The Deaf-Mute Swing

Five Hundred Subjects and the Inner Ear Organ of Equilibrium

Suspended from a ceiling beam inside Harvard's Lawrence Hall in 1880, a wooden board hung from two parallel ropes. The ropes could be twisted tightly around each other like a playground swing and released to spin rapidly downward. William James tested two hundred healthy Harvard students and instructors on the apparatus. Each subject sat on the board with closed eyes while it spun, then opened his eyes the instant the board was stopped. For almost every observer, the room appeared to whirl violently in the opposite direction. Nausea and cold sweat rose immediately from the stomach. Out of 200 healthy Harvard subjects, 199 reported acute rotary vertigo.

James built this simple torsion swing to test a physiological hypothesis proposed during the 1870s by the Viennese physicist Ernst Mach, the physician Josef Breuer, and the Edinburgh chemist Alexander Crum Brown. For generations, anatomists had assumed that the entire inner ear—both the spiral cochlea and the three fluid-filled loops of the semicircular canals—existed solely for acoustic hearing. Following Pierre Flourens's pigeon-lesion experiments in Paris, Mach and Breuer argued that the three mutually perpendicular semicircular canals are actually hydrodynamic angular accelerometers.

Inside each semicircular canal sits a closed ring of endolymph fluid obstructed by a gelatinous elastic vane called the cupula. Sensory hair cells line the base of that vane. When the head undergoes an angular acceleration $\alpha_{\text{head}}$ in the plane of a canal, the bony canal wall turns immediately with the skull. The fluid ring of endolymph lags behind by inertia. That lag exerts a hydrodynamic pressure that deflects the elastic cupula by an angle $\theta$ according to the overdamped torsion-pendulum differential equation:

Here $I$ is the moment of inertia of the endolymph ring, $B$ is the viscous damping drag of the narrow canal duct, and $K$ is the elastic restoring stiffness of the cupula. When a subject spins on a twisted rope swing and is suddenly brought to a halt, the fluid continues swirling briefly against the cupula. That post-rotatory deflection tricks the brain's oculomotor nuclei into firing reflexive eye movements (nystagmus). It simultaneously generates the visual illusion that the room is spinning.

James saw a decisive natural experiment to determine whether the semicircular canals also drive the autonomic misery of seasickness. In the nineteenth century, many students at institutions for the deaf and dumb had lost their hearing in early childhood after severe bouts of scarlet fever or cerebrospinal meningitis. Those childhood infections often calcified and destroyed the entire inner labyrinth, including the semicircular canals. Between 1880 and 1882, James traveled to the American Asylum at Hartford, the Clarke Institution at Northampton, and the Horace Mann School in Boston. He tested 519 deaf-mute subjects on his rotating swing and collected clinical logs from deaf-mutes who had crossed the Atlantic or sailed New England steamers in winter gales.

Published in the October 1882 issue of the American Journal of Otology under the title The Sense of Dizziness in Deaf-Mutes, James's ledger revealed a sharp physiological split. While only 1 out of 200 normal Harvard subjects (0.5 percent) escaped vertigo on the swing, 186 of the 519 deaf-mutes (35.8 percent) experienced zero dizziness whatsoever. Another 134 felt only a scarcely perceptible trace. Their immunity extended directly to ocean storms, though it came with a hidden hazard. Several non-dizzy deaf-mutes reported that if they dived underwater with eyes closed, they lost all sense of up and down and nearly drowned before finding the surface. On deck in a hurricane, however, their equilibrium was unshakable, prompting one instructor of the deaf to tell James that during a storm at sea, his deaf pupils walked calmly about the cabin while every hearing passenger lay prostrate.

Out of the 186 non-dizzy deaf-mutes documented in James's 1882 survey, not a single subject who traveled by ocean steamer reported experiencing seasickness. Those clinical numbers established vestibular denervation as the definitive proof of inner-ear motion sickness.