Judging by Mark Liberman’s vowel plots it looks like I was off the mark on the rarity of back nuclei in the [aj] diphthong. At least, it looks like the nucleus in Mark’s five passes through the same space as the back vowels in his caught and cot. My excuse here is that my Canadian ear hears them all as central. I’ll try to get a microphone and record similar plots for my own speech, just for fun.

There’s some interesting reading on the low vowel space by Charles Boberg at McGill, including:

Boberg, Charles. 2000. Geolinguistic diffusion and the U.S.-Canada border. Language Variation and Change 12:1-24.

I was also not quite accurate about Jeff Spicoli in the 1982 film Fast Times at Ridgemont High. I found and browsed through many clips and found only one instance of [aj], in which he says “no shirt, no shoes, no dice.” The spectrogram is fuzzy since it’s spoken in unison by Jeff and one other character, and it really doesn’t sound as back as I let on. Maybe I should look for some audio of Keanu Reeves instead.