The subjective experience of time - welfare implications (Rethink Priorities)

The subjective experience of time refers to how slow or fast time appears to pass for an individual. Animals with faster rates of subjective experience undergo more subjective moments per objective unit of time than animals with slower rates of subjective experience. Roughly speaking, animals with faster rates of subjective experience perceive the world as if it were slowed down compared to the perceptions of animals with slower rates of subjective experience. Based on human reports of alterations in the subjective experience of time, as well as general differences in behavior, neurology, and temporal resolution across animals, I estimate there is a ~70% chance that there exist morally relevant differences in the subjective experience of time across species.

Differences in the subjective experience of time would affect the perceived duration of experiences and thus would affect the quality of experiences. An animal’s subjective rate of experience determines the number of subjective moments of pain (or pleasure) a painful (or pleasurable) event of a given objective duration generates. Such differences would be relevant to most plausible theories of welfare because most plausible theories of welfare hold that the subjective nature of experience matters morally.

An animal’s maximum rate of subjective experience helps determine its capacity for welfare. Animals with faster rates of subjective experience will, all else equal, have a higher capacity for welfare than animals with slower rates of subjective experience. Unlike many other determinants of capacity for welfare, the subjective experience of time is also directly relevant to an animal’s realized welfare. The quality of experience is the product of its valence, phenomenal intensity, and subjective rate of experience. For many animals, the phenomenal intensity of experiences varies considerably throughout an individual’s lifetime. Subjective rates of experience may be malleable, but for most animals they appear to vary much less frequently than phenomenal intensity. For this reason, even those skeptical of the practical import of capacity for welfare will want to incorporate rates of subjective experience into their welfare measures.

Differences in neurology, reaction times, and temporal integration windows provide means to roughly measure the subjective experience of time across species. Based on 13 relevant metrics I have identified, I estimate that characteristic differences in the subjective experience of time span no more than two orders of magnitude, with humans falling approximately midway on the spectrum. Arranging animals on this spectrum is likely to produce a radically different ordinal ranking than arranging animals according to neuron count, encephalization quotient, brain-mass-to-body-mass ratio, or other metrics related to brain size. Incorporating considerations about the subjective experience of time into our interspecies comparisons (currently dominated by brain size considerations) would likely change the way we prioritize animals.

Although much uncertainty remains, it appears many animals have rates of subjective experience faster than that of humans. For example, convergent evidence from their neurology, behavior, and the temporal resolution of their senses indicates songbirds and honeybees experience 2-10 times as many subjective moments per objective unit of time as humans. Thus, all else equal, the painful experiences of animals like songbirds and honey bees likely generate more suffering per objective unit of time than comparable animals with slower rates of subjective experience. Incorporating this sort of information into our prioritization decisions may allow us to improve the efficiency with which we distribute resources across different groups of animals.