When is now? Perception of simultaneity

Abstract

We address the following question: Is there a difference (D) between the amount of time for auditory and visual stimuli to be perceived? On each of 1000 trials, observers were presented with a light-sound pair, separated by a stimulus onset asynchrony (SOA) between -250 ms (sound first) and +250 ms. Observers indicated if the light-sound pair came on simultaneously by pressing one of two (yes or no) keys. The SOA most likely to yield affirmative responses was defined as the point of subjective simultaneity (PSS). PSS values were between -21 ms (i.e. sound 21 ms before light) and +150 ms. Evidence is presented that each PSS is observer specific. In a second experiment, each observer was tested using two observer-stimulus distances. The resultant PSS values are highly correlated (r = 0.954, p = 0.003), suggesting that each observer's PSS is stable. PSS values were significantly affected by observer-stimulus distance, suggesting that observers do not take account of changes in distance on the resultant difference in arrival times of light and sound. The difference RTd in simple reaction time to single visual and auditory stimuli was also estimated; no evidence that RTd is observer specific or stable was found. The implications of these findings for the perception of multisensory stimuli are discussed.

Encoding of event timing in the phase of neural oscillations

“…Shifts in perceived AV simultaneity following lag-adaptation (Fujisaki et al, 2004;Miyazaki et al, 2006;Vroomen et al, 2004;Yamamoto et al, 2012) have been hypothesized to originate from mechanisms capable of adjusting the neural processing time across sensory modalities (Fujisaki et al, 2004;Moutoussis and Zeki, 1997;Stone et al, 2001;Sugita and Suzuki, 2003;Zeki and Bartels, 1998). In support of this hypothesis, our study reveals that such mechanisms may be implemented as phase shifts of neural oscillations: contrasting the sensory responses before and after AV lag-adaptation provided no evidence for a latency code hypothesis and instead revealed significant phase shifts of the entrained 1 Hz neural oscillations.…”

Shifts of criteria or neural timing? The assumptions underlying timing perception studies

“…However, the interpretative issues we have identified are relevant to all studies that have inferred different neural processing times on the basis of discrepant PSS estimates obtained in different experimental conditions (e.g. Bartels & Zeki, 1998;Stone et al, 2002;Sugita & Suzuki, 2003). In short, we believe that such data do not provide unequivocal evidence for a change in neural processing times.…”

“…Interestingly, while the function commonly used to fit TOJs has a clear modelling rationale, the function most commonly used to fit SJs (the Gaussian or truncated Gaussian; e.g. Fujisaki et al, 2004;Stone et al, 2002) is rarely discussed, and seems to have been chosen primarily for convenience. This makes it rather difficult to spell out what the PSS derived from this function (usually taken as the peak of the fitted Gaussian) might represent.…”

“…The two most common tasks used to assess perceived timing are simultaneity judgements (SJs, e.g. Fujisaki, Shimojo, Kashino & Nishida, 2004;Moutoussis & Zeki, 1997a;Moutoussis & Zeki, 1997b;Stone et al, 2002) and temporal order judgements (TOJs; e.g. Eagleman & Sejnowski, 2000;McDonald, Teder-Salejarvi, Di Russo & Hillyard, 2005;Sugita & Suzuki, 2003).…”

Perception of intersensory synchrony: A tutorial review

“…vs. "Which stimulus came second? "; see Frey, 1990;), individual differences (Mollon & Perkins, 1996;Stone et al, 2001), and the modality or location to which attention is directed (Mattes & Ulrich, 1998;Schneider & Bavelier, 2003;Stelmach & Herdman, 1991;. Here, however, we are not intending to review all of these factors, but, rather, are focusing on how simultaneity is perceived despite lags.…”