Daniel Kish has taught thousands of people all over the world how to "see" by using sound. But of all the students he's taken on, none have been quite like Ethan.
On 26 January 2015, 10-year old Ethan Loch, from Bonnybridge, near Falkirk, walked through the doors of St Mary's Music School in Edinburgh. He was there for an audition. While his parents waited outside, he was shown through to the music room. He sat down at the piano and began to play. He knew his chances were slim.
He was competing against hundreds of other children for a coveted place in one of the top music schools in the country. But his audition was unlike anyone else's. Because Ethan is blind.
"He would stand at the piano for hours when he was a toddler," his mother Larinda says. "Aged three-and-a-half he'd worked through the entire first movement of Beethoven's Moonlight Sonata." At the same age Ethan developed a fascination with sounds.
He would record them on dictaphones - things like vacuum cleaners, washing machines, trampolines, hand-dryers and trains. He'd then go to the piano, and, thanks to having perfect pitch, was able to recreate them musically. Soon, he began lessons on the piano and the accordion, and a few years later, one of his teachers suggested this obvious piano prodigy should audition for music school.
A month later he received the news he'd been hoping for- he had been offered a place. Ethan was to become St Mary's first blind pupil. But there was a problem. Ethan found getting around to be a struggle. More, perhaps, than other blind children his age, and to get to St Mary's every day, he would have to board a train and cross two main roads.
Worried that he might not easily meet this challenge, his parents turned to someone they'd got to know when they were living overseas - Daniel Kish.
Like Ethan, Daniel Kish is blind. His eyes were removed when he was 13 months old because of retinal cancer, but it had little impact on his mobility. "I'm told that the first thing I did upon awakening from the surgery was to climb out of my crib and begin wandering around the nursery," Daniel says.
As he explored, Daniel would click his tongue against the roof of his mouth and the sounds would help him work out what was around him. He was beginning to master echolocation, although he didn't know it was called that back then. It is similar to animal echolocation, which is used by bats.
"That clicking sound bounces off surfaces throughout the environment," he says. "And it comes back with information - distances, locations, positions, contours, densities. I can construct images from that information."
By the age of six, Daniel had got so good at echolocation that he could ride a bike down the road, clicking to avoid people and cars. Neuroscientists were so fascinated by his skills that they carried out an experiment with him. They found that when he clicks, he's activating the visual part of his brain. He's now in his 40s, a slim, energetic man, with bright blue prosthetic eyes. He still uses a cane - he's not suggesting that echolocation replaces it but merely enhances it - and he likes to go rock climbing and hiking.
Daniel has taught echolocation to thousands of other blind people through his school, World Access for the Blind, in California, and in July last year, he flew to Scotland to tutor Ethan, two months before he was due to start at music school. Ethan wasn't completely new to the technique - many blind people use it. But he'd never been taught as intensively as this.
Ethan began with some clicking exercises in the family's living room. Daniel held up a book a little distance from one side of Ethan's face. Ethan clicked into the air, trying to work out from the echoes where the book was. When he directed his clicks towards it, he heard a distinctive sound coming back and grabbed the book. He was a fast learner and so Daniel soon progressed on to smaller and smaller objects.
A few days later, Daniel showed him how he could use echolocation to understand the size and shape of an unfamiliar room by "clicking for corners." Daniel spun him round until Ethan was disorientated.
Ethan used his tongue to make clicks bounce off the walls of the room until he could hear the particular echo they made when he directed them against the corner. He then headed straight towards it.
With just a few clicks, Ethan could now create a sonic representation of the structure of a room in an instant. It was going well, but when they tried it outside, it was a different story.
One morning, Daniel took Ethan on a practice run of the route to his new school. When they were leaving the train station, he walked into a pole, then veered into the road. Daniel pulled him back sharply. Then, when they arrived at St Mary's, Ethan started ploughing into the bushes. "What's going on?" asked Daniel. "When have we ever gone through the bushes?"
It was a difficult day. But between them, Daniel and Ethan were beginning to work out what the problem was. It was something to do with Ethan's fascination with sounds. "Sometimes I lose track if I hear sounds in the distance," Ethan says. "I want to know where these sounds are coming from, and so I keep going towards them. My ears keep wanting to hear them."
"You can see that he knows where something is," Daniel says. "You can tell by his head movements. He'll be clicking right at something, he's almost there, within inches, and then something will just draw him off course."
Ethan was even drawn to the sound of cars in the road. So instead of sounds helping Ethan to understand the world around him - where the cars are or where the pavement is - he was getting lost in them inside his head. It was something Daniel needed to change.
A few days later, Daniel took Ethan on a four-hour walk up rocky tracks and narrow paths. The idea was to push him out of his comfort zone. Every few minutes, Daniel would shout: "Ethan - is your attention external or internal?" "External," Ethan replied. After a shaky start, Ethan began to focus. At the top of the hill, Ethan put down his cane, cupped his hands around his mouth and yelled into the sky, listening to the way his voice returned to him after bouncing off nearby hills. "Shouting for echoes," Daniel calls it.
Over the course of those few weeks, Daniel drilled Ethan - on the clicking, on his cane work, and staying focused on the world around him. He left at the end of the summer. Now it was down to Ethan.
Three months later I went to meet Ethan and his Mum, Larinda, at St Mary's for Ethan's final day of term. The difference was remarkable. As Ethan walked through the station he was much less distracted by the sounds around him. When we get to the pedestrian crossing, he "echolocated" the pole and navigated around it. When we reached the school, after firing clicks into the air to work out where the building was, he walked towards it.
Later, he went to the Church to play in the school concert. It would be his first performance in an orchestra. He'd had to learn the whole piece, and memorise his solo. It's one of the difficulties of playing in an orchestra if you're blind - there's rarely a Braille version of the music. That night, he walked on stage, clicked to find his chair, and sat down. His solo was note perfect. At the end of it, Larinda was in tears.
"When we came to the school this morning with Ethan I just couldn't believe what I was seeing," she says. "He used all the wonderful strategies that Daniel's given him. The world's a big place and he's beginning to find that out."
Ethan, too, was on a high. "I'm not walking around blind," he says. "I know I am actually blind, but I'm clicking so that I can hear echoes to help me find the way. I just see in a different way."
Later, I heard one of Ethan's latest compositions and I thought I could hear something new in his playing. It felt more confident, more free. Daniel Kish hadn't just taught Ethan echolocation. He'd helped him find something more profound - independence.
You can hear Batman and Ethan on Radio 4 at 13:30 on Sunday 14 February or listen to it on BBC iPlayer right now