Rapid volitional control of apparent motion during percept generation

Abstract How rapidly can one voluntarily influence per-cept generation? The time course of voluntary visual–spatialattention is well studied, but the time course of intentionalcontrol over percept generation is relatively unknown. Weinvestigated the latter question using “one-shot” apparentmotion. When a vertical or horizontal pair of squares isreplaced by its 90o-rotated version, the bottom-up signal isambiguous. From this ambiguous signal, it is known thatpeople can intentionally generate a percept of rotation in adesired direction (clockwise or counterclockwise). To de-termine the time course of this intentional control, weinstructed participants to voluntarily induce rotation in aprecued direction (clockwise rotation when a high-pitchedtone was heard, and counterclockwise rotation when a low-pitched tone was heard), and then to report the direction ofrotation that was actually perceived. We varied the delaybetween the instructional cue and the rotated frame (cue-lead time) from 0 to 1,067 ms. Intentional control becamemore effective with longer cue-lead times (asymptoticallyeffective at 533 ms). Notably, intentional control was reli-able even with a zero cue-lead time; control experimentsruled out response bias and the development of an auditory–visual association as explanations. This demonstrates thatpeople can interpret an auditory cue and intentionally gen-erate a desired motion percept surprisingly rapidly, entirelywithin the subjectively instantaneous moment in which thevisual system constructs a percept of apparent motion.Keywords Intentionalcontrol .Visualbistability .Apparentmotion .AttentivetrackingPrior research on the speed of intentional influences on per-ception has predominantly investigated voluntary allocationsof visual–spatial attention. In a typical paradigm, a symbolicinstructionalcue(e.g.,acentrallypresentedarrow)informstheparticipant of the likely location of an upcoming target(Bashinski and Bacharach1980; Hawkins et al. 1990,Posner, Snyder, and Davidson 1980). The time interval be-tween the instructional cue and the presentation of the target(cue-lead time) allows the experimenter to control the timeavailable for the intentional allocation of visual–spatial atten-tion (Cheal and Lyon 1989, 1991,MullerandRabbitt1989,Posner 1980). A study using this paradigm showed that foruntrained observers, the perceptual benefit of voluntary visu-al–spatial attention becomes statistically reliable within about175msofcue-leadtime,andasymptoticallyeffectiveatabout400 ms (Muller and Rabbitt 1989). These results revealed thetime course of intentionally allocating visual–spatial attentionto a specific location.Less is known, however, about the time course of theinfluence of intention on the construction of a percept. Here,we address this question using a “one-shot” ambiguousapparent-motion paradigm. For example, a trial begins witha frame comprising a vertical pair of squares. When thesesquares are replaced by their 90o-rotated (i.e., horizontal)version—the rotated frame—either a clockwise or counter-clockwise rotation is momentarily perceived. Rotation in aninstructed direction is typically seen if an instructional cueis presented sufficiently before the presentation of the ro-tated frame, so that the participant has enough time tointentionally engage appropriate processes to influence thepercept that is generated.We chose apparent rotation as our ambiguous stimulusfor the following reasons. The ambiguous motion signalavailable to generate the percept of apparent rotation isgiven only at the moment when the rotated frame appears;therefore, we know that the process of percept generationdepends on the visual signal presented at this specificmoment. In contrast, the Necker cube, face–vase figure,