The cause was complications of Parkinson’s disease, his son Mark said.

Advances in information theory, computers and experimental methods after World War II enabled scientists to challenge the dominant psychological discipline, behaviorism. Behaviorism examines stimuli to the senses and the resulting responses. In its purest permutation, it rejects the idea that the mind even exists.

Dr. Neisser (pronounced NICE-er), who loved to challenge orthodoxy and devise theoretical frameworks, sought to prove that people could think and to describe how they did it. He even named the new field with the title of his 1967 book, “Cognitive Psychology.” It set forth ideas advanced by him and other scientists that internal mental processes not only mattered, but could also be studied and measured.

“He galvanized this whole discipline,” James E. Cutting, chairman of the psychology department of Cornell University, said in an interview.

As computer technology advanced in the 1960s, students of the mind began to imagine it as an information processing system. Work in information theory, growing out of code-breaking operations in World War II, fed into the new discipline. So did new theories of linguistics that posited an innate structure to the mind.

James R. Pomerantz, a psychology professor at Rice University, said in an interview that Dr. Neisser’s genius was to combine these new understandings in constructing a new view of the mind, much as a paleontologist assembles a dinosaur skeleton from scattered fossils. The result, Dr. Pomerantz said, was “a single coherent way of thinking how the mind works.”

Dr. Neisser’s work showed that memory is a reconstruction of the past, not an accurate snapshot of it. He found that however much people think they are remembering actual events, they are really remembering memories — and probably memories of memories. The mind, he said, conflates things.

In a much-publicized experiment the day after the space shuttle Challenger exploded in 1986, Dr. Neisser asked students to write down their immediate experience upon hearing the news. Nearly three years later, he asked them to recount it. A quarter of the accounts were strikingly different, half were somewhat different, and less than a tenth had all the details correct. All were confident that their latter accounts were completely accurate.

Another memory experiment compared the testimony of John W. Dean III, the former aide to President Richard M. Nixon, during the Senate Watergate hearings with tapes of Mr. Dean’s conversations that the president had secretly recorded. He found discrepancies in detail after detail.

But Dr. Neisser said the testimony was accurate about the most important truths: that there really had been a cover-up, and that Nixon did approve it.

He also made observations about perception. In one experiment, he had participants watch groups throwing balls on a video screen. As they watched, a woman walked through the room carrying an open umbrella. Few remembered seeing her. Dr. Neisser called this phenomenon “selective looking”; other psychologists christened it “inattentional blindness.”

One result of this work on perception and memory was to cast doubt on accounts of remembered child abuse that swept the United States in the early 1980s. Dr. Neisser called into question the widely held view that extremely vivid memories cannot be false. He worked with the False Memory Syndrome Foundation and served on its board.

In 1995, Dr. Neisser headed an American Psychological Association task force that examined research suggesting that intelligence varied among ethnic groups. The panel ended up questioning the tests themselves, or, in his phrase, the assumption that “there’s something wrong with children who score low on intelligence tests.”

“Once you make that assumption,” he said, “all your later theory and research suffers from a built-in bias. To ask what’s wrong with black children is to assume that something is the matter — to locate the problem in the mind of the child.”

Ulrich Gustav Neisser was born in Kiel, Germany, on Dec. 8, 1928, and his family immigrated to the United States in 1933. He later dropped the “h” in his first name to sound more American, he said. His boyhood friends called him Dickie, and he was later known as Dick. He grew up in Swarthmore, Pa.; Washington and New York. His father, Hans, a noted economist, expected him to be a scientist. The boy had a chemistry set he did not use.

He went to Harvard and found psychology more interesting than physics. He was attracted to the Gestalt school of psychology, which takes a complex, holistic view of mental processes but lacks the scientific rigor of what became cognitive psychology. He even did some unsuccessful research on extrasensory perception, citing in an autobiographical statement “a soft spot in my heart for exciting but unlikely hypotheses.”

His contrariness extended to his own work. In 1976, he wrote “Cognition and Reality,” a book that challenged much of the field of cognitive psychology, arguing that it ignored the real world in favor of the laboratory.

Dr. Neisser earned an undergraduate degree in psychology from Harvard, a master’s degree from Swarthmore College and a doctorate from Harvard. He went on to teach and do research at Brandeis, Cornell and Emory College.

His marriage to Anna Gabrielle Peirce ended in divorce. His second wife, Arden Seidler, died before him. Besides his son Mark, he is survived by three other children from his first marriage, Philip, Tobias and Juliet Neisser; a son, Joseph, from his second marriage; a stepdaughter, Jennifer Seidler; a sister, Marianne Selph; and a grandson.

Dr. Neisser came to the realization that his own memory was as fragile as those of his research subjects. For years, he had said that he was listening to a baseball game on the radio when he heard about the attack on Pearl Harbor on Dec. 7, 1941. Finally, he said, it dawned on him that he could not have been listening to a baseball game in December.

In a graduation speech at the New School for Social Research in 1998, Dr. Neisser asked how the graduates could be sure they remembered anything accurately. He told them they could not be sure. Then he struck a more hopeful note, adding: “This is a graduation, your graduation, or perhaps your son’s or your daughter’s; for that reason you are not likely to forget it. Everything is happening just as it should, just as you will remember it years from now.”