Joseph Jastrow

Joseph Jastrow (January 30, 1863 – January 8, 1944) was an American psychologist whose work spanned experimental psychology, psychophysics, and the design of experiments. He is known for his studies of optical illusions, including the Jastrow illusion, which he either first reported or helped popularize. Jastrow held that nearly everyone carries mistaken assumptions about psychology. A key aim of his career was applying the scientific method to separate truth from error, and he worked to educate the public through lecture tours, popular magazines, and radio broadcasts.

Born in Warsaw, Poland, Jastrow was the son of Talmud scholar Marcus Jastrow and the younger brother of orientalist Morris Jastrow, Jr. He moved to Philadelphia in 1866, earning bachelor’s and master’s degrees from the University of Pennsylvania. During his doctoral studies at Johns Hopkins University, he collaborated with C. S. Peirce on psychophysics experiments that introduced randomization and blinding into repeated measures designs. After Peirce left the university due to a personal scandal, Jastrow continued his research independently. From 1888 until his retirement in 1927, he served as a professor at the University of Wisconsin–Madison, where he mentored Clark L. Hull. He later lectured at the New School of Social Research from 1927 to 1933.

At the 1893 World’s Columbian Exposition, Jastrow headed the psychological section, gathering psychophysical and reaction time data from thousands of visitors. He was a charter member of the American Psychological Association and became its president in 1900. Jastrow was active in popular media, giving public lectures and writing for magazines such as *Popular Science*, *Cosmopolitan*, and *Harper’s Monthly*. He also authored *Keeping Mentally Fit*, a syndicated column that ran in 150 newspapers, and delivered radio talks from 1935 to 1938 through the Philadelphia Public Ledger Syndicate.

Jastrow experienced bouts of depression throughout his life. He died in Stockbridge, Massachusetts. His wife was Rachel Szold, sister of Henrietta Szold; classical archaeologist Elisabeth Jastrow was his cousin. His former home in Madison, Wisconsin, now lies within the Langdon Street Historic District.

Jastrow was a founding member of the American Society for Psychical Research, which studied mesmeric, psychical, and spiritual phenomena. Early members were skeptical of paranormal claims, and Jastrow approached psychical phenomena from a psychological perspective, arguing it was unwise to separate such problems from their natural context. He resigned from the society by 1890 and became an outspoken critic of parapsychology. Because psychical researchers were rarely trained psychologists, Jastrow considered their work lacking in credibility. He believed that, given the absence of evidence for psychical phenomena, psychologists should not prioritize disproving them. In his 1918 book *The Psychology of Conviction*, he devoted a chapter to exposing the tricks of Eusapia Palladino.

A leading figure in anomalistic psychology, Jastrow published *Fact and Fable in Psychology* in 1900, debunking occult claims from Spiritualism, Theosophy, and Christian Science. He examined the occult scientifically, seeking to understand why people were drawn to it, how it gained social traction, and what evidence its supporters offered. He noted that many people treated coincidence, dreams, and premonitions as sources of knowledge superior to science, and he saw the scientist’s role as helping the public distinguish truth from fiction and prevent the spread of false beliefs. Jastrow studied the psychology of paranormal belief, viewing such phenomena as entirely unscientific and misleading, arising from delusion, fraud, gullibility, and irrationality.

Jastrow considered analogies a primitive way of interpreting the world, citing examples such as the Zulu chewing wood to soften a heart and Illinois Indians stabbing images of those they wished harm. He wrote about cultures that ate animals to gain their physical traits, noting that this tradition persisted in his own time through superstitions, rituals, and folk medicine. The underlying motivation, he argued, was the belief that one kind of connection would bring about others.

In perception research, Jastrow focused on eyesight, which he saw as more complex than a camera, with mental image processing central to interpreting the world. He illustrated this with optical illusions, including the rabbit–duck illusion, and argued that what people saw depended on their emotional state and surroundings. To detect unconscious hand movements, he invented the automatograph, finding that when subjects concentrated on an object, their hand moved unconsciously toward it; the effect varied, especially in children, whose movements were more random. He also studied dreams of the blind, discovering that those who lost eyesight after age six could still see in dreams, while those who lost it before age five could not.