The neuroscientist Alain Berthoz experimented on Russian astronauts in space to answer these questions: How does weightlessness affect motion? How are motion and three-dimensional space perceived? In this erudite and witty book, Berthoz describes how human beings on earth perceive and control bodily movement. Reviewing a wealth of research in neurophysiology and experimental psychology, he argues for a rethinking of the traditional separation between action and perception, and for the division of perception into five senses.

In Berthoz’s view, perception and cognition are inherently predictive, functioning to allow us to anticipate the consequences of current or potential actions. The brain acts like a simulator that is constantly inventing models to project onto the changing world, models that are corrected by steady, minute feedback from the world. We move in the direction we are looking, anticipate the trajectory of a falling ball, recover when we stumble, and continually update our own physical position, all thanks to this sense of movement.

This interpretation of perception and action allows Berthoz, in The Brain’s Sense of Movement, to focus on psychological phenomena largely ignored in standard texts: proprioception and kinaesthesis, the mechanisms that maintain balance and coordinate actions, and basic perceptual and memory processes involved in navigation.

Groping around a familiar room in the dark, or learning to read again after a traumatic brain injury; navigating a virtual landscape through an avatar, or envisioning a scene through the eyes of a character—all of these are expressions of one fundamental property of life, Alain Berthoz argues. They are instances of vicariance, when the brain sidesteps an impasse by substituting one process or function for another. In The Vicarious Brain, Creator of Worlds, Berthoz shows that this capacity is the foundation of the human ability to think creatively and function in a complex world.

Vicariance is often associated with proxies and delegates, but it also refers to a biological process in which a healthy organ takes over for a defective counterpart. Berthoz, a neuroscientist, approaches vicariance through neuronal networks, asking how, for example, a blind person can develop a heightened sense of touch. He also describes how our brains model physical reality and how we use these models to understand things that are foreign to us. Forging across disciplinary boundaries, he explores notions of the vicarious in paleontology, ethology, art, literature, and psychology.

Through an absorbing examination of numerous facets of vicariance, Berthoz reveals its impact on an individual’s daily decision making and, more broadly, on the brain’s creation of worlds. As our personal and social lives are transformed by virtual realities, it is more crucial than ever before that we understand vicariance within our increasingly complex environment, and as an aspect of our own multiplying identities.