This book explores how magic, the art of creating impossible effects that violate our expectations by the apparent transgression of natural laws, works. Specifically the authors explain the cognitive processes behind the art of magic. This book is fundamentally an exploration of neuroscience, through the lens of magic.
Magic works because it takes advantage of the brain’s normal processing. Magic can manipulate our memories, condition us, and influence our intuitive decisions, all without our conscious awareness that it is doing so.
Living in Illusion: We live in illusion. We construct our own reality from the information we receive from the universe around us, and we do so unconsciously. The data from the world around us is incomplete and the brain fills in these gaps using past experiences and other sources, resulting in guesses that are sometimes inaccurate.
Vision: about one third of the brain is involved in processing vision. We have more than 100 million photoreceptors in each of our retinas that receive about 70 gigabytes of information per second, equivalent to watching 70 movies per second. The brain can’t process all of this information, so it filters what we see. Only about 0.0014% of the information that hits the retinas is transmitted to the brain. Thus, the optic nerve has a transmission rate similar to an ethernet connection. Due to the hole in our vision caused by the optic nerve, the brain fills in this blind spot using the areas around it to interpolate. The brain also fills out the peripheral vision with details from the fovea.
The retina contains two kinds of photoreceptors, cones and rods. Rods make up the majority and are in the periphery with cones concentrated in the fovea. Rods are capable of responding to a single photon of light, but stop responding when the intensity of light rises. So they allow us to see well in low light conditions, but not daylight. Cones require much higher luminous flux, they are activated only when thousands of photons arrive simultaneously. They are inactive in low light conditions. This is why it is dangerous to drive at dawn or dusk. Rods don’t respond because they have adapted to the lighting of the moment, and the cones have not been activated because light is too low. Thus, magicians often use low light conditions as this favors concealment.
We only have good visual acuity in the fovea, which is only 2% of the retinal surface. Also, retinal neurons detect information primarily when there are changes in a scene. Thus, to see static images, we need to make continuous eye movements. The brain needs to fill in these jumps because between fixations, we are basically blind. This is temporal filling in, and it occurs for 3-4 hours of your day.
Magicians can exploit the limitations of the visual system by both making movements so fast that the eye is blind to them, or by making changes so slowly that the eye adapts to the change and is blind to it.
Art and vision: Why can basic outlines of something generate vivid perceptions, often more perceptively powerful than a faithful representation? The structure of the retina is such that cells can detect the basic zones of an image in which the amount of light reflected suddenly produces a local change, we call this contrast. And this occurs primarily along the edges of objects.
Why can an image that provides less visual information be more suggestive than one richer in detail? The brain cannot process all the information in a detailed image anyway, and a contour drawing directs all our attention to the most relevant parts without being dispersed to the less informative areas. We start with filtered information and fill in the rest by generating associations between what we see and our previous conceptual knowledge. Thus, by leaving so much room for the spectator’s contribution, line drawings are usually even more suggestive than a detailed and faithful image.
The brain processes color and luminance independently. “Colors are only symbols, reality is to be found in lightness alone” as Picasso said. The impressionists used this to great effect because they realized that it does not matter what colors are used to depict a difference in luminance. They used unrealistic colors to great effect. In Monet’s Impression, Sunrise, the sun is just as luminous as the background, and is only seen by the color-sensitive “what” pathway, and not by the “where” pathway. Thus, the visual system is unable to accurately establish the sun’s position in the sky, and the sun appears to be shining in a diffuse way. Monet’s paintings of La Grenouillere used black and white (high luminance contrast) next to blue and yellow (lower contrast) to create an impression of movement in the river.
The intention of the impressionists was to capture the essence of an image. They did this partially by blurring edges and making low spatial resolution paintings that don’t activate the “what” pathway strongly due to lack of hard edges, but do lead to a sense of elusive perception from the “where” pathway.
What and Where pathways: they originate in the retinal ganglion cells. The “what” pathway runs along the ventral side of the brain in the occipital and temporal lobes. Activity in this pathway correlates with our conscious recognition of objects that appear in a visual scene. The “where” pathway follows a dorsal path in the brain through the occipital and parietal lobes. This pathway processes depth as well as global and relative movement. The “where” pathway is fast, but is blind to color and lacks the spatial resolution of the “what” pathway.
Conception of Reality: We capture external stimuli through sensory memory, which briefly retains sensations. The brain filters this input through the process of attention. The authors divide memory into three main categories: sensory memory, short-term memory, and long-term memory.
Sensory memory is unconscious and ephemeral, and retained for a very short period of time. Much of this is ultimately discarded. It passes through the thalamus, goes to different sensory cortices, and finally arrives at the prefrontal cortex where it might be made available to the next stage: short term memory. If it is not attended to in short term memory, it is discarded. Magicians have learned that sensory memory is fragile and quite susceptible to interference.
Short term memory, or working memory operates not only in the present, but also in anticipating the future. It can make inferences based on past experiences.
Long term memories store large amounts of information for long periods of time and are often formed through the repetition of short term memories.
Magic and Contrast: the retina prioritizes points in space where light changes in intensity by using “on” and “off” detector neurons. “On” neurons detect local changes from less to more luminance and “off” neurons detect more to less luminance. When one is activated, the other is actively suppressed, thus enhancing contrast. Like retinal cells, they don’t respond to absolute value, but rather to change. In a scene, the points of maximum contrast are those that capture our attention, a fact that magic uses to its advantage. Contrast may be spatial or temporal or explicit (present in physical reality) or implicit (stored in our memories). Magicians must constantly modulate contrast in a scene. The aim is to have the audience’s attention under control at all times so that it can be led inadvertently to an impossible outcome. Magicians do this by either enhancing or avoiding contrast.
Some things that contribute to the logic and predictability of a magic trick are conditioned naturalness (repetitive movement to normalize an action that would otherwise draw attention) , ruses or feints (preconditioning for example in which the magician does the action accurately at first, before and trick action), and illusory correlations (takes advantage of our tendency to infer causality from correlation).
Presensory manipulation: Many methods in magic interfere with stimuli before sensory info is even detected by the perceiver’s nerve cells.
Exogenous capture of attention and open diversion: also called physical misdirection by magicians, it’s a classic methodology of magic. Magicians create new areas of attention with their body language, gestures, and gaze so they can perform secret maneuvers outside of the area of interest. Contrasting stimuli is one method (e.g. loud sounds, bright lights, unpredicted movements). Gaze of the magician and nonverbal body language cues are important in directing the attention of the audience.
Priority movements: not all movements are equally good at capturing attention. A large or fast movement can cover a small one. When several movements are presented at once, spectators tend to follow the one that starts first. Curved movements may attract more attention than straight ones.
Endogenous capture and covert deviation: endogenous capture is us directing our attention at will. This type of attention can be maintained for longer than exogenous capture. It can be manipulated by a stimulus that changes the focus and that is called covert diversion in magic. This is achieved when the focus of a spectator’s attention is shifted to another subject, fixing the spectator’s thoughts on something without necessarily changing their gaze.
Dividing attention: we can’t actually attend to two inputs at once, we switch between them and the brain builds an illusion of simultaneity. Dividing attention is one of the most effective and frequently used techniques in magic tricks. This can be done with sudden distractions for example, like asking a question.
After an active capture of attention, the audience tends to relax their attention and blink synchronously. This produces moments of deactivation that a magician can take advantage of.
Prediction: the brain is constantly predicting, and using that info to fill in perceptual gaps. Incoming sensory info is carried by feed-forward projections, while feedback projections generate predictions about the external causes of incoming sensory input. Visual information is projected onto the retina as a two dimensional image. Here a problem arises because this projection has infinite solutions in three dimensions. This is ameliorated by predictive processing to narrow these possibilities down to the most likely outcomes as informed by our past experiences. The brain is also quite slow, we’re about a third of a second behind events in the world. High accuracy predictive processing allows us to do things like drive and play tennis. In tennis, when an opponent hits a ball at 200 km/h, the other player only has about 400-thousandths of s second to position themselves to return it. This would be impossible without predictive processing.
Amodal completion: When part of an object is hidden, our brains usually apply the most regular, symmetrical interpretation of the rest of the object. Magicians take advantage of this in tricks like Chinese linking rings. The ring actually has a gap that the magician hides with their hand, but our brains fill in the missing area and assume it’s a whole ring.
Memory: as we evoke memories, we reconstruct them, and the resulting memory is never exactly the same. Many factors can lead to incorrect memory, such as emotional overload, attribution error (erroneous inference due to apparently logical assumptions), suggestion (planting a memory of being lost in a shopping mall for example), framing (how fast were the cars going when they “came in contact” vs. “smashed into each other”), information received after witnessing an event etc.
Memory manipulation in magic: these techniques are commonly used. Diverting attention: attention is diverted during a trick so that spectators do not fixate on a secret maneuver, meaning that info does not travel from short term to long term storage. Parenthesis of oblivion: this technique establishes temporal distance between a maneuver and its related effect. For example the magician hides a coin, then tells a story, and the coin reappears. Sudden erasure of short-term memory: for example with a comic gag.
Unconscious brain: whether a stimulus rises to the level of consciousness depends on two primary factors: the attention devoted to it and the intensity of the stimulus. Priming: the influence of attitudes, perceptions, and choices in an unconscious way due to previous exposure to certain stimuli. Priming is most effective when both stimuli share the same sensory mode. Perceptual and conceptual priming can both occur. Magicians can use priming to force a choice in a spectator (like exposing them to a toy giraffe to make them choose a card with a giraffe on it). Magicians try to make spectators make unconscious decisions without switching to conscious decision making. In situations of uncertainty, we often resort to general heuristics.
Forcing: For example, asking someone to choose a card, presenting cards for small fractions of a second, except the forced card, which is presented slightly longer. This technique works close to 100% of the time when done well. Right handed participants tend to choose something on the right vs left of them. When asked to choose a number between five and ten, most people choose 7.