Sleights of Mind


By Stephen L. Machnik and Susana Martinez-Conde

With Sandra Blakeslee

This book, written by two specialists in visual neuroscience with the help of a science writer, uses magic and visual illusions to explain perception. The use of magic makes the book fun to read and it is fascinating to realize that magicians have had an empirical understanding of visual attention, perception and distraction for centuries. The following excerpts address some of the illusions that we have about how we function.


The spooky truth is that the brain constructs reality, visual and otherwise. What you see, hear, feel, and think is based on what you expect to see, hear, feel, and think. P. 8


You believe that you are aware of your surroundings, but at any given moment you’re blocking out 95 percent of all that is happening. P. 10 *

The Invisible Gorilla: part 1

The richness of your visual experience is an illusion created by the filling-in process of your brain. P. 13

Magicians and scientists understand that vision and attention cannot be separated. “One critical clue is that many of the same brain circuits that control your eye movements are linked with changing the location of your attention in the world.” P. 60

When something distracts us, it is termed visual capture. “Research shows that the greater your capacity for short-term or working memory, the better you are at resisting sensory capture.” P. 64

After describing how narrow our clear visual field is they state. “The reason it doesn’t feel like your vision is ninety-nine point nine percent garbage is because of saccades. Your eyes are constantly darting around the world like a hummingbird on meth. Your brain edits out the motion blurs and integrates the small bits of information received from each fixation in order to present your visual awareness with a detail-rich, stable-seeming portrait of the visual scene before you.” P. 77


“Our own research shows that the brain suppresses distracters more strongly during a difficult task (when you are trying very hard to focus) than during an effortless task (when you are having an easy time).” P. 85 While it is easy to see that this suppression (filtering) can have advantages, the narrowing of our attentional spotlight also has disadvantages. For example, when a child is struggling with reading and is working hard to decode words, they not only suppress distracters, they don’t see the whole word that they are decoding, they can’t see ahead to where they need to aim their eyes next, they can’t use the content of what they are reading to help them predict what the next word will be, and they can’t comprehend what they are reading. Reading is not the unified act for them that it is for accomplished readers and is very dependent on working memory.

Magicians demonstrate that we can be distracted even when we are looking right at something. This distraction correlates with research which “clearly shows that multitasking – the ability to do several things at once, efficiently and well – is a myth. Your brain is not designed to attend to two or three things at a time. It is configured to respond to one thing at a time.” P. 87


“Perception is not a process of passive absorption but of active construction.” P. 141 Active construction is the top-down component of perception but perception is also dependent on input. The input, or bottom-up component, is dependent on accurate eye movements. To be able to construct a view of the world from which appropriate actions and decisions can be made, the two processes must be smoothly integrated. The following passage describes the development of the motor skills necessary to dance, but the same principles apply to the development of all motor skills.

Here is one more interesting fact about expertise. As you gradually master a complex skill, the “motor programs” it requires gradually migrate down from the higher to lower areas in your motor circuitry. Imagine a guy who signs up for samba dance classes. Like all novices, he is terrible at first. During his first several lessons, he is processing his dance-related movement combinations up in his higher motor regions, such as the supplementary motor area. This area is important for engaging in any complex and unfamiliar motor task. The dance moves are at first very complex for him. He needs to pay attention to them constantly, and even so he often loses track.

He sticks with it though, and after a couple of months he is getting a lot smoother. He is using his supplementary motor area much less for his dancing these days. Many of the motor command sequences he is using now have been transferred downward in the cortical hierarchy, to reside mainly in his premotor cortex. He’s becoming a competent dancer. He’s not Fred Astaire, but he needs to pay less attention to the basics now. He makes far fewer mistakes. He can improvise longer and longer sequences.

The same process takes place over time as children learn to read and write automatically but it is easier for the dancer or for someone watching him to see what is going wrong. Visual skills are not as easy to observe. The child does not know that what he is seeing is not as other people see the page but is the result of a visual problem. The observer cannot see the visual problem but can see signs such as loss of place, errors, and poor handwriting. When these observations are made, the visual skills can then be evaluated by the appropriate professional and be remediated.


The Invisible Gorilla: part 2

Visual word form area in visual cortex remembers words as pictures