  A model of incentive salience as a function of stimulus value and
interoceptive state has been previously proposed. In that model, the function
differs depending on whether the stimulus is appetitive or aversive; it is
multiplicative for appetitive stimuli and additive for aversive stimuli. The
authors argued it was necessary to capture data on how extreme changes in salt
appetite could move evaluation of an extreme salt solution from negative to
positive. We demonstrate that arbitrarily varying this function is unnecessary,
and that a multiplicative function is sufficient if one assumes the incentive
salience function for an incentive (such as salt) is comprised of multiple
stimulus features and multiple interoceptive signals. We show that it is also
unnecessary considering the dual-structure approach-aversive nature of the
reward system, which results in separate weighting of appetitive and aversive
stimulus features.
