Top-down and bottom-up competition in visual stimuli processing.

Limited attention capacity results that not all the stimuli present in the visual field are equally processed. While processing of salient stimuli is automatically boosted by bottom­up attention, processing of task­relevant stimuli can be boosted volitionally by top­down attention. Usually, both top­down and bottom­up influences are present simultaneously, which creates a competition between these two types of attention. We examined this competition using both behavioral and electrophysiological measures. Participants responded to letters superimposed on background pictures. We assumed that responding to different conditions of the letter task engages top­down attention to different extent, whereas processing of background pictures of varying salience engages bottom­up attention to different extent. To check how manipulation of top­down attention influences bottom­up processing, we measured evoked response potentials (ERPs) in response to pictures (engaging mostly bottom­up attention) during three conditions of a letter task (different levels of top­down engagement). Conversely, to check how manipulation of bottom­up attention influences top­down processing, we measured ERP responses for letters (engaging mostly top­down attention) while manipulating the salience of background pictures (different levels of bottom­up engagement). The correctness and reaction times in response to letters were also analyzed. As expected, most of the ERPs and behavioral measures revealed a trade­off between both types of processing: a decrease of bottom­up processing was associated with an increase of top­down processing and, similarly, a decrease of top­down processing was associated with an increase in bottom­up processing. Results proved competition between the two types of attentions.

Interactions Between the Prefrontal Cortex and Attentional Systems During Volitional Affective Regulation: An Effective Connectivity Reappraisal Study.

Reappraisal is an emotion regulation strategy used to change reactions to emotion-related stimuli by reinterpreting their meaning. During down-regulation of negative emotions, wide areas of the prefrontal cortex (PFC) inhibit emotion-related brain areas such as the amygdala. Little is known, however, about how this control activity influences the earliest stages of affective responses by modulating perceptual and attentional areas. The aim of this study is to identify the connectivity patterns between the PFC and the core regions of two well-known attentional networks: the dorsal attentional network (which controls attention volitionally) and the ventral attentional network (which controls attention spontaneously) during reappraisal. We used a novel method to study emotional control processes: the directed transfer function, an autoregressive effective connectivity method based on Granger causality. It was applied to EEG recordings to quantify the direction and intensity of information flow during passively watching (control condition) or reappraising (experimental condition) negative film clips. Reappraisal was mostly associated with increased top-down influences from the right dorsolateral PFC over attentional and perceptual areas, reaching areas including dorsal attentional regions. The left dorsolateral PFC was associated with the activation of the ventral attentional network. Passively watching clips (control condition) resulted in increased flow from attentional areas to the left dorsolateral PFC, what is interpreted as a monitoring process. Thus, reappraisal seems to be related to both volitional and automatic control of attention, triggered by the right and left dorsolateral PFC respectively.