The debate over whether invertebrates are conscious lacks both agreement and a clear methodology. Three approaches exist: theory-heavy, theory-neutral, and theory-light. Theory-heavy and theory-neutral approaches have serious problems, so the author advocates a middle path: the theory-light approach. This approach relies on a minimal hypothesis: that conscious perception of a stimulus facilitates, relative to unconscious perception, a cluster of cognitive abilities related to that stimulus. This 'facilitation hypothesis' can guide research into invertebrate consciousness. The author argues that what is needed now is not more theory or undirected data gathering, but a systematic search for consciousness-linked cognitive abilities, their relationships, and their sensitivity to masking.
A growing scientific field demonstrates that animal feelings can be investigated using rigorous methods, challenging the long-held view that subjective experiences in non-human animals are beyond scientific reach.
An essay review contrasts two major theories of animal consciousness: Peter Godfrey-Smith's view that subjective experience is widespread across many animal lineages and Joseph LeDoux's claim that consciousness depends on higher-order brain circuits found only in mammals and birds. The author discusses the motivations behind each picture and attempts to find a middle path between them, weighing evidence from evolution, emotion, and the nature of phenomenal experience.