Abstract
Knowing where things are is important. Here we examine the effect of motion context, using a frame that moves back and forth, on the perceived position of probes (Cavanagh, Anstis, & Wexler, VSS 2019). When two probe dots are flashed inside the frame at the same physical location, each at one extreme of the frame’s movement, a very large illusory offset is seen between the probes, roughly equal to the frame’s travel. Here we examine the effects of the distance, duration, and speed of the frame’s travel on the perceived spatial offset. A total of 274 York University undergraduates completed an online task (PsychoJS, hosted on Pavlovia). After screening participants for appropriate devices and self-reported understanding of the task (60), and response outliers (73), 141 remained. Reliable monitor calibration was available for about 40% of participants. The size of the stimuli in degrees of visual angle did not affect illusion strength so we combined all data. The perceived spacing approximately matched the distance the frame moved, both when varying the speed (r²=0.97, p=.001) and the duration (r²=0.92, p=.006) of the frame’s motion. Conclusion: stimuli flashed before and after a frame’s motion are seen in their coordinates relative to the frame as if the frame were stationary.