We have assessed the relation between the spatial ground-state structure and the electronic and vibrational spectroscopic properties of neutral and protonated 11-cis-retinal Schiff base models within the density functional theory framework. For the neutral Schiff base model, a comprehensive model picture emerges, which is consistent with the available spectroscopic experimental data. For the protonated models, the calculations reveal a polaronic conjugation defect in the ground state in the Schiff base region. It is found that the C-14- C-15 bond has enhanced double bond character, while the C-13 = C-14 and C-15 N bonds have reduced double bond character. This phenomenon affects the vibrational structure in an extended region of the spectrum. The C-C, C=C, and C=N stretches in the fingerprint region and the ethylenic band are significantly delocalized. In the ab initio calculations, an enhanced coupling of the C-14-C-15 and C-15=N stretching coordinates transpires, resulting in an asymmetric (C-14-C-15=N) stretching mode in the ethylenic region at 1639 cm(-1). In addition, a coupled C14H-C15H A(u) hydrogen-out-of-plane mode is found at 1019 cm(-1). The calculated C-13 NMR chemical shifts in the polyene chain are very sensitive to the perturbation of the bond length alternation pattern. The protonated models show a C-13 response that is more deshielded than C-15, supporting the presence of a polaronic charge effect in the protonated Schiff base and an accumulation of charge at C-13, in line with all NMR spectroscopic data. Finally, we have resolved an essential difference between retinylidene iminium salts and rhodopsin. In contrast with rhodopsin, the delocalization of positive charge in these model compounds is intimately connected with the polarization effects from the counterion at the Schiff base. This supports recent inferences that the negative charge of the counterion in the rhodopsin protein is strongly delocalized around the polyene chain of the chromophore, and promotes accumulation of positive charge around the cis bond.