Search

The impact of distractor previews on the search for new objects in visual surroundings is verified with the help of four experiments. The study reveals the effects of the new target object, the singleton, are reduced due to a preventive carry-over image from the previewed object based on similar features, and this prevention or suppression emerges from a process called visual marking.

An important function of peripheral vision is to provide the target of the next eye movement. Here we investigate the extent to which the eyes are biased to select a target closer to fixation over one further away. Participants were presented with displays containing two identical singleton targets and were asked to move their eyes to either one of them. The targets could be presented at three different eccentricities relative to central fixation. In one condition both singletons were presented at the same eccentricity, providing an estimate of the speed of selection at each of the eccentricities. The saccadic latency distributions from this same-eccentricity condition were then used to predict the selection bias when both targets were presented at different eccentricities. The results show that when targets are presented at different eccentricities, participants are biased to select the item closest to fixation. This eccentricity-based bias was considerably stronger than predicted on the basis of saccadic latency distributions in the same-eccentricity condition. This rules out speed of processing per se as a sole explanation for such a bias. Instead, the results are consistent with attentional competition being weighted in favour of items close to fixation. [ABSTRACT FROM AUTHOR]

Recent studies have revealed a strong relationship between visual working memory and selective attention, such that attention is biased by what is currently on our mind. However, other data show that not all memorized items influence the deployment of attention, thus calling for a distinction within working memory: whereas active memory items function as an attentional template and directly affect perception, other, accessory items do not. We review recent evidence that items compete for the status of ‘attentional template’ that contains only one object at a time. Neurophysiological results provide insight into these different memory states by revealing a more intricate organization of working memory than was previously thought. [ABSTRACT FROM AUTHOR]

Abstract: Previous work has shown that distractors present in a visual search display attract attention when they match objects kept in visual working memory. It seems that maintaining an object in working memory is functionally identical to adopting an attentional set for that object. We test this conjecture by asking observers to perform a memory task as well as a visual search task (in which memory-related distractors could return), but to leave the observer uncertain as to which of these tasks would have to be completed first. This way, observers ought to more readily look for the memorized information, rather than just remember it. Memory-related distractor effects were larger than when participants knew the order of the tasks beforehand, consistent with the idea that trying to attend to something involves additional processes or representations beyond those needed for simply storing an item. [Copyright &y& Elsevier]

Abstract: Visual search for a target among distractors is often speeded when the target-defining feature is repeated from trial to trial, compared to when it changes. It has been proposed that whether this intertrial priming effect is perceptual in nature or not, and how strong it is, depends on the perceptual ambiguity of the display. Using the event-related potential (ERP) method, Experiment 1 assessed whether perceptual ambiguity indeed resulted in increased priming, by comparing target repetitions and changes in a condition with a target-resembling distractor to a condition without such a distractor. Priming effects on response times were indeed greater in the presence of a distractor. Moreover, EEG analyses revealed latency shifts and amplitude differences in the P1 and N2pc components for the same condition, consistent with a perceptual locus of intertrial priming. Experiment 2 confirmed this by varying the perceptual similarity of the distractor to the target. Priming benefits increased with increasing similarity. [Copyright &y& Elsevier]

Abstract: The majority of studies investigating interactions between vision and touch have typically explored single events, presenting one object at a time. The present study investigates how tactile–visual interactions affect competition between multiple visual objects in more dynamic cluttered environments. Participants searched for a horizontal or vertical line segment among distractor line segments of various orientations, all continuously changing color. Search times and search slopes were substantially reduced when the target color change was accompanied by a tactile signal. These benefits were observed even though the tactile signal was uninformative about the location, orientation, or color of the visual target. We conclude that tactile–visual synchrony guides attention in multiple object environments by increasing the saliency of the visual event. [Copyright &y& Elsevier]

Abstract: The second of two targets (T2) presented in a rapid visual stream is often missed when presented shortly after the first (T1). This phenomenon has been referred to as the attentional blink. Here we show that the presentation of a synchronous sound enables T2 to escape the attentional blink, to the extent that performance was back at the level of T1. The sound also improved T1 identification, with little evidence for a trade-off between T1 and T2. Improvements were also found even if the sounds coincided with distractors on 82% of the trials, suggesting an automatic component. Sounds that preceded the targets had little to no effect on T2, suggesting that the enhancement was not due to alerting. These findings replicate and extend earlier work on audition-driven perceptual enhancement of single visual targets. They also have implications for theories of the attentional blink. [Copyright &y& Elsevier]

• High-pass filtering and standard robust detrending can displace MVPA decoding. • Artifacts shown in real and simulated EEG, especially in temporal generalization. • Baseline-correction may obfuscate and exacerbate spurious temporal displacements. • Alternative method trial-masked robust detrending does not show artifacts. • When data is clean and timing is important, using raw data is preferred. 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. 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. 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. 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. 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. [ABSTRACT FROM AUTHOR]

Searching for objects in the visual environment is an integral part of human behavior. Most of the information used during such visual search comes from the periphery of our vision, and understanding the basic mechanisms of search therefore requires taking into account the inherent limitations of peripheral vision. Our previous work using an individual differences approach has shown that one of the major factors limiting peripheral vision (crowding) is predictive of single feature search, as reflected in response time and eye movement measures. Here we extended this work, by testing the relationship between crowding and visual search in a conjunction-search paradigm. Given that conjunction search involves more fine-grained discrimination and more serial behavior, we predicted it would be strongly affected by crowding. We tested sixty participants with regard to their sensitivity to both orientation and color-based crowding (as measured by critical spacing) and their efficiency in searching for a color/orientation conjunction (as indicated by manual response times and eye movements). While the correlations between the different crowding tasks were high, the correlations between the different crowding measures and search performance were relatively modest, and no higher than those previously observed for single-feature search. Instead, observers showed very strong color selectivity during search. The results suggest that conjunction search behavior relies more on top-down guidance (here by color) and is therefore relatively less determined by individual differences in sensory limitations as caused by crowding. [ABSTRACT FROM AUTHOR]

In the visual world, attention is guided by perceptual goals activated in visual working memory (VWM). However, planning multiple-task sequences also requires VWM to store representations for future goals. These future goals need to be prevented from interfering with the current perceptual task. Recent findings have implicated neural oscillations as a control mechanism serving the implementation and switching of different states of prioritization of VWM representations. We review recent evidence that posterior alpha-band oscillations underlie the flexible activation and deactivation of VWM representations and that frontal delta-to-theta-band oscillations play a role in the executive control of this process. That is, frontal delta-to-theta appears to orchestrate posterior alpha through long-range oscillatory networks to flexibly set up and change VWM states during multitask sequences. Neural oscillations serve important regulating functions in the interaction between working memory and sensory input in sequences of visual selection tasks. During multitask sequences, alpha (∼10 Hz) oscillations above visual cortex regulate which sensory working memory representation in early visual cortex is activated and, therefore, interacts with the current sensory input, and which information is (temporarily) deactivated, to prevent such interaction. Delta-to-theta (∼2–8 Hz) oscillations above frontal brain regions orchestrate alpha oscillations above visual cortex during both the initialization and switching of representational states in VWM when executing multitask sequences. [ABSTRACT FROM AUTHOR]

• Crowding poses one of the strongest limitations on visual perception. • Recent findings suggest that crowding differs for dense and sparse visual arrays. • We present a crowding model based on local proximity and similarity-based grouping. • The model successfully accommodates both sparse and dense crowding situations. • Various crowding phenomena can thus be united under a set of simple principles. Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a relatively well-understood phenomenon. However, most investigations and theories are based on sparse displays consisting of a target and at most a handful of flanker objects. Recent findings suggest that the laws thought to govern crowding may not hold for densely cluttered displays, and that grouping and nearest neighbour effects may be more important. Here we present a computational model that accounts for crowding effects in both sparse and dense displays. The model is an adaptation and extension of an earlier model that has previously successfully accounted for spatial clustering, numerosity and object-based attention phenomena. Our model combines grouping by proximity and similarity with a nearest neighbour rule, and defines crowding as the extent to which target and flankers fail to segment. We show that when the model is optimized for explaining crowding phenomena in classic, sparse displays, it also does a good job in capturing novel crowding patterns in dense displays, in both existing and new data sets. The model thus ties together different principles governing crowding, specifically Bouma's law, grouping, and nearest neighbour similarity effects. [ABSTRACT FROM AUTHOR]

• The first study to test the public awareness of a wide range of internationally used beach warning flags in the Netherlands. • Recognition of the flags was overall poor, except for the red flags (which are associated with the highest danger levels). • Especially the yellow flag proved ambiguous in that it elicited opposite associations and behavioral intentions. • A number of recommendations on how to improve the signaling and the knowledge thereof are provided. Beach safety flags form an internationally adopted warning system intended to prevent adverse incidents, including drownings. However, little is known about people's familiarity with these flags. In this study we tested the recognition and understanding of beach warning flags in the Netherlands, a country which welcomes millions of beach visitors every year. A convenience sample (N = 174) of the Dutch population was interviewed using a structured survey which asked for the meaning of eight different flags, the respondents' confidence in their choice, as well as their intention with regard to entering the water. The results show an overall poor understanding of the meaning of all flags except for the red flags (which indicate high hazard). The level of confidence largely followed the same pattern, with low confidence for most flags except the red ones. Strikingly, the yellow flag (which indicates potential hazard and is meant to discourage bathing) evoked a considerable proportion of opposite associations (i.e., safety), combined with moderately high confidence and intentions to enter the water. More people were in fact inclined to enter the water under a yellow flag than under a red & yellow flag (which indicates a patrolled beach). Direct or indirect experience with danger in the sea did not affect people's knowledge of the flags but did reduce the intention to enter the water. We conclude that familiarity with the flag system in the Netherlands is wanting and we propose a number of recommendations to improve public understanding. [ABSTRACT FROM AUTHOR]

Loss of sharp foveal vision, as is inherent to Macular Degeneration (MD), severely impacts reading. One strategy for preserving patients' reading ability involves a one-by-one serial visual presentation (SVP) of words, whereby words are viewed extrafoveally. However, the method is limited as patients often retain the natural tendency to foveate words, thus bringing those words in the scotomal region. Additionally, SVP offers no compensation for the fact that orthographic input is degraded outside the fovea. Addressing these issues, here we tested a novel interface wherein texts are presented word-by-word, but with multiple repetitions (Multi-Res) of each word being displayed simultaneously around the fovea. We hypothesized that the Multi-Res setup would lead readers to make fewer detrimental eye movements, and to recognize words faster as a consequence of multiplied orthographic input. We used eye-tracking to simulate a gaze-contingent foveal scotoma in normally-sighted participants, who read words either in classic SVP or in Multi-Res mode. In line with our hypotheses, reading was drastically better in the Multi-Res condition, with faster recognition, fewer saccades and increased oculomotor stability. We surmise that the Multi-Res method has good potential for improving reading in central vision loss, over and above classic SVP techniques. [ABSTRACT FROM AUTHOR]

Visual search requires the maintenance of a search template in visual working memory in order to guide attention towards the target. This raises the question whether a search template is essentially the same as a visual working memory representation used in tasks that do not require attentional guidance, or whether it is a qualitatively different representation. Two experiments tested this by comparing electrophysiological markers of visual working memory maintenance between simple recognition and search tasks. For both experiments, responses were less rapid and less accurate in search task than in simple recognition. Nevertheless, the contralateral delay activity (CDA), an index of quantity and quality of visual working memory representations, was equal across tasks. On the other hand, the late positive complex (LPC), which is sensitive to the effort invested in visual working memory maintenance, was greater for the search task than the recognition task. Additionally, when the same target cue was repeated across trials (Experiment 2), the amplitude of visual working memory markers (both CDA and LPC) decreased, demonstrating learning of the target at an equal rate for both tasks. Our results suggest that a search template is qualitatively the same as a representation used for simple recognition, but greater effort is invested in its maintenance. [ABSTRACT FROM AUTHOR]

Deficits in early visual attention and perceptual organisation have frequently been shown to associate with both poor pre-morbid schizophrenia and those at a greater putative risk of psychosis. The nature of the deficit is unclear. The present study investigated the relationship between speed of visual marking and proneness to psychosis. 20 males and 20 females completed several tasks assessing speed of selection and de-selection of visual objects. As predicted, negative schizotypy was associated with poorer marking in males, but socially desirable responding potentially confounded this result. In addition, impulsive non-conformity swas associated with poorer visual marking, more prominently in females. These results are discussed in relation to possible mechanisms by which psychosis-proneness and impulsivity may restrict the top–down influences operating on early visual attention. [Copyright &y& Elsevier]

Given human capacity limitations, to behave adaptively we need to prioritise the order of visual processing to ensure that the most relevant information is available to control action. One way to do this is to prioritise processing at a particular location in space. However, there are many situations where this strategy is not possible and recent studies have shown that, in such circumstances, observers can use time as well as space to prioritise selection. We propose that selection by time can be influenced by a process of visual marking, involving an active bias applied in parallel against old items in the field. Here we describe the properties of visual marking in relation to other mechanisms of visual selection. [Copyright &y& Elsevier]