Neural evidence for reduced apprehensiveness of familiarized stimuli in a mere exposure paradigm

Abstract

Mere familiarization with a stimulus increases liking for it or similar stimuli (“mere exposure” effects) as well as perceptual fluency, indexed by the speed and accuracy of categorizing it or similar stimuli (“priming” effects). Candidate mechanisms proposed to explain mere exposure effects include both increased positive affect associated with greater perceptual fluency, and reduced negative affect associated with diminished apprehensiveness of novel stimuli. Although these two mechanisms are not mutually exclusive, it is difficult for behavioral measures to disentangle them, since increased liking or other indices of greater positive affect toward exposed stimuli could result from increases in positive feelings or decreases in negative feelings or both. The present study sought to clarify this issue by building on research showing a dissociation at the neural level in which the lateral orbitofrontal cortex (LOFC) is activated more by negatively valenced than by neutral or positively valenced stimuli, with the reverse effect for medial orbitofrontal cortex (MOFC). Supporting the reduced apprehensiveness hypothesis, we found lower LOFC activation to familiarized faces and objects (repetition suppression). We did not find evidence to support the positive affect hypothesis in increased activation to familiarized stimuli in MOFC or in other parts of the reward circuit that respond more to positively valenced stimuli (repetition enhancement), although enhancement effects were shown in some regions.

Keywords:

• Mere-exposure effect
• Generalized
• LOFC
• MOFC
• Repetition suppression
• Face race

Acknowledgments

This research was supported by NIH grants MH066836 and K02MH72603 to the first author. The authors thank Dr. Nouchine Hadjikhani for making her research assistant, Paulami Naik, available to us and to Paulami Naik, Jeff Horowitz, and Jasmine Boshyan for their help with scanning participants, and Xiaoyun Liang for his help with data analyses. Requests for reprints should be sent to Professor Leslie A. Zebrowitz, Department of Psychology, MS 062, Brandeis University, Waltham, MA 02454: [email protected].

Notes

¹While our predictions of LOFC suppression or MOFC enhancement are based on the substantial evidence that the LOFC responds more strongly to negatively valenced than neutral or positively valenced stimuli, while MOFC responds more strongly to positively valenced than other stimuli, it should be noted there are also nonlinear effects, with both regions responding more strongly to stimuli of either valence than to neutral stimuli (Elliott, Newman, Longe, & Deakin, 2003; Krendl, Macrae, Kelley, Fugelsang, & Heatherton, 2007; Liang et al., 2009; Winston et al., 2007).

²The finding that attenuation in inferior lateral occipital/fusiform gyrus was shown on the right side for the SEE effect and on the left side for the GEE effect in the case of both faces and objects is consistent with previous evidence that the right fusiform response is highly specific to a particular exemplar, with more generalization to similar stimuli in left fusiform (Blondin & Le Page, 2005; Eger, Schweinberger, Dolan, & Henson, 2005); Koustaal et al., 2001; Simons, Koutstaal, Prince, Wagner, & Schacter, 2003). The finding that fusiform gyrus showed effects for objects as well as faces is consistent with previous evidence demonstrating fMRI adaptation to inanimate objects in fusiform face area (Ewbank, Schluppeck, & Andrews, 2005).