Measuring visual search and distraction in immersive virtual reality.

An important issue of psychological research is how experiments conducted in the laboratory or theories based on such experiments relate to human performance in daily life. Immersive virtual reality (VR) allows control over stimuli and conditions at increased ecological validity. The goal of the present study was to accomplish a transfer of traditional paradigms that assess attention and distraction to immersive VR. To further increase ecological validity we explored attentional effects with daily objects as stimuli instead of simple letters. Participants searched for a target among distractors on the countertop of a virtual kitchen. Target-distractor discriminability was varied and the displays were accompanied by a peripheral flanker that was congruent or incongruent to the target. Reaction time was slower when target-distractor discriminability was low and when flankers were incongruent. The results were replicated in a second experiment in which stimuli were presented on a computer screen in two dimensions. The study demonstrates the successful translation of traditional paradigms and manipulations into immersive VR and lays a foundation for future research on attention and distraction in VR. Further, we provide an outline for future studies that should use features of VR that are not available in traditional laboratory research.

Effects of absolute luminance and luminance contrast on visual search in low mesopic environments.

Diverse adaptive visual processing mechanisms allow us to complete visual search tasks in a wide visual photopic range (>0.6 cd/m2). Whether search strategies or mechanisms known from this range extend below, in the mesopic and scotopic luminance spectra (<0.6 cd/m2), has yet to be addressed. Based on a study that addressed simple target discrimination in luminance environments using contrast-dependent behavioral efficiency functions, we assessed visual search in more complex-feature and conjunction-search paradigms. The results verify the previously reported deficiency windows defined by an interaction of base luminance and luminance contrast for more complex visual-search tasks. Based on significant regression analyses, a more precise definition of the magnitude of contribution of different contrast parameters. Characterized feature search patterns had approximately a 2.5:1 ratio of contribution from the Michelson contrast property relative to Weber contrast, whereas the ratio was approximately 1:1 in a serial-search condition. The results implicate near-complete magnocellular isolation in a visual-search paradigm that has yet to be demonstrated. Our analyses provide a new method of characterizing visual search and the first insight in its underlying mechanisms in luminance environments in the low mesopic and scotopic spectra.

Female vs. Male Ampelmännchen-Gender-Specific Reaction Times to Male and Female Traffic Light Figures.

Traffic signs are important visual guiding signals for the safe navigation through complex road traffic. Interestingly, there is little variation in the traffic signs for cars around the world. However, remarkable variation exists for pedestrian traffic signs. Following up from an earlier study, we investigated the visual efficacy of female vs. male German Ampelmännchen pedestrian traffic signs. In a Stroop-like test, 30 subjects were presented with female and male go and no-go traffic light figures that were shown either in the corresponding or opposing color. Subjects had to indicate, based either solely on the form or the color of the figure, whether they were allowed to go. Accuracy and response times across all subjects did not differ for the female vs. male signs, indicating that Ampelfrau and Ampelmann signs have equal visual efficacy. However, subjects responded faster to signs of their own vs. the opposite gender. This preference for signs of one's own gender is in accordance with effects in social psychology described by social learning theory. An introduction of such novel traffic lights may, thus, contribute to higher compliance with the traffic sign signals.

Effects of absolute luminance and luminance contrast on visual discrimination in low mesopic environments.

Recent research revealed considerable decline in visual perception under low luminance conditions. However, systematic studies on how visual performance is affected by absolute luminance and luminance contrast under low mesopic conditions (<0.5 cd/m2) is lacking. We examined performance in a simple visual discrimination task under low mesopic luminance conditions in three experiments in which we systematically varied base luminance and luminance contrast between stimulus and background. We further manipulated eccentricity of the stimuli because of known rods and cones gradients along the retina. We identified a "deficiency window" for performance as measured by d' when luminance was < 0.06 cd/m2 and luminance contrast as measured by the luminance ratio between stimulus and background was below < 1.7. We further calculated performance-based luminance as well as contrast efficiency functions for reaction times (RTs). These power functions demonstrate the contrast asymptote needed to decrease RTs and how such a decrease can be achieved given various combinations of absolute luminance and luminance contrast manipulations. Increased eccentricity resulted in slower RTs indicative of longer scan distances. Our data provide initial insights to performance-based efficiency functions in low mesopic environments that are currently lacking and to the physical mechanisms being utilized for visual perception in these extreme environments.

Attention and control of manual responses in cognitive conflict: Findings from TMS perturbation studies.

The article reviews studies that have used the perturbation approach of Transcranial Magnetic Stimulation (TMS) to assess the control of attention and manual response selection in conflict situations as elicited in three established paradigms: the Simon paradigm, the Flanker paradigm, and the Stroop paradigm. After describing the experimental conflict paradigms and briefly introducing TMS we review evidence for the involvement of different frontal and parietal cortical regions in the control of attention and response selection. For example, areas such as the frontal eye field (FEF) appear to significantly contribute to the encoding of spatial attributes of stimuli and areas of the parietal cortex, such as angular gyrus (AG), mediate the allocation of spatial attention and orienting. The dorsal medial frontal cortex (dMFC), supramarginal gyrus (SMG) and pre-supplementary motor area (pre-SMA) appear to be more related to response-related aspects of the conflicts (i.e., enhancement of signals related to correct movements, transformation of spatial information action codes, resolution of response selection conflicts, respectively). The reviewed studies illustrate crucial benefits but also limitations of TMS as well as the value of the combination of TMS with other methods. We suggest topics and approaches for future studies.

Attention and ageing: Measuring effects of involuntary and voluntary orienting in isolation and in combination.

The cueing paradigm provides an established method for eliciting involuntary and voluntary attention shifts. Involuntary orienting is traditionally measured with non-predictive peripheral cues and voluntary orienting with predictive central arrows. Recent studies with young adults have established that predictive central arrows trigger a combination of involuntary and voluntary orienting, raising the possibility that previous studies - including those with older adults - misinterpreted their findings with central arrow cues as isolating the effects of voluntary attention. The present experiment applied different cueing conditions that measured involuntary orienting, voluntary orienting, and involuntary and voluntary orienting in combination in older adults. The results show that past studies of voluntary orienting in older adults confound involuntary and voluntary orienting. Cueing effects in a condition that for the first time isolated voluntary orienting (predictive number cues) with older adults were significant, and comparable to effects for younger adults, demonstrating that older adults successfully utilize cues to direct their spatial attention strategically. A similar normal pattern of orienting was observed for involuntary orienting. Our study provides a methodology that can be applied effectively to isolate and investigate the effects of age on voluntary and involuntary attention.

Effects of spatial, temporal and spatiotemporal cueing are alike when attention is directed voluntarily.

Visual cues that allow predicting location and onset of a stimulus facilitate orienting. In a seminal study, Coull and Nobre (J Neurosci 18:7426-7435, 1998) adapted the spatial cueing paradigm to investigate temporal orienting. Recent research in the spatial domain suggests though that the cues used in the spatial and temporal conditions were not comparable. In the spatial condition predictive arrow cues engaged involuntary and voluntary attention, in the temporal condition line width cues elicited voluntary attention shifts. A valid comparison between attentional modalities on the behavioural and neurophysiological level requires though that cues differ only with respect to attentional modality (spatial, temporal) and not in other aspects. To develop cues that are comparable and to assess spatial and temporal orienting, new line width cues for spatial and temporal orienting were devised that both engage only voluntary attention, and the results were compared to the cues used by Coull and Nobre (J Neurosci 18:7426-7435, 1998). Further, catch trials were included to counteract reorienting at the late time interval to promote comparisons between spatial and temporal data at that interval. The results showed that the outcome of the comparison between spatial, temporal and spatiotemporal orienting depended on the type of cue that was used and hence the type of attention that was engaged in each condition. The results indicated that orienting is equally effective in space and in time when attention is directed voluntarily. The new cues employed here can easily be used for future studies to assess underlying brain mechanisms.

Measuring effects of voluntary attention: a comparison among predictive arrow, colour, and number cues.

The Posner cueing paradigm is one of the most widely used paradigms in attention research. Importantly, when employing it, it is critical to understand which type of orienting a cue triggers. It has been suggested that large effects elicited by predictive arrow cues reflect an interaction of involuntary and voluntary orienting. This conclusion is based on comparisons of cueing effects of predictive arrows, nonpredictive arrows (involuntary orienting), and predictive numbers (voluntary orienting). Experiment 1 investigated whether this conclusion is restricted to comparisons with number cues and showed similar results to those of previous studies, but now for comparisons to predictive colour cues, indicating that the earlier conclusion can be generalized. Experiment 2 assessed whether the size of a cueing effect is related to the ease of deriving direction information from a cue, based on the rationale that effects for arrows may be larger, because it may be easier to process direction information given by symbols such as arrows than that given by other cues. Indeed, direction information is derived faster and more accurately from arrows than from colour and number cues in a direction judgement task, and cueing effects are larger for arrows than for the other cues. Importantly though, performance in the two tasks is not correlated. Hence, the large cueing effects of arrows are not a result of the ease of information processing, but of the types of orienting that the arrows elicit.

Should I stay or should I go--cognitive conflict in multi-attribute signals probed with East and West German 'Ampelmännchen' traffic signs.

In post-unification Germany, lingering conflicts between East and West Germans have found some unusual outlets, including a debate of the relative superiority of East and West German 'Ampelmännchen' pedestrian traffic signs. In our study, we probed the visual efficacy of East and West German Ampelmännchen signs with a Stroop-like conflict task. We found that the distinctive East German man-with-hat figures were more resistant to conflicting information, and in turn produced greater interference when used as distractors. These findings demonstrate Stroop-like effects for real-life objects, such as traffic signs, and underline the practical utility of an East German icon.

Influence of stimulus type on effects of flanker, flanker position, and trial sequence in a saccadic eye movement task.

Using the flanker paradigm in a task requiring eye movement responses, we examined how stimulus type (arrows vs. letters) modulated effects of flanker and flanker position. Further, we examined trial sequence effects and the impact of stimulus type on these effects. Participants responded to a central target with a left- or rightward saccade. We reasoned that arrows, being overlearned symbols of direction, are processed with less effort and are therefore linked more easily to a direction and a required response than are letters. The main findings demonstrate that (a) flanker effects were stronger for arrows than for letters, (b) flanker position more strongly modulated the flanker effect for letters than for arrows, and (c) trial sequence effects partly differed between the two stimulus types. We discuss these findings in the context of a more automatic and effortless processing of arrow relative to letter stimuli.

Measuring the allocation of attention in the Stroop task: evidence from eye movement patterns.

Attention plays a crucial role in the Stroop task, which requires attending to less automatically processed task-relevant attributes of stimuli and the suppression of involuntary processing of task-irrelevant attributes. The experiment assessed the allocation of attention by monitoring eye movements throughout congruent and incongruent trials. Participants viewed two stimulus arrays that differed regarding the amount of items and their numerical value and judged by manual response which of the arrays contained more items, while disregarding their value. Different viewing patterns were observed between congruent (e.g., larger array of numbers with higher value) and incongruent (e.g., larger array of numbers with lower value) trials. The direction of first saccades was guided by task-relevant information but in the incongruent condition directed more frequently towards task-irrelevant information. The data further suggest that the difference in the deployment of attention between conditions changes throughout a trial, likely reflecting the impact and resolution of the conflict. For instance, stimulus arrays in line with the correct response were attended for longer and fixations were longer for incongruent trials, with the second fixation and considering all fixations. By the time of the correct response, this latter difference between conditions was absent. Possible mechanisms underlying eye movement patterns are discussed.

Attention to faces: effects of face inversion.

Attention may be biased towards faces but a face advantage may be linked to the upright orientation of a face. Three experiments, employing a flanker and a cuing paradigm, investigated effects of face orientation, perceptual load and allocation of attention. Experiment 1 demonstrated that, irrespective of load, attention is biased towards upright face distractors while inverted face distractors are easy to ignore. Experiment 2 verified that inverted face distractors can interfere provided that they are attended to volitionally, likely because the volitional allocation of attention promotes face processing and gender classification (Experiment 3).

Effects of aging on switching the response direction of pro- and antisaccades.

The present study investigated effects of task switching between pro- and antisaccades and switching the direction of these saccades (response switching) on performance of younger and older adults. Participants performed single-task blocks, in which only pro- or only antisaccades had to be made as well as mixed-task blocks, in which pro- and antisaccades were required. Analysis of specific task switch effects in the mixed-task blocks showed switch costs for error rates for prosaccades for both groups, suggesting that antisaccade task rules persisted and affected the following prosaccade. The comparison between single- and mixed-task blocks showed that mixing costs were either equal or smaller for older than younger participants, indicating that the older participants were well able to keep task sets in working memory. The most prominent age difference that was observed for response switching was that for the older but not younger group task switching and response switching interacted, resulting in less errors when two consecutive antisaccades were made in the same direction. This finding is best explained with a facilitation of these consecutive antisaccades. The present study clearly demonstrated the impact of response switching and a difference between age groups, underlining the importance of considering this factor when investigating pro- and antisaccades, especially antisaccades, and when investigating task switching and aging.

Contributions of human parietal and frontal cortices to attentional control during conflict resolution: a 1-Hz offline rTMS study.

Various brain regions contribute to aspects of attentional control in conflict resolution. Here, we used transcranial magnetic stimulation (TMS) to examine the functions of posterior parietal cortex (PPC) and dorsal medial frontal cortex (dMFC) in a visual flanker task. Participants responded to a central target that was flanked by congruent, neutral or incongruent stimuli on the left or right. Offline low-frequency repetitive TMS (1 Hz, 110% motor threshold, 20 min) was applied to right PPC or dMFC. Performance, as measured by reaction times and accuracy, was established at baseline, after rTMS, and sham stimulation before or after active rTMS. After rTMS to right PPC, the interference of flankers presented in the left visual hemispace diminished selectively. By contrast, after rTMS over the right dMFC, flanker effects in both visual fields remained. Our results suggest that right PPC specifically contributes to the assignment of spatial attention during stimulus encoding.

Involuntary but not voluntary orienting contributes to a disengage deficit in visual neglect.

Patients with left neglect are particularly slow to respond to visual targets on their left when attention is first engaged to their right. This deficit is known as the disengage deficit (DD). Studies investigating the DD typically employ nonpredictive peripheral onset cues to measure involuntary orienting and predictive central arrow cues to measure voluntary orienting. A DD has been observed with both cues, suggesting that a DD occurs for involuntary and for voluntary orienting. Recent evidence questions this conclusion because nonpredictive central arrow cues trigger involuntary orienting. This implies that predictive central arrows also involve involuntary orienting and do not measure only voluntary attention. This new knowledge suggests a new conceptualization of the DD. While it is undisputed that a DD occurs when attention is shifted involuntarily, it is uncertain whether a DD is produced by voluntary orienting because most previous cuing studies of the DD have involved shifts of involuntary attention. To address this critical question, we tested neglect and control patients with nonpredictive and predictive peripheral onset cues (Experiment 1), nonpredictive and predictive central arrow cues (Experiment 2), and predictive central number cues (Experiment 3). The experiments provide three lines of converging evidence that voluntary orienting does not contribute to a DD. First, the DD was the same whether attention was engaged involuntarily by nonpredictive peripheral cues or engaged involuntarily and voluntarily by predictive peripheral cues (Experiment 1), indicating that voluntary orienting does not modulate the DD. Second, the DD was the same whether attention was engaged involuntarily by nonpredictive central arrow cues or engaged involuntarily and voluntarily by predictive central arrow cues (Experiment 2), replicating the finding of Experiment 1 with very different cues. Third, the DD was not present when attention was only engaged voluntarily by central predictive number cues (Experiment 3).

Non-lateralised deficits in anti-saccade performance in patients with hemispatial neglect.

We tested patients suffering from hemispatial neglect on the anti-saccade paradigm to assess voluntary control of saccades. In this task participants are required to saccade away from an abrupt onset target. As has been previously reported, in the pro-saccade condition neglect patients showed increased latencies towards targets presented on the left and their accuracy was reduced as a result of greater undershoot. To our surprise though, in the anti-saccade condition, we found strong bilateral effects: the neglect patients produced large numbers of erroneous pro-saccades to both left and right stimuli. This deficit in voluntary control was present even in patients whose lesions spared the frontal lobes. These results suggest that the voluntary control of action is supported by an integrated network of cortical regions, including more posterior areas. Damage to one or more components within this network may result in impaired voluntary control.

Take a look at the bright side: effects of contrast polarity on gaze direction judgments.

Observers are inaccurate when judging the gaze direction of eyes shown in negative rather than positive polarity. On the basis of this polarity effect, it has been proposed that gaze is perceived as directed from the dark part of the eye. Our experiment investigated whether direction judgments simply follow this heuristic, as has been suggested. Participants judged the gaze direction of eyes shown at different eccentricities in positive or negative polarity. The error pattern revealed that most errors were incorrect "straight" judgments, suggesting that judgments do not merely follow the heuristic "the dark part does the looking." We suggest that gaze judgments are based on the outcome of a competition between gaze direction signals: Whereas luminance cues may indicate that gaze is directed from the dark part of the eye, geometric cues may indicate the opposite. This interpretation is supported by reduced overall error rates, and fewer incorrect "straight" responses, for more extreme gaze directions.

Impaired orientation processing in hemispatial neglect.

Patients with hemispatial neglect show deficits in size perception. We investigated how this effect would be modulated by a change in object orientation. Seven right-hemisphere-lesioned patients, with and without neglect, and a control group, were asked to indicate which one of two bilaterally presented lines was longer, shorter or the same. Depending on the participant's response, the length was increased or decreased in a staircase-like procedure. Line orientation was varied over separate blocks. All neglect patients judged a line on the left as shorter, predominantly for horizontal lines and lines rotated by 30 degrees. Moreover, the magnitude of the distortion effect varied considerably between patients from as little as 2% objective underestimation to as much as 20%.

Characterizing exploration behavior in spatial neglect: omissions and repetitive search.

In search tasks, patients with spatial neglect typically fail to respond to stimuli on the contralesional side. Such behavior has been associated with hyperattention to the ipsilesional side and a deficit in disengaging from attended stimuli. The present study investigated whether such explanations can also account for a further kind of behavior frequently shown by neglect patients: repetitive returns to previously indicated stimuli, particularly on the ipsilesional side. A group of neglect patients was tested along with a group of healthy participants and a patient control group without neglect. Participants performed an exploration task in which they searched for targets defined by their shape or for all stimuli either with the aid of vision or blindfolded. The results showed differential effects of reducing the salience of visual stimuli by blindfolding. For a subgroup of patients, detection rate improved, while for others the percentage of omissions increased. However, contrary to the control groups, blindfolding had no effect on repetitive search in the neglect group, inconsistent with hyperattention, a disengage or impaired working memory deficits. The rate of repetitive returns to previously indicated locations did not seem to be associated with the percentage of omitted stimuli, suggesting that repetitive returns may be best explained by a disruption of systematic search and lack of volitional control in spatial neglect. The results further underline the importance of considering repetitive search behavior in addition to omissions in standard neglect assessments.

Classification images of two right hemisphere patients: a window into the attentional mechanisms of spatial neglect.

While spatial neglect most commonly occurs after right hemisphere lesions, damage to diverse areas within the right hemisphere may lead to neglect, possibly through different mechanisms. To identify potentially different causes of neglect, the visual information used (the 'perceptual template') in a cueing task was estimated with a novel technique known as 'classification images' for five normal observers and two male patients with right-hemisphere lesions and previous histories of spatial neglect (CM, age 85; HL, age 69). Observers made a yes/no decision on the presence of a 'White X' checkerboard signal (1.5 degrees ) at one of two locations, with trial-to-trial stimulus noise added to the 9 checkerboard squares. Prior to the stimulus, a peripheral precue (140 ms) indicated the signal location with 80% validity. The cueing effects and estimated perceptual templates for the normal observers showed no visual field differences. Consistent with previous studies of spatial neglect, both patients had difficulty with left (contralesional) signals when preceded by a right (ipsilesional) cue. Despite similar behavioral results, the patients' estimated perceptual templates in the left field suggested two different types of attentional deficits. For CM, the left template matched the signal with left-sided cues but was opposite in sign to the signal with right-sided cues, suggesting a severely disrupted selective attentional strategy. For HL, the left templates indicated a general uncertainty in localizing the signal regardless of the cue's field. In conclusion, the classification images suggested different underlying mechanisms of neglect for these two patients with similar behavioral results and hold promise in further elucidating the underlying attentional mechanisms of spatial neglect.