Beta and theta oscillations differentially support free versus forced control over multiple-target search

Many important situations require human observers to simultaneously search for more than one object. Despite a long history of research into visual search, the behavioral and neural mechanisms associated with multiple-target search are poorly understood. Here we test the novel theory that the efficiency of looking for multiple targets critically depends on the mode of cognitive control the environment affords to the observer. We used an innovative combination of electroencephalogram (EEG) and eye tracking while participants searched for two targets, within two different contexts: either both targets were present in the search display and observers were free to prioritize either one of them, thus enabling proactive control over selection; or only one of the two targets would be present in each search display, which requires reactive control to reconfigure selection when the wrong target has been prioritized. During proactive control, both univariate and multivariate signals of beta-band (15–35 Hz) power suppression before display onset predicted switches between target selections. This signal originated over midfrontal and sensorimotor regions and has previously been associated with endogenous state changes. In contrast, imposed target selections requiring reactive control elicited prefrontal power enhancements in the delta/theta band (2– 8 Hz), but only after display onset. This signal predicted individual differences in associated oculomotor switch costs, reflecting reactive reconfiguration of target selection. The results provide compelling evidence that multiple target representations are differentially prioritized during visual search, and for the first time reveal distinct neural mechanisms underlying proactive and reactive control over multiple-target search

Oscillatory Mechanisms of Preparing for Visual Distraction

Evidence shows that observers preactivate a target representation in preparation of a visual selection task. In this study, we addressed the question if and how preparing to ignore an anticipated distractor differs from preparing for an anticipated target. We measured EEG while participants memorized a laterally presented color, which was cued to be either a target or a distractor in two subsequent visual search tasks. Decoding the location of items in the search display from EOG channels revealed that, initially, the anticipated distractor attracted attention and could only be ignored later during the trial. This suggests that distractors could not be suppressed in advance but were represented in an active, attention-guiding format. Consistent with this, lateralized posterior alpha power did not dissociate between target and distractor templates during the delay periods, suggesting similar encoding and maintenance. However, distractor preparation did lead to relatively enhanced nonlateralized posterior alpha power, which appeared to gate sensory processing at search display onset to prevent attentional capture in general. Finally, anticipating distractors also led to enhanced midfrontal theta power during the delay period, a signal that was predictive of how strongly both target and distractor were represented in the search display. Together, our results speak against a distractor-specific advance inhibitory template, thus contrary to the preactivation of specific target templates. Rather, we demonstrate a general selection suppression mechanism, which serves to prevent initial involuntary capture by anticipated distracting input

The capacity of multiple-target search

Can individuals look for multiple objects at the same time? A simple question, but answering it has proven difficult. In this review, we describe possible cognitive architectures and their predictions about the capacity of visual search. We broadly distinguish three stages at which limitations may occur: (1) preparation (establishing and maintaining a mental representation of a search target), (2) selection (using this mental representation to extract candidate targets from the visual input), and (3) post-selection processing (verifying that the selected information actually is a target). We then review the empirical evidence from various paradigms, together with their strengths and pitfalls. The emerging picture is that multiple target search comes with costs, but the magnitude of this cost differs depending on the processing stage. Selection appears strongly limited, while preparation of multiple search target representations in anticipation of a search is possible with relatively small costs. Finally, there is currently not sufficient information to determine the capacity limitations of post-selection processing. We hope that our review contributes to better targeted research into the mechanisms of multiple-target search. A better understanding of multiple-target search will also contribute to better design of real-life multiple-target search problems, reducing the risk of detrimental search failures

Venäjän federaation kansalaisten ennakkokäsitykset suomalaisista rajaviranomaisista

Ennakkokäsitykset ovat osa ihmisten ryhmäkäyttäytymistä. Viranomaiset joutuvat työssään päivittäin kohtaamaan erilaisia ennakkokäsityksiä. Rajanylittäjien ennakkokäsitykset voivat johtaa esimerkiksi aiheettomaan tarkempaan rajatarkastukseen. Tutkielmalla on tarkoitus saada rajaviranomaisille tietoa siitä, miten ennakkokäsitykset syntyvät ja millaisia ennakko-käsityksiä venäläisillä rajanylittäjillä on Suomen rajaviranomaisista. Tutkielman tuomaa tie-toa voidaan käyttää rajaviranomaisten (Poliisi, Rajavartiolaitos ja Tulli) peruskoulutuksessa ja sillä saadaan lisäarvoa esimerkiksi profilointiin. Tutkielmassani pyrin vastaamaan kahteen erilaiseen ongelmaan. Ensiksi halusin pohtia mistä ennakkokäsitykset johtuvat ja toiseksi millaisia ennakkokäsityksiä venäläisillä on Suomeen saapuessaan suomalaisista rajaviranomaisista. Osaongelmana pohdin Venäjän median vaiku-tusta ennakkokäsitysten syntymiseen tai niiden vahvistamiseen. Pyrin myös selvittämään ovatko rajanylittäjien Venäjän federaation viranomaisiin kohdistuneet ennakkokäsitykset siir-tyneet mahdollisesti sellaisenaan Suomen rajaviranomaisiin. Tutkielman aineisto on kerätty sähköisellä lomakekyselyllä, joka on toteutettu yhdessä Sai-maan ammattikorkeakoulun kanssa. Lomakekysely lähetettiin 299 tutkinto- ja vaihto-opiskelijalle, joista 12,4 prosenttia eli 37 vastasi tähän kyselyyn. Ennakkokäsitys voi olla joko positiivinen tai negatiivinen, yleensä asenteisiin tai kokemuk-siin sidonnainen käsite. Venäläisillä rajanylittäjillä on paljon ennakkokäsityksiä suomalaisista rajaviranomaisista ja ne ovat enimmäkseen positiivisia. Negatiiviset ennakkokäsitykset liit-tyivät useasti viranomaisten toimintataktiikkaan. Venäjän media esittää rajanylittäjien mu-kaan Suomen viranomaiset lainkuuliaisina ja oikeudenmukaisina. Rajanylittäjien Venäjän fe-deraation viranomaisiin kohdistuneet ennakkokäsitykset voivat siirtyä sellaisinaan Suomen rajaviranomaisiin, varsinkin jos rajanylittäjällä ei ole rajanylityskokemuksia

Visual Working Memory Adapts to the Nature of Anticipated Interference

Visual working memory has been proven to be relatively robust against interference. However, little is known on whether such robust coding is obligatory, or can be flexibly recruited depending on its expected usefulness. To address this, participants remembered both the color and orientation of a grating. During the maintenance, we inserted a secondary color/orientation memory task, interfering with the primary task. Crucially, we varied the expectations of the type of interference by varying the probability of the two types of intervening task. Behavioral data indicate that to-be-remembered features for which interference is expected are bolstered, whereas to-be-remembered features for which no interference is expected are left vulnerable. This was further supported by fMRI data obtained from visual cortex. In conclusion, the flexibility of visual working memory allows it to strengthen memories for which it anticipates the highest risk of interference

When shorter delays lead to worse memories: Task disruption makes visual working memory temporarily vulnerable to test interference

Evidence shows that visual working memory (VWM) is strongly served by attentional mechanisms, whereas other evidence shows that VWM representations readily survive when attention is being taken away. To reconcile these findings, we tested the hypothesis that directing attention away makes a memory representation vulnerable to interference from the test pattern, but only temporarily so. When given sufficient time, the robustness of VWM can be restored so that it is protected against test interference. In 5 experiments, participants remembered a single grating for a later memory test. In the crucial conditions, participants also performed a letter change detection task in between, during the delay period. Experiments 1-3 demonstrate and replicate the predicted effect: The intervening task had an adverse effect on memory performance, but only when the test display appeared immediately after the secondary task. At longer delays of 3.5 s, memory performance was on a par with conditions in which there was no intervening task. By varying the similarity of the test pattern to the memorized pattern, Experiments 4 and 5 further showed that performance suffered at early test intervals, unless the test item was dissimilar to the memory item. The results provide positive evidence for test interference, and demonstrates that the susceptibility to interference only occurs temporarily, as memory is restored when attention is allowed to return to the memorandum

Lack of Free Choice Reveals the Cost of Having to Search for More Than One Object

It is debated whether people can actively search for more than one object or whether this results in switch costs. Using a gaze-contingent eye-tracking paradigm, we revealed a crucial role for cognitive control in multiple-target search. We instructed participants to simultaneously search for two target objects presented among distractors. In one condition, both targets were available, which gave the observer free choice of what to search for and allowed for proactive control. In the other condition, only one of the two targets was available, so that the choice was imposed, and a reactive mechanism would be required. No switch costs emerged when target choice was free, but switch costs emerged reliably when targets were imposed. Bridging contradictory findings, the results are consistent with models of visual selection in which only one attentional template actively drives selection and in which the efficiency of switching targets depends on the type of cognitive control allowed for by the environment

The dynamics of saliency-driven and goal-driven visual selection as a function of eccentricity

Both saliency and goal information are important factors in driving visual selection. Saliency-driven selection occurs primarily in early responses, whereas goal-driven selection happens predominantly in later responses. Here, we investigated how eccentricity affects the time courses of saliency-driven and goal-driven visual selection. In three experiments, we asked people to make a speeded eye movement toward a predefined target singleton which was simultaneously presented with a non-target singleton in a background of multiple homogeneously oriented other items. The target singleton could be either more or less salient than the non-target singleton. Both singletons were presented at one of three eccentricities (i.e., near, middle, or far). The results showed that, even though eccentricity had only little effect on overall selection performance, the underlying time courses of saliency-driven and goal-driven selection altered such that saliency effects became protracted and relevance effects became delayed for far eccentricity conditions. The protracted saliency effect was shown to be modulated by expectations as induced by the preceding trial. The results demonstrate the importance of incorporating both time and eccentricity as factors in models of visual selection

High-pass filtering artifacts in multivariate classification of neural time series data

Background: Traditionally, EEG/MEG data are high-pass filtered and baseline-corrected to remove slow drifts. Minor deleterious effects of high-pass filtering in traditional time-series analysis have been well-documented, including temporal displacements. However, its effects on time-resolved multivariate pattern classification analyses (MVPA) are largely unknown.  New method: To prevent potential displacement effects, we extend an alternative method of removing slow drift noise – robust detrending – with a procedure in which we mask out all cortical events from each trial. We refer to this method as trial-masked robust detrending.  Results: In both real and simulated EEG data of a working memory experiment, we show that both high-pass filtering and standard robust detrending create artifacts that result in the displacement of multivariate patterns into activity silent periods, particularly apparent in temporal generalization analyses, and especially in combination with baseline correction. We show that trial-masked robust detrending is free from such displacements.  Comparison with existing method(s): Temporal displacement may emerge even with modest filter cut-off settings such as 0.05 Hz, and even in regular robust detrending. However, trial-masked robust detrending results in artifact-free decoding without displacements. Baseline correction may unwittingly obfuscate spurious decoding effects and displace them to the rest of the trial. Conclusions : Decoding analyses benefit from trial-masked robust detrending, without the unwanted side effects introduced by filtering or regular robust detrending. However, for sufficiently clean data sets and sufficiently strong signals, no filtering or detrending at all may work adequately. Implications for other types of data are discussed, followed by a number of recommendations