Simon Brown

Do animals have episodic memory—the kind of memory which gives us rich details about particular past events—or is this uniquely human? This might look like an empirical question, but is attracting increasing philosophical attention. We review relevant behavioural evidence, as well as drawing attention to neuroscientific and computational evidence which has been less discussed in philosophy. Next, we distinguish and evaluate reasons for scepticism about episodic memory in animals. In the process, we articulate three pressing philosophical issues underlying these sceptical arguments, which should be the focus of future work. The Problem of Interspecific Variation asks which differences between humans and animal memory mean that an animal has a variant of episodic memory, and which mean that it has a different kind of memory altogether. The Problem of Functional Variation asks how we should conceptualise the functions of episodic memory and other capacities across species and across evolutionary time. Finally, the Problem of Alternatives asks what, besides episodic memory, might explain the evidence—and how we should evaluate competing explanations.

Motivational trade-off behaviours, where an organism behaves as if flexibly weighing up an opportunity for reward against a risk of injury, are often regarded as evidence that the organism has valenced experiences like pain. This type of evidence has been influential in shifting opinion regarding crabs and insects. Critics note that (i) the precise links between trade-offs and consciousness are not fully known; (ii) simple trade-offs are evinced by the nematode worm Caenorhabditis elegans, mediated by a mechanism plausibly too simple to support conscious experience; (iii) pain can sometimes interfere with rather than support making trade-offs rationally. However, rather than undermining trade-off evidence in general, such cases show that the nature of the trade-off, and its underlying neural substrate, matter. We investigate precisely how.

The biological world is rich in variation, both in bodies and in minds. A particularly clear case is memory, where traditional taxonomies increasingly face challenges capturing the full extent of variation. Meanwhile, a central debate within philosophy of memory has focused on whether episodic memory requires memory traces, given the role of simulation in episodic remembering. Do other forms of memory involve traces and simulation in the same way as episodic memory, and if they do, does this undermine episodic memory’s claim to be a natural kind? Trace minimalist approaches see the role of simulation in memory retrieval as a means of extracting a rich, reliable yet fallible representation from a trace storing compressed information. This insight can be generalised to a broader class of theories, Minimal Trace Minimalism. Within this broader class, ‘Trace Pluralist’ theories suggest, surprisingly, that the basic computation of compressed storage and potentially fallible reconstruction shows up not just in episodic memory, but equally in paradigmatic cases of semantic memory. This motivates replacing the episodic/semantic distinction with a richer, more systematic array of categories, and reevaluating our understanding of semantic memory and related notions such as belief.

We seem to have rich experience across our visual field. Yet we are surprisingly poor at tasks involving the periphery and low spatial attention. Recently, Lau and collaborators have argued that a phenomenon known as “subjective inflation” allows us to reconcile these phenomena. I show inflation is consistent with multiple interpretations, with starkly different consequences for richness and for theories of consciousness more broadly. What’s more, we have only weak reasons favouring any of these interpretations over the others. I provisionally argue for an interpretation on which subjective experience is genuinely rich, but (in peripheral/unattended areas) unreliable as a guide to the external world. The main challenge for this view is that it appears to imply that experience in the periphery is not just unreliable but unstable. However, I argue that this consequence, while initially appearing unintuitive, is in fact plausible.

The biological world is rich in variation, both in bodies and in minds. A particularly clear case is memory, where traditional taxonomies increasingly face challenges capturing the full extent of variation. Meanwhile, a central debate within philosophy of memory has focused on whether episodic memory requires memory traces, given the role of simulation in episodic remembering. Do other forms of memory involve traces and simulation in the same way as episodic memory, and if they do, does this undermine episodic memory’s claim to be a natural kind? Trace minimalist approaches see the role of simulation in memory retrieval as a means of extracting a rich, reliable yet fallible representation from a trace storing compressed information. This insight can be generalised to a broader class of theories, Minimal Trace Minimalism. Within this broader class, ‘Trace Pluralist’ theories suggest, surprisingly, that the basic computation of compressed storage and potentially fallible reconstruction shows up not just in episodic memory, but equally in paradigmatic cases of semantic memory. This motivates replacing the episodic/semantic distinction with a richer, more systematic array of categories, and reevaluating our understanding of semantic memory and related notions such as belief.

Do animals have episodic memory—the kind of memory which gives us rich details about particular past events—or is this uniquely human? This might look like an empirical question, but is attracting increasing philosophical attention. We review relevant behavioural evidence, as well as drawing attention to neuroscientific and computational evidence which has been less discussed in philosophy. Next, we distinguish and evaluate reasons for scepticism about episodic memory in animals. In the process, we articulate three pressing philosophical issues underlying these sceptical arguments, which should be the focus of future work. The Problem of Interspecific Variation asks which differences between humans and animal memory mean that an animal has a variant of episodic memory, and which mean that it has a different kind of memory altogether. The Problem of Functional Variation asks how we should conceptualise the functions of episodic memory and other capacities across species and across evolutionary time. Finally, the Problem of Alternatives asks what, besides episodic memory, might explain the evidence—and how we should evaluate competing explanations.

Motivational trade-off behaviours, where an organism behaves as if flexibly weighing up an opportunity for reward against a risk of injury, are often regarded as evidence that the organism has valenced experiences like pain. This type of evidence has been influential in shifting opinion regarding crabs and insects. Critics note that (i) the precise links between trade-offs and consciousness are not fully known; (ii) simple trade-offs are evinced by the nematode worm Caenorhabditis elegans, mediated by a mechanism plausibly too simple to support conscious experience; (iii) pain can sometimes interfere with rather than support making trade-offs rationally. However, rather than undermining trade-off evidence in general, such cases show that the nature of the trade-off, and its underlying neural substrate, matter. We investigate precisely how.

One of Clayton’s major contributions to our understanding of animal minds has been her work on episodic-like memory. A central reason for the success of this work was its focus on ecological validity: rather than looking for episodic memory for arbitrary stimuli in artificial contexts, focussing on contexts in which episodic memory would serve a biological function such as food caching. This review aims to deepen this insight by surveying the numerous functions that have been proposed for episodic memory, articulating a philosophically grounded framework for understanding what exactly functions are, and drawing on these to make suggestions for future directions in the comparative cognitive psychology of episodic memory. Our review suggests four key insights. First, episodic memory may have more than one function and may have different functions in different species. Second, cross-disciplinary work is key to developing a functional account of episodic memory. Third, there is scope for further theoretical elaboration of proposals relating episodic memory to food caching and, in particular, future-oriented cognition. Finally, learning-related functions suggested by AI (artificial intelligence)-based models are a fruitful avenue for future behavioural research.

We seem to have rich experience across our visual field. Yet we are surprisingly poor at tasks involving the periphery and low spatial attention. Recently, Lau and collaborators have argued that a phenomenon known as “subjective inflation” allows us to reconcile these phenomena. I show inflation is consistent with multiple interpretations, with starkly different consequences for richness and for theories of consciousness more broadly. What’s more, we have only weak reasons favouring any of these interpretations over the others. I provisionally argue for an interpretation on which subjective experience is genuinely rich, but (in peripheral/unattended areas) unreliable as a guide to the external world. The main challenge for this view is that it appears to imply that experience in the periphery is not just unreliable but unstable. However, I argue that this consequence, while initially appearing unintuitive, is in fact plausible.

Our thinking often uses rich memories of particular past events. Yet frequently we would do better to use other forms of memory. I show that existing accounts of the function of episodic memory cannot account for such cases, then develop an account which can. Roughly: rich representations of particular past events are required for Unrestricted Learning, learning which is not limited in how much of the world’s complexity it can capture; and episodic memory’s selection for Unrestricted Learning could explain its ubiquitous (and often inappropriate) use for other tasks. This proposal suggests many avenues for further empirical and computational research.

A target question for the scientific study of consciousness is how dimensions of consciousness, such as the ability to feel pain and pleasure or reflect on one’s own experience, vary in different states and animal species. Considering the tight link between consciousness and moral status, answers to these questions have implications for law and ethics. Here we point out that given this link, the scientific community studying consciousness may face implicit pressure to carry out certain research programs or interpret results in ways that justify current norms rather than challenge them. We show that because consciousness largely determines moral status, the use of nonhuman animals in the scientific study of consciousness introduces a direct conflict between scientific relevance and ethics—the more scientifically valuable an animal model is for studying consciousness, the more difficult it becomes to ethically justify compromises to its well-being for consciousness research. Finally, in light of these considerations, we call for a discussion of the immediate ethical corollaries of the body of knowledge that has accumulated and for a more explicit consideration of the role of ideology and ethics in the scientific study of consciousness.

We should be suspicious of the idea that experiencing pain could enable animals to trade off different motivations in a common currency. It is not even clear that humans have a common motivational currency reflected in evaluative experience. Instead, pain may capture attention, inhibiting attention to competing motivations and needs, thereby making genuine trade-offs harder. Our criteria for pain in invertebrates should be part of a more subtle theory of the relationship between pain and decision-making.

Recent influential accounts of temporal representation—the use of mental representations with explicit temporal contents, such as before and after relations and durations—sharply distinguish representation from mere sensitivity. A common, important picture of inter-temporal rationality is that it consists in maximizing total expected discounted utility across time. By analyzing reinforcement learning algorithms, this article shows that, given such notions of temporal representation and inter-temporal rationality, it would be possible for an agent to achieve inter-temporal rationality without temporal representation. It then explores potential upshots of this result for theorizing about rationality and representation.