Contextual Modulation During Processing of Facial Expressions. Behavioral, fMRI and ERP Investigations.

Abstract

Facial expressions of emotions are assumed to be processed rapidly and automatically and therefore should be immune to simultaneous task induced interference. Recent functional and electrophysiological studies however reported that contextual features modulate the processing of emotional expressions when presented in the temporal and spatial context of these expressions. Therefore, additional contextual features which specifically signal incongruent emotional information compared to task-relevant facial expressions might introduce an emotional ambiguity during the recognition of these expressions and thereby interfere with their automatic processing.A behavioral, a functional MRI and an electrophysiological study were conducted to examine the impact of a low-level and an emotional associated contextual feature on fast valence categorizations of facial expressions. In each study, subjects incidentally learned to perceive negative, neutral and positive facial expressions within a specific colored context in a first experimental run. In the following experimental run subjects were asked for fast valence judgments while presented with expression-color-combinations as in the first run (congruent trials) or with systematic variations of these expression-color-combinations (incongruent trials). Emotional conflicting information during the evaluation of facial expressions induced significant effects of interference indicated by prolonged response times and a decrease in response accuracy in the initial behavioral study. Emotional incongruent trials revealed differential effects depending on the emotional valence of the facial expression. Especially for positive expressions fast valence categorization in congruent trials might likewise indicate effects of facilitation. Incongruent trials induced activations in a common fronto-parietal selective attention network in the fMRI study. Whereas incongruent trials with neutral expressions revealed distinct activations in regions particularly involved in processing both the task-relevant facial expressions and the task-irrelevant color, incongruent trials with positive facial expressions revealed only sparse activation in the frontal cortex. Contextual interference resolution during processing of negative facial expressions resulted in specific activation in regions which might be involved in implicit morphological dynamics of facial displays. A subsequent differential analysis of the fMRI data revealed widespread activations for task induced incongruence for subjects scoring high on neuroticism, anxiety and depressivity but also for subjects with an internal encoding style. Neurotic and anxious subjects have been previously shown to exhibit a neuronal dysregulation during emotional processing and emotional conflict resolution. Internal encoders strongly rely on their formerly learned schema of face-color-combination. When confronted with incongruent trials in the second experimental run, internal encoders must recruit increased processing resources to overcome their contextually instantiated and schema induced conflict. In the final ERP study, contextual interference during processing of neutral expressions confirmed early activation in occipito-temporal areas most likely involved in elaborated face processing. Differential modulatory effects during emotional face perception revealed early sensitivity within 280ms poststimulus to task-relevant and task-irrelevant emotional information irrespective of emotional incongruence of task-irrelevant information. The late temporal modulatory effect of contextual incongruence is indicated by a modulation of the N450 during interference of negative expressions processing as well as a general sustained activation of the late LPP over parietal cortex for all incongruent trials.In summary, general effects of contextual interference during emotional face processing were located in frontal and parietal regions which temporally occurred as sustained parietal activation in late stages of cognitive processing. Differential effects of contextual interference were found depending on the inherent processing demands of facial expressions. Especially incongruent trials including neutral expressions activated ventral extrastriate regions of face processing probably already during early stages of stimulus encoding. Finally, contextual effects of interference during emotional face processing depend on individual differences in trait dimensions of personality and perceptual traits like the individual encoding style.