How do we make simple purchasing decisions (e.g., whether or not to buy a product at a given price)? Previous work has shown that the attentional drift-diffusion model (aDDM) can provide accurate quantitative descriptions of the psychometric data for binary and trinary value-based choices, and of how the choice process is guided by visual attention. Here we extend the aDDM to the case of purchasing decisions, and test it using an eye-tracking experiment. We find that the model also provides a reasonably accurate quantitative description of the relationship between choice, reaction time, and visual fixations using parameters that are very similar to those that best fit the previous data. The only critical difference is that the choice biases induced by the fixations are about half as big in purchasing decisions as in binary choices. This suggests that a similar computational process is used to make binary choices, trinary choices, and simple purchasing decisions.

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A simple model is developed for predicting solvation effects on the nonlinear optical properties of charge transfer organic materials such as 1,1 dicyano,6-(di-butyl amine) hexatriene. This model is based on the valence-bond charge-transfer (VB-CT) framework, using a continuum description of the solvent. The resulting VB-CT solvation model leads to analytic formulas for the absorption frequency (Eg), the polarizability (α), the hyperpolarizabilities (β,γ,δ), and the bond length alternation with only one solvent dependent parameter (ε, the dielectric constant of the solution). The theory involves just four solvent-independent parameters, V0, t, SF, and Q which are related to the band gap, bandwidth, geometry, and dipole moment of the CT molecule [plus a length (RDA) and force constant (k) derivable from standard force fields]. The results are in good agreement with experiment.

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Relationship between static vibrational and electronic hyperpolarizabilities of π-conjugated push-pull molecules within the two-state valence-bond charge-transfer model A simple theory is developed and applied to the polarizability (a), second hyperpolarizability (y), and the saturation lengths for nine polymeric materials. The theory is based on a valence bond view of the ground and excited states and considers the excited states as charge transfer excitons. It involves just two parameters which can be extracted from simple molecular orbital calculations and/or from experimental values of band gap and bandwidth. For the one system (oligothiophenes) with experimental data on saturation length, the predicted behavior of a and y with polymer length is in good agreement with experiment. 4920

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