Jason Schukraft

Dr. Jason Schukraft is a Senior Research Manager at Rethink Priorities. He earned his Ph.D. in philosophy from the University of Texas at Austin.

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Invertebrate Sentience

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Research Summary: The Subjective Experience of Time

Thanks, that’s a great question!

Welfare is constituted by those things that are non-instrumentally good or bad for the creature. Insofar as reflexes are unconscious, they probably are not non-instrumentally good or bad. (They are, of course, often instrumentally good; they help the creature get other things that are good for it.) Conscious experiences, on the other hand, are usually non-instrumentally good or bad. Experiences with a positive valence are non-instrumentally good; experiences with a negative valence are non-instrumentally bad. (Experiences that are perfectly neural may not be non-instrumentally good or bad; experiences can also be instrumentally useful in a variety of ways.)

Differences in the subjective experience of time—assuming they exist—are relevant to welfare (both realized welfare and capacity for welfare) because they reflect differences in the amount of experience a creature undergoes per unit of objective time. I write about the moral importance of the subjective experience of time in this part of the first post.

You’re right that there are other aspects of temporal perception that may not be directly relevant to welfare. We already know that there are differences in temporal resolution (roughly: the rate at which a perceptual system samples information about its environment) across species. Enhanced temporal resolution may, among other things, enable faster unconscious reflexes. Naturally, the speed of a creature’s reflexes will indirectly contribute to its welfare, but those unconscious reflexes won’t be part of what constitutes the creature’s welfare. Whether or not there is a correlation between temporal resolution and the subjective experience of time is an open question, one that I explore in depth in the second post.

Hope that clarifies things a bit for you, but if not, please ask a follow-up question!

Does Critical Flicker-Fusion Frequency Track the Subjective Experience of Time?

Great, thanks Michael - that clarifies the argument for me.

Premise 1: Any observed conscious temporal resolution frequency for an individual X (within some set of possible conditions C) is a lower bound for the maximum frequency of subjective experience for X (within C).

While I think it's plausible that one's temporal resolution sets some sort of bound on one's rate of subjective experience, I just want to reiterate that I believe this is an empirical claim, not a conceptual claim. I'm open to the possibility that temporal resolution is just totally irrelevant to the subjective experience of time.

(As an aside, I think we have to be a bit careful how we (myself included) use the word 'conscious' in this context. In the post I distinguish behavioral methods for determining CFF from ERG methods for determining CFF. But even bees can be trained on the behavioral paradigm. This of course doesn't settle the question of whether they're conscious.)

Does it make sense to interpret the rate of subjective experience as a frequency, the number of subjective experiences per second? Maybe our conscious experiences are not sufficiently synchronized across our brains for such an interpretation?

This is another good question for which I don't have the answer. A related issue is whether experiences are discrete (countable) in the relevant sense. There are arguments that pull in either direction here. But, just to clarify, even if experiences are countable in the relevant sense, it would be an astounding coincidence if our experience frequency exactly matched our critical flicker-fusion frequency (i.e., 60 experiences per second).

Does Critical Flicker-Fusion Frequency Track the Subjective Experience of Time?

Hi Michael,

Thanks for the interesting argument. Before I can evaluate it, however, I'd need you to clarify your terms a bit for me. In particular, I'd need to know more about what you mean by "frequency of conscious experience." Based on my best reconstruction of the argument, it can't mean temporal resolution or rate of subjective experience.

I'll try clarify my position a bit, in case it's helpful to you or other readers. I don't think there's an a priori connection between temporal resolution (as measured by CFF or any other method) and rate of subjective experience. If there's a correlation between the two, that's a contingent empirical fact. There is no conceptual tension between the claim that a creature consciously perceives the flicker-to-steady-glow transition at some high threshold (200 Hz vs 60 Hz for humans, say) and the claim that the creature has the same rate of subjective experience as a typical human. (Similarly, there is no conceptual tension between the claim that some creature consciously perceives the transition at the same threshold as humans but has a different rate of subjective experience.) It's tempting to think that temporal resolution is like the frame rate of a video, and as the temporal resolution goes up or down, so too must the rate of subjective experience. But the mechanisms that govern the intake and processing of perceptual information are a lot more complicated than that, and the mechanisms that govern the subjective experience of time appear to be more complicated still.

One analogy that is sometimes helpful to me is to think of (visual) temporal resolution as a measure of motion blur. As one's temporal resolution improves, motion blur is reduced. But changes in motion blur need not have any connection to temporal experience. When I'm drunk, my motion blur greatly increases, but my rate of subjective experience doesn't change.

(Also, apologies if in elaborating my position I've missed the point of your argument. Like I said, it looks interesting, I just need to understand the terms better to evaluate it.)

Does Critical Flicker-Fusion Frequency Track the Subjective Experience of Time?

Doesn't using behavioural studies based on trained behaviour avoid this concern?

Thanks, this is a good question. The short answer is no, it doesn’t. The longer answer is a bit more complicated.

Nobody denies that differences in CFF generate differences in perceptual experience. But differences in perceptual experience are cheap. As I say in the post, the values I discuss are maximum CFF thresholds (that is, the highest CFF an individual can register in any condition). One’s actual CFF threshold is constantly shifting due to differences in things like background lighting conditions. So a light that an individual perceives as flickering in one situation may be perceived as glowing steadily in a different situation. The question is whether maximum CFF thresholds correlate with differences in subjective temporal experience.

Differences in one’s perceptual experience affect what one’s body can do unconsciously. Balancing on one foot with one’s eyes open is much easier than balancing on one foot with one’s eyes closed. The reason is that your visual system allows your body to make continual microadjustments to stay balanced.

So if differences in visual temporal resolution (as measured by CFF) confer a fitness advantage only in virtue of improvements in unconscious movements, we shouldn’t expect differences in CFF to be correlated with differences in subjective temporal experience. As I explain in the post, the temporal resolution of one’s senses doesn’t directly govern the subjective experience of time. If differences in temporal resolution correlate with differences in subjective temporal experience, it’s probably because improvements in temporal resolution make improvements in the subjective experience of time more useful (and/or vice versa).

Did the CFF estimates in your table come from behavioural studies or ERG studies, or both?

Both.

Does Critical Flicker-Fusion Frequency Track the Subjective Experience of Time?

Thanks, and apologies if the wording is unclear. To clarify, in the post I discuss both (a) situations in which it looks like a difference in CFF is not accompanied by a difference in the subjective experience of time and (b) situations in which it looks like a difference in the subjective experience of time is not accompanied by a difference in CFF.

Does Critical Flicker-Fusion Frequency Track the Subjective Experience of Time?

Yeah, sorry I define that in the previous post. Quoting from there:

I operationalize ‘characteristic and significant differences in the subjective experience of time’ as the claim that for at least half their daily waking lives, some animals maintain subjective rates of experience at least twice as fast as some other animals.

Does Critical Flicker-Fusion Frequency Track the Subjective Experience of Time?

Hi Michael,

Thanks for your comments. If temporal resolution does, under the right conditions, track the subjective experience of time, I expect it will be the temporal resolution of whichever sensory modality exerts the biggest selection pressure due to differences in the subjective experience of time. In many cases that will probably be the sensory modality with the best (fastest) temporal resolution, but that need not always be the case. As I say in the post, temporal resolution only plausibly tracks the subjective experience of time for animals in which the fitness-improving actions that the greater temporal resolution enables require conscious processing. It may be the case that for certain animals, improvements in temporal resolution in one sense enable actions that increase fitness without conscious processing, while improvements in temporal resolution in a different sense enable actions that increase fitness only with additional conscious processing.

In short, I unfortunately don’t expect there to be any simple rule that will show which measures of temporal resolution are best at tracking differences in the subjective experience of time in all circumstances. In determining whether and to what degree a particular measure of temporal resolution might track differences in the subjective experience of time within a group of species, we’ll need to pay attention to the context in which evolutionary pressures were likely to exert an influence on temporal resolution and temporal experience for the species in the group.

The Subjective Experience of Time: Welfare Implications

Hi Matt,

Yes, the reference is to people reporting that time appears to slow down during life-threatening events, such as fighter pilots ejecting from their jets and rock climbers suffering serious falls. People on certain psychedelic drugs also sometimes report that time seems to stretch out. I discuss these reports in more detail in this section.

The Subjective Experience of Time: Welfare Implications

Thanks Michael, good question. I think the key issue is that, as far as we can tell, there is no single brain region responsible for temporal experience. And because neuronal firing regimes differ so dramatically across brain regions, we can't assign overall neuronal firing rates and compare them across species.

Admittedly, this is also somewhat of an issue for some of the other neurological proxies I've identified. (For instance, as I mention in the post, axonal conduction velocity varies pretty significantly throughout the central nervous system.)

To be clear, this doesn't tell us how often signals are sent, just how long it takes a signal to get from one point to another, and an upper bound on how often signals can be sent and received?

Correct. But at least for mammals, we know that homologous brain regions in different animals all fire at roughly the same rate. On the other hand, interneuronal distance does vary across mammals (and even more so across vertebrates). If there are differences in temporal experience across species, I wouldn't expect mammals to have a uniform rate of subjective experience. So it seems to me that interneuronal distance is likely to be a more informative (though still very imperfect) metric than neuronal firing rate.

The Subjective Experience of Time: Welfare Implications

This is a really good question for which I don't yet have a clear answer, despite thinking about for a fair amount of time.

For our purposes, the morally significant differences in sensory collection, processing, and integration are those differences that affect the phenomenal duration (or quality, for that matter) of the experience.

At various points in the post I appeal to an analogy between the subjective experience of time and a movie played at various speeds. But that's not actually a good metaphor. Perceptual processing and integration is extraordinarily complicated. Our brains take in a huge range of information across our different senses, and this information comes in at different speeds. Different parts of the brain process and integrate this information in different ways, modulating the integration for differences in the speed with which different modalities deliver information, eventually presenting us with what appears to be a unified cross-sensory model of our environment. In principle at least, it seems as if the different steps in this complicated chain of events could be run at different speeds, and it's still unclear to me what the effect would be on conscious experience.

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