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In the Eriksen flanker task as well as in the Simon task irrelevant activation produces a response conflict that has to be resolved by mental control mechanisms. Despite these similarities, however, the tasks differ with respect to their delta functions, which express how the congruency effects develop with response time. The slope of the delta function is mostly positive for the flanker task, but negative for the Simon task. Much effort has been spent to explain this difference and to investigate whether it results from task-specific control. A prominent account is that the temporal overlap between irrelevant and relevant response activation is larger in the flanker task than in the Simon task. To test this hypothesis, we increased the temporal distance in a flanker task by presenting the flankers ahead of the target. This not only produced negatively sloped delta functions but also caused reversed congruency effects. We also conducted a Simon-task experiment in which we varied the proportion of congruent stimuli. As a result, the delta function was negatively sloped only if the proportion was low. These results demonstrate that a long temporal distance is necessary but not sufficient for observing negatively sloped delta functions. Finally, we modeled the data with drift-diffusion models. Together, our results show that differently sloped delta functions can be produced with both tasks. They further indicate that activation suppression is an important control mechanism that can be adapted rather flexibly to the control demands., Competing Interests: The authors have declared that no competing interests exist.

Recent research has shown that even non-salient stimuli (colored circles) can gain attentional weight, when they have been loaded with some value through previous reward learning. The present study examined such value-based attentional weighting with intrinsically rewarding food stimuli. Different snacks were assumed to have different values for people due to individual food preferences. Participants indicated their preferences toward various snacks and then performed a flanker task with these snacks: they had to categorize a target snack as either sweet or salty; irrelevant flanker snacks were either compatible or incompatible with the target category. Results of a linear mixed-effects model show that the effect of flanker compatibility on participants' performance (response times) increased with the participants' preference toward the flanking snacks. This shows, for the first time, that attentional weightings in a flanker task with naturalistic stimuli (snacks) are modulated by participants' preferences toward the flankers.

Goal-directed behavior usually requires mental control that directs attention to task-relevant information and ignores irrelevant information. For investigating how flexible this mechanism is, researchers have varied the proportion of congruent trials depending on some context, such as stimulus location. The corresponding studies revealed that attentional control indeed adapts to location-specific demands. However, until now, this flexibility has only been demonstrated for the Eriksen flanker task and for the Stroop task but not for the Simon task. Therefore, a Simon-task experiment was conducted in the present study, where the proportion of congruent trials differed for stimuli appearing above or below fixation, respectively. As a result, a reliable interaction between congruency and stimulus location was found. This demonstrates, for the first time, that location-specific control also is possible in the Simon task.

The Simon effect is usually explained by the assumption that the irrelevant stimulus location automatically activates the corresponding response. In the case of incongruent stimulus-response assignments automatically activated responses therefore have to be suppressed to ensure correct responses. This account, however, has been called into question for other than horizontally arranged visual Simon tasks. We investigated whether there is a qualitative or quantitative difference in suppression of irrelevant activation between horizontally and vertically arranged Simon tasks, using delta-function analyses. Sequential analyses revealed suppression after incongruent trials in both tasks, supporting the idea of a quantitative rather than a qualitative difference between the tasks. We conclude that automatic response activation is weaker in vertical tasks resulting in lower inhibitory demands as compared to horizontal tasks., (Copyright © 2014 Elsevier B.V. All rights reserved.)

It is well known that the Simon effect usually decreases with an increasing response time. According to a prominent account this is due to a gradually increasing suppression of irrelevant location-induced activation. What is open, however, and what was investigated in the present study, is to what extent this selective suppression can be adjusted strategically. We hypothesized that strategic suppression should depend on the availability of information about the inhibitory demands. Therefore, in two experiments the demand was modulated by varying the delay between a spatial cue and the target. In the first experiment, where target delay was randomized, there was a negative Simon effect for the longer delays. In a second experiment, where delay was blocked, the Simon effect remained positive. However, the overall Simon effect was larger than in Experiment 1. Together, our results show that the strength of selective suppression can be adjusted strategically, but that this does not necessarily lead to a smaller Simon effect., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The size of response-repetition (RR) costs, which are usually observed on task-switch trials, strongly varies between conditions with univalent and bivalent stimuli. To test whether top-down or bottom-up processes can account for this effect, we assessed in Experiment 1 baselines for univalent and bivalent stimulus conditions (i.e., for stimuli that are associated with either 1 or 2 tasks). Experiment 2 examined whether the proportion of these stimulus types affects RR costs. As the size of RR costs was independent of proportion, a top-down explanation could be excluded. However, there was an increase in RR costs if the current stimulus induced a response conflict. To account for this effect, we proposed an amplification of response conflict account. It assumes that the basic mechanism that leads to RR costs amplifies response conflict, which, in turn, increases RR costs. Experiment 3 confirmed this bottom-up explanation by showing that the increase in RR costs varies with previous-trial congruency, which is known to affect RR costs. Experiment 4 showed that the increase can also be found with univalent stimuli that induce response conflict. Altogether, the results are in line with a response inhibition account of RR costs. Implications for alternative accounts are also discussed. (PsycINFO Database Record (c) 2013 APA, all rights reserved).

A common finding is that there are response-repetition (RR) costs under task switching. Moreover, when the stimulus on the previous trial was congruent then RR costs are usually larger than when it was incongruent. This effect of the previous trial has been explained by assuming that a response category is generally inhibited after the execution of its corresponding response on the previous trial and that the amount of inhibition depends on the activation of the response category. However, up to now it was open which property of the response-category activation on the previous trial is crucial: the absolute activation of the correct response category or the activation difference between the alternative response categories. To differentiate between these two possibilities we compared RR costs after congruent, neutral, and incongruent trials. In two experiments we found similar RR costs after congruent and neutral trials, whereas the RR costs were smaller after incongruent trials. These results support the hypothesis that the amount of response inhibition is determined by the activation differences between the alternative response categories on the previous trial., (Copyright © 2011 Elsevier B.V. All rights reserved.)

An important question is whether monetary reward can increase attentional effort in order to improve performance. Up to now, evidence for a positive answer is weak. Therefore, in the present study, the flanker task was used to examine this question further. Participants had to respond sooner than a certain deadline in a flanker task. One group of participants received a performance-contingent monetary reward, whereas the other group earned a fixed amount of money. As a result, monetary reward significantly improved performance in comparison with the control group. The analysis of speed-accuracy trade-off functions revealed that monetary reward increased attentional effort, leading to an enhanced quality of stimulus coding. Little evidence was found that reward also improved selective spatial attention.

The dual-stage two-phase (DSTP) model is introduced as a formal and general model of selective attention that includes both an early and a late stage of stimulus selection. Whereas at the early stage information is selected by perceptual filters whose selectivity is relatively limited, at the late stage stimuli are selected more efficiently on a categorical basis. Consequently, selectivity is first low but then abruptly increases during the course of stimulus processing. Although intended as a general model of selective attention, in the present study the DSTP model was applied to account for the distributional data of 3 flanker task experiments. The fit of the model to the data was not only rather good but also superior to those of alternative single-stage models with a continuously increasing selectivity. All together, the model provides a comprehensive account of how early and late stages of attention interact in the control of performance., ((c) 2010 APA, all rights reserved.)

When rapidly switching between two tasks, bivalent stimuli can accidentally trigger the previously executed and therefore still activated response. Recently, it has been suggested that behavioral response-repetition effects reflect response inhibition that reduces the risk of such erroneous response repetitions. The present study investigated neural correlates of this inhibition process using lateralized readiness potentials (LRP). In three experiments, we demonstrate a response-switch bias emerging during the preparatory interval which is independent of task sequence (Experiment 1), which is linked to task preparation (Experiment 2), and which is present only under task-switching conditions (Experiment 3). These results suggest that the bias reflects a control process that adaptively regulates response preparedness.

The present study tested error detection theories of the error-related negativity (ERN) by investigating the relation between ERN amplitude and error detectability. To this end, ERN amplitudes were compared with a behavioral measure of error detectability across two different error types in a four-choice flanker task. If an erroneous response was associated with the flankers, it was considered a flanker error, otherwise it was considered a nonflanker error. Two experiments revealed that, whereas detectability was better for nonflanker errors than for flanker errors, ERN amplitudes were larger for flanker errors than for nonflanker errors. Moreover, undetected errors led to strongly reduced ERN amplitudes relative to detected errors. These results suggest that, although error detection is necessary for an ERN to occur, the ERN amplitude is not related to error detectability but rather to error significance.

The coding of stimuli and responses is crucial for human behaviour. Here, we focused primarily on the response codes (or response categories). As a method, we applied a combined dual-task and task-switch paradigm with a fixed task-to-hand mapping. Usually, negative effects (i.e., costs) are observed for response category repetitions under task switching. However, in several previous studies it has been proposed that such repetition effects do not occur, if the stimulus categories (e.g., "odd" if digits have to be classified according to their parity feature) are unequivocally mapped to specific responses. Our aim was to test this hypothesis. In the present experiments, we were able to distinguish between three different types of possible response codes. The results show that the participants generally code their responses according to abstract response features (left/right, or index/middle finger). Moreover, the spatial codes were preferred over the finger-type codes even if the instructions stressed the latter. This preference, though, seemed to result from a stimulus-response feature overlap, so that the spatial response categories were primed by the respective stimulus features. If there was no such overlap, the instructions determined which type of response code was involved in response selection and inhibition.

Under task switch conditions, response repetitions usually produce benefits if the task also repeats, but costs if the task switches. So far, it is largely undecided how to account for these effects. In the present study, we provide additional evidence in favor of the account that each response is inhibited in order to prevent its accidental re-execution. To test this hypothesis, the risk of an accidental re-execution of a given response was manipulated by modulating the activation of the response in the previous task. In Experiment 1, this was done by means of congruent and incongruent stimuli. As expected, on task switch trials, the repetition costs were larger if a congruent rather than an incongruent stimulus occurred in the previous task. In Experiment 2, the same effect occurred for stimulus-response compatible versus incompatible stimuli in the previous task. In Experiment 3, both manipulations were applied together, which produced almost additive effects. Altogether, the results support the inhibition account for the response repetition effects under task switch conditions.

The processing selectivity in the flanker task has been shown to depend on the ratio of congruent trials to incongruent trials in a task (Gratton, Coles, & Donchin, 1992). If congruent trials are more frequent than incongruent ones, the flankers are more attended and, consequently, the flanker congruency effect is increased. Recent results suggest that participants can even allocate attention on the fly to the flankers-that is, in a highly flexible way after stimulus onset-depending on the frequency of incongruent trials on a certain stimulus location. Because location plays a unique role in stimulus selection, we investigated in two experiments whether selectivity can also be adjusted on the fly depending on stimulus color. The results demonstrate that color can be used for such an adjustment, but only if the association between color and frequency has be enpreviously learned under blocked conditions.

In this study hemispheric asymmetries for categorizing objects at the basic versus subordinate level of abstraction were investigated. As predictions derived from different theoretical approaches are contradictory and experimental evidence is inconclusive in this regard, we conducted two categorization experiments, where we contrasted two experimental paradigms. In the first experiment, subjects had to verify whether a word and a laterally presented picture matched or not. In the second experiment, subjects had to identify laterally presented pictures of animals either at the basic or subordinate level by pressing a corresponding response key. Whereas the first experiment revealed an advantage of the left hemisphere (LH) for categorizing objects at the basic level and of the right hemisphere (RH) for categorizing at the subordinate level, just the opposite brain asymmetry was found in the second experiment. As the stimuli were identical in both experiments, hemispheric asymmetries seem to be strongly task dependent.

Switch costs in task switching are often assumed to reflect the strengthening of task-related associations. Recently, we provided evidence that committing an error leads to the strengthening of the wrong task (Steinhauser & Hübner, 2006). In the present study, we report how error-induced control compensates for the effects of error strengthening. We hypothesized that, although error detection cannot prevent an error from being strengthened, it initiates processes that suppress the negative consequences of error strengthening on subsequent trials. Because error-induced control is known to operate slowly, we predicted that a compensatory effect should be observable only for slow responses. In three task-switching experiments, these predictions were confirmed by distributional analyses. The results extend our understanding of the interplay between procedural learning and executive control.

Several task-switch studies show that response category repetition is favorable on task repetition trials, but disadvantageous on task switch trials. In the present study we investigated how this interaction depends on the type and number of involved response categories. In a dual-task number-categorization experiment, subjects had to respond to tasks T(1) and T(2) with one of the two fingers of their left and right hand, respectively. For one group of participants, the use of spatial response categories, and for another group the use of finger-type categories was induced. It turned out that the interaction between task switching and response category repetition was clearly related to the induced response categories, but at the same time, the spatial categories nevertheless also affected response selection in the finger-type group. However, these two effects were additive. This shows that multiple response codes can simultaneously be involved in response selection, but that they affect performance differentially.

Functional hemispheric asymmetries with respect to global/local processing have been observed more reliably in divided-attention than in selective-attention tasks. This difference has been accounted for by assuming that the hemispheres operate differently in the two tasks. In our study, the alternative hypothesis was tested that the interference between the global and local levels is increased under divided attention, and that this makes it necessary to base response selection on a more elaborated mental stimulus representation in which the levels and their content are integrated. Because the hemispheres systematically differ in this integration process, the increased interference between the levels explains why the corresponding asymmetries occur more reliably under divided attention. Two experiments supporting this hypothesis are reported, one with a divided and one with a selective attention task.

In this study, the authors used a dual-task flanker paradigm to investigate the degree to which flankers are coprocessed with the target as a function of whether flankers have to be used as stimuli for a second task. A series of experiments, in which performance in dual tasks was compared with that in single tasks, revealed that participants had a strong tendency to coprocess flankers to a large degree in dual tasks, even if this impaired performance. Coprocessing of flankers was reduced only when totally irrelevant flankers were presented at the beginning of a trial or single tasks were performed on the great majority of trials within a block. The results suggest that it was demanding to process targets and flankers serially when both had to be used for a dual task. As a consequence, target and flankers were processed in parallel, even if this was nonoptimal for target selection.

Although it is often assumed that the left and right cerebral hemispheres are specialized for local and global processing, respectively, recent studies show that this difference mainly occurs if the responses to the two levels of a stimulus are conflicting. In the present study we examined whether the favorable effect of response conflicts is caused by the increased task difficulty in this situation. To this end, the response selection for nonconflicting stimuli was complicated by frequently changing the stimulus-response mappings. As a result, the reactions to nonconflicting stimuli were as slow as those to conflicting ones. Nevertheless, hemispheric differences were again restricted to the latter situation. This shows that increased task difficulty can not explain the modulating effect of response conflicts. The results support the alternative hypothesis that different representations are needed for the response selection for nonconflicting and conflicting stimuli, and that the hemispheres differ only with respect to the latter.

It has recently been suggested that hemispheric differences for global and local processing already occur in response to visual pre-cues that direct attention to a specific level. However, in the supporting studies cue information was confounded with the form of the cues. In order to dissolve the confound, we compared event-related brain potentials towards cues differing in form with those towards identically formed color cues. As a result, hemispheric differences were found only for the former cue type. The data thus show that the mere cue information does not produce hemispheric asymmetries associated with global/local target stimulus processing.

Repetition effects are often helpful in revealing information about mental structures and processes. Usually, positive effects have been observed when the stimuli or responses are repeated. However, in task shift studies it has also been found that response repetitions can produce negative effects if the task shifts. Although several mechanisms have been proposed to account for this interaction between task shifting and response repetition, many details remain open. Therefore, a series of four experiments was conducted to answer two questions. First, are motor responses necessary to produce response-related repetition effects, or is response activation sufficient? Second, does the risk of an accidental re-execution of the last response affect the repetition costs? The results show that response activation alone can produce repetition effects. Furthermore, the risk of accidental response re-execution largely modulates these effects.

We investigated the hypothesis that mixing costs intask shifting reflect th e sequential selection of task components (e.g., stimulus categories) during task execution. This proposition was supported by Hübner, Futterer, and Steinhauser (2001), who showed that the amount of mixing costsdepends on the number of mixed task components (e.g., stimulus level and judgment). However, their results could also be explained by a task set selection account, because task components and task sets were confounded. In Experiments 1 and 2, we compared conditions in which either the number of task sets varied and the number of mixed task components was constant or vice versa. Only the number of mixed task components was predictive for the mixing costs. In Experiment 3, we replicated the additivity of mixing costs from level a ndjudgment mixing. Our results suggest thatthe mixingcosts reflect a selection strategy in which interference is reduced in a stepwise manner.

Visual attention enables observers to extract and process high-priority information in the visualfield. Controversy remains as to whether or not observers can ignore information that falls within the spatial beam of attention. We used an objective physiological measure, the steady-state visual evoked potential (SSVEP), to investigate this question. A stream of flickering small, uppercase letters was embedded in the center of a stream of large, uppercase letters. A unitary beam would result in no difference of the SSVEP amplitude elicited by the small letter stream when it was attended versus ignored (i.e., when subjects attended the large letter stream). Contrary to this prediction, SSVEP amplitude increased by almost 100% when the small letter stream was attended compared with when it was ignored. The results support the notion that the attentional spotlight can be formed like a doughnut, processing central information differentially depending on whether it is attended or ignored.

It is widely assumed that supervisory or attentional control plays a role only in the preparatory reconfiguration of the mental system in task shifting. The well-known fact that residual shift costs are still present even after extensive preparation is usually attributed to passive mechanisms such as cross talk. The authors question this view and suggest that attentional control is also responsible for residual shift costs. The authors hypothesize that, under shift conditions, tasks are executed in a controlled mode to guarantee reliable performance. Consequently, the control of 2 task components should require more resources than the control of only 1. A series of 4 experiments with 2-component tasks was conducted to test this hypothesis. As expected, more residual shift costs were observed when 2 components rather than 1 varied across trials. Interference effects and sequential effects could not account for these results.

In this study, the effects of familiarity on visual search were investigated. To avoid any confounding between familiarity and visual-feature differences between item pairs, Ns and mirror-Ns were presented as target and as distractors to a group of German participants and to a group of Slavic participants. For the Germans only N was familiar, whereas for the Slavs both N and mirror-N were familiar. The results show that search was difficult only when the Germans had to find an N among mirror-Ns. In any other case, search was efficient. Therefore, our results demonstrate that, contrary to earlier suggestions, search for a familiar item among familiar distractors can be easy. This supports the hypothesis that familiarity improves distractor grouping. However, the data are also compatible with the idea that letters are standard or basic features, which implies that basic features can be learned.

In a series of four experiments, we investigated the conditions under which target-absent responses are faster than target-present responses in visual search. Previous experiments have shown that such an absent-advantage occurs mainly for homogeneous distractors arranged in a regular pattern. From these results, it has been concluded that the absent-advantage is due to perceptual processes, such as grouping by similarity. Our data show that such processes are not sufficient. Rather, the absent-advantage is the result of interactions between perceptual and decisional processes. Certain perceptual conditions, such as randomizing stimulus patterns, lead to specific criteria settings that produce an absent-advantage. That such an account can explain our main results is demonstrated by modeling our data with a modified version of the Guided Search 2 model.

In 4 experiments, stimulus elements were arranged into an LED-like array, and letters were defined within the array by feature similarity between the elements with respect to color and form. These stimuli allowed the display of a target and a distractor letter simultaneously at the same location. They were spatially inseparable but could be separated in feature space. Participants had to identify the letter on a prespecified feature dimension (color or form). As a result, the distractors produced specific compatibility effects. This showed that nontarget features could not be ignored at an early stage (i.e., that color and form were processed automatically and in parallel up to a high stage). The target was selected from the resulting objects according to the prespecified feature dimension. Results demonstrate that object selection is possible without selecting absolute spatial arrays.

There are many conditions in which identification proceeds faster for the global form of a hierarchical pattern than for it's local parts. Since the global form usually contains more lower spatial frequencies than do the local forms, it has frequently been suggested that the higher transmission rate of low spatial frequencies is responsible for the global advantage. There are also functional hemispheric differences. While the right hemisphere is better at processing global information, the left hemisphere has an advantage with respect to local information. In accordance with the spatial-frequency hypothesis, it has been speculated that this difference is due to a differential capacity of the hemispheres for processing low and high spatial frequencies. To test whether low spatial frequencies were responsible for the global advantage and/or for the observed hemispheric differences, two experiments were carried out with unfiltered and highpass-filtered compound-letter stimuli presented at the left, right, or center visual field. The first experiment, in which the target level was randomized in each trial block, revealed that low spatial frequencies were not necessary for either global advantage or for hemispheric differences. Highpass filtering merely increased the response times. In the second experiment, the target level was held constant in each block. This generally increased the speed of responding and produced interactions between filtering and global-local processing. It was concluded that both sensory and attentional or control mechanisms were responsible for global precedence and that the hemispheres differed with respect to the latter.

Detection of auditory signals under frequency uncertainty can be improved by presenting cues to the listeners. Since various cues have been found to differ in effectiveness, three conceivable mechanisms were considered which might account for these differences. Cuing might reduce the number and/or width of the employed auditory filters or listening bands. Also, cues could modulate the precision of frequency tuning of the filters. Psychometric functions were collected in a detection experiment with frequency uncertainty employing three kinds of cues: pure tones whose frequency was identical to that of the signal (iconic cues), complex tones with a missing fundamental equal to the signal (complex cues), and pure tones with a certain frequency relation to the signal (relative cues). Compared with a no-cue condition, all cue types improved detection performance. Fitting models to the data suggests that in the no-cue condition as well as the complex-cue condition, multiple bands were utilized, and that the iconic and relative cues induced single-band listening. There is no indication that accuracy of frequency tuning was responsible for cue-efficiency differences.

In binocular brightness perception a phenomenon called Fechner's paradox can be observed. This paradox implies non-monotonicities in the psychometric functions of binocular brightness. Lehky (1983) proposed a model that describes such non-monotonicities. He suggested that Fechner's paradox also exists in binaural loudness perception. However, until now no sufficient data have been collected to test this hypothesis. Therefore, an experiment was conducted in which 36 psychometric functions were obtained using binaural stimuli in the range of intensities in which Fechner's paradox supposedly occurs. As a result, no significant non-monotonicities were found. However, it is shown that jnds derived from the psychometric functions contradict predictions derived from the limited binaural additivity model of Gigerenzer and Strube (1983).