William James and the sixth sense

All his life, William James, Harvard philosopher and psychologist, suffered from seasickness. Perhaps that's why he was interested in the function of the inner ear's semicircular canals — an interest that led him to personally conduct experiments on the inner ear and dizziness. Although James is credited with founding the first American psychology laboratory, he was not fond of experimental work. This investigation was unusual and noteworthy for him.

In the late 19th century, the notion that the inner ear was important for anything except hearing was still relatively new. The semicircular canals were thought to be involved in the localization of sound. It wasn't until 1824, when M.J. Pierre Flourens surgically sectioned a pigeon's semicircular canals that the canals' importance in balance was identified. Using a method known as ablation, Flourens systematically investigated the function of different parts of the brain by removing a section at a time and observing the consequences. Removal of the cerebellum led to loss of coordination. He also destroyed part of the pigeon's semicircular canals, which caused the pigeon to have abnormal eye movements, to turn its body in the direction of the lesion and caused the bird to lose its equilibrium.

Though these experiments were among the first to tie vertigo to the inner ear, only experimentation with human subjects could verify that the sensation of vertigo accompanied the loss of balance. Vertigo had long been attributed to the movement of "animal spirits" or "nervous humors" as a consequence of body rotation, illness, alcohol or looking down from a high place. In approximately 330 B.C., Aristotle described vertigo as a result of alcohol indulgence. He maintained, however, that there were only five senses: vision, hearing, smell, taste and touch. It took centuries to acknowledge the existence of a sixth sense — that of balance or equilibration — and to discover the organ responsible for it.

Although an American physician named William Charles Wells had published the results of several experiments on vertigo in human subjects in 1792, his work was ignored for reasons that are difficult to identify. It was Czech anatomist Jan Evangelista Purkinje who received most of the credit for experimental investigation of vertigo, which he described at length in 1820. Purkinje's experiments primarily used rotation to induce vertigo, but he also used electrical stimulation of the ears, known as the galvanic method. (The early 19th century fascination with electricity led Alessandro Volta and others to apply the galvanic method to each of the senses to observe its effect.)

Purkinje's work with humans, coupled with Flourens's observations in birds, seemed to suggest, as James reported in 1881, "that the semicircular canals of the internal ear have nothing to do with the function of hearing, but are organs of a special sense hitherto unrecognized as such." James reasoned that if this were true, "deaf-mutes" with damage to the inner ear might not be susceptible to vertigo.

To test this hypothesis, he initiated a study of dizziness in Harvard students and in deaf individuals. Participants closed their eyes and sat on a swing that was rotated until its ropes were tightly twisted together. After the swing ropes were allowed to rapidly unwind, the experimenter asked the participants to open their eyes and try to walk a straight line.

Of the 200 Harvard students and instructors, only one did not experience dizziness. But of the 519 deaf children, a majority reported only slight dizziness or none at all. James reported some preliminary results of the study in 1881 in the Harvard University Bulletin. The following year, he published his complete findings in the American Journal of Otology, acknowledging that more thorough research was needed and "in the hope that some one [sic] with better opportunities may carry on the work."

This was not James's first contribution to the American Journal of Otology. His review in 1880 of an article by German scientist C. Spamer on the physiology of the semicircular canals showed James's grasp of the literature. He suggested that Spamer's results didn't add much to "our knowledge of the function of these rather mysterious organs."

James was much more impressed with the work of Austrian physician Josef Breuer, who with physicist Ernst Mach had independently developed a hydrodynamic theory of semicircular canal function. Breuer showed that eye movements in human participants after rotation consisted of a slow movement opposite the direction of rotation and then a fast movement to reset the eyes to their original position. Inspired by Breuer, James reported in a footnote to the 1880 review his observations of similar compensatory movements in frogs. If a bowl containing a frog was rotated in one direction, the frog moved its head in the opposite direction. His attempts to test whether the semicircular canals were responsible by operating on the frogs were unsuccessful. He suggested that others with better eyesight might be more successful in testing Breuer's theory.

Breuer's work on the inner ear also showed that while the semicircular canals detected angular acceleration, the otolith organs detected gravity and linear acceleration. Breuer is better known today for his collaboration with Sigmund Freud and the study of his patient "Anna O," but his work on the vestibular system is much more extensive.

Inspired perhaps by Breuer, James reported that a number of his "non-dizzy" deaf participants were extremely disoriented in water and could not swim for fear of drowning due to an inability to distinguish where the surface was. This observation suggested that both the otolith organs and the semicircular canals were not functioning normally. In turn inspired by James's 1882 paper, Breuer resumed experimenting on the otolith organs and developed the concept that a shearing force on hair cells in the vestibular organs is the mechanism for detecting linear and angular acceleration — a theory confirmed in the 20th century by other investigators.

Interestingly, Scottish scientist Crum Brown in 1878 had made the suggestion that the study of the deaf could help clarify the relation between the inner ear and rotation. It is hard to know whether James arrived at his idea independently or whether he was aware of Brown's suggestion. In addition to conducting the swing experiments, James sent questionnaires, or "circulars," to various institutions. These uncovered the fact that large numbers of deaf people staggered or zigzagged when they walked and could not stand still with their eyes closed. (Congenitally deaf individuals never suffer these equilibrium problems, only those who become deaf due to illness or accident. Modern research suggests that children who are born deaf learn to compensate for the lost vestibular sense with the use of other visual and motor systems.)

James also asked a number of deaf individuals about their experience with sea-sickness, and with a very few exceptions most reported they did not suffer from the condition. This led James to propose that irritating or blistering the skin behind the ears would be a counterirritant that might keep the vestibular sense from being overexcited and which he tried his next sea voyage. As he wrote to his mother-in-law Feb. 14, 1883, "I may of course be mistaken, but I thought that I made a rising qualmishness disappear entirely 3 or four times by rubbing vigorously … If so, I'm a great benefactor of humanity, and no mistake."

James's flurry of experiments on the vestibular sense are interesting because they were a departure for him. Not only did he operate on frogs to try to see if he could disrupt compensatory head movements after rotation, but he enlisted the assistance of his brother Bob to carry out the swing experiments with deaf children at various schools and institutions. James certainly was active in his laboratory at least for teaching purposes — as, for instance, when he guided student experiments on hypnosis and automatic writing. He was known, however, for grumbling about experiments and was thought not to have the patience or physical stamina for laboratory work.

Katharine S. Milar, PhD, of Earlham College is the historical editor for "Time Capsule."