However, I am less persuaded by the paradigm of achieving AI through digital symbol manipulation that has dominated for the past half century. Throughout history, the current explanation of mind has always reflected the latest technology. Descartes envisaged it in terms of reflexes and the cuckoo clock. Freud's terminology of obstructed channels, diverted flows, and buildups of pressures was inspired by the complexity of the sewer system of Vienna. By the thirties the brain had become a telephone exchange, and with World War II an interacting network of servo loops and feedback circuits. These days, naturally, it has to be a computer ... but I'm not convinced that we've reached the end of the line yet.