Lateralized Suppression of Alpha-Band EEG Activity As a Mechanism of Target Processing

Abstract

Alpha-band (8 -12 Hz) EEG activity has been linked to visual attention since the earliest EEG studies. More recent studies using spatial cuing paradigms have shown that alpha is suppressed over the hemisphere contralateral to a to-be-attended location, suggesting that alpha serves as a mechanism of preparatory attention. Here, we demonstrate that alpha also plays a role in active target processing. EEG activity was recorded from a group of healthy male and female human subjects in two visual search experiments. In addition to alpha activity, we also assessed the N2pc event-related potential component, a lateralized transient EEG response that has been tightly linked with the focusing of attention on visual targets. We found that the visual search targets triggered both an N2pc component and a suppression of alpha-band activity that was greatest over the hemisphere contralateral to the target (which we call "target-elicited lateralized alpha suppression" or TELAS). In Experiment 1, both N2pc and TELAS were observed for targets presented in the lower visual field but were absent for upper-field targets. However, these two lateralized effects had different time courses and they responded differently to manipulations of crowding in Experiment 2. These results indicate that lateralized alpha-band activity is involved in active target processing and is not solely a preparatory mechanism and also that TELAS and N2pc reflect a related but separable neural mechanism of visuospatial attention.The very first EEG studies demonstrated that alpha-band (8 -12 Hz) EEG oscillations are suppressed when people attend to visual information and more recent research has shown that cuing an individual to expect a target at a specific location produces lateralized suppression in the contralateral hemisphere. Therefore, lateralized alpha may serve as a preparatory mechanism. In the present study, we found that a similar lateralized alpha effect is triggered by the appearance of a visual target even though the location could not be anticipated, demonstrating that alpha also serves as an active mechanism of target processing. Moreover, we found that alpha lateralization can be dissociated from other lateralized measures of target selection, indicating that it reflects a distinct mechanism of attention.

Dynamics of the straight-ahead preference in human visual cortex

“…7). Previous EEG studies showed that pre-stimulus alpha power suppression is associated with enhanced evoked activity (Bacigalupo and Luck 2019;van Dijk et al 2008) and modifications of the P1 amplitude (Fellinger et al 2011). Our observations are also in line with the pre-stimulus preparatory activity found in the occipital areas for simple reaction tasks by Di Russo et al (2019).…”

Lateralized alpha activity and slow potentials shifts over visual cortex track the time course of both endogenous and exogenous orienting of attention

“…Using peripheral, salient sounds, it was shown that lateralized changes in alpha oscillations can be induced quickly and can be relatively short-lived Feng et al, 2017; see also, Bacigalupo, & Luck, 2019).…”

Effects of eccentricity on the attention‐related N2pc component of the event‐related potential waveform

“…The N2pc is sometimes accompanied by a lateralized suppression of alpha‐frequency EEG activity (Bacigalupo & Luck, ; Worden, Foxe, Wang, & Simpson, ), and we analyzed this activity using time‐frequency analysis to see if it varied across eccentricities. Because this was a secondary analysis, the methods and results are provided in online Supporting Information.…”

“…Although the N2pc can be observed across a range of different physical stimuli, N2pc amplitude varies according to the vertical position of the target, with a substantially reduced N2pc for targets in the upper field compared to those in the lower field (Bacigalupo & Luck, ; Luck, Girelli, McDermott, & Ford, ). This may be a result of the anatomy of the neural generators of the N2pc, which are believed to lie in intermediate to high level areas of the ventral visual processing stream such as area V4 and the lateral occipital complex (Hopf et al, , ).…”