In training, each actor watched a simulation of a theatre auditorium, as if on stage, while wearing electrodes on their scalp. The lights and sounds of the simulation were programmed to change in response to the wearer’s brain activity. Each actor was told to control their brainwaves to take the lights and crowd noise to a given level. The brain activity needed to achieve this was somewhere between slow-wave activity, associated with sleep, and fast-wave activity, associated with alert wakefulness.
"It’s the natural relaxed state of focused attention," says Gruzelier. It’s what actors refer to as "listening"; what you need to achieve a Judy Dench-class performance, he adds.