In this study, the ultrafast pump-probe spectroscopy of the all-trans protonated Schiff base of retinal (trans-PSB) in solution, is compared to that of two retinal analogues, trans-PSB5.12 and 13-cis-PSB5.13, in which C-13=C-14 torsional motion is inhibited by a rigid five-membered ring structure. The objective is to obtain measures of internal conversion (IC) dynamics in these polyenes. Contrasting the results with those obtained for the same pigments when attached to their opsin protein, serve to appreciate the protein role in catalyzing energy transduction in bacteriorhodopsin. Several major features appear to be common to all three PSBs: (i) A 50-100 fs process due to a primary relaxation out of the Franck-Condon (FC) region, (ii) A subsequent biexponential decay (t(1) = 1-2 ps and t(2) = 4-7 ps) of the fluorescent state (FS) assumed to be due to IC, and (iii) Spectral modulations in the FS emission. The three are only marginally effected by locking of the C-13=C-14 bond. With respect to features (i) and (iii) the PSB model compounds behave analogously to the related retinal protein bacteriorhodopsin (bR). However, this does not apply to the FS decay. While in bR, the IC takes place with a 0.5 ps decay time, locking of the C-13=C-14 bond in bR markedly increases the FS lifetime to similar to 15 ps. These observations demonstrate the crucial role played by the protein in directing the isomerization action to the active double bond and enhancing the rate of IC. They also prove that these coordinates are not exclusive pathways of IC in the isolated PSB of retinal. The mechanism of ground-state repopulation in the PSBs is discussed in light of these results.