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Neuropsychologia 50 (2012) 1178– 1189

Contents lists available at SciVerse ScienceDirect

Neuropsychologia

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ow does phasic alerting improve performance in patients with unilateraleglect? A systematic analysis of attentional processing capacitynd spatial weighting mechanisms

athrin Finkea,∗, Ellen Matthiasa, Ingo Kellerb, Hermann J. Müllera,erner X. Schneiderc, Peter Bublakd

General and Experimental Psychology/Neuro-Cognitive Psychology, Ludwig Maximilian University, Munich, GermanySchoen Clinic Bad Aibling, Bad Aibling, GermanyNeuro-Cognitive Psychology, University of Bielefeld, Bielefeld, GermanyNeuropsychology Unit, Hans Berger Department of Neurology, University Clinic, Jena, Germany

r t i c l e i n f o

rticle history:eceived 10 January 2012eceived in revised form 6 February 2012ccepted 15 February 2012vailable online 23 February 2012

eywords:ttentionsychophysicsntrinsic alertnesshasic alertnesshalamus

a b s t r a c t

In visual hemi-neglect, non-spatial deficits such as reduced intrinsic alertness can significantly modulatethe degree of left visual field inattention. However, to date, the precise mechanisms mediating this effectare hardly understood. In the present study, we assessed the influence of increased alertness on both gen-eral attentional capacity (perceptual processing speed) and spatial attentional selection processes (spatialdistribution of attentional weighting). For this purpose, a whole-report paradigm based on Bundesen’s‘theory of visual attention’ (TVA) was combined with a non-spatial, visual alerting cue. Three differentcue-target stimulus onset asynchronies (SOAs; of 80, 200, and 650 ms), allowed us to observe the timecourse of the alerting-cue effects. A group of six patients with visual hemi-neglect was examined andtheir performance compared with six healthy control subjects matched for age, gender, and education.

In neglect patients, the alerting cue evoked a phasic increase of perceptual processing speed. However,this effect was mainly found in the ipsilateral, i.e. in the “preserved” hemifield. Importantly, however,patients displayed a fast-evolving and short-lasting, phasic modulation of spatial attentional weighting,with a re-distribution of attentional weights from the pathological rightward bias to a normal, more bal-anced distribution of visual attention. In control participants, the cueing effects on perceptual processingspeed and spatial weighting were generally less pronounced than in neglect patients. Replicating resultsof a prior study, cueing induced a stable, slightly leftward, distribution of attentional weights, whilst in

the no-cue condition, a temporary rightward shift of attentional weights was found.

This pattern of effects suggests a close interaction between alertness and spatial-attentional weightingin the syndrome of visual hemi-neglect. It supports the hypothesis that the manifestation of spatial neglectinvolves at least in part intrinsic alertness deficits. It also provides clues to a more detailed account ofthe mechanisms responsible for alleviating neglect in patients following manipulations of the alertness

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level, both in the short (c

. Introduction

It is now well established that both spatially lateralized andon-lateralized deficits of attention contribute to the clinical pic-ure of left-sided visual hemi-neglect (Husain & Rorden, 2003;amuelsson, Hjelmquist, Jensen, Ekholm, & Blomstrand, 1998; van

essel, van Nes, Brouwer, Geurts, & Fasotti, 2010). Although, at

he behavioural level, a spatially lateralized preference for stim-li and objects on the right side of space combined with a lack

∗ Corresponding author. Tel.: +49 0 89 218072520.E-mail address: finke@psy.lmu.de (K. Finke).

028-3932/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.oi:10.1016/j.neuropsychologia.2012.02.008

) and in the long term (alertness training).© 2012 Elsevier Ltd. All rights reserved.

of awareness for those in the left hemi-field is the most promi-nent feature of neglect (Bartolomeo & Chokron, 2002; Bisiach& Vallar, 1988; Heilman, Watson, & Valenstein, 2003; Karnath,1988), patients also show non-spatial deficits such as, for exam-ple, a prolonged attentional blink (Husain, Shapiro, Martin, &Kennard, 1997), impaired working memory (Danckert & Ferber,2006; Wojciulik et al., 2001), and deficient vigilance (Hjaltason,Tegnér, Tham, Levander, & Ericson, 1996; Robertson et al., 1997).In fact, these non-spatial symptoms may even be more importantfor the severity and persistence of hemi-neglect than the spatial

bias itself (Husain & Rorden, 2003). They may result from reducedalertness, a foundational form of attention or processing capacity,which more complex cognitive functions draw from (Raz & Buhle,2006).

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Lowered alertness, i.e. an impeded ability to achieve and main-ain a state of high sensitivity to an impending stimulus (Posner,008; Raz & Buhle, 2006), is a common observation in neglectatients (Heilman et al., 1978). Whilst ‘tonic’ alertness refers tohe intrinsic and more long-term control of the arousal level inde-endent from external warning cues, ‘phasic’ alertness denotes therief adaptive increase of the arousal level pending on an upcom-

ng warning stimulus (Posner, 2008; Raz & Buhle, 2006; Sturm Willmes, 2001). Functional brain imaging studies have shown

substantial overlap between the cerebral networks underlyingonic and phasic alertness on the one hand, and those engaged inoverning spatial attention on the other, with the right inferior pari-tal cortex, the most frequent lesion site in neglect patients, being

key node in both (Coull, Frackowiak, & Frith, 1998; Kinomura,arsson, Gulyas, & Roland, 1996; Robertson, Mattingley, Rorden, &river, 1998; Sturm & Willmes, 2001; Sturm et al., 1999, 2006).

n congruence with these overlapping brain networks of attention,ess alert neglect patients have been shown to have greater leftwardnattention (Bartolomeo & Chokron, 2002; Funk, Finke, Müller, Utz,

Kerkhoff, 2010; Heilman et al., 2003; von Cramon & Kerkhoff,993). The alertness and spatial attention networks represent dis-ociable brain systems (Husain & Rorden, 2003), however, and theurrent knowledge about the nature and dynamics of their interac-ion is only sparse. The present study is aimed at investigating thisuestion.

Robertson et al. (1998) were the first to directly examine ineglect patients, on a trial-by-trial basis, the causal relationshipetween alertness changes induced by sudden onset tones andodifications of the rightward spatial bias. The authors found that

he pathological asymmetry of spatial attentional selection indeedas alleviated by such a phasic enhancement of alertness. The alert-

ng cues temporarily reduced the tendency of neglect patients toeport the rightmost of two bars as coming first in a temporal orderudgement task. This result demonstrates, that even the severelyamaged attentional system of neglect patients bears the potentialo rapidly adapt in response to a warning cue so that their chronicnattention to the left hemi-field can be overcome, resulting in a

ore balanced spatial lateralization.However, the underlying mechanisms remain unclear. A closer

nderstanding of the nature and time course of the effects of alert-ess changes on non-spatial and spatial attention could, though,rovide important clues as to the cognitive architecture of attentionetworks. For example, the exact relationship between phasic and

ntrinsic alertness is still under debate (Posner, 2008; Raz & Buhle,006) and the question whether they are supported by the samer by different systems remains unresolved. Furthermore, closernowledge about alertness effects could also have implications forherapeutic intervention. Current treatment approaches suggest toe based on the modulation of intrinsic alertness (Thimm, Fink,ust, Karbe, & Sturm, 2006) or both phasic and intrinsic aspects

DeGutis & van Vleet, 2010), whilst clear evidence about the rele-ant mechanisms mediating improvement in neglect is still lacking.

To investigate this issue, we used an approach based on a for-al ‘theory of visual attention’ (TVA, Bundesen, 1990, 1998) that

llows simultaneous assessment of non-spatial and spatial aspectsf attention within the same subjects and with the same task. Ineglect patients, such a method had been applied for the first timey Duncan et al. (1999). These authors used whole and partial reportf briefly presented letter arrays to obtain parametric estimates oferceptual processing speed as a non-spatial component and lat-ral bias as a spatial component of visual selective attention. Theyound, confirming the presence of non-spatial attentional deficits

n neglect, processing speed to be significantly reduced in patients

ithin both visual hemi-fields.In a recent study, Matthias et al. (2010) used an analo-

ous methodology to assess the nature and time course of the

ia 50 (2012) 1178– 1189 1179

interaction between alertness, non-spatial and spatial attentionin healthy subjects. To that end, whole-report performance wascompared between two conditions: a no-cue condition, assumedto reflect possible changes in intrinsic alertness over the course ofa trial (Coull & Nobre, 1998; Posner, 1978; Sturm et al., 1999), andan alerting-cue condition, assumed to reflect modulations of phasicalertness. In this way, it was possible to examine whether differentlevels of alertness would affect non-spatial (i.e. processing speed)and spatial attentional components differentially or, alternatively,in a global manner. In addition, by introducing different cue-targetSOAs, it was also possible to map the time course of these effects,so as to ascertain whether alertness-related effects on non-spatialand spatial attention develop in a parallel or a sequential manner.Matthias et al. (2010) found that an increase in the level of alert-ness – irrespective of whether this was phasically or intrinsicallyinduced – first enhanced general processing speed and was thenfollowed by a leftward shift of spatial attention. They interpretedthese results as indicating that intrinsic and phasic alertness effectsinvolve the same processing route, on which spatial and non-spatialmechanisms of attention are mediated by independent processingsystems which are activated, as a result of enhanced alertness, intemporal succession.

Based on these preceding results in healthy young subjects, weapplied the same procedure in neglect patients. Six patients withleft visual hemi-spatial neglect following right temporo-parietallesions and six healthy normal control subjects were assessed witha whole-report task, in which they had to name stimuli presentedeither unilaterally, on either side of the visual field, or bilaterally, inthe left and the right hemi-field. As in the prior study on normal sub-jects (Matthias et al., 2010), the whole-report task was presented ina no-cue and an alerting-cue condition. SOA variations were usedto map the time course of the effects of the alertness level on anindex of processing speed (i.e. sensory effectiveness) and spatialattentional weighting. We expected to find similar results in normalcontrol participants as in our preceding study and wanted to anal-yse, which of the processes and mechanisms prevalent in normalsubjects would be altered or impaired in neglect patients.

Before presenting our method and the results, however, we pro-vide, for those readers unfamiliar with TVA, a brief description ofits main ideas and concepts.

1.1. Theory of visual attention (TVA)

In TVA (for a detailed mathematical description see Bundesen,1990, 1998; Duncan et al., 1999; Kyllingsbaek, 2006), visual objectsand their features are assumed to be processed in parallel andcompete for selection. The race amongst objects and featuresis decided according to a speed criterion: features which entervisual short term memory (VSTM) first cause the complete encod-ing of these objects into VSTM. Biases can arise if some objectsreceive higher attentional weights than others due to either auto-matic (‘bottom-up’) or intentional (‘top-down’) factors, conferringa speed advantage in the race for selection. According to TVA, theprobability with which an object is selected (when VSTM is not yetfilled up to capacity) is thus determined by (i) the general process-ing capacity available – reflected by an object’s basic processingrate (speed) – and (ii) the attentional weight assigned to an object.

Independent quantitative estimates of these two atten-tional components – general processing capacity and attentionalweight – are derived from the patients’ whole-report performance.

One aspect of weighting in TVA, which is especially relevant tothe present study, concerns the lateral distribution of attentional

weights within the visual field. In TVA, the spatial distribution ofattention across the visual field is indicated by a spatial lateralityindex (parameter w�), relating the attentional weights for objectsin the left and the right visual hemi-field (wleft and wright). These

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Table 1Demographic and clinical details for each participant. Abbreviations: Age, age inyears; School, school education in years; Vision, visual field impairment; TSI, timesince injury in months; F, female; M, male; H (l), hemianopia in the left visualhemi-field; Q (ll), quadrantanopia in the lower left visual hemi-field; SD, standarddeviation.

Gender Age School Vision TSI

PatientPB F 76 10 H (l) 2OB F 79 10 H (l) 2KKL M 65 13 Q (ll) 3ML M 73 10 – 4FP M 72 10 – 2EW M 71 13 – 6

Mean – 72.67 11.00 – 3.17SD – 4.76 1.55 – 1.60

ControlC1 F 71 10 – –C2 M 75 10 – –C3 M 71 13 – –C4 F 81 10 – –C5 F 74 10 – –C6 M 69 13 – –

Mean – 73.50 11.00 – –SD – 4.28 1.55 – –

Table 2Scores in the subtests and total score of the conventional part of the ‘BehaviouralInattention Test’ (BIT, Wilson et al., 1987) for each neglect patient, together with cut-off scores. Scores below the cut-offs are highlighted in bold. Abbreviations: Lines, linecrossing; letters, letter cancellation, stars, star cancellation; copying, figure/shapecopying; bisection, line bisection; drawing, representational drawing; sum, sum ofscores.

Lines Letters Stars Copying Bisection Drawing Sum

PatientPB 36 23 53 0 7 1 120OB 36 32 49 2 5 3 127KKL 36 35 40 3 6 3 123ML 36 31 48 4 6 3 128FP 36 33 45 1 6 3 124

180 K. Finke et al. / Neuropsy

eights can be derived from performance accuracy in conditionsn which patients have to report a stimulus that is accompaniedy another stimulus in either the same or the opposite hemi-eld (see Kyllingsbaek, 2006). In case of a rightward attentionalias, as in neglect, stimuli in the right hemi-field receive a higherttentional weight than competing stimuli in the left field, so thatccuracy of report for the left hemi-field will decline when stim-li are presented bilaterally (Duncan et al., 1999). Since such annbalanced competition favouring rightward stimuli would haveo effect with unilateral, but a strong effect with bilateral targetisplays, the biased competition account provides a suitable expla-ation why contralesional extinction is a characteristic neglectymptom (Desimone & Duncan, 1995). In extinction, a contrale-ionally presented stimulus is detected or identified relatively wellhen presented alone (i.e. without competing stimuli in the ipsile-

ional field), but the same stimulus is disregarded (‘extinguished’)r only poorly identified in the presence of simultaneously pre-ented ipsilesional input (Bender, 1952).

However, the probability with which an object is identified doesot only depend on its attentional weight, but also on the sensoryffectiveness, which is influenced by stimulus properties (such asiscriminability, luminance, contrast, retinal eccentricity) and byhe observer’s rate of information uptake. In TVA, the parameteror sensory effectiveness, si (which is assumed to be independentf spatial attentional weighting), refers to the accuracy of reporting

single element presented alone, under conditions of no stimu-us competition. Thus, s reflects the total processing rate, ratherhan how capacity is divided between the various objects of a dis-lay, providing a further TVA-based indicator of processing speedDuncan et al., 1999). Whilst parameter si can only be estimated bysing a variety of exposure durations, parameter Ai, a more indirecteasure of sensory effectiveness, can be derived from an experi-ent with constant exposure duration. It is defined as a compound

f sensory effectiveness multiplied by the effective exposure dura-ion (i.e. physical exposure time minus the perception threshold,ee Duncan et al., 1999). If, as in the given study, stimulus fea-ures and the effective exposure duration are held constant within

given participant, Ai is proportional to si. Variations in A-valuesan be therefore taken as (indirect1) measures of changes in sen-ory effectiveness of that participant across different experimentalonditions, such as stimulus position and alerting conditions (seeatthias et al., 2010).

. Methods

.1. Participants

Six right-handed patients with unilateral right hemisphere lesions from strokeffecting the medial cerebral artery (MCA) and six healthy control subjects weretudied. Age, gender distribution and education did not differ significantly betweenatients and control subjects (all ps > .70). In Table 1, the demographic characteristicsre listed for all subjects, and, additionally in neglect patients, the presence of visualeld deficits and the time since the brain lesion occurred are listed.

Brain damage in each patient, as demonstrated by CT or MRI scans thatere taken mostly in the acute state, was plotted by a neuroradiological

xpert blinded to the behavioural results of the patients, using MRICro soft-are (http://www.mccauslandcenter.sc.edu/mricro/), and a lesion overlap was

onstructed (see Fig. 1). As can be seen, all patients exhibited a temporo-parietal

esion in the right hemisphere.

At the time of investigation, all patients had mild visuo-spatial neglect accord-ng to their performance in the conventional part of the ‘Behavioural Inattentionest’ (BIT, Wilson et al., 1987), a standard test battery, including line crossing,

1 Although parameter A is (unlike the direct measure s) only an indirect esti-ate of sensory effectiveness under constant exposure conditions, we will use the

erm “sensory effectiveness A” throughout the article up from now. We will, how-ver, restrain from making comparisons between individuals who have been givenomewhat different exposure durations and who presumably have also differencesn visual thresholds.

EW 36 32 45 1 6 3 123

Cut off 34 32 51 3 7 2 129

letter, and star cancellation, figure and shape copying, line bisection and repre-sentational drawing. The results of each patient in the BIT are listed in Table 2.Patients were tested by an orthoptician in order to measure visual-field deficits.Patients with visual field deficits were only included when, due to macular sparing,the region of the central 5-degrees stimulus array used in our study proved to beunaffected.

All participants had normal or corrected-to-normal visual acuity and none ofthem suffered from colour blindness or any psychiatric or neurological disease (apartfrom the current event in the neglect group). They were naïve as to the purpose ofthe experiment. Written informed consent according to the Declaration of HelsinkiII was obtained from all participants and the study was approved by the local ethicalcommittee.

2.2. Apparatus and stimuli, design and procedure

2.2.1. Whole report taskFollowing previous studies of whole report tasks (e.g. Finke et al., 2005), on each

trial, either a single target letter (0.5◦ high × 0.4◦ wide) or two target letters werepresented. Targets appeared with equal frequency at each of the possible stimuluslocations in the corners of an imaginary square (with an edge length of 5◦): upperleft, lower left, upper right, lower right corner (see Fig. 2, bottom panel). Thus, tar-gets were presented 2.5◦ away from the fixation cross in the parafoveal fields onboth sides. Dual targets were placed either vertically (column display) or horizon-tally (row display), but never diagonally. All target stimuli were masked. The masksconsisted of letter-sized squares (of 0.5◦) filled with a ‘+’ and an ‘×’ and presented

for 500 ms at each letter location. The letters for a given trial display were chosenrandomly from the set (ABEFHJKLMNPRSTWXYZ), with a particular letter appearingonly once at a time.

The participants’ task was to verbally report the letters they had recognized withcertainty. The target letters could be named in any, arbitrary order, and there was

K. Finke et al. / Neuropsychologia 50 (2012) 1178– 1189 1181

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ig. 1. Lesion locations for neglect patients (PB, OB, KKL, ML, FP, and EW, from topagittal orientation (right-hand side); numbers above each slice document the z-scf patient group’s lesions is shown in light red, the lowest overlap in dark red.

o emphasis on reporting speed. The experimenter entered the reported letter(s)sing the computer keyboard and initiated the next trial after the participants had

ndicated that they were ready. The intertrial interval was 1000 ms.

The target exposure duration was individually determined for each participant

n a pretest part and then introduced into the experimental phase. The pretest con-isted of 72 single target trials (without alerting cues), presented for an exposureuration of 171 ms. It was used to determine whether a participant was able toeach an accuracy of 60–80% for single-target report. If the participant performed

ttom) reconstructed for 8 transversal slices (left-hand side) and their positions in Talairach coordinates and lesion overlap (at the very bottom); the highest overlap

outside this range, the exposure duration in the experimental phase was adjustedaccordingly. The individual exposure durations of each participant are givenin Table 3.

2.2.2. Alertness conditionsWe compared an alerting-cue condition (assumed to involve a phasic alert-

ness enhancement for a period of a few hundred milliseconds) with a no-cuecondition (purely involving intrinsic alertness). In the alerting-cue condition,

1182 K. Finke et al. / Neuropsychologia 50 (2012) 1178– 1189

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ig. 2. Sequence of frames presented on a no-cue trial (top panel) and an alerting-ual targets in the same hemi-field and dual targets presented in opposite hemi-fie

white outline frame (5◦ × 5◦) flashed briefly around the whole (potential) dis-lay array. In the no-cue condition, the screen remained blank for the same lengthf time.

The alerting cue was non-informative as to the location of the upcoming targetetters. Thus, although alerting the participants to the imminent appearance of the

arget array, this warning signal was designed to induce a spatially diffuse distri-ution of attentional weighting across the (potential) stimulus display (i.e. it couldot be used to systematically orient spatial attention to the stimulus locations).he non-informativeness of the alerting-cue with regard to the upcoming target

able 3arget exposure durations (in ms) for each participant.

Neglect patients Control subjects

Participant Exposure duration Participant Exposure duration

PB 200 C1 157OB 200 C2 171KKL 171 C3 157ML 157 C4 171FP 157 C5 157EW 200 C6 128

ial (middle panel), together with the eight possible target displays: single targets,ottom panel; the ‘T’ symbols denote target locations).

location is likely to have discouraged patients from making eye movements. In anycase, because the stimulus exposure durations were relatively short (≤200 ms), eyemovements were unlikely to affect performance systematically. However, espe-cially in neglect patients, suboptimal fixation might occur already at the beginningof a trial. Thus, to better control for eye- and head-movements during testing,we used a light-sensitive web-cam. With this device, eye and head movementscould be observed on-line by the experimenter with minimal distraction of theparticipant. When eye or head movements occurred, participants were remindedto hold the fixation and to try to avoid further movements.

2.2.3. SOA variationThree cue-target stimulus onset asynchronies2 were used: 80, 200, or 650 ms.

Because the SOAs were randomized, the alerting cue was expected to primarily

2 In the no-cue condition, the time frame within a trial was identical to the cuedcondition except for the presentation of the cue itself. Because, in the no-cue condi-tion, the screen remained blank when, in the cued condition, the cue appeared, thegiven SOAs of 80, 200 and 650 ms between cue and target presentation are, strictlyspeaking, only valid for the cued condition. However, we will use the term SOA forboth the cued and the no-cue condition, in order to compare performance of subjectsat the same time point within a given trial.

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nduce a more general alerting/arousing effect, rather than supporting any specificemporal expectations about the onset of the stimulus array.

.2.4. ProcedureThe PC-controlled experiment was conducted in a dimly lit room. Stimuli were

resented on a 17 in. monitor (1024 × 768 pixel screen resolution, 70 Hz refreshate). Participants viewed the monitor from a distance of 50 cm, controlled with theid of a head- and chinrest.

Fig. 2 illustrates the sequence of frames presented on a no-cue (top panel) andn alerting-cue (bottom panel) trial. Following initiation of a trial sequence (by thexperimenter), participants fixated a white fixation cross (0.3◦ × 0.3◦) which wasresented for the entire trial duration in the centre of the screen, on a black back-round. Then, after 1100 ms, either the alerting cue appeared for 50 ms or the screenemained blank for the same length of time. After the variable cue-target SOA, thehole-report display was presented for the pre-set exposure duration. Following

egistration of the participant’s report, the next trial started after an intertrial inter-al of 1000 ms. Cue/no-cue conditions as well as the three SOAs were presented inandom order within the same block.

In the first session (lasting around 30 min), the whole-report pre-test waspplied to determine the individual presentation times. In neglect patients, fur-hermore, the BIT was performed. The second to the fourth session (lasting around5 min each) consisted of the experimental phase of the whole report. It com-rised of eight different target conditions (four single-target and four dual-targetonditions) for each SOA (80, 200, 650 ms) and each of the two cueing conditionsno-cue, alerting-cue). In total, the experiment comprised 846 trials per subject.tandardized verbal instructions were given before each block of trials. In order tovoid or minimize a possible influence of the alerting cue on the no-cue condition,lerting-cue and no-cue trials were presented in different blocks. The order of thelocks and sessions was counterbalanced across subjects to control for sequenceffects. Hence, for three patients and three control subjects, the sequence was AB,A, AB, and for the other three subjects of each group BA, AB, BA (with A = blockith no-cue trials, and B = block with alerting-cue trials). To control for time-

n-day effects, the participants completed each of the four sessions at the sameime of day and within one week. A 5-min break was included in the middle ofach session.

.2.5. Estimation of the TVA parametersThe whole-report task permitted quantitative estimates to be derived of visual

ensory effectiveness A and of attentional weight w, applying the algorithmsescribed in detail by Kyllingsbaek (2006) and used in several recent studies (e.g.ublak et al., 2005; Duncan et al., 1999; Finke et al., 2005; Habekost & Bundesen,003). These parameters were estimated separately for the four positions used inhe task (upper left, upper right, lower right, lower left): parameters Ai and wi ,espectively, where i is the stimulus position.

Enhancement of global processing capacity of a given participant by an alert-ng cue would be reflected in higher estimates of A across all stimulus positions.ndices of sensory effectiveness were calculated for each hemi-field (by averagingcross the respective values for the upper and lower positions within each hemi-eld): Aleft and Aright. This permitted us to examine whether alerting cues enhancedensory processing globally (across hemi-fields) in neglect patients, or whether,ossibly, sensory processing in the neglected contralesional hemi-field would par-icularly benefit (and, thus, would specifically impact the lateralized disturbancesn the syndrome).

The parameter attentional weight is related to performance losses in multi-lement displays. Stimuli with higher weight are stronger competitors and, thus,isturb report accuracy for further stimuli more than stimuli with lower attentionaleight. The estimated attentional weights for upper and lower stimulus positionsere averaged in order to receive separate indices of attentional weighting for eachemi-field, wleft and wright. However, the relative, rather than the absolute, amountf attentional weight attributed to each hemi-field provides useful information onpatial attentional selection. Thus, a laterality index – the parameter ‘spatial distri-ution of attentional weighting’ (w�) – was computed. This index (which is relatedo performance losses with (row) multi-element- compared to single-element dis-lays) indicates whether one hemi-field is favoured in the spatial selection process.

f attentional weights are biased towards one hemi-field, performance in bilateralcompared to unilateral) presentation conditions will suffer more for targets pre-ented in the hemi-field with relatively low attentional weight, compared to targetsn the hemi-field with high weight. Formally, this index is defined as the ratio ofalues across the two hemi-fields, w� = wleft/(wleft + wright). Hence, a value of w� = .5ndicates a balanced distribution of weights, values of w� > .5 indicate a leftward,nd values of w� < .5 a rightward spatial-attentional bias. If attentional weights areiased towards one hemi-field, performance in bilateral (compared to unilateral)resentation conditions will suffer more for targets presented in the hemi-fieldith relatively low attentional weight, compared to targets in the hemi-field with

igh weight. Note, though, that under bilateral stimulus conditions, it is in prin-iple also possible that a difference in performance between left- and right-sideargets is due to reduced sensory effectiveness in target discrimination on oneide. This factor was controlled for by the hemi-field-specific analyses of sensoryffectiveness A.

ia 50 (2012) 1178– 1189 1183

3. Results

In what follows, we will first describe the qualitative accuracypattern (correctly identified letters) obtained across the differentgroups and experimental conditions. Second, we will present theparameter estimates derived in TVA-based model fits to the data,that is, sensory effectiveness and spatial attentional weighting.Next, in order to compare sensory effectiveness and spatial atten-tional weighting effects across groups, SOAs and cueing conditions,mixed ANOVAS were carried out on the TVA parameters in ques-tion.

3.1. Report accuracy: raw data indicators of sensoryenhancement and of changes in the spatial distribution ofattention

To illustrate sensory effectiveness and attentional weightingacross the two hemi-fields, Fig. 3 shows separately the mean pro-portion of target letters correctly identified by patients and controlsin each hemi-field and at each SOA for five experimental conditions:single-target letter; target accompanied by a target in the ipsilat-eral field (column displays) and target accompanied by a target inthe contralateral field (row displays). In general, the performancelevels of both groups are in accordance with the prediction fromthe TVA model: accuracy was highest in single-target conditionsand decreased in dual target conditions.

Accuracy in single target conditions (first two bars of each fig-ure) can be taken as a raw data indicator of how well a stimulus isbasically processed, at a given exposure duration, under conditionsof no stimulus competition, that is, of pure sensory effectiveness, ineach hemi-field. Due to individually adjusted exposure durationsfor each participant, between-group comparisons do not makesense with respect to the general level of accuracy. However, accu-racy changes across alerting conditions and hemi-fields can betaken as indicators of changes of sensory effectiveness and of spa-tial weighting. Fig. 3a shows that in neglect patients an alertingcue seems to enhance accuracy for single targets at the 80-ms and200-ms SOAs. However, this improvement does mainly occur in theright hemi-field; only at the longest, 650-ms SOA, an improvementis also manifest in the left field. In control participants, an alertnesscue does not seem to enhance single-target report in general. How-ever, also in this group, an enhancement is evident for left visualfield single targets at the longest SOA (Fig. 3b).

A comparison between accuracy losses in column displays onthe one hand and row displays on the other indicates possiblechanges in spatial attentional weighting processes. As would beexpected in neglect patients with a reduced awareness of theleft side, in the no-cue condition, report accuracy was lowest forrow displays (i.e. in conditions with competition between the twohemi-fields), especially for the left side. However, this pattern wasmodified in the alerting-cue conditions. Especially at the shortestSOA, report accuracy for the left side even exceeded that for theright side (Fig. 3a).

3.2. TVA parameter estimates

For each participant, cueing condition and SOA, sensory effec-tiveness and attentional weights were quantified for each of thefour possible target locations. The empirically assessed mean accu-racy scores for the different experimental conditions and the valuestheoretically predicted (based on the best fits of the TVA modelparameters) showed a close correspondence: the average corre-

lation between the observed and the predicted scores across allSOAs in the no-cue condition was .92 (neglect patients, SD = .04) and.86 (control participants, SD = .07). In the alerting-cue condition, itwas .88 (neglect patients, SD = .09) and .83 (control participants,

1184 K. Finke et al. / Neuropsychologia 50 (2012) 1178– 1189

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Fig. 3. (a and b) Mean proportions of correctly identified target letters (% correct) presented in either the left or the right hemi-field in the different experimental conditions,separately for neglect patients (a) and for control participants (b). Each bar represents the mean in one condition: single target (ST), target accompanied by a target in thesame hemi-field/dual targets in column displays (DT column), target accompanied by a target in the opposite hemi-field/dual targets in row displays (dual target row). Foreach group, separate figures are shown for the two cueing conditions (no-cue, alerting-cue) and the three SOAs (80, 200, 650 ms). Error bars give the standard errors.

K. Finke et al. / Neuropsychologia 50 (2012) 1178– 1189 1185

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separately for the two hemi-fields. As can be seen, the temporarysensory enhancement in the right field is reliably observed at the80-ms and 200-ms SOAs, in each single case. Cue-induced sensoryeffects in the left, neglected, field are generally more variable across

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ig. 4. Parameter A (sensory effectiveness) for the left (left half) and the right hemlower half). The different lines depict sensory effectiveness for the two cueing contandard errors.

D = .04). Thus, in the no-cue condition, the model explained 84%neglect patients) and, respectively, 74% (control participants), andn the alerting-cue condition it explained 77% (neglect patients)nd, respectively, 68% (control participants) of the variance.

.3. TVA parameter sensory effectiveness A: quantitativestimation of global and/or lateral processing capacitynhancement

Fig. 4 presents the time course of the effect of the alerting cue,ompared to the no-cue condition, on sensory effectiveness A inach hemi-field, for each group.

Separate ANOVAs were conducted for the neglect patients andor the control participants, each with the within-subject factorsOA (80, 200, 650 ms), cue (no-cue, alerting-cue), and side (leftemi-field, right hemi-field).

.3.1. Neglect patientsIn neglect patients, all main effects were significant [cue: F(1,

) = 11.13; p < .05; SOA: F(2, 4) = 6.78; p < .05; side: F(1, 5) = 7.19; < .05]. As can be seen in Fig. 4, the alerting cue did indeed inducehe global attentional resource enhancement in question (mainffect of cue). However, significant interactions of SOA × side [F(2,) = 4.62; p < .05] and, more importantly, of SOA × cue × side [F(2,) = 4.31; p < .05] showed that the time course of sensory changesnd the impact of cueing on these changes differed between hemi-elds. In accordance with the accuracy pattern for single targets,he three-way interaction reflects the fact that, in the right hemi-eld, the alerting cue induced a significant enhancement of sensoryffectiveness for a relatively short period of time. Sensory effective-ess was higher following an alerting cue compared to the no-cueondition at the SOAs of 80 ms [t(5) = 5.57; p < .01] and of 200 mst(5) = 3.26; p < .05], but not at the SOA of 650 ms (p > .75). In con-

rast, in the left hemi-field, sensory effectiveness was enhancednly at the longest SOA of 650 ms (t(5) = −2.48; p < .05).

In Fig. 5, the time course of cue-induced sensory effectivenesshanges is illustrated for each neglect patient (single-case data),

d (right half), separately for neglect patients (upper half) and control participantss (no-cue, alerting-cue) as a function of SOA (80, 200, 650 ms). Error bars give the

Fig. 5. Single case data of parameter A (sensory effectiveness) for each of the neglectpatients, separately for the left (upper figure) and the right hemi-field (lower fig-ure). For each participant, solid and dashed lines depict sensory effectiveness in theno-cue and the alerting-cue condition, respectively, as a function of SOA (80, 200,650 ms).

1 chologia 50 (2012) 1178– 1189

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186 K. Finke et al. / Neuropsy

atients, and no systematic enhancement effect seems to prevail.otably, the three patients with visual field defects (PB, OB, KKL)

howed values that were comparable to those of patients withoutisual field defects in each condition, and, furthermore, they alsohowed comparable SOA- and cue-induced effects in both hemi-elds.

To summarise, with respect to sensory effectiveness, neglectatients showed a marked cue-induced enhancement at the short-st SOA and, too a lesser degree, also at the medium SOA withinhe right hemi-field. In contrast, within the left hemi-field, sen-ory effectiveness increased at the longest SOA, only, in the cueondition. Notably, neglect patients did not show any dynamics inensory effectiveness whatsoever in the no-cue condition, in bothemi-fields.

.3.2. Control participantsIn control participants, the main effect of side [F(1, 5) = 7.09;

< .05] and the SOA × cue × side interaction [F(2, 4) = 12.56; p < .01]ere significant. Mirroring somewhat the results for neglectatients in the left hemi-field, sensory effectiveness was enhancedy an alerting cue at the longest SOA of 650 ms in the right hemi-eld in control subjects (t(5) = −2.16; p < .05). For the left hemi-field,ensory effectiveness increased from the 200-ms to the 650-msOA [t(5) = 3.16; p < .05] in the alerting-cue condition,; and only athe latter (the longest SOA) was there a tendency towards a higherensory effectiveness for the alerting-cue compared to the no-cueondition [t(5) = 2.34; p < .07]. Another (non-significant) tendencyuggested sensory processing to be somewhat higher at the 200-s compared to the 80-ms SOA in the no-cue condition [t(5) = 2.36;

< .07].In sum, in control subjects, the enhancement of sensory effec-

iveness at the longest SOA in the right hemi-field following a cueirrored the performance of neglect patients within the left hemi-

eld. And the same result was obtained in control subjects alsoithin the left hemi-field, with even a more marked increase of

ensory effectiveness at the longest SOA. In the no-cue condition,ontrol subjects showed the largest differences of sensory effective-ess within the left hemi-field: There was a strong increase fromhe shortest to the medium SOA, where sensory effectiveness evenxceeded that in the cueing condition, and then a decline to theongest SOA. This pattern was quite different from the right hemi-eld, where sensory effectiveness achieved its greatest value at thehortest SOA.

.4. TVA parameter spatial distribution of attentional weighting

�: quantitative estimation of laterality changes in selectionrocesses

Fig. 6 illustrates the average SOA-dependent time course of thepatial distribution of the attentional weighting parameter w� forhe no-cue and the alerting-cue condition. As can be seen, theue induced changes of spatial attentional weighting mainly in theatient group and mainly at the shorter SOAs.

A mixed ANOVA with the factors group, SOA and cue and with� as dependent variable confirmed this pattern statistically. This

nalysis revealed all main effects [group: F(1, 10) = 55.76; p < .01;OA: F(2, 9) = 5.18; p < .05; cue: F(1, 10) = 22.17; p < .01] and two-ay interactions [group × SOA: F(2, 9) = 4.95; p < .05; group × cue:

(1, 10) = 6.35; p < .05; SOA × cue: F(2, 9) = 3.89; p < .05], and the

hree-way interaction group × SOA × cue [F(2, 9) = 5.57; p < .05] toe significant. Separate repeated-measures ANOVAs were con-ucted subsequently in order to examine the effects of cue andOA within both groups.

alerting-cue), as a function of SOAs (80, 200, 650 ms). Error bars give the standarderrors. Values of w� > .50 = leftward attentional bias; w� < .50 = rightward attentionalbias; w� = .50 = no bias.

3.4.1. Neglect patientsIn neglect patients, the main effect of cue [F(1, 5) = 51.26; p < .01]

was significant, whilst that of SOA [F(2, 4) = 3.52; p > .10] was not.Furthermore, a significant SOA × cue interaction [F(2, 4) = 5.61;p < .05] was obtained. As illustrated in Fig. 7, compared to the no-cuecondition, the alerting cues induced a significant re-distribution ofattentional weights towards the left hemi-field at the SOAs of 80 ms[t(5) = −3.92; p < .01] and 250 ms, [t(5) = −6.48; p < .01]; whilst thiseffect disappeared at the longest SOA of 650 ms [p > .70].

Additional analyses examined whether the spatial distributionof attentional weighting was significantly biased towards eitherside, compared to the optimal, balanced value of .5. As illustrated inFig. 6, in no-cue conditions, neglect patients were generally biasedtowards the right (w� < .05). This was confirmed by significant orborderline significant effects at all SOAs [80 ms: t(5) = −3.15; p < .05;200 ms: t(5) = −6.86; p < .01; 650 ms: t(5) = −1.93; p < .07]. Follow-ing an alerting cue, a significant leftward bias (w� > .5) appearedat the shortest, 80-ms SOA [t(5) = 5.93; p < .01], followed again by asignificantly rightward biased distribution of weights at the longer,200-ms [t(5) = 3.05; p < .05] and 650-ms [t(5) = −6.00; p < .01] SOAs.

From Fig. 7, the single case neglect patient data can be seento confirm the changes of attentional selection laterality inducedby the alerting cue and also its time course (again, there was

no indication of any difference between patients PB, OB, andKKL with visual field deficits and patients without visual fielddeficits). In the no-cue conditions, a general, more or less pro-nounced rightward spatial attentional bias (w� < .5) is evident

K. Finke et al. / Neuropsycholog

Fig. 7. Single case data of parameter w� (spatial distribution of attentional weight-ing) for each of the neglect patients in the no-cue condition (upper figure) andthe alerting-cue condition (lower figure), as a function of SOA (80, 200, 650 ms).Error bars give the standard errors. Values of w� > .50 = leftward attentional bias;w

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� < .50 = rightward attentional bias; w� = .50 = no bias.

n each patient and cueing condition. Following an alerting cue,he overall pattern described above at the group level was con-istently present in each single case. Each patient showed aateral redistribution of attentional weights towards the left side,nd even a slight leftward bias in each single case (w� > .5)t the shortest, 80-ms SOA which gradually disappears as SOAncreases.

In summary, cueing had a marked impact on the spatial bias ofttention in neglect patients. In fact, at the shortest SOA, the right-ard bias disappeared and turned into a leftward spatial weighting

f attention. This effect dropped linearly at the later SOAs, so that athe longest SOA, a rightward bias was again obtained. In contrast,

ore or less the same rightward bias prevailed across all SOAs inhe no-cue condition.

.4.2. Control participantsThe main effect of cue was not significant [F(1, 5) = 1.61; p < .01],

ut the ANOVA revealed a significant main effect of SOA [F(2,) = 8.31; p < .05] and a tendency for an SOA × cue interaction [F(2,) = 3.32; p < .08]. Mainly driven by the no-cue condition (see Fig. 6),

slight but significant shift of spatial attentional weights from theeft to the right side occurred from the shortest SOA of 80 ms to thatf 200 ms (t(5) = 3.60; p < .05) and another significant shift back tohe left side from the SOA of 200 ms to that of 650 ms (t(5) = −4.27;

< .01). The spatial distribution of attention did not differ signif-cantly between the shortest and the longest SOA (p > .75). In theue condition, there was a slight leftward shift of spatial attentional

ia 50 (2012) 1178– 1189 1187

weighting as a function of SOA, but this effect was not significant(t(5) = −1.56; p > .15).

Comparisons against the optimal value of 0.5 did not indicatea lateralization in any of the cueing conditions at the shortest andthe intermediate SOA (all t < 2.00, all p > .10). At the longest SOAof 650 ms, control participants were significantly biased towardsthe left in both cueing conditions [no-cue: t(5) = 3.66; p < .05; cue:t(5) = 4.20; p < .01].

To summarise, concerning the bias of spatial attention, controlsubjects showed a complementary pattern compared to the resultsof sensory effectiveness in the no-cue condition: At the mediumSOA, a slight rightward shift occurred, whereas a leftward biasprevailed at both the shortest and the longest SOA. In the cue-ing condition, there was a slight leftward bias, which was largelyconsistent across SOAs.

4. Discussion

The aim of the present study was to investigate the nature andtime course of the effect of a phasic alerting cue on spatial andnon-spatial aspects of attention, as compared to a no-cue condi-tion, in patients with unilateral neglect for contralesional space. Byusing a TVA-based whole-report paradigm our study was designedto independently and separately examine the influence of cue-induced phasic alertness on processing capacity (i.e. on sensoryeffectiveness as an indicator of processing speed) and on the spa-tial distribution of attentional weights across the two hemi-fields(i.e. on the laterality of selection). We assessed (1) whether cueingwould affect sensory and/or spatial attentional-components and, ifso, (2) in what time ranges these various effects would occur and(3) whether they would differ from those found in normal controlparticipants.

As a first main result of our study, control subjects showedthe greatest effects in the no-cue condition, with complemen-tary, even opposing patterns for sensory effectiveness (left-fieldenhancement) and spatial weighting of attention (rightward shift),especially at the medium SOA. This result is in close correspondencewith the data presented by Matthias et al. (2010) in their Experi-ment 2, which had applied the same paradigm as in the presentstudy, in particular using a randomised variation of SOA, in younghealthy subjects. Matthias et al. (2010) interpreted this result asreflecting the effects of top-down mediated modulations of intrin-sic alertness and confirmed this assumption by showing that thepattern disappeared when SOAs were presented blockwise, so thatadaptation of a mental set on a trial-by-trial basis was no longernecessary. The seemingly contradictory overlay between enhancedintrinsic alertness and a, in relation to the other SOAs, more right-ward spatial bias at the medium SOA, was interpreted as indicatingthat enhanced alertness influences two separate systems – one sup-porting processing speed, the other governing spatial attention –that act independently from each other, but on a different timescale. The enhancement of processing speed occurs first, and isfollowed by a leftward shift of spatial attention, observable at thelongest SOA.

Following this assumption, the results of the control subjects inthe present study can be interpreted as further evidence that spatialand non-spatial mechanisms of attention are mediated by inde-pendent processing systems which exert their effects, as a result ofenhanced intrinsic alertness, in temporal succession. According tothe neuro-cognitive model proposed by Heilman et al. (2003) andPosner and Petersen (1990), modulations of intrinsic alertness are

exert top-down control, via thalamic nuclei, on posterior corticalareas related to perceptual processing, by activating noradrenergicnuclei of the ponto-mesencephalic part of the brainstem (see also

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esulam, 2000, for a similar idea). Consistent with right temporo-arietal damage interfering with this system, and in congruenceith empirical evidence that regulation of intrinsic alertness is defi-

ient in neglect patients (Bartolomeo & Chokron, 2002; Heilmant al., 2003), there was almost no sign of any modulation of theerformance of neglect patients in the no-cue condition of ourtudy.

In contrast, and as the second main result of our study,eglect patients showed the greatest effects in the cue condi-ion, especially at the shortest SOA. Interestingly, as for controlubjects – though complementary concerning the hemi-field – theattern for sensory effectiveness (right-field enhancement) andpatial bias (leftwards) was opposing. Especially because the sam-le size was relatively small in our study, it is noteworthy that thisesult was highly consistent across patients at the single case level.his pattern is compatible with the above presented interpretationf separate systems for speed and spatial attention. However, bothystems bring about their effects not in temporal succession, but inarallel, already shortly after cue-induced phasic enhancement oflertness. Moreover, the switching of the hemi-field, in which theffects are observed for patients as compared to control subjects,equires an explanation. After all, if a right-hemispheric dominanceor alertness is assumed, the greatest effects would be expected toe observed within the left hemi-field, as was the case in controlarticipants.

Taking into account the damage to the right-sided alerting net-ork in neglect patients (indicated by the lack of intrinsic alertnessodulations), and the fact that a phasic alerting cue exerted effects

n both hemi-fields (although predominantly on the right side), thereater enhancement of sensory effectiveness in the ipsilesionaleld can be explained in the following way: Phasic alertness mightctivate a system supporting processing speed (indicated by sen-ory effectiveness in our study) that leads to a global stimulationithin both hemispheres. When only a single stimulus is presentithin one hemi-field, then the intact hemisphere (the left one

n the neglect patients) will always outperform the damaged one,iving rise to a right-hemi-field advantage in single target displays.

The simultaneous effect of phasic alertness on the spatial biasoints to the additional cue-induced activation of a second system,evoted to spatial attentional weighting, which exerts a specificallyight-hemispheric effect. This system would become especially rel-vant in situations of inter-hemispheric competition, as in theilateral target displays of the whole-report paradigm of our study,nd, thus, would lead to a more balanced spatial weighting in theseonditions.

The rapidly evolving effects on sensory effectiveness and spa-ial bias following the cue suggest that the two simultaneouslyctivated systems mediating speed and spatial weighting ratherepresent lower-level centres. Therefore, one plausible neural can-idate structure underlying these effects is the thalamus, which

s known to be relevant both in the ascending thalamic mes-ncephalic phasic alertness system (Fan, McCandliss, Fossella,lombaum, & Posner, 2005; Posner & Petersen, 1990; Sturm &illmes, 2001; Thiel & Fink, 2007) and which has also been

roposed to be critical for visual extinction by several authorsFimm et al., 2001; Karnath, Himmelbach, & Rorden, 2002; Rafal

Posner, 1987). For instance, Habekost and Rostrup (2006)eported a rightward spatial bias in a comparable TVA-basedaradigm following stroke in the right-sided pulvinar nucleus ofhe thalamus. In fact, on the neural interpretation of the TVA‘NTVA’) proposed by Bundesen, Habekost, & Kyllingsbæk (2005),he pulvinar nucleus of the thalamus is assumed as the critical

egion mediating spatial-attentional weighting across the visualeld.

Based on our results, we would suggest that both thala-ic subsystems are simultaneously activated by another system

ia 50 (2012) 1178– 1189

which is directly related to phasic alertness and responds tothe alerting cue. A possible candidate for this would be theascending reticular activating system, which receives direct sen-sory input (Jones, 2003). These assumptions would predict thatneglect patients with thalamic lesions do not show effects ofcue-induced enhancement of phasic alerting, and, therefore, noincrease of sensory effectiveness and no balanced spatial weightingshould be observed in these patients after presenting an alertnesscue.

Our data clearly show that enhanced phasic alerting bringsabout a re-distribution of attentional weights in neglect patients.Whilst a rightward spatial bias prevailed in the no-cue conditionand also at the longest SOA in the cue condition, a more balanced, infact even slightly leftward spatial bias was found 80 ms and 200 msafter cue presentation. This effect was very consistent on the singlecase level and was found in each of the six patients assessed (seeFig. 7). This result is in congruence with the earlier data presentedby Robertson et al. (1998) for a different paradigm, and demon-strates the adaptive potential of a damaged attentional network.However, it also raises the question of the clinical implications ofsuch a short-lived effect. After all, at the longest SOA, the patho-logical rightward bias reappeared and the neglect pattern was fullyre-established.

It should be taken into account, however, that a core functionof an alertness cue is to initiate an orienting response (Posner,2008). In reality settings, this is typically accomplished by eyeor head movements which support the aim to foveate a salientstimulus that is available afterwards for close examination. In ourstudy, when such a stimulus did not appear within the 650 ms fol-lowing the alertness cue, the neglect pattern was re-established.However, this does not imply that, in case visual stimulation isindeed provided, the cue-induced benefit resulting is necessarilyonly shortlived. In our study we only used briefly presented stim-uli. It remains an open empirical issue whether, under conditionsof enduring sensory stimulation (such as, e.g. the unlimited pre-sentation of a visual search display), the alertness-induced effectmight be more stable and even remain significant for the dura-tion of any target scene presentation. Furthermore, it should betested whether, using a systematic alertness training, the effec-tive period, i.e. the gap between cue and target, without sensorystimulation, can be prolonged. Nevertheless, should alerting cuesbe used as a therapeutic tool in a clinical setting, then the SOAbetween an alerting cue and a target should be adjusted to theeffective short-time window documented in our study in order toreach the maximum benefit, at least at the beginning of an alertnesstraining.

In summary, based on the present results, it can be concludedthat higher levels of alertness can help overcome the typical neglectsymptoms, such as rightward lateralization and unilateral extinc-tion, indicative of the relevance of alertness in disturbed attentionalcompetition and, thus, spatial-attentional asymmetries. Notably,a quick redistribution of attentional weights across both hemi-fields has been identified as the major source of the performancebenefit even at the single case level, i.e. in each of the patientstested. Our results are in accordance with previous studies showinga rightward bias in exploration behaviour and a unilateral right-ward lateralization in neglect (e.g. Bartolomeo & Chokron, 2002;Bublak et al., 2005; Duncan et al., 1999; e.g. Heilman et al., 2003;Karnath, 1988). In addition, they provide important clues as toboth the time course and the effective mechanism responsible forthe alleviation of these deficits. Due to our low sample size andthe limitations of our neuroanatomical evidence, these clues have

to be further corroborated by future studies with larger samplesizes also aiming at a closer examination of longer-term trainingeffects and a better understanding of the precise neuroanatomicalcorrelates

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