Ladefoged and Maddieson, in The Sounds of the World's Languages describe Toda as having a sub-apical palatal which actually contrasts with an apical postalveolar, so the language has two types of "retroflex" sibilant, which I suppose would correspond to Canepari's pictures B and F. (I confess to a fairly strong anti-Canepari prejudice, though the pictures seem plausible enough.)Travis B. wrote: Because I was not sure what the dots were supposed to signify. For instance, I would not have assumed that there would have been any apical palatals like that, so that first dot must have been marking a dental POA and not an alveolar POA.
Ladefoged and Maddieson take "palato-alveolar" to mean "apical or laminal domed post-alveolar", and "alveolo-palatal" to mean "laminal palatalised post-alveolar", with "domed" meaning some raising of the tongue behind the constriction but not as much as in a fully palatalised sound. They also talk about "laminal flat post-alveolar" sounds, in e.g. Polish (sz), Mandarin and Ubykh, which don't have the doming at all and are sometimes called "retroflex" even though they're laminal. They transcribe such sounds with an [s] with an underdot.
For what it's worth, which probably isn't very much, given that it's based on introspection, what I have in English seems to be as follows.
- /s/ is generally a laminal alveolar.
- /ʃ/ is generally an apical domed postalveolar. Not dissimilar to picture E, but I think that it's more apical than that.
- The affricate /tʃ/ is generally a laminal postalveolar, also domed. (I don't think I can feel what my tongue is doing well enough to distinguish between pictures A and C.)
- Historic /tr/ starts with an affricate which is also a laminal postalveolar, but seems to be less domed than for typical /tʃ/, suggesting something like the laminal flat post-alveolars mentioned above. I still tend to identify it with /tʃ/, though. /s/ assimilates to the same type of articulation in words like "strange".
- Historic /tj/ (as in "tune") is some sort of apical postalveolar affricate. Again /s/ assimilates to this type of articulation in words like "stew", "stupid". Comparing the beginnings of "stew" and "shoe" suggests that my /ʃ/ articulation is more domed than my /tj/ one, which seems slightly surprising.
(Plus voiced/lenis counterparts, of course.)