Femtosecond spectroscopy of the first events of the photochemical cycle in bacteriorhodopsin

The first steps in the photochemistry of bacteriorhodopsin (BR) are investigated with light pulses of 160 fs duration. Four samples are studied: (i) the purple membrane, (ii) deuterated purple membrane, (iii) BR trimers and (iv) BR monomers. In all samples the first intermediate J is formed within 430±50 fs. No isotope effect is observed in the formation of J upon deuteration, in contrast to previous reports with much higher excitation energies. Thus proton movement to or from the retinal Schiff's base is not relevant during the first step. Comparing the data for trimeric and monomeric BR suggests an upper limit of 50 fs for the transfer of excitation energy from the excitonically coupled trimer to a single retinal chromophore

Motivational Objects in Natural Scenes (MONS): A Database of >800 Objects

In daily life, we are surrounded by objects with pre-existing motivational associations. However, these are rarely controlled for in experiments with natural stimuli. Research on natural stimuli would therefore benefit from stimuli with well-defined motivational properties; in turn, such stimuli also open new paths in research on motivation. Here we introduce a database of Motivational Objects in Natural Scenes (MONS). The database consists of 116 scenes. Each scene contains 2 to 7 objects placed at approximately equal distance from the scene center. Each scene was photographed creating 3 versions, with one object (“critical object”) being replaced to vary the overall motivational value of the scene (appetitive, aversive, neutral), while maintaining high visual similarity between the three versions. Ratings on motivation, valence, arousal and recognizability were obtained using internet-based questionnaires. Since the main objective was to provide stimuli of well-defined motivational value, three motivation scales were used: (1) Desire to own the object; (2) Approach/Avoid; (3) Desire to interact with the object. Three sets of ratings were obtained in independent sets of observers: for all 805 objects presented on a neutral background, for 348 critical objects presented in their scene context, and for the entire scenes. On the basis of the motivational ratings, objects were subdivided into aversive, neutral, and appetitive categories. The MONS database will provide a standardized basis for future studies on motivational value under realistic conditions