When your brain attempts to detect faint signals in noisy environments, it can improve its chances either by boosting the signal relative to the noise (e.g. turning up the TV over the racket of a neighbor's lawn mower), or turning down the noise more than the signal (e.g. asking the neighbor to mow later). Although the second method for increasing the "signal-to-noise-ratio" is just as effective as the first, sometimes it can produce startling results.