Attention and cognitive control: Unfolding the dichotic listening story

Scandinavian Journal of Psychology, 2009, 50, 11–22 DOI: 10.1111/j.1467-9450.2008.00676.x

© 2008 The Authors. Journal compilation © 2008 The Scandinavian Psychological Associations. Published by Blackwell Publishing Ltd., 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA. ISSN 0036-5564.

Blackwell Publishing Ltd Cognition and Neurosciences

Attention and cognitive control: Unfolding the dichotic listening story

KENNETH HUGDAHL,1,2 RENÉ WESTERHAUSEN,1 KIMMO ALHO,3 SVYATOSLAV MEDVEDEV,4 MATTI LAINE5 and HEIKKI HÄMÄLÄINEN6

1Department of Biological and Medical Psychology/Cognitive NeuroScience Group, University of Bergen, Norway 2Division of Psychiatry, Haukeland University Hospital, Bergen, Norway 3Department of Psychology, University of Helsinki, Finland 4Institute of the Human Brain, Russian Academy of Sciences, St Petersburg, Russia 5Department of Psychology, Åbo Akademi University, Turku, Finland 6Department of Psychology and Center for Cognitive Neuroscience, University of Turku, Finland

Hugdahl, K., Westerhausen, R., Alho, K., Medvedev, S., Laine, M. & Hämäläinen, H. (2009). Attention and cognitive control: Unfolding the dichoticlistening story. Scandinavian Journal of Psychology, 50, 11–22.

In this article we present a theoretical approach to cognitive control and attention modulation, as well as review studies related to such a view, usingan auditory task based on dichotic presentations of simple consonant-vowel syllables. The reviewed work comes out of joint research efforts by the‘Attention-node’ at the ‘Nordic Center of Excellence in Cognitive Control’. We suggest a new way of defining degrees of cognitive control based onsystematically varying the stimulus intensity of the right or left ear dichotic stimulus, thus parametrically varying the degree of stimulus interferenceand conflict when assessing the amount of cognitive control necessary to resolve the interference. We first present an overview and review of previousstudies using the so-called “forced-attention” dichotic listening paradigm. We then present behavioral and neuroimaging data to explore the suggestedcognitive control model, with examples from normal adults, clinical and special ability groups.

Key words: Cognitive control, executive function, attention, auditory laterality, dichotic listening.

Kenneth Hugdahl, Department of Biological and Medical Psychology, University of Bergen, Jonas Lies vei 91, N-5009 Bergen, Norway. E-mail:[email protected]

COGNITIVE CONFLICT AND COGNITIVE CONTROL

Cognitive control has been defined as the formation, maintenance,and realization of internal goals (Miller & Cohen, 2001). Assuch cognitive control shares properties and characteristics withthe concept of executive functions (Lezak, 1983), and whatEngle (2002) named executive attention, that is, the ability tostay focused on a task despite the presence of interfering stimuli.Jurado and Rosselli (2007) point out that although executivefunction and cognitive control (in the following we will usethese concepts as synonymous) may lack an exact definition,there is a consensus in the literature on a cognitive module thatallows individuals to shift their mind-set quickly and adapt todiverse situations while at the same time inhibiting inappropriatebehaviors. As an integrated part of goal-directed behavior,cognitive control is therefore essential to cope with cognitivechallenges in everyday life, like in school and at work. In anearly attempt at definition of executive functions, Baddeley andHitch (1974) identified four different components; goal-formation,goal-performance, planning, and effective performance. Otherauthors have used other terms and concepts, e.g. Lezak (1983)stated that cognitive control and executive functions essentiallyis about socially acceptable adult self-serving behavior. In thisway, cognitive control and executive functions would be similarto higher cognitive functions, and some authors have also arguedthat cognitive control represents the essence of human cognitive

characteristics, conceptually sharing properties with generalintelligence (see Engle, 2002 for a discussion of this). Cognitivecontrol is also anatomically related to the functioning of thefrontal lobes (Stuss, Alexander, Floden et al., 2002), and it mayhave been Luria (e.g. 1973) who first suggested that the frontal lobeswere the site for organizing and executing intellectual ability.Although there is no agreed upon definition of either whethercognitive control is a unitary concept or not, there seems to beconsensus that it contains inhibition and suppression of currentprocessing focus and shifting of focus. In this sense there is ageneral consensus that cognitive control involves overcoming aprocessing conflict set up by conflicting stimulus features withone or several features being perceptually more salient, setting thestage for a default response action to the exclusion of responsealternatives (cf. Miller & Cohen, 2001). In a similar way, althoughthere is no consensus of the exact neuronal representation ofcognitive control and executive function, there is consensus thatcognitive control requires intact frontal lobes, and particularlythe dorsolateral and ventral parts of the prefrontal cortex (Braver,Cohen & Barch, 2002), as well as the dorsal part of the anteriorcingulate (Bush, Luu & Posner, 2000). This view would also beconsistent with the findings in the review by Duncan and Owen(2000) who concluded after reviewing the existing literature atthe time that “patterns of frontal-lobe activation are associatedwith a broad range of different cognitive demands, including aspectsof perception, response selection, executive control, working

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12 K. Hugdahl et al. Scand J Psychol 50 (2009)

© 2008 The Authors. Journal compilation © 2008 The Scandinavian Psychological Associations.

memory, episodic memory and problem solving” (see also Freitas,Bahar, Yang & Banai, 2007). These authors further stated that“the results show a striking regularity: for many demands, thereis a similar recruitment of mid-dorsolateral, mid-ventrolateraland dorsal anterior cingulate cortex. Much of the remainder offrontal cortex, including most of the medial and orbital surfaces,is largely insensitive to these demands” (p. 475). In this paperwe review data and present a new theoretical approach relatedto stimulus inhibition and suppression, also addressing the issueof localization in the brain of a cognitive control mechanism.Many studies on cognitive control and executive function, havefocused on the conflicting information inherent in the Strooptask, and the cognitive processes involved in resolving Stroopinterference (e.g. Freitas et al., 2007; Miller & Cohen, 2001).

THE STROOP PARADIGM

In operational terms, cognitive control is invoked by environ-mental stimuli that are perceptually salient, or that trigger defaultaction tendencies (Braver and Cohen, 2000; Braver et al., 2002;Miller and Cohen, 2001). Thus, a major function of cognitivecontrol is to successfully manage cognitive conflict and stimulusinterference, that is, to exert mental flexibility in situationswith conflicting or changing information. Several experimentalapproaches have been developed to study cognitive control, suchas the flanker task (Eriksen & Eriksen, 1974), and the atten-tional network test (Fan, McCandliss, Sommer, Raz & Posner,2002; Posner, Snyder & Davidson, 1980). However, the classicand probably most widely known example of a stimulus situa-tion that fits the above operational definition is the Stroop task(MacLeod, 1991; Stroop, 1935) with the presentation of colorwords written in a conflicting ink, like the word RED written ina blue ink. The Stroop situation has a built-in perceptual biassince in the ink color naming condition, the semantic informa-tion is perceptually more salient than the non-semantic informa-tion. This initiates a default action tendency to respond with thecolor word even when the instruction is to respond with the inkcolor. A limitation with the classic approach to cognitive controlis, however, that the paradigms used do not allow for a parametricvariation in degree of cognitive conflict and a similar parametricvariation of the need for cognitive control. In the classic Strooptest the conflict is either present (“read the ink color”) or absent(“read the color word”). In other words, a fine-grained analysisof, for example, gradual differences in cognitive control impair-ment between different patient groups would not be possible.What is needed is a situation that would allow for quantitativemanipulations of degree of cognitive conflict and a correspondingquantification of the degree of cognitive control necessary toresolve the conflicting information.

THE DICHOTIC LISTENING PARADIGM

We have been approaching the topic of cognitive control usingan auditory task with repeated presentations of simple speechsounds, like consonant-vowel (CV) syllables, that are phono-

logically salient, but semantically meaningless (Hugdahl, 2003;Tervaniemi & Hugdahl, 2003). By systematically varying instruc-tions about attention focus, on either the right or left ear syllable,it is possible to set up a cognitive conflict situation where aperceptual saliency effect is either congruent or incongruentwith the top-down attention focus instruction. The experimentalsituation involves dichotic presentations of the stimuli, i.e. twodifferent syllables are presented simultaneously, one to the rightear and one to the left ear (Bryden, 1988). Due to the crossingof the auditory pathways across the midline, and the fact thatthe pathways to the auditory cortex from the contralateral aremore preponderant than the ipsilateral pathways, the right earsignal will have a more direct access than the left ear signal tothe speech processing systems in the left hemisphere (Hugdahl,2003; Kimura, 1967). This results in more correct responses forthe right ear stimulus, which is labeled a right ear advantage (REA).By adding instructions to explicitly focus attention on either theright or left ear stimulus, top-down attentional modulation ofthe lateralized perceptual REA effect is obtained. The experi-mental procedure with the forced-attention dichotic listeningparadigm in our studies (e.g. Hugdahl, Westerhausen, Alho,Medvedev & Hämäläinen, 2008; Tallus, Hugdahl, Alho, Medvedev& Hämäläinen, 2007) is described in more detail in Appendix 1.The stimuli and exact procedures described in the Appendixhave been slightly varied between the different dichotic listeningstudies reviewed below. The general outline and basic charac-teristics of the stimuli have, however, been the same across ourstudies and any slight variation between the studies has addedto the error variance working against any directed hypothesisregarding differences between conditions and groups.

Attention modulation in dichotic listening

We have extensively studied the effects of top-down attentionmodulation of the REA effect (Alho, Salonen, Rinne, Medvedev,Hugdahl & Hämäläinen, 2007; Hugdahl, 2003; Hugdahl &Andersson, 1986; Hugdahl, Carlsson & Eichele, 2001; Milovanov,Tervaniemi, Takio & Hämäläinen, 2007). See also Bryden,Munhall and Allard, 1983. For this purpose, we have establisheda database including more than 1,500 healthy individuals, fromthe age of 5 to 89 years. The database is being shared by theparticipating laboratories in the Nordic Center of Excellenceconsortium. The REA effect for males and females, right- andleft-handers are seen in Fig. 1.

When the subjects are instructed to focus attention on, andreport from the right ear (forced right attention, FR), the REAis significantly (p < 0.05) increased, while when they areinstructed to focus attention on and report from the left ear(forced left attention, FL), the REA is significantly decreased(p < 0.05) and often shifted to a left ear advantage (LEA)(Hugdahl et al., 2001). The effect of attention modulation of theREA is seen in Fig. 2, shown as scatter plots of the distributionof subjects across number of correct reports for the right andleft ear stimulus, respectively. The subjects in Fig. 2 are thesame subjects as in Fig. 1 (N = 1507).

Scand J Psychol 50 (2009) Attentive and cognitive control 13


Cognitive conflict and executive function in dichotic listening

We now believe that instructions to focus attention on theright or left ear stimulus induces different degrees of cognitiveconflict and a corresponding need for cognitive control strategies.We have below described the process that brings us to thisconclusion.

The puzzle occurred when interpreting the results in twoprevious studies from our laboratory (Hugdahl, Rund, Lund et al.,2003; Løberg, Hugdahl & Green, 1999) with the “forced-attention”dichotic listening paradigm (Hugdahl & Andersson, 1986)where it was found that patients with schizophrenia could notmodulate the REA when instructed to focus attention on andreport only the left ear stimulus, while they were able to

Fig. 1. Percentage correct reports for the right and left ear stimulusin a dichotic listening situation, with no specific instruction aboutattention focus. Notes: RH = right-handers, LH = left-handers, fem = females, male = males.Source: Data from the Bergen Dichotic Listening data base.

Fig. 2. Scatter-plots of the distribution of subjects across percentagecorrect right ear scores (x-axis) and percentage correct left ear scores(y-axis), creating a “response-space”: (a) NF instruction condition; (b) FRinstruction condition; and (c) FL instruction condition. Notes: The 45-degree line in the scatter-plots represents the “symmetry-line”.Dots below the symmetry-line indicate individuals with a REA, dotsabove the line indicate individuals with a LEA. The size of the blobscorresponds to increasing number of subjects occupying the samecoordinates in the DL response space. Source: Data from the Bergen Dichotic Listening data base.



modulate the REA when instructed to focus on the right earstimulus. Healthy control subjects could easily perform both tasks,that is, they increased the REA when instructed to focus attentionon and report the right ear stimulus, and reduced the REA, shift-ing to a LEA when instructed to focus attention on the left earstimulus.

Considering that the CV-syllable task is quite easy to perform,it should not be more difficult for the patients to understand andperform the task of reporting the left ear stimulus than to performthe task of reporting the right ear stimulus. Thus, the selectiveleft ear reporting failure of patients was surprising. However, ifthe “forced-attention” paradigm (Hugdahl, 2003; Hugdahl &Andersson, 1986) is thought of as a situation involving a top-down (instruction-driven) modulation of a bottom-up (stimulus-driven) lateralized REA effect (cf. Asbjørnsen & Hugdahl, 1995;Hiscock, Inch & Kinsbourne, 1999; Mondor & Bryden, 1991;Voyer & Ingram, 2005; Wood, Hiscock & Widrig, 2000) it wouldqualify as a cognitive conflict situation according to the definitiongiven above, and hence the surprise could be explained. Seen assuch the failure of schizophrenia patients to modulate the REA mayhave been caused by a failure of top-down attention modulation,rather than a failure of bottom-up lateralized perception.

This would make sense since schizophrenia patients repeatedlyhave been shown to be impaired compared with healthy controlsin top-down cognitive control (Green, 1998; Heinrichs, 2000;Rund, Sundet, Asbjørnsen et al., 2006) and that this most likelyhas a fronto-parietal neuronal basis (Berman, Zec & Weinberger,1986; Blakemore and Frith, 2000; Goldberg, Gold, Greenberget al., 1993). What it could not explain, though, is why failureof top-down modulation should be seen only when the patientswere instructed to pay attention to and report the left ear stimulus,but not when instructed to pay attention to and report the rightear stimulus. Intuitively, one would think that both instructionsituations should involve the same demands for attention focusing.

Previous research on attention focusing in dichotic listening doesnot provide an explanation either, because it has been assumedthat focusing of attention on the left or right ear stimulusshould reflect the same underlying attentional processes (Brydenet al., 1983; Hiscock et al., 1999; Holender, 1986; Kirstein &Shankweiler, 1969; Mondor & Bryden, 1991; Voyer, 2003;Voyer & Ingram, 2005; Wood et al., 2000), and that differencesbetween the two instruction conditions would only reflect thedifferential impact of the non-forced (NF), bottom-up REA.

FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI) DATA

A clue to an explanation of the selective FL effect seen in thepatients as an example of cognitive control may be the fMRIstudy by Thomsen, Rimol, Ersland & Hugdahl (2004; see alsoHugdahl, Law, Kyllingsbæk, Brønnick, Gade & Paulson, 2000;Jäncke, Buchanan, Lutz & Shah, 2001) where it was shown thathealthy subjects uniquely showed activation in the left prefrontaland anterior cingulate cortex areas when the BOLD activationimages acquired during the FL task were contrasted with

images obtained during the FR task, while the reversed contrastshowed no remaining significant activations.

This finding was replicated in a recent study in our laboratorywhere 16 healthy individuals between 20 and 30 years of ageperformed the “forced-attention” dichotic listening task, whilebeing in the MR scanner. The results confirmed the originalfindings in the Thomsen et al. (2004) study, with remainingsignificant activations in the medial frontal gyrus and the ante-rior cingulate cortex when we contrasted the images obtainedduring the FL instruction condition with the images obtainedduring the FR instruction condition. The reversed contrast showedonly a small activation in the precuneus. The localization of theanterior cingulate cortex activation was overlapping with theso-called “cognitive” part of the anterior cingulate cortex, justdorsal to the genu of the corpus callosum as revealed in the meta-analysis by Bush et al. (2000). See Fig. 3 for further details.

Considering that the prefrontal and anterior cingulate cortexhave been linked to increased cognitive load, as seen in execu-tive and other cognitively demanding tasks (Duncan & Owen,2000), it could be argued that the FR and FL attention situationsdiffer in the degree to which they reflect cognitive control.

MAGNETOENCEPHALOGRAPHY (MEG) DATA

A parallel MEG study at the BioMag Laboratory of the HelsinkiUniversity Central Hospital (Alho et al., 2007) from 15 healthyadult individuals showed higher enhancement of activity under-lying the sustained field (SF, a slow event-related responsefollowing the N1m response; Hari, Hämäläinen, Kaukoranta,Mäkelä, Joutsiniemi & Tiihonen, 1989) in the auditory cortex ofthe left hemisphere in the NF condition compared with a visualattention condition in which both auditory inputs were ignored(Fig. 4). The same was true in the FR condition, but in the FLcondition, the right auditory cortex showed higher SF activitythan the left cortex. These preliminary MEG findings supportthe proposal that in the NF condition the subject’s attention isbiased to the right ear, resulting in enhanced activity in the contra-lateral (left) auditory cortex. While the FR instruction supportsthis bias, the FL condition results in enhancement of event-relatedresponses in the right auditory cortex (contralateral to the attendedear). This would indicate that attentional control may reverse theright ear advantage to a left ear advantage by biasing processingof speech sounds at a relatively early stage of processing.

INHIBITORY COGNITIVE CONTROL

Thus, the FL situation seems to involve requirements for a cog-nitive conflict and particularly inhibitory control to counteracta bottom-up and stimulus-driven right ear response tendency(cf. Foundas, Corey, Hurley & Heilman, 2006). This would besimilar to what Engle (2002; see also Kane & Engle, 2002)labeled executive attention, defined as the ability to maintainfocus in the presence of competing or interfering stimuli. Itwould also be in line with what Moran and Desimone (1995)called reactive versus volitional, or intentional, attention (see



also Nadeau & Heilman, 1991), where intentional attentioncould be thought of as playing a relatively greater role in the FLattention situation.

Assuming that the FR and FL situations differ in the demandsfor cognitive control, the failure of the schizophrenia patients touse attention to modulate the stimulus-driven REA in the FLcondition could now be explained as a failure of cognitivecontrol. Such an assumption could also explain the fMRI datareported by Thomsen et al. (2004) since prefrontal and anterior

cingulate activations typically are observed to tasks involvingrequirements for cognitive control (Duncan & Owen, 2000;Landrø et al., 2001; Stuss, 2006). This conclusion is furthersupported by the results shown in Fig. 5, based on data from 14patients with schizophrenia undergoing the same forced-attention DL task as the 16 healthy subjects seen in Fig. 3, anddescribed above. Figure 5 shows that the schizophrenia patientsfailed to activate anterior cingulate cortex areas during the FLinstruction task that were activated in the healthy subjects.

Fig. 3. Remaining activation in medial frontal gyrus and the anterior cingulate cortex when contrasting the BOLD-fMRI images obtained during theforced-left (FL) instruction condition minus the images obtained during the forced-right (FR) condition (left panel), and when reversing the contrast(right panel).

Fig. 4. Grand-average minimum current estimates of brain activity during the sustained field (SFs) event-related MEG response at 300–400 ms fromthe onset of dichotically presented pairs of randomly combined syllables during a non-forced (NF) attention condition in which the subjects were torespond with a button press to one of the six syllables whenever it occurred in either ear. Source: Data from Alho et al. (2007).



Old age and cognitive control

Another group of subjects that could be predicted to selectivelyfail to perform the FL instruction condition is elderly people.There is evidence that individuals aged 60 and above showimpairments in episodic and semantic memory (Rönnlund, Nyberg,Bäckman & Nilsson, 2005), executive functions and cognitivecontrol as measured with the Stroop test (Lund-Johansen et al.,1996) or the Wisconsin Card Sorting Test (Traykov, Raoux,Latour et al., 2007). The cognitive decline seen in old age hasalso been correlated with brain structural and functional anomaliesincluding reduced hippocampal volumes and increased pre-frontal activation (Persson, Nyberg, Lind et al., 2006). Thus, if theFL condition taps cognitive control and executive functioning,older individuals should be selectively impaired when performingthe FL condition. Figure 6 shows the results from 60 subjectsbetween 20–30 years compared with 63 subjects aged 60–89years. Both groups showed a significant REA in the NF and FRinstruction conditions (p < 0.05), with no significant differencesbetween the groups. As can be seen in Fig. 6, however, the oldersubjects failed to report more items from the left ear during the FLinstruction condition, revealing a selective deficit in this condition.

If the explanation for the selective deficit in the older groupas an instance of failure of cognitive control is accepted, thereshould also be a negative correlation between age and perform-ance in this group, with the greater impairment in reporting theleft ear stimulus, the older the patients are. This is a straightforwardprediction from the findings that older individuals are more

prone for signs of mild cognitive impairments (Traykov et al.,2007), and that such patients show clear deficits on cognitivecontrol tasks. The results from the correlation analysis is seenin Fig. 7, and showed a significant negative correlation (r = −0.32)for the left ear scores with age, but with a zero correlation (r =0.006) for the right ear scores.

Congenitally blind and bilingual individuals

The suggested cognitive control model would be strengthenedif it also could be shown that certain groups of individualswould perform better than normal controls on the FL instruc-tion condition. If individuals who for good reasons could behypothesized to have superior attentional and/or cognitive controlabilities would show superior performance in the FL instructioncondition than normal controls, then the model would bestrengthened. Congenitally blind individuals may be such agroup of individuals. Blind individuals have not only enhancedperceptual sensitivity for auditory stimuli, due to brain plasticityand reorganization, but they are also better in focusing andshifting of attention to an auditory stimulus (Kujala, Alho &Näätänen, 2000) and for auditory spatial tuning (Röder, Teder-Sälejärvi, Sterr, Rösler, Hillyard & Neville, 1999). Thus, con-genitally blind individuals could be predicted to be significantlybetter than seeing individuals in the forced-attention dichoticlistening paradigm, and particularly for the FL instruction con-dition. A study performed at the Center for Cognitive Neuro-science, University of Turku, Finland (Hugdahl, Ek, Takio

Fig. 5. BOLD-fMRI activation in the anterior cingulate cortex in healthy control subjects (above) and patients with schizophrenia (below). Thenumbers in blue colors represent distance in mm from the midline.



et al., 2004) showed that this actually was the case. Fourteencongenitally blind individuals were compared with 129 seeingindividuals, using a Finnish version of the standard forced-attention DL paradigm. The results showed that (a) the blind

individuals reported overall more correct items (p < 0.05), and(b) when instructed to focus attention to and report only from theleft ear they were again significantly (p < 0.05) better than theseeing control subjects. The findings in the Hugdahl et al. (2004)study confirmed that blind individuals both show enhancedperceptual accuracy in the auditory modality, and have superiorability for attention and cognitive control. Thus, the resultsprovided additional empirical support for the current model.

With regard to seeing individuals, it is possible that thosewith a bilingual language background might excel their mono-lingual peers in the FL condition. The reason we suggest thishypothesis is that there is evidence for a bilingual advantageespecially in tasks calling for inhibition of task-irrelevant cues(e.g., Bialystok, 2001). This is thought to result from theirextensive experience in language switching and inhibition of thelanguage not in use. Furthermore, if the language experience ofbilinguals would result in a top-down inhibitory advantage inthe forced attention DL task, such an advantage could perhapsbe obtained by other means as well. Earlier studies on theStroop interference effect have indicated that it can be reduced(albeit not abolished) by training (MacLeod, 1998). Thus, it isan open issue whether training also could modify forced atten-tion DL performance.

Effects of training?

It could also be hypothesized, from the outlined model, that itmay be possible to apply a training procedure with extensiverepeated exercises with the DL task to improve performance inthe FL instruction condition. This could be thought of as effec-tive in both healthy individuals as well as in clinical populationswho fail to shift to a LEA in this condition. An argument forsuch a hypothesis is that another important aspect of cognitive

Fig. 6. Comparison of percentage correct reports between young adult(20–30 years) and old adult (60–89 years) individuals, split for the threeinstruction conditions (NF, FR, FL). Note the failure of the older adults to convert a significant REA to aleft ear advantage (LEA) during the FL instruction condition. A =young adults, O = old adults.

Fig. 7. Scatter-plots of the correlation between age and percentage correct reports for the left ear (left panel) and right ear (right panel) during theFL instruction condition. Notes: FLRE = Forced Left Right Ear correct reports, FLLE = Forced Left Left Ear correct reports.



control and executive function, working memory, has beenshown to exhibit behavioral and neural plasticity in normalhumans as a result of intensive training (Olesen, Westerberg &Klingberg, 2003). Since working memory capacity is an inte-grated aspect of executive control function (Baddeley & Hitch,1974) it is reasonable to assume that there would be a trainingeffect in the DL forced-attention situation, particularly for theFL instruction condition. If this would turn out to be possibleto demonstrate, it could be of specific importance when over-coming impaired control functions in clinical groups like schizo-phrenia or dementia. Considering the lack of a direct empiricalevidence for a training effect in the forced-attention situation,the presented ideas are speculations. However, an argument infavor of the current theoretical approach and experimental par-adigm is that the task in itself is extremely simple (listening toand discriminating between syllables) and would thus not be abarrier for the ability of the patient to perform the task at all.This is sometimes a problem in more traditional neuropsycho-logical approaches to impairment of higher cognitive function-ing in clinical populations in that the tasks and tests used toassess different cognitive functions also differ in terms of testdifficulty, reliance on level of education, previous experiencewith such tasks etc. A second argument for the current approachis that the DL task has very low or zero learning effects, thereis simply “nothing to learn” since the task consists of repeatedseries of meaningless syllables. A third argument is that executiveand other control functions traditionally are treated as traitvariables, not amendable to training or other experience basedinfluences.

Parametric manipulation of the strength of cognitive conflict

In order to induce a gradual manipulation of cognitive conflictwe have initiated a series of new experiments where we haveparametrically varied the intensity of the right or left earstimulus in steps of 3 dB as a way of quantifying degrees ofstimulus salience and cognitive conflict (Hugdahl et al., 2008).Gradually increasing the right ear stimulus intensity results in acorresponding increase in the REA, while at the same timegradually increasing the left ear stimulus intensity results in anincrease in the left ear advantage (LEA). This is seen in Fig. 8,which is based on data from Hugdahl et al. (2008).

The data in Fig. 8 also show that the non-forced REA with-stands up to 9 dB stimulus intensity difference favoring the leftear, before it yields to a significant left ear advantage. Thus, bysystematically varying the interaural intensity difference eitherfavoring the right or left ear stimulus it is possible to quantifythe relative strength of the ear advantage in the non-forced (NF)instruction condition that would make the top-down instructedattention effect more easy or more difficult depending onwhether the instruction goes in favour of the stronger or weakerstimulus, respectively. From the outlined model, we predict that itwould be more difficult to use attention to “overcome” a rightear intensity increase when instructed to focus attention on theleft ear stimulus, than the other way around. A first clue that it

would be more difficult to overcome a “strong” REA wheninstructed to focus attention on the left ear stimulus than theother way around was seen in a study by Tallus et al. (2007),conducted at the University of Turku node in the Center ofExcellence consortium. These authors manipulated interauralintensity differences with 15 dB, favoring either the right or leftear stimulus, while at the same time instructing the subjects tofocus attention on the right or left ear stimulus. The results areseen in Fig. 9, and show that when there was a 15 dB interauraldifference with the left ear signal being the weaker signal, thesubjects did not show a significant LEA when instructed tofocus attention on the left ear stimulus. On the other hand, whenthere was a 15 dB difference with the right ear signal being theweaker signal, the subjects nevertheless showed a significantREA. Thus healthy individuals could more easily use a top-down strategy to overcome a 15 dB stimulus intensity differencein the FR instruction condition, than in the FL instructiondifference.

Specifying the relative degree of cognitive control impairment in clinical groups

It should now be possible to predict the relative degree of cog-nitive control impairment in clinical groups based on the abilityto overcome an intensity difference in disfavor of the directionof focus of attention. From the study by Tallus et al. (2007) weknow that healthy individuals fail to use focused attention toovercome an interaural intensity difference of 15 dB. We do notknow, however, what the lower limit is, that is, whether they would

Fig. 8. Mean (± 95% confidence limit) number of correct reports (max= 24) for the left and right ear syllables as a function of systematicallychanging the interaural intensity difference in 15 steps of 3 dB. Notes: Positive values indicate stronger signal in the right ear, negativevalues indicate stronger signal in the left ear. A significant differencewas found for all intensity levels except level −6 dB. A significant leftear advantage was observed first at −9 dB intensity difference.Source: Figure from Hugdahl et al. (2008) reprinted with permissionfrom the publisher.



also fail at a 12 dB difference or lower, and whether differentclinical groups would fall at an even lower level of interauraldifference. For example, can patients with schizophrenia notwithstand more than a 5 dB in disfavor of the left ear signal,while patients with a beginning dementia can withstand, forexample, a 7 dB difference, and patients with ADHD can with-stand, for example, a 10 dB difference? On the other hand, onecould predict, for instance, that congenitally blind individualscan use attention to overcome a greater interaural difference infavor of the right ear than other special ability groups, such as

professional translators, or bilinguals in general, which could bepredicted to have a special ability to solve a cognitive conflictcaused by interfering language signals. We have illustrated thisin Fig. 10 with examples of both impaired and superior abilitygroups placed on both sides of the “equal intensity horizontaldivider”. These illustrations should be read as hypotheticalexamples of how the current approach can be used, and theactual ability of each clinical and other group to use cognitivecontrol to overcome a parametric intensity manipulation willhave to await empirical studies. We hope, however, that thecurrent article can act to encourage such studies.

Limitations with the proposed model should be pointed out.One obvious limitation is that the clinical groups studied havea temporal lobe abnormality to start with, which would weakenthe bottom-up effect in the NF condition. This would be true forpatients with schizophrenia, but would not apply to aged individuals.Another limitation could be that the FL effect is, at least partly,caused by the REA in the NF condition, making it harder toswitch to a LEA in the FL condition. Although this is unlikely,we hold it still as an option before new data have been acquiredto test it out.

SUMMARY AND CONCLUSIONS

We believe that the results from the neuroimaging studies aswell as the observations in patients and elderly subjects supportthe notion that the FL situation involves a conflict betweenbottom-up and top-down processes, with the bottom-up processpushing for a right ear response and the top-down process push-ing for a left ear response. This would be in contrast to the FRsituation where the two processes would act synergistically,both pushing for a right ear response. Thus, the three instructionprocedures together with a dichotic stimulus presentationmodus can be summarized to contain three different cognitiveprocesses, or different degrees of such processes; a lateralized

Fig. 9. Percentage correct reports for the left and right ear stimulus for the three instruction conditions. Source: Data from Tallus et al. (2007); figure re-drawn with permission from the publisher.

Fig. 10. Illustration of a hypothetical example of how parametricalmanipulation of interaural stimulus intensity differences (shown on they-axis) could be used in a forced left (FL) dichotic listening conditionto quantify the ability of cognitive control (x-axis) in normal controls, twoimpaired groups (patients with schizophrenia, elderly subjects), and twospecial ability groups (professional translators, congenitally blind subjects).Notes: Controls and the two special ability groups should be able toovercome the bottom-up right ear advantage (i.e. showing a left earadvantage) even when the right ear stimulus is more intense than theleft ear stimulus (R > L). The elderly subjects and the patients withschizophrenia, however, would only be able to override the bottom-upright-ear advantage if the left ear stimulus is more intense than the right(L > R).



perceptual process (NF), an attention process (FR), and an executivecognitive control process (FL). The three instruction conditionsare moreover thought to increase in their need of cognitive loadand effort, from the NF to the FL instruction condition. Bysystematically increasing the intensity of the right or left earstimulus, the cognitive conflict will be stronger or weakerdepending on which stimulus is intensified and which ear theattention instruction favors. We further suggest that the degreeof cognitive control impairment in different clinical groups canbe quantified in a new way according to how much of an intensitydifference in disfavor of the top-down instruction of attentionfocus the subjects can withstand and still show a significant earadvantage effect.

The present research was financially supported by from the NordicCouncil (NOS-S) to the Nordic Center of Excellence in Cognitive Control(Coordinator Prof. Lars Nyberg, Umeå University, Sweden), and grantsto Kenneth Hugdahl from the Research Council of Norway (RCN) andthe Health Authority for Western Norway (Helse-Vest).

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Received 24 January 2008, accepted 16 April 2008

APPENDIX 1: THE FORCED-ATTENTION DICHOTIC LISTENING PROTOCOL.

Stimuli

The stimuli are typically paired presentations of the six stop-consonants /b/, /d/, /g/, /p/, /t/, /k/ together with the vowel /a/ toform dichotic consonant-vowel (CV) syllable pairs of the type/ba/ - /ga/, /ta/ - /ka/ etc. The syllables are paired with each otherfor all possible combinations, thus yielding 36 dichotic pairs,including the homonymic pairs. The homonymic pairs are notincluded in the statistical analysis. The maximum score is 30for each ear. Each CV-pair is recorded three times, with threedifferent randomizations of the 36 basic pairs. Thus, the totalnumber of trials is 108. The 108 trials are divided into three 36trial-blocks, one trial-block for each instructional condition,non-forced attention (NF), forced right attention (FR), forcedleft attention (FL). Each subject is given a standardized set ofinstructions prior to the test (see procedure below). No significantdifferences for either the right or left ear scores have emergedwhen comparing different language sub-samples, most notablywhen comparing Norwegian and Swedish samples with Finnishsamples, but also when comparing with German- and English-speaking samples.

The syllables are typically read by a male voice with constantintonation and intensity. Mean duration is 350–400 ms (allow-ing for differences in voice-onset time length for unvoiced vs.



voiced CVs) and the inter-trial interval is on the average 4 s.The syllables are read through a microphone and digitized forlater computer editing on a standard PC using state-of-the-art audio editing software (SWELL, Goldwave, CoolEdit orcomparable packages). In the original version of the task, thesyllables were recorded with a sampling rate of 44,000 Hz andamplitude resolution of 16 bit. After digitization, each CV-pairwas then displayed on the PC screen and synchronized forsimultaneous onset at the first identifiable energy release in theconsonant segment between the right and left channels. Theexact editing procedure, however, may vary between laborato-ries due to ever more refined editing software packages. Thestimuli are finally played to the subject using digital play-backequipment, connected to high-performance headphones, withintensity between 70–75 dB. The exact equipment used mayvary between laboratories.

Procedure

NF condition (NF). This condition is always presented as thefirst condition in order not to confuse the subjects with regardto the later conditions. The reason for this is that if an explicitinstruction regarding attention is given in the first condition, itwould be difficult for the subject to “un-attend” once he/she hasbeen instructed to attend. The subject is therefore just told thathe/she will hear repeated presentations of the six CV-syllablesand that he/she should report on each trial which one he/shehears from the six possible syllables. The subjects are further-more told that “on some occasions there seems to be twosounds coming simultaneously”. They should ignore this andjust report the syllable they hear “first or perceive best”. Theyare sometimes shown a cardboard sheet with all six syllableswritten before the experiment started. The subject is explicitlyinstructed to orally report one item on each trial irrespective of

whether he/she perceived one or both items. This procedure wasoriginally introduced by Bryden (1988) in order to reduceworking memory loading as when the subject has to provide tworesponses at the same time, or as in the original Kimura (1961)studies when the subject had to withhold his/her response untilfour stimulus pairs had been presented, and then perform arecognition procedure. Whenever more than one response isrequired in a trial, the subject will have to retain one item inworking memory while providing his/her response to the firstitem. This inevitably creates a confounding situation, making itdifficult to know if an observed ear advantage is caused by aperceptual or working memory effect.

FR and FL conditions. During the FR and FL attention focusinstruction conditions, the subjects are requested to “only listento, and report from the right (left) ear, and to ignore any soundsthey might hear in the other ear”. The experimenter also pointsto the respective ear and side of the head before each instructioncondition began. In all other respects, the FR and FL procedurewas identical to the NF procedure. The FR and FL instructionconditions are counterbalanced.

Hearing accuracy testing

It is important that the subjects do not have a general hearingimpairment and that they do not have a relative hearing deficitin one ear relative to the other. This is the more important inolder samples and sometimes when testing clinical samples.Whenever possible, screening audiometry should therefore beperformed, particularly for frequency ranges up to 2.5–3.0 KHzwhich is the energy range in the CV-syllables presented. Typi-cal values are that subjects should not have a general hear-ing impairment of more than 20 dB for all frequenciestested, and an interaural hearing threshold difference of morethan 10 dB.

Attention and cognitive control: Unfolding the dichotic listening story

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