Theta power in the EEG of humans during ongoing processing in a haptic object recognition task

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1 Cognitive Brin Reserch 11 (001) locte/ bres Reserch report Thet power in the EEG of humns during ongoing processing in hptic object recognition tsk *, b c d e Mrtin Grunwld, Thoms Weiss, Werner Kruse, Lothr Beyer, Reinhrd Rost, b Ingmr Gutberlet, Hermnn-Josef Gertz EEG Reserch Lbortory, Deprtment of Psychitry, University of Leipzig, Emilienstrße 14, D Leipzig, Germny b Deprtment of Biology nd Clinicl Psychology, Institute of Psychology, Friedrich Schiller University Jen, Jen, Germny c Institute of Psychology, Deprtment of Generl Psychology, Friedrich Schiller University Jen, Jen, Germny därztehus Mitte, Jen, Germny e Deprtment of Neurophysiology 1, Institute of Physiology, Friedrich Schiller University Jen, Jen, Germny Accepted 19 September 000 Abstrct Dynmic chnges in spectrl thet power (TP) in the EEG over frontl regions were reported previously during the processing of visully presented sptil nd verbl tsks [Cereb. Cortex, 7 (1997) ]. Lower TP ws found t the beginning compred to the end of processing. In order to test nother modlity, we exmined thet power during the explortion of hptic stimuli with different complexity. A liner correltion between thet power nd men explortion time (s mesure of stimulus complexity) ws found t the end of explortion but not t its beginning. These dt re in line with our hypothesis since one could expect miniml lod of working memory independent of stimulus complexity t the beginning of explortion wheres working memory would hve integrted the stimuli of differing complexity into perceptul model t the end of explortion. 001 Elsevier Science B.V. All rights reserved. Theme: Neurl bsis of behvior Topic: Lerning nd memory: systems nd functions Keywords: EEG; Thet power; Memory lod; Working memory; Hptic perception 1. Introduction gies seem to follow the schem tht informtion of detils of the object will be ssessed successively [9,10]. In Gevins nd coworkers [4] found for visully presented different studies it ws ssumed tht cognitive processing sptil nd verbl tsks significnt increse in thet of hptic object recognition is seril process tht involves power (TP) over frontl regions t the end of processing working memory [1,16]. Thus, it ws demonstrted tht compred to the beginning. Thus, it hs been shown by the velocity of processing hptic stimulus depends on the these uthors tht dynmic chnges of TP occur during the mount of informtion inherent to the stimulus (i.e. of the processing of visully presented stimuli. However, it hptic object). Additionlly, we showed tht explortion remins uncler whether or not similr dynmic chnges time for hptic object recognition increses with subjective exist during the processing of stimuli in other modlities. stimulus complexity (r50.634, P,0.001) [5]. In these Therefore, we investigted chnges of TP during hptic studies s well s in some others functionl reltionship perception tsks. ws hypothesized between spectrl power density within Hptic object recognition tsks usully re relized by the thet bnd of the EEG (thet power) nd working successive hnd explortions [14]. The explortion strte- memory lod during the processing of the stimulus mteril [1 3,6,7,11,13,15,18]. If this hypothesis is correct one *Corresponding uthor. Tel.: ; fx: should expect tht thet power is suitble prmeter to detect different stges within the seril processing of hptic E-mil ddress: mgrun@medizin.uni-leipzig.de (M. Grunwld). object recognition. One might postulte tht t the begin / 01/ $ see front mtter 001 Elsevier Science B.V. All rights reserved. PII: S (00)

2 34 M. Grunwld et l. / Cognitive Brin Reserch 11 (001) ning of the explortion no knowledge bout the structure processing of hptic stimuli differing in complexity in or complexity of the stimulus exists, i.e. one would expect delyed recll design. The hptic explortion tsk conthet power to be independent of the stimulus mteril sisted of plpting the structure of 1 sunken reliefs of during the initil prt of explortory processing. However, cm which were presented in pseudorndom order percept of the object will be built up in the course of with eyes closed. The structure of the reliefs consisted of explortion. Thereby, informtion bout the object will be milled trces with depth of 3 mm nd width of 7 mm. processed successively leding to working memory lod Then 10 s fter the end of explortion (retention), subjects depending on the complexity of the given stimulus. In were sked to reproduce ech relief by drwing it on ccordnce with the hypothesis of functionl reltionship sheet of pper with their eyes open. Explortion time per between thet power nd working memory lod, these stimulus ws not limited but ws registered by mens of different lods should be ccompnied by different levels pressure sensors nd PC time-keeping (in seconds). Subof thet power. Thus, we hypothesize tht thet-power t jects were prevented from gthering visul informtion on the beginning of hptic explortion is not relted to the the stimuli. They received no feedbck on the qulity of complexity of the stimuli wheres cler liner reltion- their reproduction or on the stimulus structure. The timing ship is expected t the end of explortion. The im of the sequence of typicl tril nd two exmples of hptic present study ws to test this hypothesis using hptic stimuli re shown in Fig. 1. explortion tsk. EEG (Wlter Grphtek, Bd Oldesloe, Germny) ws continuously recorded during rest, hptic explortions, nd dely (retention) conditions. In ccordnce with the Inter-. Mterils nd methods ntionl 10-0 System [8], Ag-AgCl electrodes were ttched to the sclp t stndrd electrode positions (Fp1, A totl of six subjects (three femles, three men, 18 3 Fp, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, yers old, ll unfmilir with the im of the study) P4, O1, O; reference: linked erlobes, smpling rte: 333 volunteered for this study which ws pproved by the locl Hz, time constnt: 0.3 s, low pss filter: 70 Hz). Horizontl ethics committee. We investigted thet power during the nd verticl eye movements were recorded from bipolr Fig. 1. Schemtic time course of single tril. The upper prt illustrtes the different intervls (rest, explortion, retention, drwing) nd the exmined beginning nd end intervls. The lower prt shows two exmples of the stimulus mteril, more complex one (left) nd less complex one (right).

3 M. Grunwld et l. / Cognitive Brin Reserch 11 (001) montges with the sme smpling prmeters. During dt tively. The segments were submitted to fst Fourier cquisition, the EEG ws displyed on monitor nd trnsform (FFT) nlysis nd smoothed with seven-point stored on hrd disk. Segmenttion of EEG dt nd low-pss filter (weights 1/ 64, 3/ 3, 15/ 64, 5/ 16, 15/ 64, subsequent clcultions of the men spectrl power density 3/3, 1/64) in order to blnce out between resolution of were performed with n EEG nlyticl softwre pckge the power spectr nd their vrince. Men spectrl power [17]. Artefct-free segments of 1.53 s (51 smples/ chn- density ws clculted s the men mplitude of the nel) from the rest period (R), from the beginning (BI) nd spectrl lines of ech EEG bnd (thet: 4 8 Hz, lph: from the end of hptic explortion (EI) were used. Artefct 8 13 Hz, lph1: 8 10 Hz, lph: Hz). contminted segments were detected using visul inspection nd cross correltion nlysis between frontl EEG nd EOG electrodes (r crit.,0.5) nd subsequently re- 3. Results moved. Two rtefct-free successive segments were chosen for ech stimulus locted 500 ms fter the onset of The reltionship between explortion time nd thet explortion (BI) nd 500 ms before its end (EI), respec- ctivity ws nlysed with liner regression model. In Fig.. Regression plots for significnt (P,0.05, r.0.3) individul tests of the liner regression model between men z-trnsformed thet power from the end intervl nd men explortion time.

4 36 M. Grunwld et l. / Cognitive Brin Reserch 11 (001) previous experiment we hve shown tht subjective com- estimtes (r,0.3) nd no significnt differences in regresplexity of the stimuli correltes with explortion time [5,6]. sion coefficients. Thus, stimuli were rrnged in order of incresing explor- The regression estimtes for lph, lph1, lph, tion time for ech subject to ccount for individul bet1, nd bet power in the EEG showed no significnt differences in perceived stimulus complexity nd to nor- differences either for BI or for EI. mlize for complexity. The regression nlysis used z-trnsformed (men50, S.D.51) men thet power for BI nd EI segments. When 4. Discussion testing the centrl hypothesis, we focused on systemtic liner trends between thet power nd men explortion We observed lck of correltion between thet power time in 19 single tests for BI nd 19 single test for EI nd explortion time (s mesure of stimulus complexity) (50.05, Bonferoni corrected ). Furthermore, t the beginning of hptic explortion (i.e. during BI). In we lso exmined the liner regression model for ll contrst, thet power nd explortion time were found to individul comprisons between 19 chnnels nd men correlte t the end of hptic explortion (EI). The explortion time in order to justify this pproch. correltion ws observed for ten out of 18 electrodes No significnt chnges were found estimting the liner including centrl, prietl, nd prieto-temporl regions model (r ) for the BI intervl, i.e. none of the P-vlues bilterlly. This is in line with our hypothesis postulting reched the criticl For the EI intervl, signifi- miniml working memory lod t the beginning of explocnt liner trends were found between z-trnsformed thet rtion. At tht time, working memory lod should be power nd men explortion time. The estimtes (r ) for independent of stimulus complexity since no priori the liner model were highest for F3, C3, C4, P3, P4, O, knowledge exists concerning the given hptic stimulus, s T5, T6, Cz, nd Pz. Regression plots with significnt cn be seen from the lck of correltion between thet coefficients for EI re shown in Fig.. Tble 1 shows the power nd stimulus complexity during BI. In contrst, t F-sttistics for testing the null hypothesis for BI nd EI. As the end of explortion nerly ll fetures of the stimulus cn be seen from Tble 1, the regression coefficient (b1) should be integrted into perceptul model of the object, ws found to be significntly different from zero in ten out since the subjects could explore the hptic object s long of 19 tests. During EI the vlue ws below the criticl s they considered necessry. It seems plusible tht for electrode Cz. Therefore, significnt liner working memory lod during this period depends primrily reltionship between thet power nd men explortion on the complexity of the stimulus mteril. This is in line time cn be ssumed. The tests of the liner model for Fp1, with the observed liner trend between thet power s Fp, F4, O1, F7, F8, T3, T4, nd Fz showed smller model postulted mesure of working memory lod nd explor- Tble 1 Results of the liner regression nlysis between z-trnsformed thet-power during the beginning (BI) nd ending intervls (EI) nd men explortion time Elect. BI EI r df F Sig. F b0 b1 r df F Sig. F b0 b1 Fp Fp F F C C P P O O F F T T T T Fz Cz Pz Significnt coefficients re in bold. Elect., electrode; r, model estimtes; df, degrees of freedom; F, F-sttistic; Sig. F, significnce level; b0 nd b1, model coefficients.

5 M. Grunwld et l. / Cognitive Brin Reserch 11 (001) tion time s postulted mesure of stimulus complexity. [7] K. Irmin, S. Ueno, S. Mtsuok, MEG nd EEG topogrphy of However, our dt cn only spotlight the continuous frontl midline thet rhythm nd source locliztion, Brin Topogr. 8 (1996) processing of hptic stimuli. Specil prdigms re neces- [8] H.H. Jsper, The Ten Twenty Electrode System of the Interntionl sry to llow the exmintion of the proposed seril Federtion, Electroenceph. Clin. Neurophysiol. 10 (1958) processing of such stimuli in more detil. [9] R.L. Kltzky, S.J. Ledermn, D.E. Mtul, Hptic explortion in the presence of vision, J. Exp. Psychol. Hum. Percept. Perform. 19 (1993) [10] R.L. Kltzky, J.M. Loomis, S.J. Ledermn, H. Wke, N. Fujit, Acknowledgements Hptic identifiction of objects nd their depictions, Percept. Psychophys. 54 (1993) The uthors would like to thnk G. Kruse nd U. Krft [11] W. Klimesch, M. Doppelmyr, H. Schimke, B. Ripper, Thet for their technicl support. This reserch project ws synchroniztion nd lph desynchroniztion in memory tsk, supported in prt by grnt from the Friedrich Schiller Psychophysiology 34 (1997) [1] S. Knecht, E. Kunesch, A. Schnitzler, Prllel nd seril processing University Jen. of hptic informtion in mn: effects of prietl lesions on sensorimotor hnd function, Neuropsychologi 34 (1996) [13] A. Mecklinger, Gedchtnissuchprozesse-eine Anlyse ereigniskor- References relierter Potentile und der EEG-Spontnktivitt, Psychologie Verlgs-Union, Weinheim, 199. [14] B.A. Morrongiello, G.K. Humphrey, B. Timney, J. Choi, P.T. [1] R.S. Dniel, Alph nd thet EEG in vigilnce, Percept. Motor Rocc, Tctul object explortion nd recognition in blind nd Skills 5 (1967) sighted children, Perception 3 (1994) [] A. Gle, B. Christie, V. Penfold, Stimulus complexity nd the [15] P. Pennekmp, R. Bosel, A. Mecklinger, H. Ott, Differences in occipitl EEG, Br. J. Psychol. 6 (1971) EEG-thet for responded nd omitted trgets in sustined ttention [3] P.S. Goldmn-Rkic, Corticl locliztion of working memory, in: tsk, J. Psychophysiol. 8 (1994) J.L. McGugh, N.M. Weinberger, G. Lynch (Eds.), Brin Orgniz- [16] B. Roeder, F. Rosler, E. Hennighusen, Different corticl ctivtion tion nd Memory, Oxford University Press, New York, ptterns in blind nd sighted humns during encoding nd trns- [4] A. Gevins, M.E. Smith, L. McEvoy, D. Yu, High-resolution EEG formtion of hptic imges, Psychophysiology 34 (1997) mpping of corticl ctivtion relted to working memory: effects of [17] R. Rost, E. Hnsen, L. Beyer, T. Weiss, EEG topogrphy softwre tsk difficulty, type of processing, nd prctice, Cereb. Cortex 7 for description of centrl nervous ctivtion, in: W. Hschke, E.J. (1997) Speckmnn, A.I. Roitbk (Eds.), Slow Brin Potentils nd Mg- [5] M. Grunwld, Hptische Reizverrbeitung und EEG-Vernderungen, netic Fields, Friedrich Schiller Universitt Jen, Jen, 199, pp. unpublished thesis, Jen, [6] M. Grunwld, T. Weiss, W. Kruse, L. Beyer, R. Rost, I. Gutberlet, [18] D.L. Schcter, EEG thet wves nd psychologicl phenomen: H.J. Gertz, Power of thet wves in the EEG of humn subjects review nd nlysis, Biol. Psychol. 5 (1977) increses during recll of hptic informtion, Neurosci. Lett. 60 (1999)