Functional neuroanatomy of unconscious affective priming

Affectively significant stimuli have the capacity to influence human behavior even if they remain outside conscious awareness. An influential view in the cognitive neurosciences proposes that such unaware processing of affective stimuli can occur in subcortical (thalamic and amygdalar) structures without any significant involvement from the cortex, while these subcortical processes may in turn modulate cortical activity. Consistent with this view, brain imaging studies have found amygdala responses to masked affective stimuli, which were correlated with changes in thalamic and cortical activity. The present project intends to resolve two critical issues concerning this evidence. First, presentation times of masked stimuli of 15 ms and longer, which have been used in previous studies, may prevent conscious awareness, but not necessarily extensive cortical processing of these stimuli. Thus, cortical activity, instead of resulting from amygdala output, may have substantially contributed to amygdala responses. Second, it is unclear which structures mediate potential behavioral effects of masked affective stimuli. The first of two studies in this project will develop a novel method to address these questions much more rigorously than earlier studies. First, it will combine functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) in order to investigate both subcortical and cortical structures with the best available spatial and temporal resolution. Second, a tachistoscope apparatus will enable us to present masked affective stimuli (pictures of faces) for as short as 5 ms, a substantial improvement over earlier studies. Third, 5 ms and 20 ms presentations of masked stimuli will be compared in a within-participant design to directly test the possibility that cortical processing without awareness critically contributes to amygdala responses. To assess the extent of processing without awareness for masked stimuli objectively, individual participants will complete forced-choice detection and recognition tasks. The modulation of cortical activity by subcortical affective processing will be addressed in two ways. Study 1 will compare happy and fearful faces with neutral faces and scrambled images (all masked): cortical activity changes in response to the two affective, but not to two neutral stimulus types would hint at affective modulation in the absence of cortical stimulus processing proper. Study 2 will go one step further and investigate behavior regulation by embedding the procedure developed in Study 1 in an affective priming task. The design of this study enables us to link amygdala activation to behavioral effects of masked affective stimuli (influence on valence judgments) and to activity changes in structures involved in affect-related decision making, e.g., the medial prefrontal cortex, or the anterior cingulate cortex. The present project investigates an important everyday phenomenon: humans are constantly engaged in monitoring their environment for potentially significant stimuli, much of which necessarily remains outside focal attention due to the limited capacity of conscious processes. In addition to the cognitive neuroscience of emotion, the findings of this project will therefore be relevant to areas such as social cognition, affective communication, and the theoretical understanding of the affect-cognition relationship.

Affectively significant stimuli have the capacity to influence human behavior even if they remain outside conscious awareness. An influential view in the cognitive neurosciences proposes that such unaware processing of affective stimuli can occur in subcortical (thalamic and amygdalar) structures without any significant involvement from the cortex, while these subcortical processes may in turn modulate cortical activity. Consistent with this view, brain imaging studies have found amygdala responses to masked affective stimuli, which were correlated with changes in thalamic and cortical activity. The present project intends to resolve two critical issues concerning this evidence. First, presentation times of masked stimuli of 15 ms and longer, which have been used in previous studies, may prevent conscious awareness, but not necessarily extensive cortical processing of these stimuli. Thus, cortical activity, instead of resulting from amygdala output, may have substantially contributed to amygdala responses. Second, it is unclear which structures mediate potential behavioral effects of masked affective stimuli. The first of two studies in this project will develop a novel method to address these questions much more rigorously than earlier studies. First, it will combine functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) in order to investigate both subcortical and cortical structures with the best available spatial and temporal resolution. Second, a tachistoscope apparatus will enable us to present masked affective stimuli (pictures of faces) for as short as 5 ms, a substantial improvement over earlier studies. Third, 5 ms and 20 ms presentations of masked stimuli will be compared in a within-participant design to directly test the possibility that cortical processing without awareness critically contributes to amygdala responses. To assess the extent of processing without awareness for masked stimuli objectively, individual participants will complete forced-choice detection and recognition tasks. The modulation of cortical activity by subcortical affective processing will be addressed in two ways. Study 1 will compare happy and fearful faces with neutral faces and scrambled images (all masked): cortical activity changes in response to the two affective, but not to two neutral stimulus types would hint at affective modulation in the absence of cortical stimulus processing proper. Study 2 will go one step further and investigate behavior regulation by embedding the procedure developed in Study 1 in an affective priming task. The design of this study enables us to link amygdala activation to behavioral effects of masked affective stimuli (influence on valence judgments) and to activity changes in structures involved in affect-related decision making, e.g., the medial prefrontal cortex, or the anterior cingulate cortex. The present project investigates an important everyday phenomenon: humans are constantly engaged in monitoring their environment for potentially significant stimuli, much of which necessarily remains outside focal attention due to the limited capacity of conscious processes. In addition to the cognitive neuroscience of emotion, the findings of this project will therefore be relevant to areas such as social cognition, affective communication, and the theoretical understanding of the affect-cognition relationship.