Is absence of evidence of pain ever evidence of absence?

Abstract

Absence of evidence arguments are indispensable to comparative neurobiology. The absence in a given species of a homologous neural architecture strongly correlated with a type of conscious experience in humans should be able to be taken as a prima facie reason for concluding that the species in question does not have the capacity for that conscious experience. Absence of evidence reasoning is, however, widely disparaged for being both logically illicit and unscientific. This paper argues that these concerns are unwarranted. There is no logical barrier to formulating cogent absence of evidence arguments; indeed, accepting such arguments is part of what it is to be committed to falsifiability as a critical aspect of the scientific method. Absence of evidence arguments can always be blocked, however, by assuming that psychological properties are ‘multiply realizable’. While we take multiple realizability to be highly likely at some level of analysis, we argue that it is question-begging to assume that it exists at every level of analysis, and thus it should not automatically be thought to undermine absence of evidence reasoning in the animal consciousness debate. Using the example of pain and focusing on homologies at the level of information processing tasks, we show how, in the science of consciousness, an absence of evidence might well serve as evidence of absence.

A First Principles Approach to Subjective Experience

“…For now, this question remains unanswered. Nonetheless, our framework has already provided insights into the sorts of organisms that most likely lack subjective experience, such as plants ( Brown and Key, 2021b ), insects ( Key et al, 2021 ), molluscs ( Key and Brown, 2018 ), and fish ( Brown and Key, 2021a ). It should be noted that it is not forward models per se , but rather it is their deployment and implementation within the correct architectural framework—as revealed by the hierarchical forward models algorithm —that countenances the likelihood of subjective experience.…”

“…The idea is that if different neural structures can generate the same functional process in different brains, then it is impossible for any specific type of neural structure to be necessary for subjective experience. We have argued previously that multiple realisation need not apply at all levels of abstraction ( Brown and Key, 2021a ), and hence constitutes an unwarranted assumption in arguments against identity theory. Returning to the analogy of mathematics, it is obvious that arithmetic operations can be multiply realised at some level of description.…”

“…If such structures could be identified, they could be used to support the inference that creatures lacking such architectures would not be capable of subjective experience. Abstract characterisation of a minimal neural architecture has been used to explain the possibility of left-right locomotion despite variation in the number of neuronal elements ( Brown and Key, 2021a ), suggesting that the same strategy might work for subjective experience as well. The problem would then become the empirical one of identifying the correct level of abstraction and the minimal structural condition (we return to this matter in section “Applying First Principles to Understand the Neural Basis of Subjective Experience”).…”

“…To allay any claims that subjective experience (or its underlying necessary functions) could be multiply realised by any neural circuit (structure), we emphasise the covenant, “appropriate level of abstraction.” As mentioned, multiple realisation does not necessarily apply at all levels of analysis ( Brown and Key, 2021a ). For example, animal wings can be formed by many different tissues—think insects, bats, and birds—but at the same time share structural features that are necessary for the aerodynamic lift needed for non-gliding flight.…”