Abstract
More and more evidence seems to indicate that suddenly presented transient stimuli can alter the perceived organization of an already present stimulus. For example, Sekuler et al. (Nature, 1997, vol. 385, p. 308) showed that a sound presented near the point of coincidence can make two moving dots bounce instead of passing each other. Moreover, Shams et al (Nature, 2000, vol. 401, p 788) reported that observers saw multiple flashes whenever a single flash was accompanied by more than one beep.
In this study we looked at the effect of transient interrupts on ambiguous stimuli. Among these were the Necker cube and Wertheimer's ‘windmill’ (a cross that rotates in steps of 45 degrees, which is directionally ambiguous because the clockwise displacement equals the counterclockwise displacement). The results show that when a transient stimulus, like a suddenly appearing dot, a sound, or a change of color changes the perceptual experience completely. For example, The Necker cube inverses its perspective. Moreover, if Wertheimer's ambiguous windmill is tracked with attention — and as a result a clear motion direction is perceived — the direction reverses in the opposite direction as soon as the transient stimulus is present. These results show that interpretations given to ambiguous stimuli — that is, when the visual system has disambiguated the presented stimulus — are overruled in favor of a competing solution, even when the interrupting stimulus enters trough another modality.