As I get older, the question of how we perceive speech becomes more interesting (people don’t talk as clearly as they used to!). So I was intrigued by this latest research that reveals that it is not so much a question of whether consonants or vowels are more important (although consonants do appear to be less important than vowels — the opposite of what is true for written language), but a matter of transitions. It’s all a matter of the very brief changes across amplitude and frequency that make sound-handling neurons fire more often and easily — after all, as we know from other perception research, we’re designed to recognize/respond to change. Most likely to rate as high-change sounds are "low" vowels, sounds like "ah" in "father" or "top" that draw the jaw and tongue downward. Least likely to cause much change are "stop" consonants like "t" and "d" in "today." The physical measure of change corresponds closely with the linguistic construct of sonority (or vowel-likeness).