Slow brain potentials and the "tunnel effect".

Abstract

The present study investigated electrocortical concomitants of the "tunnel effect." The tunnel effect refers to the following perceptual phenomenon: if a continuously moving object disappears behind a shield ("enters a tunnel") the observer has the impression that the same object continues to move with the time point of reappearance usually being underestimated. In the present study, an object moved across a tv-screen for 6 s; it either disappeared behind a shield (tunnel condition), disappeared at once (explosion condition), or remained visible until the end of its trajectory (control condition). Subjects had to press a button whenever they believed that the object had arrived at its trajectory's end. The object's flight was accompanied by a continuously rising slow negative shift of the EEG that resembled the contingent negative variation (CNV). Either type of object disappearance produced a positive-going potential that may reflect brain processes associated with memory rehearsal and/or time estimation. A late P300-like positivity was prominent under tunnel conditions only. Response latency was shorter under disappearance than under control conditions. The positive deflection is discussed as sign of amodal brain processing (memory rehearsal and/or time estimation). The P300-like wave elicited by the object's disappearance activates these memory representations. Based on these considerations, an attempt was made to interpret the premature motor responses, which are commonly observed for tunnel conditions but not for other time estimation tasks.