An Immense World: How Animal Senses Reveal the Hidden Realms Around Us
by Ed Yong.
Random House, 449 pp., $30.00; $20.00 (paper)
Sentient: How Animals Illuminate the Wonder of Our Human Senses
by Jackie Higgins.
Atria, 308 pp., $18.99 (paper)
When Animals Dream: The Hidden World of Animal Consciousness
by David M. Peña-Guzmán.
Princeton University Press, 259 pp., $24.95; $17.95 (paper)
Recent writing about perception by neuroscientists and philosophers has tended toward a disconcerting message: we have nothing like the simple, direct contact with the world around us that we might suppose. Instead, we are told, our brains actively synthesize a picture of the world, continually guessing, extrapolating, and projecting. Stronger versions of this view hold that what we perceive is a kind of simulation or model—not one imposed on us by some malevolent being but one we fashion ourselves. The simulation is constrained by physical stimuli from the environment—from something outside us, anyway—but the constraint can be tenuous, and ordinary perception may be akin to a “controlled hallucination,” as the neuroscientist Anil Seth has argued.
Against this background, it’s interesting to read two recent books by science writers—Sentient by Jackie Higgins and An Immense World by Ed Yong—that describe, among other things, the sometimes astounding detail with which our senses mediate our contact with the world. The senses of many animals, including ourselves, could hardly be more finely tuned to what goes on around us.
Decades ago scientists found that, in some circumstances, human eyes can detect a mere handful of photons, the basic units of light. More recent work seems to show that in laboratory settings we can respond to just a single photon, though there is some controversy over this finding. It’s not that each photon is seen as a tiny flash, but we can make judgments at a better-than-chance level about when a photon has reached our eye. Our visual system is operating around the absolute limit that physics allows.
Other species are similarly sensitive according to their lifestyles and needs. Higgins, noting that some birds respond to magnetic fields when they navigate, writes that although the Earth’s own magnetic field is quite weak, a bird’s compass “can respond to forces that are one fifty-thousandth of the natural magnetic field.” One researcher told her, “The levels are substantially below anything previously thought to be biophysically plausible.” Male silk moths can track pheromones in the air at a level of one or two parts per quadrillion.
Yong discusses how crickets and spiders both detect air currents, and hence movement, with be used to see. “Put another way,” Yong writes, “it would be almost impossible to make these hairs more sensitive without breaking the laws of physics.” And onward: sharks can sense electric fields, and one species of hammerhead can detect a field with a strength of a billionth of a volt across a centimeter of water.
