Do Stressed Vowels Attain a Target?

One might suppose that stressed vowels are more likely to attain the phonetic target of the vowel phoneme than unstressed vowels. Unstressed vowels should be more reduced and more coarticulated with adjacent sounds, which amounts to being more spread out over vowel space than their stressed counterparts. This section tests this supposition, the ``Stressed-Target'' hypothesis, in a simple way, with Rita's data.

If stressed vowels reach a target more than unstressed vowels, their nuclei should be more tightly distributed across vowel space, while unstressed vowels should be more spread out, since they are more likely to be modified by adjacent sounds, etc. In order to compare the scatter in these distributions, then, Table  shows the standard deviations of F1 and F2 for stressed and unstressed tokens of each vowel.

Table: Standard Deviations in Hz of F1, F2 for stressed and unstressed vowels (Rita)

	F1		F2
	Stressed	Unstressed	Stressed	Unstressed
	148	147	276	362
ow	108	130	289	290
iy	84	98	352	393
æ	130	129	271	255
ay	127	112	195	193
	146	151	328	426
	84	111	232	248
I	115	128	359	378
	143	133	247	224
uw	124	128	623	531
	126	163	161	196
ey	115	115	307	372
U	79	108	366	451
aw	125	72	207	153
l	148	147	276	362
oy	108	130	289	290

If the stressed vowels are less widely scattered than the unstressed vowels, then the stressed standard deviations should be smaller than the unstressed standard deviations. The claim is that a target is more likely to be achieved in a stressed vowel than in an unstressed vowel. These data give only mild support to this theory. 11 of 17 vowels (about 2/3) have a smaller F1 standard deviation when stressed than when unstressed; a different subset of 11 of the 17 have a smaller F2 standard deviation when stressed than when unstressed. So about two-thirds of the vowels are more tightly distributed in each dimension when stressed than when unstressed.

However, since about a third of the vowels fail to observe the predicted pattern, the stressed-target hypothesis is at best a fairly weak generalization.