Trehub's 'moon illusion' theory draws new notice

by Daniel J. Fitzgibbons, Chronicle staff

early everyone's experienced the "moon illusion," that brief time when the celestial orb looms huge on the horizon and then seems to shrink away as it rises into the night sky.

      More than a decade ago in his book, "The Cognitive Brain," adjunct professor of Psychology Arnold Trehub offered a neurological explanation for the illusion that has tantalized skywatchers for centuries. Now a new book is giving new credence to his theory about the moon illusion.

      In their newly published work, "The Mystery of the Moon Illusion," Helen E. Ross of the University of Stirling and Cornelis Plug of the University of South Africa credit Trehub with developing a "wide-ranging" model that offers "levels of explanation at the purposive level and at the neurological level."

      For nearly 30 years, Trehub worked at the Veterans Administration Medical Center in Leeds, where he directed a research laboratory focusing on psychology and neurophysiology studies. Though he retired from the VA in 1982, Trehub sustained a keen interest in the workings of the human brain, which led to the writing of his book, which was published by the MIT Press.

      "I wasn't trying to solve the moon illusion. I was trying to figure out how the brain does important cognitive work having to do with imagery," he said. "We attribute functions to the brain that are taken for explanations for what people do. That wasn't satisfactory for me."

      Trehub's explanation of the moon illusion places him in the company of scores of philosophers, astronomers and psychologists who have tried to unravel the riddle for more than 2,000 years. The mystery even attracted the attention of Aristotle, who suggested that atmospheric vapors magnified objects near the horizon. Up until the 16th and 17th centuries, the moon illusion was attributed to refraction, the same effect that make objects appear larger under water. As science progressed, more complicated theories of human perception were posited.

      As Trehub notes, "All the explanations were found wanting."

      Moreover, as human perception was studied more and more, some curious contradictions arose, he said. For example, people generally perceive the sky overhead to be closer than the horizon. That perceptual "flattening" of the vault-shaped sky should mean the moon on the horizon would be seen as farther away, but instead it's generally visualized as closer. "The reasoning is kind of flaky," said Trehub.

      Another visual phenomenon, known as size constancy, also added to the debate. Size constancy is the ability of humans to recognize the same object at different distances even though the image on the retina is substantially different, said Trehub.

      Some psychologists who studied the process said if the moon appears the same size on the retina at the horizon, then size constancy must make it appear bigger even though the moon is perceived as farther away.

      But Trehub rejects that explanation, noting that "most people will say it looks closer on the horizon."

      Struck by the contradictions offered by perception researchers, Trehub searched for a neurological answer. His theory employs an evolutionary explanation for how the human brain processes visual information.

      Trehub suggests that neuronal structure in the brain, the retinoid, determines how visual information is interpreted. The retinoid, he theorized, is key to the human brain's ability to construct a three-dimensional world from two-dimensional information captured on the retina.

     As humans evolved, he said, their focus was literally on things that were most important for survival. That area around them, which Trehub refers to as "egocentric space," was key to finding shelter and food and detecting danger. Objects well above or below that relatively horizontal terrestrial environment were generally less important to day-to-day living.

      As a result, he said, the human brain gradually evolved so more neural resources were devoted to egocentric space, he said. "There were fewer resources for things high in the sky because they didn't need to deal with them."

      When "The Cognitive Brain" was published, said Trehub, some researchers dismissed his ideas as premature because science hadn't yet advanced far enough to test his theory. "Others said this is the kind of theorizing that needs to be done."

      For Trehub, an adjunct faculty member since 1972, the new recognition of his model raises the possibility that his theory "will be taken as valid down the road."

     At the very least, Trehub hopes his ideas will stimulate more discussion and research. In the spirit of deeper investigation, he said, "I would like to see opposing theories put forth."

     Gratified that his theory may be guiding future research, he added, "It's my impression that the field is moving in this direction. ... "I'll wait and see what happens. I feel optimistic that it will be recognized."