Vancouver, B.C., is one of many cities have audible crosswalk signals for blind pedestrians. When my wife and I were up there last December, she pointed out that there are actually two different sounds: one a steady chirp and the other a cuckoo. As soon as she said this I realized two things: (1) the different sounds indicate whether you are traveling north-south or east-west and (2) the exact same convention has been in place for Seattle for years and I’d never noticed it.
It’s not like I hadn’t noticed the audible crosswalks back home. They were installed a few years back. I cued in to the novelty at first, then gradually tuned it out. But at no point in the process did I notice that there were two sounds. It’s not like I’m physically unable to perceive the difference, or that I wasn’t listening. In fact, I often idly whistle along with the sound while I’m standing at in intersection, which means I have reproduced both the chirp and the cuckoo. But I had still never perceived them as anything other than the single crosswalk sound.
I wonder if my collapsing these two very distinct stimuli into the same category happened because they speech-like: they’re different allophones of the same crosswalk phoneme, conditioned by direction of travel. Phoneticists, are people more likely to lump together noises that are used for communication?