Human memory manipulated: using morphed faces and scenes

The medial temporal lobe (MTL) is well known to subserve memory functions. Yet, it is unknown whether MTL activity is related more to the subjective status of the stimulus or to the subjective feeling of memory. In this work, the objective status of the stimulus is controlled by a parametric manipulation in specifically controlled steps. Morphing was applied to faces while a sliding window was applied to scenes. This process created varying degrees of similarity with previously studied targets at 0%, 20%, 40% or 60%. With this manipulation on one side, and the subjective responses on the other, the separation between the two factors is performed in a fully parametric framework. Moreover, the application of similar methods to spatial (i.e., faces) and non-spatial (i.e., scenes) allows the investigation of a potentially important distinction of functional organization in the MTL. Results and interpretation are presented for three parallel experiments: behavioral, EEG, and fMRI.