Abstract
When two probes are flashed at the same physical location within a moving frame, their perceived location can be offset by as much as the frame moves (Özkan et al, PNAS, 2021). Here we examine the extent of the frame’s influence in space and time. First, we positioned the flashed probes in front of or behind the frame in depth (or both) using red/cyan anaglyph glasses. The illusion strength was unaffected by these depth mismatches. In contrast, placing the flashed probes outside the frame did influence the illusion. The illusion strength dropped to 50% magnitude once the probes were 5.4 dva to the left of the frame. In the vertical direction, the 50% decrease required an offset of 6.9 dva between the frame and the probes. Offsets in time from the presentation of the frame caused a complete loss of the illusion. The frame was presented for one to three cycles of left-right motion and when the probes were flashed before or after the frame presentation, there was no illusion, no matter how long the frame had been present. This suggests that the illusion depends on immediately present sensory information without any influence of the frame’s motion before or after its actual presence on the screen. In conclusion, the frame effects do extend outside the boundaries of the frame in space but not in time.