SEMANTIC CAPABILITIES OF THE LEFT AND RIGHT CEREBRAL HEMISPHERES IN CATEGORIZATION TASKS: EFFECTS OF VERBAL-PICTORIAL PRESENTATION ANTONIE~A NIETO,* *Department

SERGIO

HERNANDEZ,* Lurs GONZALEZ-FERIA~ and Josh: BARROSO*~

of Psychobiology. School of Psychology; and tDepartment of Neurosurgery. University of La Laguna. Tenerife. Canary Islands. Spain (Recei&

21 Octohrr

Medical

School.

1988; accepted 12 April 1990)

Abstract-Two lateral tachistoscopic experiments were carried out to test semantic capabilities of the left and right cerebral hemispheres through categorization tasks with verbal and pictorial presentations. RVF advantages were obtained for verbal presentations in both category-membership and category-matching tasks. However, no significant visual-field differences were found for any pictorial presentation. We also found a higher degree of sensitiveness of the positive judgements for the detection of hemispheric differences and sex differences in patterns of functional asymmetries with a greater lateralization in males.

INTRODUCTION THE REPORTSon the verbal capacity of the right hemisphere (RH) were one of the starting points for the formulation of the quantitative-relative nature of hemispheric asymmetry [8, 93. This formulation has, in turn, led to the study of the contribution of the RH to a process traditionally linked to the left hemisphere (LH). Among the studies on brain-damaged subjects, those carried out by GAINOTTI et ul. [lg. 191 stand out. According to the results of their research the RH lacks the capacity to carry out phonetic analyses but has a certain capacity for lexico-semantic analyses evidenced by their alteration as a result of the impairment. Similar conclusions may be found in several recent clinical studies [lo, 32, 541. Another line of research is the study of split-brain patients. The first reports [22, 521 revealed the existence of certain, though limited, verbal capacities in the RH. Subsequent research carried out by Ziidel pointed out that the RH has a rich lexical system together with some reduced syntactic and phonological systems and without any phonetic mechanism [.57-593. Gazzaniga, on the contrary, maintains that the capabilities showed by most splitbrain subjects are very rudimentary and, moreover, they cannot be generalized to the normal population in which the RH would lack linguistic capacity [20, 21, 231. Some research on neurologically normal subjects has revealed that the LH superiority in the processing of verbal material is not absolute (see BRADSHAW and NETTLETON [9] and SEARLEMAN [48] for a review). .

ZRequests for reprints and all correspondence should be addressed to Dr J. Barroso, Department Psychobiology. School of Psychology. University of La Laguna. Tenerife, Canary Islands. Spain. 1175

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These results have been obtained using different procedures among which the \ isual onch stand out and constitute the methodological framework for our research. According to some authors. the habitual RVF superiority in the making of lesical decisions and even in verbal identification tasks diminishes or disappears when concrete or high imagery words are presented [14, 1.5. 16. 561. For some authors the determining factor in this result might not be the imageability in itself but rather some factor which covariateh with it. such as the age of word acquisition. though evidence in this respect is not \er! satisfactory [S. 171. The effect of the concrete-abstract dimension seems to be. in turn. affected by the frequency or familiarity of the words. since the reduction of the RVF advantage in the processing of concrete material occurs mainly with familiar or frequenti), used words [7.X. 293. and by their syntactic class [ 15.24.28]. In general. these findings ha\c been interpreted as supporting the RH capacities for the lexical processing ofconcrete nouns. presumably, using an internal imagery-based lexical code [6. 15. 163. Several studies. however, have not found evidence ofa RH processing for words of such characteristics. Thu>. SCHMULLER and GOODMAU [47]. LAMBERT and BEAUMONT [34. 351. CHIARELLO v[ trl. [I I]. JACKMAN [31]. and HOWELL and BRYDEN [30], for example. have failed to reproduce these results or have provided only partial evidence. A second group of data on the possible contribution of the RH to the linguisitic processing arises from research studies on hemispheric differences in semantic processing using categorization tasks. The results are considerably contradictory showing both LH superiority [2.5] and no lateralization effect [ 141. Factors such as activation, practice and familiarity have been proposed to account for these inconsistencies [33. 531. The need for systematic and in depth studies to reveal the RH capacities and to perceive the variations among the already small visual-field differences is clear. In this point we come across two important difficulties. On the one hand, the limitations imposed by the technique of stimulus lateralization itself. inherent in the use of visual procedures. which determine the type of tasks and stimuli to be used. On the other hand. the existence of important variations among the different studies regarding the kind of presentation of stimuli. type of response. quality of the input. factors related to the practice/fatigue. memory load, attentional factors. etc. The influence of these factors has been the object of study in numerous research studies. with no definite conclusions being drawn in most cases [I 2, 36, 46. 49-51). We must also point out two subject-variables closely related to cerebral functional asymmetry and which should. at least. be carefully controlled: hand preference [6.7] and sex differences. As regards the latter, the review carried out b\, MCGL.ONE [37] provides evidence of a greater lateralization of functions or hemispheric specialization in male adults than in females. Although such a tendency is not confirmed by the results obtained in other research. especially in those which use very simple tasks or non-verbal tasks [26.42]. results obtained in our own laboratory lead us to point out the need to include sex as a factor in research on hemispheric specialization both in order to achieve a deeper study of the sexual differences and because they constitute an important source of variation in results [I -31. In this line. the purpose of the present paper is the study of RH semantic capacities in neurologically normal subjects. using visual procedures and emphasizing methodological controls. We presented two complementary research studies. In the first place (Experiment II we studied the hemispheric diffcrenccs in the establishing ofcategorizations, using basic-level concepts which must be considered as mcmbcrs or non-members ofa super-ordinate semantic category. that is. in the carrying out of ;I category-membership task. In Experiment II a category-matching task was used: to determine whether two concepts belong to the same

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superordinate category. In all cases they are natural, non-arbitrary, categories that correspond to the structure of the environment [38,44]. Our purpose was to study whether the RH capacities for the lexical processing of high imagery words suggested by several authors [14, 15, 16. 561, are also present in a deeper semantic task, i.e. in the making of membership or matching category judgements using nouns with the same characteristics. Previous studies have not found differences between visual fields in category-membership tasks, concluding that the RH can detect semantic relationships between certain nouns and their superordinate categories as efficiently as the LH [14,53]. Concerning the results in the category-matching tasks, GROSS [25] found a RVF superiority, while subsequent studies by URCUIOLI et al. [53] and KLEIN and SMITH [33] found that the RVF advantage in categorymatching tasks does not appear in the first blocks of experimental trials but it does in the following blocks and only when the same categories are maintained. According to Klein and Smith the emergence of a RVF advantage depends upon category constancy. However. some methodological aspects of these studies, such as the use of a vertical and simultaneous presentation, the use of a very limited number of categories. the repetition of stimuli. and the typicality and imagery control of those stimuli. present certain difficulties and may determine, at least partially, part of the results obtained. In our study we introduced some methodological modifications which. we believe. help to clarify the results. Thus, for example, we used a horizontal and successive presentation, a large number of categories and concepts which permitted to present each stimuli only once in each visual field, and we used concepts of high typicality and imagery. In addition, different modalities of stimulus presentation are used in order to study their effect on the access to their meaning. Sepecifically, we represent the basic concepts by high imagery nouns and drawings. We expect to find RVF advantages when the lateralized stimuli are nouns, even when they are high imagery ones, and no differences when pictorial representations of those stimuli are lateralized.

S~th/~~r.~. Thirty-two (16 males and 16 females) university students particlpatcd 111the e\pcrmwnt (mean age 20 yr. 5 months). All subjects were right-handed, with a mean of the LQ of +X7.6 according to the Edlnhurgh Handedness Inventory [40]. Their participation was voluntary. All had normal or corrected-to-n~)rmal vision and had no neurological damage. The sample was randomly divided into two groups ofsixteenwhjccts. the proportion between sexes being kept. S~~rmrlirrwl ir~.~trwwr.~. We used a total of 40 pairs of items made up ot”two consccutlvcly-prchclltcd stimuli. the first one represented the element and the second one rcprcscntcd the catcgor!. Half of them rcqulrcd allirmatlvc rcsponsca. mahlng up those items corresponding to the t\pc “altirmativc _iudgcmcnt”. The 20 remaining items belonged to the type “negative judgement”. In order to select the stimuli. we used a study carried out at this Um\cr\lr> Hhich had dctcrmlncd a group or \emantic cntc@es of supcrordinate level and the hierarchical posItton of wch mcmbcr. that 15. its typ~caht) or the extent IO ahich that member is more or less representatw of that catcgor! 1131. FIrstI!. the 2 moht rcprcwnt;nivc clement\ of each category farm. bird. clothing. flower. fruit. furniture. mammal. tool. whlclet uerc mcludcd m ;I prckmu\ stud! carried out to obtain the imagery ratings of ;Lset or Spanish u.~xd\. uhlnc ;I wmplc or IX9 auh~cct~ I 127 males and 67 fcmaleh. apt range I9 30). Four hundred and ten high Ircqucnt words wrc rated for Inwgcq in two questionnaires with randomly reverse orders (A and B). The ~cncral proccdurc and Instructions gven to the wh~ccts &crc similar to those used by PIZIVIO~ (11.[4l] and JActchfAl [ 3 I]. u\mg a live-pomt wale. Mean scow. SDs and SEM ticrc obtalncd for each sex. ror the type of presentation (A or H) and for the total group. Mean dilkrcnccs (I-test) bet~cen the scores In Imagery of each group were obtained. climmatlnp those word\ \rhox scow w;i\ slgnilicantly all’ccted h! se\ or order of presentation. Secondly. 40 elcmont\ whose nouns had four or live lcttcr\ and an Imagery score of 4.S 5 lhlgh imagery) were randomly chosen. Twent) elcmcnts wcrc prcscntcd in ;ISSOCI;IIK~ with thctr own catcgorl Ifor example. Car-Vehicle) (aflirmatlve judgemcnt ). the 20 rcmaimng cIcmcnt5 wcrc aswctatcd to any orthe

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catqor~es 3s long as II wab obclous that they did not belong to that category (for example. Aeroplsne-Fruit 1. T\\o modahtles for the preaenta~lon ofst~mull correspondme to the two expcrlmental groups uerc used. Group I : verbal presentation. Nouns corrcspondmp to the 40 elements were presented horzontall? in upper ux framed by a square with 4.5 cm sides. The names of the categorres also appeared horlzontall~ In upper cat framed b) a rectangle of 4.5 x 7 cm. Group 2: pictorial verbal presentation. Draulngs reprehentlng each of the above-mentloncd elements \tcrc‘ made. The drrlwinFs were simple. with those details not relevant for their Identification hems ellmmatcd. and wtthout shading. The drawings were made In black on a white background and approximately occupy? an arca correpondmg to a square Hith 3 cm sides. The names of the categories were presented follow lng the same procedure 3s m the pre\ lous modalit>. Stimuli were presented on 22.5 x 32.3 cm white cards. In a Gerbrnnds. G-l IZOT-IC-3 2-tield tachlstohcopc. 4 dot of phosphorescent paint placed at the centre of the visual field served as ;I fixlitton pomt. The firsr element of each Item (noun or drawmg) was presented unilateralI) and onl) once. either in LVF or R\‘F (tieId I of the lachlstoscope): the second element (name of the category) u’a\ centrally presented lFleld 2). The dra\+lng\ and the four-letter uords subtended a horizontal visual angle of 2.5 to sub_iects. The distance from the tiuation point to the nearest edge was 2.75 , and to the furthest was 5.25 The tive-letter nouns subtended a blsua1 angle of! the Inner edge wcaa2.5 and the outer edge 5.5 of visual angle from the fixation point. Reaction time5 wcrc measured using a millisecond chronoscope LalTayette. model-63012. connected t