| Adrian Thompson used genetic algorithms to design a kind of voice-recognition
software. |
| Evolution of
electronic circuits became possible with the invention of Field-Programmable Gate Arrays (FPGA),
arrays of logic cells whose functions are determined by programs loaded into the FPGA. |
| Thompson's initial goal was to design a circuit that, given a
low-pitch sound (1 kHz) would return no signal, and given a high-pitch
sound (10kHz) would return a constant (nonzero) signal. |
| He began with a population of 50 random circuits and applied the genetic algorithm methodology:
assess fitness with a test problem (distinguish low from high pitch), remove the least-fit
programs, and let the more fit reproduce by crossover with occasional mutation. |
| Here is a summary of Thompson's results. |
| * After 220 generations, the best circuit could reproduce both sounds. |
| * After 650 generations, the best circuit produced a mostly constant signal when presented
with a high-pitch sound, but reproduced the low-pitch sound. |
| * After 1400 generations, the best circuit produced mostly constant signals in the
appropriate ranges. |
| * After 2800 generations, the best circuit met the design expectations, and further
evolution produced no changes. |
|
| A discriminator designed by a person would use a clock to
count the time between successive peaks of the input signal. |
| More clock ticks between successive peaks of the signal means
lower frequency and so a 0 should be returned. |
| Thompson's evolved circuit does not contain a clock. |
| It appears that the signal is sent through a complicated collection of feedback loops,
making a time-delayed reflection of the signal that cancels the low-pitch input, and converts
the high-pitch input into a constant. However, there's
a surprise. |
| Some argue if we don't know how a circuit works, we shouldn't trust it with
important tasks. |
| However, we don't know in detail how more traditionally designed microcircuits
work, nor are all possibilities tested. |
| Remember the problem with one of the Pentium chips, only
discovered a year after it was marketed. |