eeg differences and cognitive style

Biological Psychology 51 (1999) 23–41

EEG differences and cognitive style

Alan Glass *, Richard J. RidingAssessment Research Unit, School of Education, Uni6ersity of Birmingham, Birmingham B15 2TT, UK

Received 13 August 1998; received in revised form 14 December 1998; accepted 14 January 1999

Abstract

Individuals differences in information processing related to cognitive style were investi-gated by EEG recording during cognitive tasks. Fifteen adults received the Cognitive StylesAnalysis which assessed their positions on two dimensions: the wholist-analytic and theverbal-imagery. The EEG from midline, paramedial and lateral electrode clusters wasrecorded, while subjects viewed words presented at different rates. A button was pressedwhen a word was in a target conceptual category. Off-line analysis produced spectral powersfor delta, theta, alpha, beta 1, beta 2 and gamma bands. For the midline, the wholists hadhigher output than analytics in theta and alpha, but lower in gamma. In the paramedialcluster, verbalisers had greater right power than imagers for all bands except alpha. Further,the overall power was greater on the right for imagers than verbalisers frontally, and theconverse occipitally. In the lateral grouping, the wholist-verbalisers had greater overall powerleft antero-temporally than other sub-groups. © 1999 Elsevier Science B.V. All rightsreserved.

Keywords: Cognitive style; EEG frequency bands; EEG power; Individual differences

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1. Introduction

An earlier report (Riding et al., 1997) described individual differences in the EEGassociated with cognitive style dimensions only for the alpha frequency range. Thepurpose of the present report, is to determine, using data from the same exploratorystudy, whether the cognitive style effects found in the alpha range are also presentin some of the other frequency bands.

* Corresponding author.E-mail address: [email protected] (A. Glass)

0301-0511/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved.

PII: S0301 -0511 (99 )00014 -9

A. Glass, R.J. Riding / Biological Psychology 51 (1999) 23–4124

Cognitive style is seen as an individual’s preferred and habitual approach toorganising and representing information (Riding and Rayner, 1998, p. 8). It is afundamental hypothesis in studying cognitive style that individuals process the sameinformation differently, probably using alternative cortical regions. The objective ofthis investigation of the EEG concomitants of differences in cognitive style, is firstlyto find support for the hypothesis of an underlying cerebral basis for individualdifferences in cognitive style. A subsidiary aim, is to illuminate the relationship ofEEG rhythms to individual differences in cognitive processing by discoveringwhether differences in cerebral mechanisms linked to variation in cognitive styleaffect these intrinsic rhythms. Thus, individual differences could be elucidated inthe dynamics and topography of EEG rhythms in relation to cognitive processing,and the associated functional anatomy of information processing in discrete neuralarrays, which may be related to differences in the underlying cortical connections(see Zeki and Shipp, 1988).

1.1. Cogniti6e style

The background to cognitive style has been extensively reviewed by Riding andCheema (1991), and Riding and Rayner, (1998), chapter 2). They concluded thatthe various style labels could be accommodated within two fundamental dimensions– the wholist-analytic and the verbal-imagery – which may be summarised asfollows:1. The wholist-analytic dimension describes whether an individual tends to or-

ganise information in wholes or parts.2. The verbal-imagery dimension indicates whether an individual is inclined to

represent information during thought, verbally or in mental pictures.The two basic dimensions may be assessed using the computer-presented Cogni-

tive Styles Analysis (Riding 1991). It directly assesses both ends of the wholist-ana-lytic and verbal-imagery dimensions, and comprises three sub-tests. The firstassesses the verbal-imagery dimension by presenting statements one at a time to bejudged true or false. Half of the statements contain information about conceptualcategories, while the rest describe the appearance of items. Half of the statementsof each type are true. It is assumed that imagers respond more quickly to theappearance statements, because the objects can be readily represented as mentalpictures and the information for the comparison can be obtained directly andrapidly from these images. In the case of the conceptual category items, it isassumed that verbalisers have a shorter response time, because the semanticconceptual category membership is verbally abstract in nature and cannot berepresented in visual form. The computer records the response latencies to eachstatement and calculates the verbal-imagery ratio. A low ratio corresponds to averbaliser, and a high ratio to an imager. An intermediate position is described asBimodal. It may be noted that in this approach, individuals have to read both theverbal and the imagery items, so that reading ability and reading speed arecontrolled for.

A. Glass, R.J. Riding / Biological Psychology 51 (1999) 23–41 25

The other two sub-tests assess the wholist-analytic dimension. The first of thesepresents pairs of complex geometrical figures which the individual is required tojudge either the same or different. Since this task involves judgements about theoverall similarity of the two figures, it is assumed that a relatively fast response tothis task by wholists is possible. The second test involves presentation of a simplegeometrical shape (e.g. a square or a triangle) and a complex geometrical figure. Inthis case the individual is asked to indicate whether or not the simple shape iscontained in the complex one by pressing one of the two marked response keys.This task requires a degree of disembedding of the simple shape within the complexgeometrical figure in order to establish that it is the same as the simple stimulusshape displayed, and it is assumed that analytics are relatively quicker at this.Again, the computer records the latency of the responses, and calculates thewholist-analytic ratio. A low ratio corresponds to a wholist, and a high ratio to ananalytic. Ratios between these positions are labelled intermediate. The backgroundto the development of the Cognitive Styles Analysis is given in Riding and Cheema(1991). Each of the cognitive style dimensions is a continuum. The dimensions areindependent of one another, in so much as position on one dimension, does notinfluence position on the other.

Cognitive style has been found to affect a wide range of behaviours such as,learning performance, learning preferences, subject matter preferences and socialbehaviour, and this evidence for its construct validity has been reviewed by Riding(1997) and Riding and Rayner (1998), chapters 5–8). Further, style had been foundto be independent of intelligence (Riding and Pearson, 1994; Riding and Agrell,1997), and also of common personality measures such as extroversion and neurot-icism (Riding and Wigley, 1997).

1.2. Cortical factors and EEG cortical localisation

Evidence from a wide variety of sources indicate that the neocortex is subdividedneuroanatomically into a large number of anatomical regions, which are specialisedfor different functions (Crick and Asunuma, 1988). It is assumed that if anelectrode is placed over a discrete functional area, when a specific cognitive functionis carried out, the ‘active’ electrode overlying the area subserving that function willreveal desynchronisation, i.e. blocking or suppression of the alpha range(Williamson et al., 1997), indicating cortical activation of the specific area. Thesame argument can be extended to the study of the neurophysiology of left/rightbrain differences by comparing lateral electrodes located over homotopic corticalregions, i.e. approximately over Broca’s or Wernicke’s areas (F7 and T5, respec-tively) on the left, compared with the homotopic area on the right hemisphere.

1.3. Hemispheric specialisation

Earlier theories of hemispheric specialisation have proposed lateralisation ofcertain cognitive attributes, for example, the verbal and visuospatial dichotomies(Bogen, 1969). Of more particular relevance to the psychophysiology of cognitive


style is the concept of hemisphericity (Bogen et al., 1972), i.e. the propensity of anindividual to use the functional attributes of one hemisphere rather than the other.

The verbal-visuospatial hemispheric dichotomy is of particular relevance to theverbal-imagery dimension of the Cognitive Styles Analysis, and provides an initiallyuseful interpretative link between EEG-alpha asymmetry and cognitive style (Rid-ing et al., 1993).

Although the association of verbal function with the left hemisphere has longbeen accepted in clinical neurology, the extensions of the concept of hemisphericspecialisation to normal cerebral functioning have been challenged on methodolog-ical grounds (Schofield, 1987; Biseach and Berti, 1990; Efron, 1990). However, ifstudies have neglected individual differences in cognitive styles and strategies(Cohen, 1982; Riding et al., 1993) it is not surprising that the evidence is sometimesconflicting (e.g. Butler and Glass, 1987; Butler, 1988).

Links between EEG characteristics and visual imagery style were investigatedmainly at parieto-occipital locations by Golla et al. (1943), Short and Walter(1954), O’Connor and Shaw (1978). More recently, lowered alpha activity wasfound during visual imagery in vivid and non-vivid imagers (Marks and Isaacs,1995) and alpha enhancement during motor imagery (Williams et al., 1995).However, to investigate cognitive style psychophysiologically, cognitive task-relatedeffects are required.

1.4. Assumptions underlying interpretation of EEG changes

The assumptions underlying interpretation of EEG changes have been proposedwith respect to the alpha rhythm in the main, but may be applicable to the otherfrequency ranges. The classical theory is that alpha power is inversely related tolocal cortical activation (Glass, 1967; Vogel et al., 1968; Dolce and Waldeir, 1974;Glass, 1984; Earle, 1988; Fernandez et al., 1995) and expressed analogously asevent-related desynchronisation (10 Hz, ERD) (Pfurtscheller and Aranibar, 1977;Pfurtscheller and Klimesch, 1992). In contrast, when alpha rhythm is more abun-dant, and the subject is actually ‘at rest’, the underlying cortex is assumed to beinactive, ‘idle’ or in a ‘nil-work’ situation (Pfurtscheller, 1992; Pfurtscheller et al.,1996). However, there are alternative models which attempt to explain the so-called‘paradoxical’ alpha response, in which the alpha rhythm is actually enhanced whencircumstances are such that the cortex can be assumed to be more active, (forexample, Creutzfeldt et al., 1969; Shaw, 1992; for more recent evaluation anddiscussion of brain alpha activity in a functional context see, for example, Basar etal., 1997). More parsimonious explanations derive from the concept of U-shapedcurve of arousal in relation to alpha frequency range abundance (Lindsley, 1952;Kozima et al., 1981; Ota et al., 1996). On the lower side of the inverted-U arousalcurve (during a lower baseline level), an arousal increase could cause an enhance-ment of alpha activity, whereas starting (more often the case experimentally) froma higher baseline of arousal, an increase in arousal would cause a suppression ofalpha. This model can be extended, in principle, to other frequency ranges. Alpha(and other frequency ranges), as suggested above, have long been known to be


suppressed by visual stimulation and mental activity, such as mental arithmetic.Suppression by the latter has been quantified, for example, by Mundy-Castle(1957), Glass (1964, 1967), Pollen and Trachtenberg (1972), Osborne and Gale(1976), Ehrlichman and Wiener (1980), Earle (1988), and Vijn et al. (1991) (forvisual stimulation).

The application of the suppression of alpha as a result of local cortical activationto the interpretation of lateral EEG asymmetries related to task-type, verbal orvisuospatial, (the so-called task-related asymmetries) has been discussed by Glass(1984), Butler (1988), Glass (1991) and Glass and Driver (1996).

1.5. Neuronal basis for cortical acti6ation

The neuronal elements immediately underlying the recording electrode can besupposed to become synchronously active in a ‘nil-work’ situation; when informa-tion is not being processed: the alpha rhythm enhances, perhaps partly underthalamic control (Andersen and Andersson, 1968; Steriade and Llinas, 1988). Theneuronal basis of the alpha rhythm probably depends on when the potentials of thedendritic trees of the cortical neurones are synchronised, (Elul, 1971; Lopes daSilva, 1991). It is relevant that in contrast the genesis of the 40–70 Hz (gamma)rhythm is typically in the visual cortex, and the neurones in multiple spatially-sep-arate columns synchronise their oscillations using functional and spatial factors(Gray et al., 1989; Jeffreys et al., 1996), (see Basar-Eroglu et al., 1996a).

1.6. Cogniti6e style and EEG alpha

Riding et al. (1997) reported individual differences in the EEG-alpha frequencyrange associated with cognitive style dimensions. For the wholist-analytic styledimension, wholists had higher levels of alpha power at all electrode sites relativeto the analytics during solution of a series of verbal tasks. In the verbal-imagerydimension, the verbalisers had higher levels of alpha power over right posteriortemporal regions compared with the homologous regions on the left and reverseasymmetry in the imagers.

1.7. Proposed aim

The purpose of the present analysis is to determine whether the cognitive styleeffects in the alpha range are present in all or some of the other bands: delta(0.0–2.9 Hz); theta (3.0–7.9 Hz); beta 1 (13.0–17.9 Hz) and beta 2 (18.0–24.9 Hz);and gamma (25.0–70.0 Hz). The appraisal of the frequency bands would be carriedout in the context of specific predictions of more global, widespread corticalactivation in analytics compared to wholists, and greater left-hemisphere activationin verbalisers compared to imagers. The subjects were given a verbal-categorisationtask presented on a VDU, while their EEG was recorded. This was followedimmediately by the Cognitive Styles Analysis.


2. Method

2.1. Subjects

The subjects were 15 volunteer adults (nine male and six female) whose agesranged from 18 to 36 years (mean: 23.6, S.D. 4.8). All were right handed asdetermined by self-report.

2.2. Assessing cogniti6e styles

The computer-presented Cognitive Styles Analysis, (Riding, 1991) was employedto assess cognitive style. This was administered after EEG recording.

2.3. Information processing tasks

During EEG recording, subjects did 40 computer-presented word-targeting trials,in which words appeared on a high refresh-rate VDU. Five presentation conditionswhich represented different information processing loads were used. The tasks were:one word at a time at rates of two words/s, five words/s and 10 words/s, and twowords at a time, one above the other, at rates of five word-pairs/s and 10word-pairs/s. There were eight trials at each rate. The blocks of trials werepseudo-randomly presented. The words were selected at random from a largedictionary and the task required subjects to monitor the displayed words (presentedat the centre of the VDU) and respond with a button press whenever a noun fromthe superordinate categories ‘fruit’ or ‘vegetable’ was displayed (e.g. apple orcarrot). Within each trial there were always three target words, which werepseudo-randomly set.

2.4. EEG recording

Each trial lasted 30 s. The EEG was stored over the bandwidth from DC to aroll-off point of 70 Hz for each 30-s epoch after recording from Ag-AgCl electrodesin positions Fp1, Fp2, F7, Fz, F8, T3, C3, Cz, C4, T4, T5, Pz, T6, O1 and O2 accordingto the International 10–20 System with respect to mastoid electrodes (A1/A2) incommon reference (routinely used in EEG asymmetry studies). Subjects satcomfortably in a sound-attenuated chamber during the recording and task perfor-mance.

2.5. Artefact rejection

As the task involved eye-fixation on the words on a VDU, it was consideredunlikely that there was significant eye-movement during a trial. However,the recording system was set so that if there was a high amplitude wave abovea specific threshold in Fp1 and Fp2, then this resulted in the rejection of that trial


in all channels. This excluded eye-movement artefact, and, incidentally otherartefacts.

2.6. Data processing

The EEG data was digitised at 200 Hz and stored on an optical disc for off-line processing. The signal was DC-recorded and was subjected to fastFourier transform to produce band spectral powers for each trial epoch.The specified bands were: delta (0.0–2.9Hz); theta (3.0–7.9Hz); alpha (8.0–12.9Hz), beta 1 (13.0–17.9Hz), beta 2 (18.0–24.9Hz); and gamma (25.0–70.0Hz).DC was removed, wave forms were detrended, and any DC introduced bythis process was removed before the data were windowed at start and finish ofepochs, in order to prevent low frequency artefact caused by discontinuities.Absolute power values in arbitrary units were computed for each specified fre-quency band.

2.7. Statistical analysis

For convenience in analysis the electrode positions were grouped in topographi-cally meaningful clusters or ‘lines’. These were: midline (Fz, Cz and Pz); paramedial(Fp1, C3 and O1-left and Fp2, C4 and O2-right); and lateral (F7, T3 and T5-left andF8, T4 and T6-right). The electrode clusters covered frontal, central, parietal,temporal and occipital regions over both hemispheres.

For each subject, the Cognitive Styles Analysis gave two independent ratios-one indicating the position on the wholist-analytic dimension and the otheron the verbal-imagery dimension. Since each dimension is a continuumdivision into groupings is to some extent arbitrary and a matter of descriptiveconvenience. The subject sample was divided close to the median ratios oneach of the two cognitive style dimensions: wholist 0.82–0.99 (n=7), anal-ytic 1.00–1.63 (n=8); verbaliser 0.93–0.99 (n=7), imager 1.00–1.53 (n=8).This gave to four groupings: wholist-verbaliser (n=3), analytic-verbaliser(n=4), wholist-imager (n=4) and analytic-imager (n=4). Three repeatedmeasures analyses of variance were carried out, one for each cluster of elec-trodes. In the midline case this was of wholist-analytic style (two levels)by verbal-imagery style (two levels) with repeated measures for region (threelevels of electrode position) and frequency band (six levels). For each ofthe paramedial and lateral cases this was of wholist-analytic style (two levels)by verbal-imagery style (two levels) with repeated measures for frequency band(six levels) and electrode position: hemisphere (two levels) and region (threelevels).

In repeated measures analyses with more than two levels, the Huynh–Feldtprocedure was used to compensate for violations of sphericity, and the epsilonvalue and the adjusted probabilities will be reported in these cases. Post hoc t-testswere performed on the significant interactions, and all significant t values will bereported.


3. Results

3.1. Midline (Fz, Cz and Pz)

3.1.1. Region and frequency rangeThere was a significant interaction of region and frequency range (F=14.86; df

2.25, 24.76; pB0.001; epsilon=0.23), and inspection of Table 1 indicates thatpower output for delta and theta decreased from Fz to Pz, while alpha increased.Further, gamma peaked at Cz.

3.1.2. Wholist-analytic style and frequency rangeThe interaction of wholist-analytic style with frequency range was significant

(F=2.80; df 3.44,37.83; p=0.047; epsilon=0.69). Fig. 1 shows that in frontal,central and parietal regions midline, wholists have greater power than analytics fordelta, theta and alpha, but not the beta 1, beta 2 and gamma bands, with theanalytics having higher gamma output than wholists. Post hoc t-tests showed thatwholists differed significantly from analytics for alpha (t=3.05; df 13; p=0.009).

3.2. Paramedial group (Fp1, C3, O1-left; Fp2, C4 and O2-right)

Table 2 shows the mean power output for each frequency band, region andhemisphere for the verbalisers and imagers.

3.2.1. Region and frequency rangeAs in the midline cluster, there was a significant interaction of region and

frequency range (F=19.50; df 1.50, 16.47; pB0.001; epsilon=0.15) such thatpower output for delta and theta decreased from Fp to O, while alpha increased.

3.2.2. Verbal-imagery style, hemisphere and frequency rangeThe interaction of verbal-imagery style with hemisphere and frequency range was

significant in the paramedial cluster of electrodes (Fp1, C3, O1-left; Fp2, C4 andO2-right) (F=3.90; df 2.05,22.60; p=0.034; epsilon=0.41). Inspection of the

Table 1Mean power output for band and region

Band Mean power output for region (arbitrary units)

PzCzFz

Delta 4896 367777674341 3842 2409Theta

301820251621Alpha711 782 643Beta 1610Beta 2 547744

99413371232Gamma


Fig. 1. Mean power at midline electrode positions (Fz, Cz and Pz) for wholists and analytics for statedfrequency ranges.

overall mean values across regions in Table 2 shows that the asymmetry of meanpower over regions for this electrode group varied with frequency range andcognitive style. In the delta range, cognitive style affected the asymmetries such thatthe verbalisers had greater overall mean delta power on the left than right, whereasthe imagers had greater delta power on the right than the left. In the beta 2 andgamma ranges, mean asymmetries across regions also varied with cognitive style.verbalisers had greater overall beta 2 and gamma power on the left than rightwhereas with imagers beta 2 and gamma power was more symmetrical.

In order to show this more clearly, because there was a wide range in output inthe different bands, the ratio of the overall mean power output (right/left) wastaken for each region, and is shown in Fig. 2. Post hoc t-tests of the left versus rightratios showed that the difference between verbalisers and imagers for delta ap-proached significance (t= −1.92; df 13; p=0.078).

3.2.3. Verbal-imager style, hemisphere and regionThe interaction verbal-imager style by hemisphere by region was also significant

(F=5.43; df 2.00,22.00; p=0.012; epsilon=1.00), as shown in Table 2 by thecolumn ‘means over all bands’. In order to illustrate this, the ratio of the meanpower output over all bands (right/left) was taken for each region (Fp, C, O) forverbalisers and imagers, and is shown in Fig. 3.

Fig. 3 shows that frontally (Fp1 and Fp2), the R/L ratio in all frequency rangeswas greater for imagers than for verbalisers and occipitally (O1 and O2) greater for


verbalisers than imagers. Centrally, the ratios were almost equal. Hence, frontalpower in all frequency bands in verbalisers is greater on the left (Fp1) than the right(Fp2), but power in imagers in all frequency bands is greater on the right than onthe left. Occipitally, left overall power is considerably greater than right forimagers, but left almost equals right for verbalisers.

Fig. 3 indicates that the R/L ratio considered overall, shows a reversalin asymmetry from anterior to posterior with the imagers having higher out-put on the right than verbalisers at Fp and lower on the right at O in all fre-quency bands. Post hoc t-tests of the left versus right ratios showed that thedifference between verbalisers and imagers at Fp was significant (t= −2.61; df 13;p=0.021).

3.3. Lateral groups: F7, T3, T5 (left) and F8, T4 and T6 (right)

As in the other clusters, there was a significant interaction of region andfrequency range (F=14.41; df 10,110; pB0.001).

Table 2Mean power output for band and region for style group

Mean power output for style group andHemisphere and region Means over all bandsband (arbitrary units)

d t a b1 b2 g

VERBALISERRightFp2 89345986176591618511229830781

1576772713 1761165624473404C42149 1698 2891 765 788 2433O2 1787

12111 5481 2133 798Overall mean 1108 3332 (4161)

Left10315741326721056Fp1 19391333835472

3408 2446 1610 657 675 1274C3 167818541553O1 29661984 884 896 2843

(4616)5779 2172 866 1414Overall mean 384313621IMAGER

Right13547591262542622817Fp2 59844286

124621273014 577C4 647 1977 159813041356 1851 478 503O2 15422092

(2962)2970 1459 605 835Overall mean 26029307

Left20682 5315 1284 740 1332 4042Fp1 5516

3298 2290 1182C3 530 499 1006 14682071 166629348616022013O1 1514

(2899)266189762414933040Overall mean 8684


Fig. 2. Ratio of right/left (RL) mean power output over all regions for verbaliser and imager stylegroups. R/L\1: right power greater than left.

3.3.1. Cogniti6e style, hemisphere, regionThere was also a significant interaction between wholist-analytic style (2), verbal-

imagery style (2), hemisphere (2) and region (3) across frequency ranges (F=3.88;df 2, 22; p=0.036). The interaction is shown in Fig. 4.

Consideration of Fig. 4 suggests that compared with the other sub-groups thewholist-verbalisers showed much more power at all frequency bands on the leftantero-temporal region (T3). There were no marked asymmetries in either thefrontal (F7/8) or posterior temporal (T5/6) regions of any of the sub-groups. Post hoct-tests of the cognitive style groups showed that the difference between wholist-ver-balisers and analytic-verbalisers at T3 approached significance (t=1.90; df 5;p=0.116).

4. Discussion

The present paper further explores issues raised in earlier publications (Riding etal., 1993, 1997).


Before attempting to interpret these results from a relatively small sample, thecharacteristics of the tasks the subjects performed during EEG recording should benoted. It should be emphasised that the EEG findings relate solely to the period ofactual task solution. There were no formal ‘resting’ EEG data for comparison,which makes interpretation of inter-subject comparisons less easy. However, controlof resting EEG is, in any case, difficult. Also, the nature of the tasks was verbal andanalytic (not wholist and visuospatial). Further, the tasks necessitated that the eyesbe kept open, which reduces the alpha rhythm. Subjects looked at a monitor screenwhile words were presented and pressed a key-button if the word was in aparticular category. It can be seen that the task required perception of the words onthe screen and occasional movement, (button pressing). These are all task sub-com-ponents which have underlying neurophysiological concomitants in specific regionsand which in turn have EEG correlates, in addition to the analytic (separation ofwords with defined categories) and verbal (unconnected nouns rather than pictures)cognitive processes. Thus, EEG findings might be affected by the indirectly cogni-tive-related components, i.e. motor aspects of button pressing. Also, the lack of avisuospatial task element limited interpretation of the relation of EEG asymmetriesto hemispheric specialisation.

Fig. 3. Ratio of R/L power outputs for verbaliser and imager style groups. Regions: frontal (Fp), central(C) and occipital (O).


Fig. 4. Output for style, region and hemisphere for subgroups at left and right electrodes, as indicatedin Figure. WV, wholist-verbaliser; WI, wholist-imager; AV, analytic-verbaliser; AI, analytic-imager.

4.1. Region and frequency range interaction

The significant interaction of region and frequency range in the midline, parame-dial and lateral clusters which showed that alpha increased from Fz to Pz and deltaand theta decreased, is consistent with the well-known distribution of abundance ofalpha parieto-occipitally and is an important supporting validation of neurophysio-logical data.

4.2. Wholist-analytic effects

The findings in the wholist-analytic dimension of cognitive style were thatwholists had increased alpha power in frontal, central and parietal regions midline,(Fz, Cz and Pz) but the wholists also had somewhat increased power in otherfrequency ranges (delta and theta), except beta 1 and beta 2, and the gamma band.The analytics had more power than wholists in all three regions. Midline parietally(Pz) the wholist’s alpha superiority was maximal, that is, the difference betweenwholist and analytics was greatest. With respect to the relatively generalised midlinealpha superiority of the wholists compared with the analytics, the interpretation isthat the wholists generally showed more alpha synchronisation than analytics andwere, therefore, less aroused. It is likely because of the nature of the task beingcarried out and visual vigilance (with eyes open) required, that both wholists andanalytics would be in the upper part of the inverted-U shaped arousal curve (Otaet al., 1996). The lower alpha power of the analytics, therefore, indicates their


enhanced level of arousal compared with the wholists. Alternatively, the increasedarousal associated with low alpha power can be equated with increased mentalactivity that occurs during mental arithmetic (Glass, 1967; Pollen and Trachten-berg, 1972; Fernandez et al., 1995) and in regard to 10 Hz event-related desynchon-isation (ERD) (Pfurtscheller and Klimesch, 1992) reflecting greater generalisedcortical activation in the analytics. Interestingly, alpha power was lower in giftedthan average adolescents (Alexander et al., 1996). The reduction in the power atother frequency ranges (theta and delta) in analytics compared to wholists is lesseasy to interpret. One possibility is that it could be a result of a leakage from thehigher alpha frequency range power as part of the fast Fourier transform to deltaand theta bands. It is likely that beta 1 tends to follow alpha in respect ofsuppression by cortical activation, at any rate for visual stimulation (Vijn et al.,1991). Increased delta is contrary to this tendency, however, because it is associatedwith low arousal, particularly during sleep. Paradoxically, delta increased during amental task (Harmony et al., 1996).

A marked difference, between midline parietal alpha and other regions inwholists’ alpha superiority over analytics, if confirmed, would imply that it is acharacteristic of analytics that their posterior parietal lobes — the tertiary sensoryanalytic area of Luria (see Kolb and Whishaw, 1990) are more active in the solutionof verbal-analytic tasks than the parietal lobes of wholists. This is unexpectedbecause the posterior parietal lobe is also commonly associated with spatialprocessing.

4.3. Gamma band effect

In the midline, the gamma band showed greater power for the analytics. As thisband is supposed to reflect intracortical information transfer, (Basar-Eroglu et al.,1996a) and also as decision-making and focused attention are cognitive factorscontributing to frontal gamma (Basar-Eroglu et al., 1996b), it can be deduced thatthe analytics have greater intracortical information transfer than the wholists whilecarrying out the task. This is consonant with lower parietal and global alpha in theanalytics — both pointing to increased cortical activation. Also, it would implythat analytics have greater parietal cognitive capacity for factors such as focusedattention and decision-making than the wholists.

4.4. Verbal-imagery cogniti6e style

In the paramedial cluster, (Fp1, C3, O1; Fp2, C4, and O2), in considering theinteraction (verbal-imager style by hemisphere by frequency range), verbalisersexhibited greater left than right hemisphere preponderance of delta, beta 2 andgamma and this asymmetry was significantly stronger for imagers.

In the delta band, the greater mean delta power over the left hemisphere couldindicate lower left cortical activation than right cortical activation for verbalisersacross frontal, central and occipital regions and for the imagers lowered corticalactivation (high delta) over the right hemisphere. This is unexpected, as left


activation would be anticipated for verbalisers unless imagers’ left hemispheresmight, as it were, be ‘trying harder’ on a verbal task than the left hemispheres of theverbalisers. In contrast, the increased left gamma power for verbalisers mightindicate increased left hemisphere intracortical information transfer in the verbalis-ers, and might be predicted from consideration of enhanced left hemisphere verbalspecialisation in this style.

The beta 2 band has been related to cognitive activity (Ray and Cole, 1985) andfinger movement (Stancak and Pfurtscheller, 1995). It may be argued that anypossible increase in left beta 2 in verbalisers because of cognitive activity might beconfounded with asymmetry (especially centrally) because of a concomitant in-crease attributable to unilateral button pressing (finger movement) in verbalisers,although the finger movement related beta 2 synchronisation might be too transientto account for enhanced left beta 2 given three such movements in the 30-s trialperiod.

Interpreting increased gamma power as indicative of an increase in intracorticalinformation transfer, (Basar-Eroglu et al., 1996a) and focused attention, (Basar-Eroglu et al., 1996b), then it follows that focused attention and intracorticalinformation transfer are enhanced in the right cortex of verbalisers compared withimagers, whereas on the left the levels of these cognitive factors are equal. Thesecognitive dynamic asymmetry differences could be linked to field differences in theway verbalisers register the monitor screen to read the words. Gamma asymmetrydifferences have also been linked to emotional recall in high and low hypnotisables(De Pascalis et al., 1989). However, gamma localising and lateralising effectsespecially should be interpreted cautiously, because of cranial volume conductionfactors and overlapping fields of tangential and radial sources, particularly inregard to cortical sulci. The problem will be addressed in a future study.

It is noteworthy that the alpha R/L asymmetry index showed the least differencewith respect to the verbal-imagery dimension of style. This is unexpected givenlateralisation of the alpha band suppression for tasks involving the left hemisphere,(e.g. Butler and Glass, 1974; Klimesch et al., 1990a,b; Vijn et al., 1991). It would beexpected that the alpha band would be the most, not the least, asymmetrical ifverbalisers use their left hemisphere more than their right in verbal tasks, than doimagers. However, this may be an effect of using only verbal tasks in this study, butit might be predicted that the alpha range would show greater power for differenti-ating verbal-imagery style dimensions, if visuopatial tasks were used.

4.5. Region, hemisphere and 6erbal-imagery style

The significant interaction between region, hemisphere and verbal-imagery styleshowed that the asymmetry (R/L ratio) of total power reversed from anterior toposterior. Imagers had higher overall power on the right than verbalisers frontally,and lower occipitally. This must be regarded as a hemispheric difference betweenverbalisers and imagers in respect of neurophysiological activity in frontal andoccipital regions, but cannot readily be explained in underlying neurological terms,because the neurological significance of power over all frequencies is not under-


stood. It is akin to the measure of global field power which is associated withvarious aspects of modes of mentation (Lehmann, 1984; Lehmann and Koenig,1997) and linked to the envelope amplitude modulation (AM-EEG) also related tomentation (Etevenon, 1997).

4.6. Wholist-analytic by 6erbal-imagery interaction

The wholist-verbalisers differ from the other style groups in that the mean powerover all frequency ranges at T3 (left anterior temporal region) is greater than at T4.The precise significance in cortical terms of overall frequency range enhancement isunclear (see above) as for example, delta has the opposite significance in arousaland cortical activation terms from alpha and increased gamma power indicatesenhanced intracortical information transfer. If, however, it were the case that thealpha frequency range predominated at T3, then the lower overall power level in T4

compared with T3 would indicate greater right antero-temporal activity reflectingperhaps increased conceptual categorisation (used in the experimental task) in thewholist-verbaliser sub-group. Conceptual categorisation is postulated as a rightanterior temporal lobe function (Damasio et al., 1990).

In any case, the dynamics of the frequency range asymmetry may point to acorresponding difference in dynamics of functional asymmetry between the wholist-verbalisers and the other sub-groups.

5. Conclusion

In conclusion, it should be emphasised that although these were preliminaryfindings, several cognitive style-related EEG differences emerge from considerationof the full range of frequency bands.

Firstly, wholists had a higher level of midline alpha, but this style also showedsuperiority in the other frequency ranges, except beta 1 and 2 and gamma. Gammapower enhancement in analytics reinforced the alpha indication of increased globalcortical activation.

In comparison with imagers, verbalisers had greater gamma, delta and beta 2power on the left, over all the paramedial group of electrodes. This may possiblyreflect a differential interaction of left and right visual and motor systems in thiscognitive style dimension. Also, the wholist-verbaliser sub-group had greater powerover all frequency ranges on the left than the right antero-temporal region than theother three sub-groups. This may reflect a greater capacity for conceptual categori-sation in the wholist-verbalisers during the tasks.

The results appear to reflect a fundamental electrophysiological distinctionbetween style dimensions. The wholist-analytic dimension demonstrates a midlinealpha arousal effect whereas the verbaliser-imager dimension reflects more later-alised and localised effects.

Moreover, the results provide further reinforcement for the concept of thefunctional relevance of EEG frequency ranges, particularly the alpha range, tocognitive processes.


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