ERP experiments generate massive datasets, often containing thousands of values for each participant, even after averaging. The richness of these datasets can be very useful in testing sophisticated ...hypotheses, but this richness also creates many opportunities to obtain effects that are statistically significant but do not reflect true differences among groups or conditions (bogus effects). The purpose of this paper is to demonstrate how common and seemingly innocuous methods for quantifying and analyzing ERP effects can lead to very high rates of significant but bogus effects, with the likelihood of obtaining at least one such bogus effect exceeding 50% in many experiments. We focus on two specific problems: using the grand‐averaged data to select the time windows and electrode sites for quantifying component amplitudes and latencies, and using one or more multifactor statistical analyses. Reanalyses of prior data and simulations of typical experimental designs are used to show how these problems can greatly increase the likelihood of significant but bogus results. Several strategies are described for avoiding these problems and for increasing the likelihood that significant effects actually reflect true differences among groups or conditions.
Researchers have long debated whether salient stimuli can involuntarily ‘capture’ visual attention. We review here evidence for a recently discovered inhibitory mechanism that may help to resolve ...this debate. This evidence suggests that salient stimuli naturally attempt to capture attention, but capture can be avoided if the salient stimulus is suppressed before it captures attention. Importantly, the suppression process can be more or less effective as a result of changing task demands or lapses in cognitive control. Converging evidence for the existence of this suppression mechanism comes from multiple sources, including psychophysics, eye-tracking, and event-related potentials (ERPs). We conclude that the evidence for suppression is strong, but future research will need to explore the nature and limits of this mechanism.
Researchers have long debated whether salient stimuli involuntarily attract visual attention. However, much of this research has failed to consider the potentially crucial role of inhibitory processes in preventing distraction.
ERP studies demonstrate that when salient items fail to capture attention they elicit a distractor positivity (PD) that reflects a suppressive process.
Psychophysical and eye-tracking studies demonstrate that processing at the location of a salient distractor can be inhibited below baseline levels. This suppression manifests as a reduced probability of reporting stimuli presented at that location, or a reduced probability of directing gaze to that location.
Current research is exploring exactly how the visual system determines which items should be suppressed.
ERPLAB toolbox is a freely available, open-source toolbox for processing and analyzing event-related potential (ERP) data in the MATLAB environment. ERPLAB is closely integrated with EEGLAB, a ...popular open-source toolbox that provides many EEG preprocessing steps and an excellent user interface design. ERPLAB adds to EEGLAB's EEG processing functions, providing additional tools for filtering, artifact detection, re-referencing, and sorting of events, among others. ERPLAB also provides robust tools for averaging EEG segments together to create averaged ERPs, for creating difference waves and other recombinations of ERP waveforms through algebraic expressions, for filtering and re-referencing the averaged ERPs, for plotting ERP waveforms and scalp maps, and for quantifying several types of amplitudes and latencies. ERPLAB's tools can be accessed either from an easy-to-learn graphical user interface or from MATLAB scripts, and a command history function makes it easy for users with no programming experience to write scripts. Consequently, ERPLAB provides both ease of use and virtually unlimited power and flexibility, making it appropriate for the analysis of both simple and complex ERP experiments. Several forms of documentation are available, including a detailed user's guide, a step-by-step tutorial, a scripting guide, and a set of video-based demonstrations.
Highlights • Visual working memory capacity can be assessed reliably with very simple tasks. • The capacity for simple visual features is highly correlated with cognitive ability. • Capacity varies ...substantially across individuals and groups. • Researchers debate whether capacity reflects discrete slots or a flexible resource. • Capacity limits can be understood in terms of recurrent neural networks.
In human scalp EEG recordings, both sustained potentials and alpha-band oscillations are present during the delay period of working memory tasks and may therefore reflect the representation of ...information in working memory. However, these signals may instead reflect support mechanisms rather than the actual contents of memory. In particular, alpha-band oscillations have been tightly tied to spatial attention and may not reflect location-independent memory representations per se. To determine how sustained and oscillating EEG signals are related to attention and working memory, we attempted to decode which of 16 orientations was being held in working memory by human observers (both women and men). We found that sustained EEG activity could be used to decode the remembered orientation of a stimulus, even when the orientation of the stimulus varied independently of its location. Alpha-band oscillations also carried clear information about the location of the stimulus, but they provided little or no information about orientation independently of location. Thus, sustained potentials contain information about the object properties being maintained in working memory, consistent with previous evidence of a tight link between these potentials and working memory capacity. In contrast, alpha-band oscillations primarily carry location information, consistent with their link to spatial attention.
Working memory plays a key role in cognition, and working memory is impaired in several neurological and psychiatric disorders. Previous research has suggested that human scalp EEG recordings contain signals that reflect the neural representation of information in working memory. However, to conclude that a neural signal actually represents the object being remembered, it is necessary to show that the signal contains fine-grained information about that object. Here, we show that sustained voltages in human EEG recordings contain fine-grained information about the orientation of an object being held in memory, consistent with a memory storage signal.
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.
Limits on the storage capacity of working memory significantly affect cognitive abilities in a wide range of domains, but the nature of these capacity limits has been elusive. Some researchers have ...proposed that working memory stores a limited set of discrete, fixed-resolution representations, whereas others have proposed that working memory consists of a pool of resources that can be allocated flexibly to provide either a small number of high-resolution representations or a large number of low-resolution representations. Here we resolve this controversy by providing independent measures of capacity and resolution. We show that, when presented with more than a few simple objects, human observers store a high-resolution representation of a subset of the objects and retain no information about the others. Memory resolution varied over a narrow range that cannot be explained in terms of a general resource pool but can be well explained by a small set of discrete, fixed-resolution representations.
Researchers have long debated whether attentional capture is purely stimulus driven or purely goal driven. In the current study, we tested a hybrid account, called the signal-suppression hypothesis, ...which posits that stimuli automatically produce a bottom-up salience signal, but that this signal can be suppressed via top-down control processes. To test this account, we used a new capture-probe paradigm in which participants searched for a target shape while ignoring an irrelevant color singleton. On occasional probe trials, letters were briefly presented inside the search shapes, and participants attempted to report these letters. Under conditions that promoted capture by the irrelevant singleton, accuracy was greater for the letter inside the singleton distractor than for letters inside nonsingleton distractors. However, when the conditions were changed to avoid capture by the singleton, accuracy for the letter inside the irrelevant singleton was reduced below the level observed for letters inside nonsingleton distractors, an indication of active suppression of processing at the singleton location.
Much is known about the mechanisms by which attention is focused to facilitate perception, but little is known about what happens to attention after perception of the attended object is complete. One ...possibility is that the focus of attention passively fades. A second possibility is that attention is actively terminated after the completion of perception so that the brain can be prepared for the next target. The present study investigated this issue with event-related potentials in humans, focusing on the N2pc component (a neural measure of attentional deployment) and the Pd component (a neural measure of attentional suppression). We found that active suppression occurred both to prevent the allocation of attention to known distractors and to terminate attention after the perception of an attended object was complete. In addition, the neural measure of active suppression was correlated with a behavioral measure of trial-to-trial variations in the allocation of attention. Active suppression therefore appears to be a general-purpose mechanism that both prevents and terminates the allocation of attention.
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