The vibrational infrared and Raman spectra of a series of t-butyl substituted oligomers of para-phenylenevinylene and of the corresponding polymer in the pristine and potassium-doped states have been recorded for the first time and interpreted on the basis of the theory of the effective conjugation coordinate. The Raman spectra of selectively deuteriated materials have also been analyzed. Evidence is found of strong phonon confinement. The information derived from the spectra is that the charge carrier is confined over a few monomer units and that when the polymer is doped with electron donors the benzene ring is preferentially perturbed. The data collected in this work are compared With the results from UV spectroscopy and ESR experiments which indicate a larger dimension of the charge carrier. The information which can be derived by using in a complementary way the data from these spectroscopies are presented and discussed.