We investigated whether the distinction between primary stress and secondary stress was ever correlated with vocal tract shape difference, which is acoustically realized as F1 and F2 transition differences. Since the syllables with secondary stress are usually shorter than those with primary stress, a natural prediction is that vocal tract articulators undergo some target undershoot when the secondary stress vowels are produced, which is in turn reflected as the target undershoot of F1 and F2 values. Our investigation of the F1 and F2 values of the first syllable of the DIgest(n)-diGEST(v) pair and the IMport(n)-imPORT(v) pair indicates that both F1 and F2 formants of the secondary stress vowels do not fully achieve their target values. That is, there is a phonetic reduction (target undershoot) of F1 and F2 values of the secondary stress vowels.