Hi Massimiliano,

That's a good question. I'm not aware of any specific convention. For audiovisual stimulus pairs, I would think that it would be the most logical convention that positive values would indicate that the auditory stimulus follows the visual one, because the strongest multisensory integration effects are usually reported when the auditory stimulus is presented briefly after the visual one. A quick literature scan also suggests that this is the convention followed by Van Wassenhove, Grant, and Poeppel (Neuropsychologia, 2007). In our work, (Senkowski et al, 2007 and Talsma et al 2009) we made sure to explicitly indicate which of the two stimuli was presented first. Even if a convention is to be established, that's probably a good thing anyhow.

I've never really worked with other modality combinations, so I don't have any idea what the convention would be there.

Hope this helps; obviously I'd also be interested to hear other peoples opinions.

Cheers,

Durk

I don't know if there is a principled way to determine this. In my own work negative values refer to auditory first, but that's probably because I am a visual (not auditory) psychophysicist, and so it is the onset of the visual stimulus which is fiducial. In an admittedly non-exhaustive survey of the literature I note that negative SOAs refer to auditory first in 8 of 12 total papers I found.

I'm reading a paper about AV asynchrony right now (Audiovisual synchrony and temporal order judgments: effects of experimental method and stimulus type. van Eijk et al (2008) Perception and Psychophysics, 70 (6), 955-968) and they use negative values to indicate audio first. I don't know if this is the convention.

Durk is referring to early research (Hershenson, 1962; Miller, 1986) which suggested that optimal AV multisensory integration occured at AV SOAs where the A signal was delayed relative to the V signal. However, our recent research indicates that optimal AV multisensory integration, as indexed by violations of the race model inequality, occur when the A and V signals are, in fact, simultaneous.

Leone, L. & McCourt, M.E. (2013). The roles of physical and physiological simultaneity in audiovisual multisensory facilitation. i-Perception (in press).

Leone, L. & McCourt, M.E. (2012). The question of simultaneity in audiovisual multisensory integration. Proceedings of the SPIE, 8291, 82910J1-J8; http://dx.doi.org/10.1117/12.912183.

Hello all,

There is one aspect not mentioned so far: linguistically spoken, "audio-visual" suggests that sound is regarded first and visual stimulus second. Thus, positive values of SOAs refer to this order and negative values to the reverse order (ie, visual signal precedes the auditory one). Because typically auditory processing delays for perception are shorter than visual ones, in order to have satisfied the requirement for PSS, SOA appears as having negative value (say, -35 ms). In the literatuse there are both versions of AV timing conventions used, but I suggest stem from how it is written down.

Interesting question, I've also wondered about this convention. Not sure there are any benefits either way as long as it's stated. We have done AV sync experiments on spatially moving stimuli and denoted +ve values as auditory leading.

In A-T / V-T experiments we reference against the tactile stimulus.