Top-Down Modulation of Early Visual Processing in V1: Dissociable Neurophysiological Effects of Spatial Attention, Attentional Load and Task-Relevance.

Until today, there is an ongoing discussion if attention processes interact with the information processing stream already at the level of the C1, the earliest visual electrophysiological response of the cortex. We used two highly powered experiments (each N = 52) and examined the effects of task relevance, spatial attention, and attentional load on individual C1 amplitudes for the upper or lower visual hemifield. Bayesian models revealed evidence for the absence of load effects but substantial modulations by task-relevance and spatial attention. When the C1-eliciting stimulus was a task-irrelevant, interfering distracter, we observed increased C1 amplitudes for spatially unattended stimuli. For spatially attended stimuli, different effects of task-relevance for the two experiments were found. Follow-up exploratory single-trial analyses revealed that subtle but systematic deviations from the eye-gaze position at stimulus onset between conditions substantially influenced the effects of attention and task relevance on C1 amplitudes, especially for the upper visual field. For the subsequent P1 component, attentional modulations were clearly expressed and remained unaffected by these deviations. Collectively, these results suggest that spatial attention, unlike load or task relevance, can exert dissociable top-down modulatory effects at the C1 and P1 levels.

Fearful face scrambles increase early visual sensory processing in the absence of face information.

Emotional facial expressions elicit distinct increased early electrophysiological responses. Many studies report even emotional modulations of very early sensory processing at about 80 and 100 ms after stimulus presentation, indexed by the P1. These early effects are often interpreted to index differential responses to biologically relevant expressions. Since specific spatial frequencies differ between fearful and neutral expressions, it has recently been suggested that these early modulations are substantially driven by such low-level visual differences. However, it remains unclear whether similar P1 effects are also observed in experiments in which no recognizable face information is presented at all. This study investigated this question and explored also whether any effects depend on colour information and attentional conditions. Participants (N = 20) performed a continuous perceptual task of low or high difficultly and were presented with task-irrelevant black/white and colour images of fearful and neutral faces, rendered unrecognizable by doing Fourier phase transformation. ERP findings revealed increased P1 amplitudes for fearful scrambles regardless of experimental conditions. Taken together, our findings show early emotional effects in the absence of any facial expression. Specific low-level frequency information seems to increase P1 amplitudes which thus might have implications for the interpretation of very early sensory emotional expression effects.

Effects of emotion on auditory ERPs are independent of manipulated target relevance.

Emotional attention describes the prioritized processing of emotional information to help humans quickly detect biologically salient stimuli and initiate appropriate reactions. Humans can also voluntarily attend to specific stimulus features that are target-relevant. Electrophysiological studies have shown specific temporal interactions between voluntary and emotional attention, while no such studies exist for natural sounds (e.g., explosions, running water, applause). In two experiments (N = 40, each), we examined event-related potentials (ERPs) toward target relevant or irrelevant negative, neutral, or positive sounds. Target relevance was induced by the instruction to respond blockwise to either negative, neutral, or positive sounds. Emotional sounds elicited increased fronto-central N1 and P2 amplitudes and a larger late positive potential (LPP), with more sustained effects for negative sounds. Target relevance increased amplitudes during an early LPP interval (400-900 ms) but did not interact with the valence of the sounds. These results show early and late ERP modulations for natural sounds, which do not interact with the target relevance of the sound valence, in contrast to findings from the visual domain. Thus, findings indicate little temporal overlap between emotional processes and target relevance effects in the auditory domain. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Early ERP functions are indexed by lateralized effects to peripherally presented emotional faces and scrambles.

A large body of research suggests that early event-related potentials (ERPs), such as the P1 and N1, are potentiated by attention and represent stimulus amplification. However, recent accounts suggest that the P1 is associated with inhibiting the irrelevant visual field evidenced by a pronounced ipsilateral P1 during sustained attention to peripherally presented stimuli. The current EEG study further investigated this issue to reveal how lateralized ERP findings are modulated by face and emotional information. Therefore, participants were asked to fixate the center of the screen and pay sustained attention either to the right or left visual field, where angry or neutral faces or their Fourier phase-scrambled versions were presented. We found a bilateral P1 to all stimuli with relatively increased, but delayed, ipsilateral P1 amplitudes to faces but not to scrambles. Explorative independent component analyses dissociated an earlier lateralized larger contralateral P1 from a later bilateral P1. By contrast, the N170 showed a contralateral enhancement to all stimuli, which was most pronounced for neutral faces attended in the left hemifield. Finally, increased contralateral alpha power was found for both attended hemifields but was not significantly related to poststimulus ERPs. These results provide evidence against a general inhibitory role of the P1 but suggest stimulus-specific relative enhancements of the ipsilateral P1 for the irrelevant visual hemifield. The lateralized N170, however, is associated with stimulus amplification as a function of facial features.