static band-pass noise (2 to 8 cpd) on motion sensitivity of a 0.5-cpd Gabor drifting at temporal frequencies from 0.9375 to 15 Hz. The noise was full-screen and continuously displayed to avoid being spatial or temporally informative. The contrast of the noise was set to optimize the facilitation on contrast sensitivity based on a pilot study. Static noise was found to facilitate motion sensitivity at all temporal frequencies with a similar amplitude as observed for contrast sensitivity. The fact that static noise at high spatial frequencies can improve motion sensitivity suggests that the facilitation is caused by cross-frequency interactions occurring before form and motion are processed by distinct pathways.