Brain and Cognition 87 (2014) 39–51

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Brain and Cognition

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Task preparation and neural activation in stimulus-specific brainregions: An fMRI study with the cued task-switching paradigm

http://dx.doi.org/10.1016/j.bandc.2014.03.0010278-2626/� 2014 Elsevier Inc. All rights reserved.

⇑ Corresponding authors. Address: Department of Psychology, Ludwig-Maximil-ians-University Munich, Leopoldstraße 13, 80802 Munich, Germany.

E-mail addresses: ssyyqq.s@gmail.com (Y. Shi), torsten.schubert@psychologie.hu-berlin.de (T. Schubert).

Yiquan Shi a,b,⇑, Thomas Meindl c, Andre J. Szameitat a, Hermann J. Müller a,d, Torsten Schubert a,e,⇑a Department of Psychology, Ludwig-Maximilians-University, Munich, Germanyb Neuroimaging Center, Department of Psychology, Dresden University of Technology, Dresden, Germanyc Department of Clinical Radiology, University Hospitals–Grosshadern, Ludwig-Maximilian-University, Munich, Germanyd Department of Psychological Sciences, Birkbeck College, University of London, UKe Department of Psychology, Humboldt-University, Berlin, Germany

a r t i c l e i n f o a b s t r a c t

Article history:Accepted 5 March 2014

Keywords:Preparatory modulationStimulus-specific regionsSelective enhancementFunctional connectivityResidual activation

To investigate the role of posterior brain regions related to task-relevant stimulus processing in taskpreparation, we used a cued task-switching paradigm in which a pre-cue informed participants aboutthe upcoming task on a trial: face discrimination or number comparison. Employing an event-relatedfMRI design, we examined for changes of activity in face- and number-related posterior brain regions(right fusiform face area (FFA) and right intraparietal sulcus (IPSnum), respectively), and explored thefunctional connectivity of these areas with other brain regions, during the (preparation) interval betweencue onset and onset of the (to-be-responded) target stimulus. The results revealed task-relevant posteriorbrain regions to be modulated during this period: activation in task-relevant stimulus-specific regionswas selectively enhanced and their functional connectivity to task-relevant anterior brain regionsstrengthened (right FFA – face task, right IPSnum – number task) while participants prepared for the cuedtask. Additionally, activity in task-relevant posterior brain regions was influenced by residual activationfrom the preceding trial in the right FFA and the right IPSnum, respectively. These findings indicate that,during task preparation, the activation pattern in currently task-relevant posterior brain regions isshaped by residual activation as well as preparatory modulation prior to the onset of the critical stimulus,even without participants being instructed to imagine the stimulus.

� 2014 Elsevier Inc. All rights reserved.

1. Introduction 2000; but see Wylie, Javitt, & Foxe, 2006). However, little effort has

A fundamental characteristic of executive control is that in achanging environment, humans can selectively prepare for a spe-cific task even prior to the presentation of the task-critical stimu-lus. Such task preparation is crucial for flexible and preciselytimed behavior in many situations. Much of the previous workon this issue has focused on the neural correlates of the taskpreparation process in general, and specifically on localizingactivation foci for critical components of task preparation, suchas task configuration and rule activation, in the prefrontal cortex(PFC) and the parietal cortex (e.g., Bode & Haynes, 2009; Brass &von Cramon, 2002, 2004; Gruber, Karch, Schlueter, Falkai, &Goschke, 2006; Luks, Simpson, Feiwell, & Miller, 2002; Shi, Zhou,Müller, & Schubert, 2010; Sohn, Ursu, Anderson, Stenger, & Carter,

been expended on investigating the role of posterior brain regionsthat are related to task-relevant stimulus processing during taskpreparation. This is surprising because it has long been suggestedthat the PFC and the parietal cortex modulate stimulus processingduring task performance in posterior brain regions in a goal-direc-ted manner (e.g., Corbetta, Kincade, Ollinger, McAvoy, & Shulman,2000; Corbetta, Kincade, & Shulman, 2002; Desimone & Duncan,1995; Hopfinger, Buonocore, & Mangun, 2000; Miller & Cohen,2001; Serences, Schwarzbach, Courtney, Golay, & Yantis, 2004).Therefore, in the present study, we aimed to elucidate the charac-teristics of the preparation-related changes in those posterior brainregions that are related to the processing of the task-relevant andtask-irrelevant stimuli.

The mechanisms and neural substrate of task preparation haveoften been investigated using the cued task-switching paradigm(e.g., Bode & Haynes, 2009; Brass & von Cramon, 2002, 2004;Gruber et al., 2006; Luks et al., 2002; Meiran, 1996, 2000; Shiet al., 2010; Sohn et al., 2000; Sudevan & Taylor, 1987; Wylieet al., 2006). In this paradigm, participants have frequently to

40 Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

switch between two tasks, requiring them to repeatedly preparefor a new task. For instance, participants may be presented witha face which is overlaid with a digit, and they have to indicatethe gender of the presented person (i.e., male or female) on sometrials and the magnitude (i.e. larger or smaller than 5) of the pre-sented digit on other trials. A task cue, in the present example:the word ‘gender’ or ‘digit’, is presented before the target stimulusto indicate the upcoming task, thus permitting anticipatory taskpreparation. This paradigm makes it possible to temporally disso-ciate the task preparation (time interval from cue presentation un-til target presentation) from the task execution period (followingtarget presentation) (e.g., Meiran, 1996). It has been shown thatin the cued task-switching paradigm, participants’ performancebenefits from a prolonged cue–target interval (CTI), with the over-all reaction time becoming faster and the error rate and the cost oftask switching lower with increasing CTI (e.g., over CTI durationsfrom 0 to about 1000 ms). These benefits are suggestive of taskpreparation occurring within the cue–target interval (e.g., Meiran,1996, 2000). However, extending the time allowed for task prepa-ration by increasing the CTI even further does not usually translateinto increased performance gains, possibly because such long CTIsmay pose extra demands on working memory and so discourageactive task preparation (Brass & von Cramon, 2002; Monsell,2003) The components involved in task preparation in theparadigm sketched above are commonly thought to include:task-relevant stimulus processing and retrieval, or pre-activation,of stimulus–response (S–R) rules (see Kiesel et al., 2010, for re-view). Assuming that preparation for a specific task includestask-relevant stimulus-specific processing, this processing shouldbe associated with pre-activation of posterior brain regions thatare specifically involved in task-relevant stimulus processing.

Recent neuroimaging studies have provided reliable evidencefor the existence of several, separable stimulus-specific brain re-gions in posterior cortices (e.g., Dehaene, Piazza, Pinel, & Cohen,2003; Kanwisher, McDermott, & Chun, 1997; Liu, Harris, & Kanw-isher, 2010; Tootell et al., 1995; Zeki et al., 1991). Based on thefindings of these studies, it becomes possible to investigate theneural activity in posterior stimulus-specific brain regions duringthe task preparation processes in the cued task-switching para-digm. Note that most fMRI studies that employed this paradigmdid not localize the task-relevant stimulus-specific regions toexamine for neural activation related to stimulus processing dur-ing task preparation (Brass & von Cramon, 2002, 2004; Gruberet al., 2006; Luks et al., 2002; Shi et al., 2010; Sohn et al., 2000;but see Wylie et al., 2006). These studies consistently revealed afronto-parietal network to be activated in cued task-switching,including the lateral frontal cortex, the pre-supplementary motorarea, and the inferior parietal lobule during task preparation (Brass& von Cramon, 2002, 2004; Gruber et al., 2006; Luks et al., 2002;Shi et al., 2010; Sohn et al., 2000). Some of these studies also re-ported preparatory activation in posterior brain regions in extras-triate cortical areas (e.g., fusiform gyrus, inferior, superioroccipital, and the lingual gyri) and striate cortical areas (e.g., calca-rine sulcus). However, it is not clear from these reports whetherthe observed posterior brain activations relate to sensory processesinvolved in the encoding of the task cue after its presentation, or tospecific preparation for the upcoming task. An exception is thestudy of Wylie et al. (2006), who required participants to switchbetween a motion and a color task; however, this study yieldedonly partial evidence of preparation for the critical stimuli for thecolor (but not the motion) task, and for rather long preparationperiods (2 or 4 s), which makes it difficult to generalize the findingsto other task situations with shorter preparation times.

There is good evidence for the existence of posterior stimulus-specific regions that are sensitive to specific stimulus informationsuch as faces, houses, motion, or numbers. While these regions

may be activated by the presentation of the region-specific stimuli,it has been shown that their degree of activation may additionallybe modulated by selective attention or demands to imagine,expect, or hold the stimulus in memory (e.g., Chelazzi, Miller,Duncan, & Desimone, 1993; Esterman & Yantis, 2010; Fuster &Jervey, 1981; Lepsien & Nobre, 2007; Miller, Li, & Desimone,1993; Miller & Desimone, 1994; Miyashita & Chang, 1988; O’Cravenand Kanwisher, 2000; Puri, Wojciulik, & Ranganath, 2009; Serenceset al., 2004; Stokes, Thompson, Nobre, & Duncan, 2009; Yantis &Serences, 2003). For example, Serences et al. (2004) presented par-ticipants with a stream of faces with overlapping houses and askedthem to selectively attend to either the face or the house for a cer-tain period of time. Activity in the house-specific region was foundto be increased when participants were asked to pay attention tohouses as compared to faces, and vice versa. While this patternshows that activation in posterior stimulus-specific brain regionsmay indeed be modulated by the allocation of attention to the rel-evant stimulus or object, it is not conclusive as to whether prioractivation occurs during the preparation for a task in the task-switching paradigm. In this paradigm task, preparation may startat different points in time, for example, immediately upon presen-tation of the task cue, at some time before, or only at the onset of thetarget stimulus. Because there is no specific instruction to, forinstance, actively imagine the upcoming stimulus, whether pre-acti-vation of posterior brain regions occurs at all and, if it does, at whichpoint in time is likely to depend on whether or not participants actu-ally intend to prepare for the task in advance (Shi et al., 2010).

On this background, the present study was designed to investi-gate whether pure preparation for an upcoming task induces cue-related changes (commencing with or after the task cue) of neuralactivity in stimulus-specific regions even prior to the presentationof the actual target stimulus. To examine this, we employed a facediscrimination and a number comparison task in a cued task-switching paradigm in which the upcoming task was indicatedby a symbolic pre-cue. The fusiform face area (FFA) is known tobe associated with the processing of faces, relative to other stimulisuch as houses (e.g., Kanwisher et al., 1997); and a region in thehorizontal segment of the intraparietal sulcus (IPS), the IPSnum,is systematically activated whenever numbers are manipulated,independently of number notation (e.g., ‘one’ or ‘1’; Dehaeneet al., 2003). We identified each individual participant’s task-relevant region in the FFA and IPSnum and analyzed the activitychanges in these regions both during the time interval betweenpre-cue and target onset (i.e., the task preparation period) andduring the task execution period. Given that task preparation pro-cesses are thought to involve task-relevant stimulus processing(Kiesel et al., 2010), we expected selective pre-activation patternsin the face- and number-specific brain regions, respectively.

We were able to analyze the neural activation specifically re-lated to the task preparation period by presenting different typesof trials, namely: cue–target trials and cue-only trials, in randomlyintermixed fashion (e.g., Brass & von Cramon, 2002, 2004; Corbettaet al., 2000, 2005; Shi et al., 2010; Weissman, Gopalakrishnan,Hazlett, & Woldorff, 2005). Most of the trials (see Section 2) werecue–target trials in which participants responded to the targetdepending on the task cue. However, the sequence of trials also in-cluded some (cue-only) trials on which only the pre-cue was pre-sented without any target. Because participants did not know inadvance whether or not a target would follow the cue, they hadto prepare for the task on every trial, including cue-only trials. Con-sequently, analysis of the activation on cue-only trials (comparedwith null trials, i.e., trials in which no target stimulus but onlythe central fixation point was presented) permitted the activationrelated to task preparation to be calculated. In particular, weanalyzed the activation in the face- and number-specific regionsduring the task preparation period, to examine whether or not

Y. Shi et al. / Brain and Cognition 87 (2014) 39–51 41

the activation in the respective stimulus-specific region would beselectively enhanced while preparing for the task.

Execution-related processes are revealed by contrasting activitybetween cue–target and cue-only trials. Because the activation oncue–target trials consists of both activation related to task prepara-tion and activation related to task execution, subtracting the cue-related activation from the activation on cue–target trials wouldisolate the execution-related activation. We analyzed the face-and number-specific regions’ activation in the task execution per-iod, to examine whether or not the activation in the respectivestimulus-specific region would be selectively enhanced while per-forming the task.

What must also be taken into account is that the activation inposterior brain regions during preparation for an upcoming taskmay not only be influenced by processes related to the active prep-aration for this (new) task. Rather, there may also be residual activ-ity relating to processes on the preceding trial, which mayinfluence the current-trial activity in posterior stimulus-specificbrain regions through carry-over mechanisms (e.g., Yeung,Nystrom, Aronson, & Cohen, 2006). Behavioral evidence shows thatas a result of ‘task set inertia’, the preceding task settings may con-tinue to persist during processing of the current (changed) task(Allport, Styles, & Hsieh, 1994; Wylie & Allport, 2000; Yeung &Monsell, 2003a,b). If residual activation from the previous trialwere indeed affecting current-trial activation, then the preparatoryactivation of a certain task-stimulus-specific region on the currenttrial should be modulated by whether or not the preceding taskwas the region-specific task. To illustrate, consider the FFA: if thepreceding task was a face task, rather than a number task, thenresidual activation from the preceding task would enhance FFAactivation by carry-over (and analogously for the IPSnum regionif the preceding task was a number task). To address this, we exam-ined whether task-specific prior activation would still be observedeven if the preceding task was different from the current task.

In addition, we explored whether or not task preparationengenders an anticipatory modulation of the functional connectiv-ity between posterior stimulus-specific regions and other brain re-gions, by examining for Psychophysiological Interactions (PPI;Friston et al., 1997). Previous studies had already demonstratedchanges in functional connectivity as a result of participants oper-ating cognitive control in Stroop (Egner & Hirsch, 2005a) and dual-task situations (Stelzel, Brandt, & Schubert, 2009). However, withregard to the cued task-switching paradigm, there is as yet (toour knowledge) no evidence for an anticipatory modulation ofthe functional connectivity between task-relevant brain regions.

2. Methods

2.1. Participants

Fourteen healthy right-handed volunteers with normal or cor-rected-to-normal vision took part in the experiment (six males;age range 19–33 years, mean: 24.9 years, SDV: 4.4 years) afterobtaining informed consent according to the Declaration of Hel-sinki. Each participant was paid 20 €. The data of two participantswere excluded from further analysis owing to their exceedinglyhigh error rates (>20%). Thus, ultimately, the data sets of 12 partic-ipants were available for analysis (six male; age: mean [±standarddeviation] 24.4 [±4.6] years, range 19–33 years).

2.2. Task procedure

2.2.1. Procedure for the main taskThe task to be performed by the participants was either gender

discrimination (female vs. male) or number comparison (larger vs.

smaller than five, ‘large’ vs. ‘small’ in short). There were three typesof trials: two of them were event trials, namely, cue-only andcue–target trials; the other type was null trials. Each event trialbegan with the presentation of a cue for a fixed duration of1200 ms, which was considered to be sufficiently long to permittask preparation (e.g., Rogers & Monsell, 1995; Meiran, 1996). Foraddressing a question not directly related to the primary focus ofthe present study, we used two kinds of cues, both displayinginstruction information about the up-coming task: task cues andrule cues (Fig. 1c). In addition to specifying the task to beperformed, the latter cues provided precise information aboutthe stimulus–response (S–R) mapping required for performingthe task correctly (e.g., for the face task, the task rule information[male ? left button; female ? right button] was given explicitly;please refer to Fig. 1 for the exact protocol). Shi et al. (2010) hadshown that rule cues can be more efficient in evoking rule activa-tion during task preparation than task cues. Given this, a compar-ison between the two cue conditions was expected to beinformative about whether or not activity changes in posteriorstimulus-specific regions are additionally affected by the ruleinformation specified in the cue display. On cue-only trials, cue off-set was followed by a blank black screen (rather than a face/num-ber word stimulus) which lasted for 600 ms, and there was no needfor participants to make a response (Fig. 1b). In contrast, on cue–target trials (Fig. 1a), the cue was followed by a target presentedfor 600 ms. The target was a picture of a face with a number wordlocated in the region of the depicted person’s nose. Two male andtwo female face pictures were used (Collection of Facial Images:Faces94; http://cswww.essex.ac.uk/mv/allfaces/faces94.html); thenumber could be ‘‘EINS’’ (one), ‘‘ZWEI’’ (two), ‘‘ACHT’’ (eight), or‘‘NEUN’’ (nine). As a result, 16 face-&-number pictures were em-ployed as target stimuli. The stimuli (cue stimuli and target stim-uli) were presented on a black background in the center of thescreen and subtended 5� of visual angle. Participants responded,as fast and as accurately as possible, to either the face or the num-ber, depending on the task instruction provided by the cue. Partic-ipants made a two-alternative forced-choice response using eithertheir left or their right index finger, with response sets counterbal-anced across participants. For half the participants, the S–Rmapping rule was male ? left, female ? right (face task) and,respectively, large ? left, small ? right (number task). This map-ping was reversed for the other half of the participants. Responsetimes (RTs) were recorded only if they were faster than 1800 ms.On null trials, only the central fixation marker was presented for1200 ms, followed by a 600-ms black screen.

After the 600-ms black screen (on null or cue-only trials) or theoffset of the target picture (on cue–target trials), respectively, therewas a variable interval of 1800, 2500, 3100, 3900, or 4600 ms be-fore the next trial started. The next trial could then either be anevent trial or a null trial. In total, there were 200 cue-only trials(100 face and 100 number tasks, with the same number of rulecue and task cue trials for each task; e.g., the face task rule cue con-dition included 50 cue-only trials), 280 cue–target trials (140 faceand 140 number tasks, again with the same number of rule cue andtask cue trials for each task; e.g., the face task rule cue conditionincluded 70 cue–target trials), and 140 null trials.

Since one study aim was to examine for possible residual acti-vation from the preceding trial, the factor ‘task transition’ was alsoconsidered. Depending on the instruction cue presented prior tothe target, the current trial was classified as a repetition trial ifthe current task was identical with that on the previous event trial,independently of whether the trial (i.e., current or previous) was acue-only trial or a cue–target trial. Similarly, the current trial wasclassified as a switch trial if the current task was different from thepreceding one independently of whether the trial was a cue-onlyor a cue–target trial. We presented equal numbers of task switch

Fig. 1. Illustration of the experimental procedure and details of the cue displays. Panel (a) panel shows a cue–target trial (of the number task, rule-cue condition). Panel (b)shows a cue-only trial (of the number task, task-cue condition). In the bottom panel (c), the rule-cue and task-cue displays are illustrated. In both cue conditions, theupcoming task was indicated by the German words ‘‘ANZAHL’’ (number) and ‘‘GESICHT’’ (face), respectively. In the rule-cue condition (upper row), additional informationindicated the assignment of the response keys to the stimulus categories male and female in the gender task, and larger and smaller in the number task.

42 Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

and repetition cue-only and cue–target trials for both the face andnumber tasks.

In sum, there were three factors in the main task: task (numbervs. face), cue type (rule cue vs. task cue), and task transition(switch vs. repetition). For the resulting eight conditions, therewere each 25 cue-only trials and 35 cue–target trials. Task orderwas pseudo-randomized. All event trials (n = 480) and null trials(n = 140) were assigned to four runs each lasting 12 min 40 s. Par-ticipants took a short break, of one or two minutes, between tworuns. At the beginning of each run, the word ‘‘Achtung’’ (Attention)was presented for 2 s to remind participants of the tasks to beperformed.

2.2.2. Task procedure for the localization taskIn order to identify the individual task-relevant regions, FFA and

IPSnum, participants performed an independent localization taskafter the main task. In this task, participants responded to thepicture containing either only a face or only a number word inalternating blocks of trials without presentation of a pre-cue. Par-ticipants performed 18 alternating task blocks to localize the FFAand the IPSnum, respectively. Each block consisted of 8 trials, witha trial duration of 2 s. Accordingly, the resulting whole run lasted9 min, 36 s. On each trial, stimulus duration was 600 ms (as inthe main experiment). In the face blocks, participants performedthe face discrimination task, and in the number blocks they per-formed the number discrimination task, using the same responserules as in the main experiment. There were four face pictures (2female and 2 male) and four number words (‘‘EINS’’, ‘‘ZWEI’’,‘‘ACHT’’, ‘‘NEUN’’), each of which also appeared in the main task.Importantly, in the localization task, the target pictures were

presented as sole targets (i.e., the stimuli displayed only a face oronly a number). Accordingly, target stimuli could be presentedwithout prior cues (specifying the task) in the localizer tasks, andparticipants responded blockwise to the presented face or, respec-tively, number stimuli. Larger activity in the FFA was expected inthe face compared to number localization task; and vice versa, lar-ger activity was expected in the IPSnum in the number comparedto the face localization task (see section Determination of ROIs be-low for the methodological details of defining the individual faceand number ROIs).

2.3. fMRI measurement

Imaging was performed employing a SIEMENS TRIO 3-Teslascanner at the Klinikum Großhadern (Institute for Clinical Radiol-ogy), Ludwig-Maximilians-Universität München. T2⁄-weightedecho-planar images (EPI) with blood oxygenation level-dependentcontrast were acquired (TR = 1500 ms, TE = 30 ms, flip angle = 80�,matrix size = 64 � 64 voxels). Twenty-three axial slices (thick-ness = 4 mm, spacing = 1 mm) were acquired parallel to theAC-PC plane, covering the whole cortex. The order of acquisitionof the slices was interleaved. The first four volumes (dummy vol-umes) were discarded because of possible instabilities in the mag-netic field at the beginning of a run. Stimuli were displayed on aback-projection screen mounted in the bore of the magnet behindthe participant’s head, by using an LCD projector. Participantsviewed the screen by wearing mirror glasses. The four runs ofthe main task were scanned first; then the run of the localizationtask was scanned.

Y. Shi et al. / Brain and Cognition 87 (2014) 39–51 43

2.4. fMRI data analysis

2.4.1. Preprocesses and data modelingPreprocessing of all functional images (of main task and locali-

zation task) was carried out using SPM5 (Wellcome Department ofCognitive Neurology, London, UK). Images of the main task wereinterpolated in time to account for the differences in acquisitiontime between slices (slice timing). All images were spatiallyrealigned to the first volume for head movement correction, andthen normalized into MNI space (images were re-sampled to2 � 2 � 2 mm3 isotropic resolution) with default normalizationestimation. The data were then smoothed with a Gaussian kernelof 8 mm full-width half-maximum to account for inter-participantanatomical variability.

Then for the main task, the image data were modeled by apply-ing a general linear model (Friston et al., 1995). In event-relatedsingle-participant analyses, the 8 cue-only and the 8 cue–targetconditions – resulting from the factorial combination of the twotask types (face vs. number), two cue types (rule cue vs. taskcue), and two types of task transition (switch vs. repetition) – weremodeled. These 16 events were locked with the onsets of the (ruleor task) cues. In addition, the null trials, all error trials, and theperiods with the instruction word ‘Attention’ at the beginning ofeach run, were modeled separately. The resulting 19 conditionswere modeled as events of zero duration; they were convolvedwith the hemodynamic response function (HRF) to generate 19corresponding regressors, and then beta values of these regressorswere estimated according to the ordinary least-squares (OLS)method.

As activation parameters for the preparation period activation,we calculated the beta values of the cue-only trials minus the betavalues for null trials; as parameters for the execution-related activa-tion, we calculated the beta values for the cue–target trials minusthe beta values for their cue-only trials (e. g., Shi et al., 2010).

2.4.2. Region(s)-of-Interest (ROI) analysisThe FFA, typically the right side, has been shown to be consis-

tently involved in the processing of faces (e.g., Kanwisher, 2000;Kanwisher et al., 1997). In numerous earlier studies, the bilateralIPSnum has been shown to be consistently involved in theprocessing of number categories; however the right-hemisphereactivation was stronger than that in the left hemisphere in thenumber comparison task (e.g., Chochon, Cohen, van de Moortele,& Dehaene, 1999; Pinel, Dehaene, Riviere, & Le Bihan, 2001). Giventhis, we identified the individual task-relevant ROIs in the right FFAand right IPSnum.

The precise ROIs for each participant were determined based onthe localization task. For this task, all the face and, respectively,number task trials were modeled as events; next, these two condi-tions were convolved with the HRF to generate the two regressors,and the beta values of the regressors were estimated according tothe OLS method. Then, for the whole-brain group analysis, one-sample t-tests of contrast maps across participants (random-effects model treating participants as a random variable) were cal-culated to ascertain whether the differences between conditionswere significant. The contrast ‘face – number’ and the reversedcontrast ‘number – face’ were calculated to find the group activitypeaks in the right FFA and right IPSnum, respectively; a statisticalthreshold of p < 0.05, FDR corrected, was used, with 10 continuousvoxels. Starting from the group peaks, we then localized individualface-specific and number specific-regions as ROIs in the right FFAand right IPSnum, respectively; for determining these individualROIs we used a more relaxed statistical threshold of p < 0.001,uncorrected, with 10 continuous voxels.

We determined the nearest peak (relative to the correspond-ing group peak) per participant (for the individual contrasts of

‘face – number’ and ‘number – face’) as the center of the individualcube ROI mask (6 mm side length). From the voxels covered bythese masks, we extracted the parameter estimates from the timeseries of every individual participant for all 16 task conditions(produced by the beta values). The 8 activation parameters ob-tained for the preparation period, which were of most interestfor the current questions at issue, were examined by an analysisof variance (ANOVA) with the factors task type (face vs. number),cue type (rule cue vs. task cue), and task transition (task switchvs. task repetition). The 8 parameters for the cue–target trials, afterfollowing subtraction of the corresponding cue-only-trial parame-ters to provide the parameters for execution period activation,were also subjected to an ANOVA with the factors task type, cuetype, and task transition.

2.4.3. PPI analysisWe conducted a Psychophysiological Interaction (PPI) analysis

(Friston et al., 1997) to examine the functional connectivity be-tween posterior and other brain regions (see also Egner & Hirsch,2005a; Stelzel et al., 2009). The aim of a PPI analysis is to explainthe neural responses in one brain region in terms of the interactionbetween the neural responses in another brain region and a spe-cific psychological context. In the present study, we investigatedwhether a given posterior task-relevant region (FFA or IPSnum)was differentially coupled with other brain regions during thepreparation for its relevant and, respectively, the irrelevant task.

We used the FFA and IPSnum ROIs of each participant as ‘‘seedregions’’ and extracted the time courses from these seed regions(with SPM’s VOI module). Separately for the two regions, SPM’sPPI module was used (i) to obtain the seed regions’ neural signalsby de-convolving the extracted time courses with HRF; (ii) thesede-convolved time courses and the respective psychological vari-able (for FFA: face compared to number task preparation; for num-ber: number compared to face task preparation) were used togenerate the psychophysiological interaction term. Then, for eachseed region, all three variables generated by the PPI module (de-convolved time course in seed region, psychological variable, andthe interaction term) were entered into a new general linear mod-el. This way, we could identify regions that were significantly cor-related with the activity in the sensory seed regions depending onwhether participants prepared for a seed-region-relevant or anirrelevant task. In particular, there might be enhanced functionalconnectivity between FFA and another brain region during thepreparation for the face, compared to the number, task, while theremight be enhanced functional connectivity between IPSnum andother brain regions during the preparation for the number, com-pared to the face, task. A statistical threshold of p < 0.001, uncor-rected, was used, with an extent threshold of 10 voxels. Thisthreshold is commonly used in studies of cue-related processingand PPI analyses for exploratory purposes (see, e.g., Egner & Hirsch,2005b; Ruff & Driver, 2006; Wendelken, Bunge, & Carter, 2008).

3. Results

3.1. Behavioral results

Mean RTs and error rates were submitted to separate 2 � 2 � 2repeated-measures ANOVA, with the factors task type (face ornumber), cue type (rule cue or task cue), and task transition(switch or repetition) (see Fig. 2).

For RTs, we did not find a significant effect for the factor tasktype (F(1,11) = 0.1, p = 0.76), nor any significant interaction be-tween the factor task type and the other two factors (bothFs < 0.22, ps > 0.65). Therefore, the data of the two tasks weremerged; see Fig. 2 for the (merged) data. RTs showed a tendency

Fig. 2. Reaction times (RT) as a function of task transition and cue type (left graph); error rates as function of task type, task transition, and cue type, separately for the faceand the number task (middle and right graphs, respectively). Error bars show one standard error of mean.

44 Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

for being faster in the rule cue than in the task cue condition (maineffect of cue type, F(1,11) = 4.30, p < 0.06, the rule cue benefit was18 ms), which indicates that participants effectively utilized therule cue information during the preparation period. In addition,RTs were significantly slower for task switch than for taskrepetition trials (main effect of task transition, F(1,11) = 10.70,p < 0.01), with switch costs amounting to 22 ms on average.Finally, the interaction between cue type and task transition wasnon-significant (F(1,11) = 1.64, p = 0.13).

For error rates, no significant effect was found for the factorstask type (F(1,11) = 0.96, p = 0.35) and task transition(F(1,11) = 1.94, p = 0.19).

A significant effect was found for the factor cue type (F(1,11) =12.1, p < 0.005): the error rate was lower in the rule cue comparedto the task cue condition (3.8% vs. 5.3%), indicating that the addi-tional rule information provided by the rule cue helped to reduceerrors. The interaction between task type and cue type was signif-icant (F(1,11) = 11.2, p < 0.01). Further analyses with separatet-tests revealed a significant benefit for the rule cue compared tothe task cue condition during performance of the face task (meanbenefit of 3%, t(11) = 5.47, p < 0.0001), but not of the number task(mean benefit of 0.1%, t(11) = 0.12, p = 0.90). This indicates thatparticipants utilized the rule cue information more effectively forthe preparation of the face task, as compared to the number task.

3.2. Imaging results

We analyzed activity changes in the right FFA and IPSnum ROIsand the changes of their functional connectivity during the taskpreparation period. In addition, we analyzed activation changesin the execution period and the possible influence of residual acti-vation from the preceding task. Considering the limited samplesize of the study, all these analyses were conducted after checkingwhether our data are reliable in terms of in replicating the typicalpattern of findings in cued task-switching paradigms, namely,switch-related brain activation and the general task preparationnetwork (e.g., Brass & von Cramon, 2002, 2004; Dove et al., 2000;Gruber et al., 2006; Luks et al., 2002; Shi et al., 2010; Sohn et al.,2000). Consistent with previous findings, right inferior frontalgyrus, bilateral precuneus, right superior parietal lobule, bilateralcingulate gyrus, right lentiform nucleus, and thalamus exhibitedhigher activation in the task switch vs. repeat conditions ofcue–target trials. Furthermore, the general preparation network,including lateral frontal cortex, pre-supplementary motor area,and inferior parietal lobule, was activated during the cue intervalin the present study. Because the present design did not includea short (e.g., 300-ms) preparation interval, we were unable toassess task preparation by comparing long vs. short intervals.

However, the fact that the general preparation network was acti-vated points to successful preparation actually taking place duringthe preparation interval in the present experiment.

3.2.1. Determination of ROIsWe calculated the contrasts of ‘face – number’ and ‘number –

face’ for the data of the localization tasks and determined the cor-responding ROIs by focusing on the group peaks in the right FFAand bilateral IPSnum, respectively.

For the individual face-task relevant ROIs, the group peak in theright FFA in the ‘face – number’ contrast was located at MNI coor-dinates (46, �44, �24), (Fig. 3a). All twelve participants showedsignificant activation in the ‘face – number’ contrast near this peak(mean distance = 11.6 mm). The nearest individual peak was iden-tified for each participant, then all significant activation voxelswithin a cube mask of 6 mm side length were selected to definethat participant’s specific ROI for face. Next, the activations in theseROIs were extracted for the subsequent ROIs analysis.

For the individual number-task-relevant ROIs, the group peak inthe right IPSnum in the ‘number – face’ contrast was located atMNI coordinates (56, �30, 50), (Fig. 3b). Eleven of the twelveparticipants showed significant activation in the ‘number – face’contrast near this peak in the right IPSnum (mean distance =16.5 mm). The nearest individual peak to the right IPSnum wasdetermined for those eleven participants, and then all significantactivation voxels within a 6-mm side length cube mask were se-lected to define a given participant’s specific ROI for number pro-cessing. Next, the activations in the eleven right-sided ROIs wereextracted for the subsequent analysis. Note that the only one par-ticipant who did not exhibit number dominant activation in theright IPSnum showed such activation in the left IPSnum. We alsoextracted this participant’s data from the left IPSnum and checkedthe pattern of results: it does not change if the data of this partic-ipant are included in the data set.

3.2.2. Activation in the preparation periodParticipants’ individual activation parameters for cue-only trials

were subjected, separately for the right FFA and the right IPSnumregions, to 2 � 2 � 2 repeated-measures ANOVAs with the factorstask type (face or number), cue type (rule cue or task cue), and tasktransition (switch or repetition). For both regions, there was a sig-nificant main effect of task type on the activation values during thepreparation period; this is illustrated in Fig. 4. In particular, in theFFA, preparation-period-related activation was larger for the facetask compared to the number task (F(1, 11) = 6.25, p < 0.05,çp

2 = 0.362); conversely, in the right IPSnum, activation was largerfor the number task compared to the face task (F(1,10) = 5.56,p < 0.05, çp

2 = 0.357). No significant main effect of cue type was

Fig. 3. Panels (a) and (b) show group activation in the localization runs (p < 0.05, FDR corrected, with 10 continuous voxels). Illustrated are the peaks of the FFA and IPSnumactivations in MNI coordinates (for details, see Section 2). Panel (c) examples of target pictures in the localization runs: face task (left) and number task (right).

Fig. 4. Right FFA and IPSnum’s activity in preparation period for the relevant and irrelevant task. Preparation period activation was detected by calculating the beta values ofthe cue-only trials minus the beta values for null trial. Error bars show one standard error of mean (only positive).

Y. Shi et al. / Brain and Cognition 87 (2014) 39–51 45

found for either ROI (the FFA and IPSnum regions) (both Fs < 0.33,both ps > 0.5). Task transition (switch vs. repetition) had no signif-icant effect on the activation in either the right FFA or the right IPS-num ROIs (both Fs < 1.27, both ps > 0.2). For the interactions, wefound a significant interaction between current task type and tasktransition for the FFA region (F(1,11) = 10.00, p < 0.01, çp

2 = 0.476).Other interactions were not significant (all Fs < 3.12, all ps > 0.1).

In more detail, for both ROIs, we checked whether or not theyshowed selective enhancement during the preparation for the dif-ferent tasks, and then we examined for possible effects of residualactivation and of task transition on the activation in the currenttrials.

3.2.2.1. Preparation for the task. As mentioned, there was a signifi-cant main effect of task type on the activation values during thepreparation period for both regions (both ps < 0.05). In order to fur-ther test whether FFA and IPSnum showed increased activity com-pared to null trials exclusively while participants prepared for theregion-specific relevant task, but not to the other, region-non-specific task, separate follow-up t-tests were performed. Thesetests showed that in the FFA region, both the task cue and the rulecue elicited significant activity, compared to null trials, during thepreparation for the face task (both ts > 1.9, both ps < 0.05); by con-trast, no significant FFA activity was found during the preparationfor the number task in either cue type condition (both ts < 1.34,

46 Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

ps > 0.2). In the IPSnum region, both the rule cue (t(10) = 1.77,p = 0.05) and the task cue (t(10) = 1.58, p < 0.08) elicited or tendedto elicit increased activation compared to null trials during thepreparation for the number task; by contrast, the activation valuesin the IPSnum were not significantly increased during the prepara-tion for the face task, in either cue type condition (both ts < 1.08,ps > 0.3). Thus, with regard to the task information, both types ofcue (rule cue and task cue) elicited prior activation in the ROI ofthe task-relevant stimulus, whereas the additional rule informa-tion in the rule, as compared to the task, cue did not yield any addi-tional activation in the ROI of the task-relevant stimulus.

These results indicate that the FFA and IPSnum regions can beselectively enhanced during the preparation period for the respec-tive relevant task. Furthermore, the amount of preparatory activa-tion in posterior stimulus-specific brain regions is not influencedby the type of cue (rule cue or task cue), which may indicate thatthe rule information is not represented in the stimulus-specific re-gions; rather, it is more likely represented in the PFC and/or theparietal cortex (Bode & Haynes, 2009; Bunge, Kahn, Wallis, Miller,& Wagner, 2003; Montojo & Courtney, 2010; Sakai & Passingham,2003, 2006; Woolgar, Thompson, Bor, & Duncan, 2011).

3.2.2.2. Effects of residual activation. The residual activation fromthe preceding task is illustrated in Fig. 5. We found a significantinteraction between current task type and task transition for theFFA region (F(1,11) = 10.00, p < 0.01), which reflects an influenceof the residual activation on the current trial. Further t-tests re-vealed that when the current task was a face task, the FFA tendedto show stronger activation in the task preparation period whenthe previous task was also a face task, rather than a number task(repetition > switch, t(11) = 1.75, p < 0.06); note, though, that whenthe current task was the number task, the FFA showed also stron-ger activation in the preparation period when the previous taskwas a face task (switch > repetition, t(11) = 2.96, p < 0.01). In otherwords, no matter which task was to be performed on the currenttrial (face or number), the right FFA showed increased activationduring the preparation period when the preceding task had beena face task. This is likely due to residual activation from the preced-ing face task, in spite of the current task type (Fig. 5, left). Theexamination of the interaction between task type and task transi-tion in the right IPSnum revealed an activation pattern that was

Fig. 5. Activation in the preparation period as a function of preceding and current task tytask is a number task and the current task a face task. Error bars show one standard er

similar to that exhibited by the FFA; however, the interactionwas statistically non-significant (F(1,10) = 0.84, p = 0.38) (seeFig. 5, right).

We also examined the correlation between the amount of neu-ral activity and behavioral performance during task switching.Eight variables were used for representing neural activity: FFAand IPSnum activation in the task preparation period for the faceand the number task, respectively (yielding 2 � 2 = 4 variables);and the difference between task switch and repeat trials for thetwo tasks in FFA and IPSnum, respectively (accounting for theother 2 � 2 = 4 variables). As parameters for behavioral perfor-mance, we used four parameters: mean reaction time and switchcosts for the face and number tasks, respectively. Correlations werecalculated between each one of the eight neural activity variablesand each one of the four performance parameters.

These analyses revealed only one correlation to be significant:that between the activation in the FFA_number task_(switch-re-peat) (Fig. 5, the 2nd two-bars group) and the switch costs in thenumber task (Pearson correlation coefficient r = 0.606, p < 0.05)This finding indicates that it was the more difficult to switch (fromthe preceding face) to the current number task the greater theresidual activation (from the preceding face task) that existed inFFA. Importantly, this finding is consistent with an observationby Yeung et al. (2006), that switch cost magnitude correlates sig-nificantly with activity in the (after the change) task-irrelevantposterior brain region of preceding trial.

Finally, it is worth noting that neural activity in the correspond-ing ROIs was nevertheless significantly increased even if partici-pants prepared for a switch trial. This was revealed by anadditional analysis in which we extracted the right FFA’s activationon face switch trials (i.e., during preparation for the face task whenthe preceding task was a number task) and compared this activa-tion with that on null trials: the resulting activation was still signif-icant (t(11) = 2.06, p < 0.05). Similarly, when the preceding taskwas a face task, the activation in the right IPSnum during the prep-aration for the upcoming number task was still significantly higherthan that on null trials (t(10) = 1.83, p < 0.05). These latter effectsindicate that the task-specific prior activation in the right FFAand the right IPSnum was induced by active preparation processesfor the respective relevant task, rather than being attributablesolely to residual activity from the previous trial.

pe; the number task is denoted by N and the face by F; NF means that the precedingror of mean (only positive).

Fig. 6. Functional connectivity between activation in posterior ROIs (regions-of-interests) and other (anterior) brain regions in the preparation period (psychophysiologicalinteraction analysis; for details, see text). Panel (a) Stronger functional connectivity between right FFA and rACC (peak at MNI �4, 30, �2) was found during preparation forthe face, compared to the number, task. Panel (b) Stronger functional connectivity was found between right IPSnum and right anterior part of SFG (peak at MNI 22, 50, �8)during the preparation for the number, compared to the face, task.

Y. Shi et al. / Brain and Cognition 87 (2014) 39–51 47

3.2.2.3. Task transition effects. Task transition (switch vs. repetition)had no significant effect on the activation in either the right FFA orthe right IPSnum ROIs (both Fs < 1.27, both ps > 0.2). In addition tothe ROI-based analysis of task transition effects, we examined alsowhether brain regions other than the right FFA and the IPSnumwould show larger activity on switch compared to repeat trials,by performing a whole-brain analysis (task switch vs. task repeat,p < 0.001, uncorrected, with 10 continuous voxels.). This analysisrevealed larger activity during the preparation for switch com-pared to repeat trials in the left medial superior frontal gyrus (meS-FG, MNI (�10, 14, 44)), left medial frontal gyrus (meFG, MNI (�8, 0,60)), and right superior temporal gyrus (STG, MNI (52, �34, 6)).

3.2.3. Execution-related activationThe parameters for the execution-related activation in the right

FFA and, respectively, the right IPSnum were subjected to separate2 � 2 � 2 repeated-measures ANOVAs, with the factors task type(face vs. number), cue type (rule cue vs. task cue), and task transi-tion (switch vs. repetition). No main effect of task type was foundin either region (all Fs < 1.52, ps > 0.2); that is, unlike the period ofpreparing for the task to be performed, there was no selectiveenhancement of activation in task-relevant stimulus processing re-gions while actually executing the task. Further t-tests disclosedsignificant additional activity compared to null trials in the rightFFA and the right IPSnum for both component tasks (i.e., the faceand the number task) and for the two cue conditions (i.e., rule cuesand task cues) (all ts > 2.47, ps < 0.05). This finding likely reflectsthe fact that the current target display contained both face andnumber stimulus information, giving rise to increased activationsimultaneously in both task-relevant regions during the executionof each individual task. Furthermore, the observed pattern of anundifferentiated increase of activation during task execution inthe face and number task regions may indicate that the task-rele-vant region had already been sufficiently up-modulated during thetask preparation period, doing away with a need for an additionaltask-specific activation increase during task execution. Anotherpossibility would be the assumption that the resolution was occur-ring ‘downstream’ in processing – for example, in response-relatedareas.

3.2.4. PPI analysisTo assess the functional connectivity between the activation in

posterior task-relevant brain regions and other brain regions dur-ing task preparation, we conducted a PPI analysis (see Fig. 6). For

the number-task-relevant region, the right IPSnum, this analysisrevealed increased functional connectivity with the right anteriorSFG (MNI coordinates 22, 50, �8) during the preparation for thenumber, compared to the face, task (p < 0.001). With a lower signif-icance threshold (p < 0.005), a further important region in the leftinferior parietal lobule (MNI coordinates �58, �32, 50) was foundto show increased functional connectivity to the right IPSnum dur-ing the preparation for the number, compared to the face, task. Forthe face-task-relevant region, the right FFA, increased functionalconnectivity was revealed during preparation for the face, as com-pared to the number, task with the rostral anterior cingulatedcortex (rACC; MNI coordinates �4, 30, �2). Lowering the signifi-cance criterion to p < 0.005 did not change the PPI data patternwith respect to the FFA region.

4. Discussion

In the present study, we found that the neural activation instimulus-specific posterior brain regions is modulated during thepreparation for a cued-face and, respectively, a cued-number task(presented in random order) in a cued task-switching paradigm.Activity in the right FFA was significantly increased, compared tonull trials, in the preparation period for the face task, and the func-tional connectivity between the right FFA and the rACC was in-creased. Analogously, activity in the right IPSnum region wassignificantly increased, compared to null trials, in the preparationperiod for the number task, and the functional connectivity be-tween the right IPSnum region and the right anterior SFG was in-creased. These findings indicate that even without presentationof the task-relevant stimulus, task preparation can modulate theneural signals within specific posterior regions, and these regions’connectivity with other brain regions, which are related to the pro-cessing of the task-relevant stimulus. The results show further thatin addition to the preparatory modulation, there is another factorthat can influence prior activation in task-relevant posterior brainregions, namely: (residual) activation from the preceding task-rel-evant posterior brain region persisting into the preparation periodfor the current trial in the right FFA and tending to persist in theright IPSnum.

Thus, both preparatory modulation and residual activationshaped the activation pattern in the current task-relevant, andtask-irrelevant, posterior regions: activation in the current task-relevant, as compared to the task-irrelevant, region was enhancedby preparatory modulation; at the same time, residual activation

48 Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

from the preceding task set persisted to influence the activation inthe relevant posterior region.

4.1. Preparatory modulation in posterior task relevant stimulusspecific regions

Previous studies had shown that the presentation of certainspecific stimuli can activate posterior stimulus-specific brain re-gions (e.g., Dehaene et al., 2003; Kanwisher et al., 1997; Liuet al., 2010; Tootell et al., 1995; Zeki et al., 1991), and that the de-gree of activation in these regions can be modulated by processesof attentional selection (e.g., Serences et al., 2004). For example, inthe study of Serences et al. (2004), participants were presentedwith ambiguous stimuli, such as pictures of faces with overlaidhouses, and told to attend to either faces or houses for a certainperiod of time; the face-specific region’s activity was found to beincreased while participants had to attend to faces compared tohouses, and vice versa (see also Esterman & Yantis, 2010; Lepsien& Nobre, 2007; O’Craven & Kanwisher, 2000; and others). Thereare studies that investigated the stimulus-specific regions’ activa-tion while no stimulus was physically presented in the relevanttask conditions. In these studies, however, participants were askedeither to imagine the stimulus (e.g., O’Craven & Kanwisher, 2000)or to maintain the stimulus in memory (e.g., Corbetta et al.,2005; Lepsien & Nobre, 2007) for a certain period of time (usuallymore than 10 s).

The results of the present study extend these earlier findingsbecause, during task preparation, no specific stimuli were actuallypresented in the current paradigm and there was no (explicit)instruction to imagine or expect specific stimuli or maintain themin memory. Nevertheless, the presentation of a cue (without pre-sentation of specific stimuli) indicating the up-coming task led rap-idly to pre-activation in posterior stimulus-specific brain regions.These findings show that even without presenting specific stimuli,preparatory attention on its own can bias the activation in theseregions.

In addition, the current findings add to several prior studies thathave pointed to the possibility of preparatory modulation in pos-terior brain areas for certain attention tasks, such as selection ofspatial locations (Corbetta et al., 2000; Kastner, Pinsk, De Weerd,Desimone, & Ungerleider, 1999; Hopfinger et al., 2000; Ress,Backus, & Heeger, 2000; Serences, Yantis, Culberson, & Awh,2004; but see Corbetta et al., 2005). For example, in the study ofHopfinger et al. (2000), a cued spatial-attention task was used,with the cue display consisting of two arrows, one yellow andone blue, pointing in opposite directions. Participants wererequired to covertly orient their attention to a location in the visualhemifield indicated by an arrow of a certain color (e.g., the yellowone). The attentional control centers (e.g., in superior frontal andinferior parietal cortex) were activated by the directional cue inthe task preparation period, and their activations were accompa-nied by activity changes in location-specific posterior brain regions(e.g., right extrastriate-cortex activation was found with left- vs.right-ward pointing cues).

Shulman et al. (1999) found preparatory modulation of featureprocessing in a task in which participants had to discriminate thedirection of coherent motion in visual displays of moving dots,where coherent-motion displays were presented randomized withsome (catch) trials on which no coherent motion was present. Acti-vation in motion-related brain regions (e.g., MT+) was found to beincreased during the preparation period, that is, in response to adirectional arrow pre-cue arrow pointing left or right to indicatethe direction of the coherent dot motion, compared to a neutral-cue (fixation cross) condition.

The present study extends these earlier findings of location-specific modulations and feature-relevant preparation in

single-task situations, by showing that when switching betweentwo different discrimination tasks, the mere preparation for oneor the other task specified by a pre-cue can modulate activity inthe respective stimulus-specific posterior brain regions.

4.2. Modulation of activation in posterior task relevant regions: taskpreparation and task execution

In the current study, selective modulation of activity occurredin both the FFA and the IPSnum specifically during task prepara-tion. However, later on during the task execution period, we didnot find any selective enhancements in either region above the le-vel that had already been reached before. Arguably, this is so be-cause the modulation of activation in posterior task-relevantregions may not necessarily occur exclusively in either the taskpreparation or the task execution period. The specific point in timeat which the modulation may occur and the degree to which par-ticipants prepare during the cue period depend on several factors,such as the time available for preparation, the amount of explicittask information provided by the cue, and participants’ task strat-egies (e.g., Brass & von Cramon, 2002; Gruber et al., 2006; Meiran,1996, 2000; Shi et al., 2010).

Recent neuroimaging studies have shown that the extent towhich the experimental settings allow, or encourage, preparationfor an upcoming task strongly influences the degree to which pre-paratory processes are actually engaged, as well as having a bear-ing on the strength of the processes operating in the subsequenttask execution period (Brass & von Cramon, 2002; Gruber et al.,2006; Shi et al., 2010). For instance, in the study of Gruber et al.(2006), the cue–target interval (CTI) varied between 0 and1500 ms. When the CTI was long (i.e., 1500 ms), a network of fron-tal and parietal brain areas was activated during advance prepara-tion for the upcoming task, and the subsequent processes of taskexecution were associated with activation in areas involved in vi-sual processing and motor execution. By contrast, when the CTIwas too short to permit effective advance preparation, the samenetwork of frontal and parietal brain areas was activated – thoughonly later, during the task execution period. These findings suggestthat the point in time at which the preparation-related control net-work is activated depends on when control is demanded (ratherthan this network being activated exclusively in either the taskpreparation or the task execution period).

Temporal flexibility of modulation processes in posterior brainregions has also been revealed in studies using different paradigms(e.g., Corbetta et al., 2005; Shulman et al., 2002). For instance,Corbetta et al. (2005) employed a matching-to-sample task inwhich the sample picture to be remembered could be either a faceor a place. The test screen, presented after a delay, contained fourpictures including two faces and two places, and participants hadto decide whether or not the sample picture was present. Similarto the current pattern of findings, Corbetta et al. observed neuralactivation in the FFA to be selectively enhanced in the delay (prep-aration) period of the face (as compared to the place) task, but notin the test (task execution) period. In contrast, and different to thecurrent data pattern, no selective enhancement of activation wasfound in the place-related region (parahippocampal place area,PPA) during the task preparation period; rather, an enhancementmanifested only later during the test (task execution) period (Corb-etta et al., 2005).

Taken together, various studies indicate a considerable degreeof flexibility in the timing of task preparation, which is likely tocontribute to the specific patterns of preparatory modulatory influ-ence on neural activity in posterior task-relevant regions. The mod-ulation may not necessarily take place exclusively in either the taskpreparation or the task execution period. Rather, if control pro-cesses are sufficiently effective to induce the requisite modulation

Y. Shi et al. / Brain and Cognition 87 (2014) 39–51 49

of activation in the posterior task-relevant region already duringthe preparation period, there would be no need for (re-) engagingthis modulation in the task execution period, and vice versa. Fur-ther studies are required to examine the particular factors that per-mit the timing of task preparation processes to be controlledprecisely during task performance (Corbetta et al., 2005; Shulmanet al., 2002).

4.3. Functional connectivity during task preparation

Earlier work had shown that the functional connectivity be-tween the activity in posterior stimulus-specific regions and inanterior executive-control regions or other task-relevant regionsmay change during task processing (e.g., Egner & Hirsch, 2005a;Li et al., 2010; Prado, Carp, & Weissman, 2011; Prado & Weissman,2011; Stelzel et al., 2009). With respect to the cued task-switchingparadigm, it was still an open question whether or not task prepa-ration leads to modulations of the functional connectivity betweenthe respective posterior stimulus-specific region and other brainregions.

During preparation for number comparison (as compared to theface discrimination) task, the present findings suggest increasedfunctional connectivity between the right IPSnum and the rightanterior SFG; and between the right IPSnum and the left inferiorparietal lobule at a lower threshold (p < 0.005). This fits well withfindings of previous imaging studies that inferior parietal lobuleand prefrontal cortex are involved in the number comparisontask (e.g., Chochon et al., 1999; Dehaene, Spelke, Pinel, Stanescu,& Tsivkin, 1999; Pinel et al., 2001; Pesenti, Thioux, Seron, & DeVolder, 2000) and that bilateral IPS and anterior portions of theright PFC are critical for processes of approximate calcula-tion (Kucian et al., 2006). Most importantly, however, the presentfindings show that the functional connectivity between the criticalregions for the number comparison task (i.e., right IPSnum, rightanterior SFG, and left inferior parietal lobule) was increased specif-ically during the preparation for the number comparison task. Con-sidering the different functions of these regions, it is tempting tospeculate that they may have played different roles in the currenttask situation. For instance, the bilateral IPS may play a major rolein the representation of numbers (e.g., Dehaene et al., 1999, 2003)and the PFC may implement abstract response strategies requiredfor basic mathematical operations (Bongard & Nieder, 2010).

During the preparation for the face (as compared to the num-ber) task, the functional connectivity between the right FFA andthe rACC was increased. Face perception would not appear to bea process primarily associated with the rACC. However, severalfindings suggest a role of the rACC in emotional processing andsocial awareness/cognition (e.g., Bush, Luu, & Posner, 2000; DeMartino, Kalisch, Rees, & Dolan, 2009; Lieberman, 2007; Satpute& Lieberman, 2006; Amodio & Frith, 2006). Here, we speculate thatthe increased functional connectivity between the FFA and therACC while preparing for the face, as compared to the number, taskmay represent those aspects of task preparation that are related tosocial task ‘reflection’ and social awareness.

4.4. The residual activity from preceding trials in the posterior brainregions

In the present study, we found that residual activation in thepreceding task-relevant posterior brain region still persisted dur-ing the preparation period for the current trial in the right FFAand tended to persist in the right IPSnum. There are many behav-ioral reports of an influence of the preceding task set on the perfor-mance of the current task, which has been attributed to (residual)task set inertia (e.g., Allport et al., 1994; Allport & Wylie, 1999,2000; Yeung & Monsell, 2003a,b). The persistent activity in the

posterior brain regions observed in the present study fits well withthis interpretation. It has been shown that the persistent activitycan be a source of task switching costs, because it interferes withthe performance of the current task if this is different from the pre-ceding task (e.g., Allport et al., 1994; Allport & Wylie, 1999, 2000;Yeung et al., 2006).

In the present study, we found that the greater the residual acti-vation from the preceding face task that persisted in the right FFA,the more difficult it became to switch to the current number task,likely owing to interference. This finding is consistent with Yeunget al. (2006) findings: their study revealed the magnitude of switchcosts to be significantly correlated with the level of activity in the(after the change) task-irrelevant posterior brain region of the pre-ceding trial (Yeung et al., 2006). Arguably, however, task set inertiacan be at least partially overcome by intentional task preparation.For example, Wylie et al. (2006) had participants switch between acolor and a motion task, and observed larger cue-related activationin the switch, compared to the repetition, condition of the colortask in the color-specific region. Importantly, there was no evi-dence of a behavioral switch cost in the color task, suggesting thatthe increased (cue-related) activity during the preparation periodreflects enhanced efficiency with which the new task is set up ina switch situation.

4.5. Switch-related activation in the preparation period

The effect of task transition (i.e., task switch vs. repetition) wasnot significant in either region. A reason for this observation maybe that the activation in the posterior regions can depend on theperformance in the behavioral tasks. For instance, in the alreadymentioned study of Wylie et al. (2006), for the color task, partici-pants prepared effectively on the switch trials, permitting themto react as fast and accurately on switch trials as on repeat trials.Correspondingly, successful preparation was associated with ro-bust preparatory activity in color-related regions, which was evenhigher than the activity on the repeat trials. In contrast, partici-pants showed relatively slower reaction times (on average morethan 100 ms slower compared to the color task) and considerableswitch costs in the motion task, with motion-processing areasexhibiting no activation during the preparation period.

The findings of activation during the current preparation periodstrongly suggest that participants did prepare for the respectivetask prior to target presentation in the current study (recall thefinding of prior activation in the FFA during preparation of the facetask, and in the right IPSnum during preparation of the numbertask). Also, participants expended more effort on preparing for aswitch trial compared to a repeat trial. In the present study as wellas a previous one of our group (Shi et al., 2010), we consistentlyfound higher activation in the pre-SMA during preparation forswitch trials, compared to repeat trials. This pattern is consistentwith the assumed operation of a task reconfiguration process(e.g., Monsell, 2003). However, the effort may not have been suffi-cient to evoke additional activation in posterior brain regions. Suchactivation may be an important precondition for observing areduction or even abolishment of behavioral switch costs (e.g.,see Wylie et al., 2006).

5. Conclusions

The findings of the present study provide evidence for prepara-tory modulations of task-relevant posterior brain regions. In partic-ular, the activation of task-relevant stimulus-specific brain regionscan be enhanced and their functional connectivity to other(task-relevant) anterior brain regions strengthened during taskpreparation. These findings clearly demonstrate the task-relevant

50 Y. Shi et al. / Brain and Cognition 87 (2014) 39–51

posterior brain regions’ role in task preparation, significantlyextending our understanding of task preparation processes.

Acknowledgments

This research was supported by grants from Cluster of Excel-lence ‘‘Cognition for Technical Systems (CoTeSys)’’ Grant No. 439to T.S. and by a grant of the German Research Foundation to T.S.and H.M. We thank Ute Coates (Department of Clinical Radiology,LMU Munich) for her help with data collection.

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