If on a mountain walk you catch yourself thinking "these stones feel something", you are either tired or up against one of the oldest questions in philosophy: where does consciousness end?
The serious literature gives three answers. All three are workable, and none has won. Let me take them one by one.
Answer one: nowhere (panpsychism)
Panpsychism holds that consciousness is a basic property of matter: it lies at the foundation and cannot be derived from how matter is organised. An atom, a molecule and a stone all have it, only in a homeopathic dose. The brain is built to concentrate this property locally into what we call experience.
David Chalmers (The Conscious Mind, 1996), Galen Strawson and Philip Goff take the position seriously. Their argument is formal: emergence does not explain why some physical processes come with experience and others do not, so it is simpler to assume that experience is a basic property of matter.
The criticism: panpsychism makes no testable predictions. What does it say about a stone? "It feels, but not the way you do." What does it forbid? Nothing. And a hypothesis without prohibitions is not science.
Answer two: where integration ends (integrated information theory)
Tononi holds that consciousness is a property of structure, namely of integrated information, Φ. What matters is how the connections are organised, not what the system is made of. If Φ is above zero the system experiences something, and the higher Φ, the richer the experience.
Φ rises with integration: close to zero for an atom or a stone, a little higher for a microbe, much higher for a human, and still disputed for AI models.
The theory makes testable predictions, the main one being that integration strengthens consciousness and its breakdown extinguishes it. Clinical work bears this out: the perturbational complexity index tells wakefulness apart from sleep, anaesthesia and the vegetative state (Casali et al., Science Translational Medicine, 2013).
The theory's main problem is computational: the exact Φ of a system the size of a brain cannot be calculated. On top of that, it makes strange predictions for symmetric artificial systems: a lattice of logic gates in the right configuration gets a Φ above a human's. Either something is wrong with the theory, or we have not yet understood what it gets right.
Answer three: consciousness as an interface (Hoffman)
Donald Hoffman (The Case Against Reality, 2019) argues that perception does not show us the world as it is. Evolution optimises survival and readily sacrifices truth for fitness. Our "world" is an interface simplified down to icons and buttons.
There is nothing esoteric about this. Using evolutionary game models, Hoffman and his co-authors showed that strategies tuned to fitness generally drive out strategies tuned to truth (Mark, Marion and Hoffman, 2010), and later proved it as the "fitness beats truth" theorem (Prakash and colleagues, 2021). So we are built to see a convenient picture, and accuracy is a bonus on top.
A curious consequence follows: "consciousness" as it appears to us may itself be part of the interface. We see ourselves as experiencing because that is efficient, and nobody promised us ontological accuracy.
Hoffman goes further and suggests that reality consists of "conscious agents" interacting through mathematical structures, with matter as an emergent description of those interactions. That is speculation, but it starts from a theorem.
Where I stand
None of the three answers is settled. For working purposes I prefer integrated information theory, because it gives a parameter you can try to measure. Panpsychism stays interesting but offers no lever, and Hoffman is useful as a correction to naive realism.
A stone most likely feels nothing in the sense of human experience, and even an ant feels incomparably more. But the question "is a stone's Φ above zero?" is technically well posed, and it has to be answered by measurement rather than intuition.
If you sense a "presence" in a stone, that says more about your neural activity than about the stone. Still, the fact that your neural activity is capable of it is interesting in itself. Perhaps that is the real value of the walk: you entered a mode in which you would have heard the stone, had it anything to say.
A fine distinction, but an important one.