Second-order conditioning, with which a “conditioned stimulus can be associated with some other conditioned stimulus or action, and so on, building up long chains of associative links between stimuli and actions”, and unlimited associative learning, which requires second-order conditioning as well as conditioning on compound and novel stimuli, have been proposed as markers of consciousness. Apparently there haven’t been any studies on whether second-order conditioning is possible on subliminal stimuli, though. Some discussion in this review by Jonathan Birch of the book The Evolution of the Sensitive Soul: Learning and the Origins of Consciousness by Simona Ginsburg and Eva Jablonka:
They use this marker (unlimited associative learning) to defend a generous view about the distribution of consciousness in the natural world, on which a capacity for conscious experience is common to all vertebrates, many arthropods and some cephalopod molluscs.
For example, I don’t know of any demonstration of the possibility of second-order conditioning of any kind on subliminal stimuli. This raises the intriguing possibility that second-order conditioning alone might already be a positive marker of consciousness, whether or not the stimuli are compound or novel. Second-order conditioning (but not on novel, compound stimuli) has been found in honey bees (Hussaini et al. 2007) and even snails (Papini 2010, p. 366). Yet I also don’t know of any experiments that have actively looked for second-order conditioning on subliminal stimuli in humans and failed to find it.
In short, the link between UAL and consciousness is promising yet largely uncharted territory. The hypothesis that UAL requires consciousness must be considered very tentative, since it has not been directly tested.
Second-order conditioning, with which a “conditioned stimulus can be associated with some other conditioned stimulus or action, and so on, building up long chains of associative links between stimuli and actions”, and unlimited associative learning, which requires second-order conditioning as well as conditioning on compound and novel stimuli, have been proposed as markers of consciousness. Apparently there haven’t been any studies on whether second-order conditioning is possible on subliminal stimuli, though. Some discussion in this review by Jonathan Birch of the book The Evolution of the Sensitive Soul: Learning and the Origins of Consciousness by Simona Ginsburg and Eva Jablonka: