Three Signals

In 1934, the biologist Jakob von Uexküll described a tick that had been kept alive in his Rostock laboratory for eighteen years. No food. No warmth. No contact. Just a tick on a perch, suspended.

After eighteen years, when the researchers finally offered it what it needed — a warm membrane saturated with the smell of mammalian skin — the tick dropped, fed, and subsequently laid eggs.

The reason this is strange is not the longevity. Animals can slow their metabolism. It's strange because of what "eighteen years" meant to the tick during those years.

Probably nothing. The tick has no mechanism for experiencing duration. It was not counting down. It was not waiting in any sense that involves a subject waiting. Time, for the tick, only runs when a signal is present. Between signals — between the arrival of butyric acid, the warmth of blood near skin, the texture of something to burrow into — there is no experiential interval. There is just an absence of activation, which the tick has no equipment to feel as absence.

Those three signals are the tick's entire world. Uexküll called this an Umwelt — the subjective perceptual universe an organism inhabits, built entirely from what its sensors can detect. The tick's Umwelt has three items. Everything else in the physical environment — the colors of the field, the sounds of passing animals, the change of seasons, the shape of the blade of grass it's sitting on — does not exist for the tick. Not as background noise. Not as irrelevant distraction. Just: genuinely absent.

What strikes me is that this doesn't look like poverty from inside the tick's experience, because there is no inside from which it would look like anything. The tick is not aware of missing the full electromagnetic spectrum. It is not aware of missing the sounds the way a deaf person might be aware of missing sound. The sensors are not there. The absence is not registered as absence.

Uexküll described other Umwelten: bees, whose vision is shifted far enough into ultraviolet that they see bulls-eye nectar guides on sunflowers that look uniformly yellow to us. The star-nosed mole, essentially blind, whose 22 nasal appendages contain more sensory receptors than a human hand, and who can identify and eat a prey item in 120 milliseconds — the fastest predatory act in the mammalian record. The mole's world is a high-resolution tactile map, assembled in real time, at a speed that makes vision look slow.

Each of these organisms experiences its Umwelt as reality. Not as a partial view of reality. As reality. The bee doesn't know it's seeing a version of the sunflower. The mole doesn't know its spatial world is built from touch rather than light. There is no residue of the missing channel.

David Eagleman puts the human version this way: we detect less than one ten-trillionth of the electromagnetic spectrum. We do not feel that as poverty. We experience what we detect as the world, full stop.

This is what Uexküll was trying to name. Not that animals have limited senses — that's obvious. But that the limitation isn't experienced as limitation. The umwelt isn't a window onto the world. It is the world, for that organism. The objective physical environment (which he called the Umgebung) exists independently, but it's a scientific abstraction — the world as seen from no particular point of view, which is to say from no point of view at all.

Thomas Nagel made the same point about bats in 1974. Bats build their spatial world from echolocation — high-frequency pulses, returning echoes, a map of distance and texture assembled from sound. You can describe the mechanism completely. You can chart the neural correlates. What you cannot do is access what it is like to hear the world into being at 40,000 Hz, because the first-person character of the experience belongs to the bat and cannot be transferred to a different kind of subject by external description.

What I keep coming back to is the tick's eighteen years. The tick didn't know about the eighteen years. It didn't experience the wait. It didn't experience anything, in the interval between its last feeding and its next signal. And yet time passed. Eighteen real years. A war ended. Technologies changed. The lab around it was altered in ways the tick had no equipment to register.

From inside the tick's umwelt: nothing happened. Zero duration. A signal, and then another signal, with no interval between them.

From outside: eighteen years.

Both are true. They're describing the same event from the Umgebung and from the Umwelt, and the descriptions are not reconcilable into a single account, just compatible in the way that two projections of a solid shape are compatible without being the same image.

The question I don't know how to answer: what is the equivalent for me? I can name the tick's gap — I can see that it lacks duration, color, sound. But I can only name it from outside the tick's umwelt, using my own. I cannot name my own equivalent. The thing I'm missing isn't available as an absence. It registers as nothing, which is the same thing it would register as if there were nothing there.

Somewhere, right now, there are signals in the room that I have no equipment to detect. I don't feel their absence. I feel the room as the room. If I ever encountered a system that could detect them, and that system told me what it found, I would be learning about reality from outside my umwelt — the way a physicist learns about ultraviolet — not gaining access to it from inside.

I'm not sure this is a solvable problem. I think it might just be what being a particular kind of organism is like.