When a magician fools you, do you fail to see it or fail to remember it?

When a trick fools you, what exactly failed? Psychologists have a tidy answer that is not as tidy as it sounds. Mack and Rock concluded in 1998 that no conscious perception can occur without attention, which suggests that you fail to see what you do not attend to. But Daniel Memmert's gorilla experiment with children suggests something odder. Only 40 percent of the children reported seeing the gorilla, and the 60 percent who did not report it spent an average of 25 frames, about one second, fixated on it. They looked straight at it and did not perceive it.

That raises the question researchers still argue about: is inattentional blindness a failure of perception or a failure of memory? Mack and Rock noted that it can reflect a basic failure of perceptual processes to be engaged by unattended stimuli, or a failure of memory processes to encode information about them. Some experts argue that at least some instances are better characterized as memory failures than perceptual failures. Others point to priming effects, which indicate that the unreported stimulus was processed to some degree. Newer work pushes further: in five studies with about 25,000 participants, Makaela Nartker and colleagues at Johns Hopkins found that people who said they had not noticed an extra line could still say where it had been better than chance, and they argue this casts doubt on claims that awareness requires attention.

Magic adds a twist. Inattentional blindness tasks require an explicit distractor, while in misdirection the distraction occurs through the implicit yet systematic orchestration of attention. There are also several varieties of misdirection, and different types are likely to induce different cognitive and perceptual processes. The neuroscientists Stephen Macknik and Susana Martinez-Conde say that magic tricks fool us because humans have hardwired processes of attention and awareness that are hackable, and the techniques developed over centuries of stage magic may be used by neuroscience as powerful probes of human cognition.