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Rejoinder 2: Apparent Simultaneity and Absent Duration

Power 2010 argues that it is a mistake to treat apparent simultaneity as some property or entity that is apparent. Apparent simultaneity is merely the non- appearance of something else: duration.

There are two ways perceptual experience—or cognition generally—can fail:

  • 1. A perceptual experience fails because it perceptually appears as if there is more than there is.
  • 2. A perceptual experience fails because it perceptually appears as if there is less than there is.

The difference is significant. 1 is a genuine illusion: for the subject, there appears to be something, such as a property, which is not there. However, 2 gives no reason to think there is a genuine illusion. The error is only because the experience is limited: it is only some of what is there. It does not include everything that is there.

Limited Experience in Time

If I peer into a dark shop from the street, and only see a few dim objects in the shop, my perceptual experience misses some of what is in the shop. This does not mean that I am under an illusion of something in the shop. It only means that I have a limited perception.

Even in the brightest, clearest act of perception, we have limitations like this: in bright sunlight, we look at the surface of a stone and see a mustard stain of lichen; we cannot see the gaps between the patches of lichen.

There are also limits to our detection of the timing of what we perceive. As discussed in Chapter 6, there are time-lags in our perception: the distant objects that we seem to perceive are at different times to the moment when we perceive. This duration is absent from the phenomenology or appearances of this perception. We do not perceive it or seem to perceive it. Yet, the duration is still there.

There are multiple ways to understand this point. If one is a representa- tionalist about experience, then there is no representation going on. We are not representing this hidden duration, such as the time-lag. We are not even representing an absence of this duration. We simply do not represent it at all.

If we apply this thinking to simultaneity, an appearance of simultaneity is misleadingly described. Simultaneity can be also thought of as an absence of something. It is an absence of duration, for example, between events. When we look at a multitude of different distant stars, they appear to shine simultaneously. However, all there is to this apparent simultaneity is that we cannot detect the (often significant) durations between them.

Again, denying the appearance of something that is an absence is not a problem for any theory. It is not the sort of phenomenology that must be saved— in part because it is not really an appearance at all.

Along with removing background assumptions in Libet’s work, this point about simultaneity generalizes to any experiment which times a subject’s introspective judgements by the subject’s observations of some external timer, such as a clock. We need not assume that the subject’s report of simultaneity between the timer (clock) and their own cognition is evidence of their own cognition’s timing. It only means that they do not detect an actual duration between clock and cognition. They may very well be unable to detect such a thing, and it may very well be there.

Simultaneity Thresholds

Furthermore, there are other cases of perceptual error that seem to involve merely apparent simultaneity like this. These are cases in which there is a coincidence or simultaneity threshold. A simultaneity threshold is a lower limit to perceptual awareness, beneath which a difference in time between stimuli cannot be detected.

For example, in visual perception, the simultaneity threshold is 20ms; in auditory perception, it is 2-3ms (Dainton 2000, 170; see also Elliott et al. 2006). If we visually perceive stimuli separated by less than 20ms, we do not perceive them as separated by any duration. If we auditorily perceive stimuli separated by 2-3ms, again, we do not perceive them as separated by any duration. In these cases, they seem to happen at the same time and, thus, appear to be simultaneous.

We need not posit illusions to explain simultaneity thresholds (or spatial thresholds, for that matter). We need only posit a perceptual incapacity to detect such fine distinctions. We need only posit a limit to perception. Where there is only such a limit, there is no illusion. Otherwise, again, we are under illusions whenever we cannot see.

This is evident with cases of blurred motion: the stages in the position of a fast-moving object seem to be simultaneous; as a result, the object seems spread over a space all at one time; however, it is not spread out in the space, at least not all at one time; it passes through the space, being at different locations at different times. As such, this is a case of apparent simultaneity between things that are not actually simultaneous (for more on motion blurs and the philosophy of time, see Power 2015).

This need not be an illusion. It can be due to the limits of perception. We cannot detect the difference in times of the different events. With this analysis of apparent simultaneity on hand, as something akin to simultaneity thresholds, we turn to consider illusions—and, in particular, temporal illusions.

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