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ISSN 03621197, Human Physiology, 2011, Vol. 37, No. 2, pp. 137–142. © Pleiades Publishing, Inc., 2011. Original Russian Text © O.M. Razumnikova, N.V. Volf, 2011, published in Fiziologiya Cheloveka, 2011, Vol. 37, No. 2, pp. 14–19.

Information Processing Specialization during Interference between Global and Local Aspects of Visual Hierarchical Stimuli in Men and Women O. M. Razumnikova and N. V. Volf Research Institute of Physiology, Russian Academy of Medical Sciences, Siberian Branch, Novosibirsk, 630117 Russia Received March 3, 2010

Abstract—Sexrelated differences in global/local hemispheric selective processing were examined by hierar chically presented letters in conditions of their perception and comparison. Fiftysix righthanded men and 68 women (aged 17–22 years) participated in the experiment. During the interference between global and local aspects of stimuli, the mean reaction time for correct global responses was shorter than for local responses, and the right hemisphere dominated during global selective processing independently of sex. Sex related differences in perception of visual hierarchical stimuli were more pronounced than during their com parison: men preferred the righthemispheric global strategy of information processing, and women, the left hemispheric local one. The dominance of the global strategy in men and local strategy in women during visual hierarchical stimuli perception, together with the absence of sexrelated differences in correct responses indi cates the possibility of obtaining the same efficiency of cognitive activity in different ways. Keywords: sexrelated differences, strategies of information selection, hemispheric asymmetry. DOI: 10.1134/S0362119711020186

In studying hemispheric features of the cognitive activity of different species, including creative activity, it was found that the solution of creative tasks of both images and those that are verbal in nature is accompa nied by different forms of interaction of hemispheres in men and women and, apparently, by different strat egies of search for the original solution of the problem [1, 2]. On the other hand, the hypothesis is known that sexrelated differences in cognitive functions can be related to specific features of selective processes: the predominance of the strategy of local search and detailed processing of separate information elements in women and a global strategy with an inclination for heuristic decision making in men [3]. Considering that the right hemisphere is characterized by a greater specialization in the integral perception of a signal and a global strategy of information analysis [4] and that there are data on sexrelated differences and the func tional asymmetry of hemispheres in selective pro cesses [5, 6], the purpose of our study was to clarify specific features of the hemispheric selection of visual hierarchic stimuli at the global and local levels in men and women. The clarifying of these specific features is of interest not only for experimental checking of Mey ers and Levy’s hypothesis, but also because this makes it possible to come nearer to clarifying the principles of selective processes forming the basis of efficient cre ative activity. We used Navon’s [7] paradigm, which is widely used for clarifying individual specific features of the

organization of visual perception in humans. Conflict variants of the perception of large letters hierarchically composed of small ones not coinciding in their mean ing make it possible to clarify which effect of interfer ence, global or local, is the most typical of the given individual. The recently published paper by Machin skaya et al. indicates the existence of different strate gies of perception: “global,” i.e., with preference of the choice of the global characteristic of the stimulus or the “local” one [8]. Since it is known that men are characterized by a more pronounced, as compared to women, functional asymmetry of hemispheres [9– 11], one could suggest that in an experimental situa tion intended for clarifying sexrelated differences in the preference of a global or local strategy, they will be more inclined to use the former strategy of analysis of visual stimuli. This study was performed to test this hypothesis. METHODS One hundred and twentytwo students (56 men and 68 women aged 17–22 years) with normal or corrected to normal vision participated in the study. All of them were righthanded according to the Annette question naire. The subjects gave their informed consent to par ticipate in the experiment that was approved by the Ethical Committee of the Research Institute of Phys iology.

137

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Fig. 1. An example of hierarchically organized letters used as stimuli in this study.

To study specific features of global and local atten tion, Navon’s paradigm was used [7]. Global stimuli were large letters H, E, A, B that consisted of the same stimuli of smaller sizes (local). All combinations of large and small letters, i.e., HE, HA,HB, EH, etc. were used (examples of the letters are shown in Fig. 1), except congruent combinations (for instance, EE or HH), because it is known that the conflict between the local and global levels of information processing is more pronounced in the case of the noncoincidence of the meanings of letters [4]. The vertical size of large letters was 4.5°, and of horizontal letters, 3.3°; those of small letters, 0.7° × 0.6°, respectively (the author of the program is K.Yu. Bortsov). Stimuli in a pseudorandom order were presented on a 15inch monitor (resolution 1280 × 800 pixels, frequency of regeneration of images 60 Hz) at a dis tance of 5° from the left or from the right from the point of fixation. The time of presentation of the point of fixation was 500 μs. Simultaneously, stimuli were 5.5

*

5.4 5.3 5.2

*

5.1 5.0

gl loc gl loc RH LH Men

gl loc gl loc RH LH Women

Fig. 2. The number of correct answers in the tasks of rec ognizing global (gl) and local (loc) stimuli addressed to the right (RH) and left (LH) hemispheres in men and women. Significant differences are indicated by asterisks.

presented for 160 μs. The interval between the starts of stimulus presentations was 1500 μs. Four series of stimuli presentation were used. The purpose of the first two series was to study specific fea tures of the perception of global and local stimuli. For this purpose, in the first series, the subject had to press one key of the computer keyboard if a large letter “H” appeared on the screen, and another, when a large “E” appeared, ignoring all the remaining characteristics of the stimuli. All subjects worked with the right hand. The target stimuli (50% of the total set of stimuli) were presented to the left or right fields of the vision, mak ing 20 presentations of each target letter. In the second series, the subject had to respond, in contrast, to the small letters “h” or “e.” Two other series of the exper iment were intended to study the selection of global and local stimuli in different situations, namely, upon presentation of two stimuli either to the left or to the right field of vision or simultaneously to both. In the third series of the experiment, it was necessary during the comparison of the two letters to respond to similar global stimuli “H” or “E”, and in the fourth series, to similar local stimuli “n” or “e”. The time of stimuli presentation in the fourth series of the experiment was increased to 170 μs since the previous experiments demonstrated a great number of errors at 160 μs. A training session preceded each series of the experi ment. In all series, the time of response for the correct answers and their number for different variants of stimuli presentation was recorded. RESULTS Recognition of hierarchic stimuli at global and local levels. ANOVA of correct answers was performed with the independent variable SEX and dependent variables STIMULUS (global/local) and HEMISPHERE (right/left). A significant interaction of factors SEX × STIMU LUS × HEMISPHERE (F1.120 = 4.91; p = 0.028) was found. Post hoc analysis of this interaction using Fisher’s test showed that in men the number of correct answers for global stimuli addressed to the right hemi sphere was significantly greater than for local ones (p = 0.03). According to the planned data analysis, in men, the number of correct answers depending on the type of the target stimulus also differed: for global stimuli, their number was greater upon addressing the right hemisphere, and for local stimuli, the reverse; while in women, only the number of correctly recog nized local stimuli with best results upon addressing the right hemisphere (Fig. 2). According to the ANOVA of the index of the response time, the interaction of SEX × STIMULUS (F1.118 = 3.85; p = 0.952) was significant; it was deter mined by the fact that in men, the time of response to global stimuli is shorter than for local stimuli and smaller than in women (p = 0.01 according to planned comparisons), who have no significant differences HUMAN PHYSIOLOGY

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Response time for the recognition of global and local stimuli dependent on sex and the side of presentation SEX

HEMISPHERE

Stimulus men

women

left

right

Global

774 ± 63*

829 ± 57

825 ± 35#

785 ± 27#

Local

873 ± 59*

884 ± 55

888 ± 32

870 ± 29

Notes: Identical symbols indicate the values that significantly differ from each other (p < 0.004, Fisher’s test).

between local and global stimuli (table). The interac tion STIMULUS × HEMISPHERE (F1.118 = 4.59; p = 0.034) was also significant: a smaller time of recog nition of global stimuli than of local stimuli was more pronounced for the right hemisphere than for the left (table). To clarify whether there are sexrelated differences in the preference for global and local strategies of per ception of hierarchic visual stimuli, the time of the response to the global stimulus was subtracted from the time of the response to the local one. At positive values of the difference, the subjects were assigned to those who prefer a global strategy; at negative values of the difference, the subjects were assigned to those who prefer a local strategy; and those subjects who upon a change of the field of vision or the letter type showed different symbols, comprised a mixed group. It turned out that most subjects (67.2%) preferred the global strategy of perception of visual images; a few subjects (12.6%) preferred the local strategy; and 20.2% of the subjects preferred a mixed strategy. The local and mixed strategies were used by women to a greater extent than by men: 41.5 and 22.2%, respectively (р = 0.05 according to the χ2 test). Comparison of hierarchic stimuli at global and local levels. Dispersion analysis ANOVA of the correct answers was performed with the introduction of the same factors, SEX and STIMULUS, as in the first part of the analysis, and for the factor HEMISPHERE, three levels were used: left/right/both. The common effect for the factor STIMULUS was discovered (F1.118 = 3.96; p = 0.049): the number of correct com parisons of global stimuli was greater than for local ones, and the interaction STIMULUS × SEX (F1.118 = 4.11; p =0.045): a great number of correct answers in the comparison of global stimuli were sig nificant only in men (р = 0.007); in women, there were no differences. Another common effect was obtained for the factor HEMISPHERE (F2.234 = 9.30; p = 0.0001): the number of correct answers upon presenta tion of stimuli to the two fields of vision was greater than upon addressing each hemisphere (6.8, 6.6, and 7.0 for the left, right, and both fields of vision, respec tively). The interaction STIMULUS × HEMI SPHERE was significant (F2.234 = 33.24; p < 0.0001): a greater number of correct answers found for the sit uation of stimuli presented to both fields of vision was typical of global stimuli. Only for this situation did the HUMAN PHYSIOLOGY

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numbers of correct answers during the comparison of global and local stimuli differ, and for the two other sit uations, they did not. Post hoc analysis of the correct answers for different situations of the presentation using Fisher’s test demonstrated that significant dif ferences for global stimuli arose not only in the case of the comparison of the situation with the presentation in the two fields of vision but a greater number of cor rect answers was obtained also in the case of addressing stimuli to the right hemisphere than to the left (Fig. 3a). For local stimuli, a smaller number of cor rect answers were found upon presentation to both fields of vision as compared to the right or left fields. The analysis of the time of response showed signif icant common effects: STIMULUS (the time of the response in the comparison of local stimuli was greater than it was for global stimuli), HEMISPHERE (the time of response at the presentation of stimuli to the two fields of vision was smaller than it was at the pre sentation of stimuli to the left or right fields of vision), and the interaction STIMULUS × HEMISPHERE (F2.230 = 19.90; p < 0.0001) (Fig. 3b). The maximum differences in the time of response were typical of the situation with stimuli presentation to both fields of vision; and the differences were minimal, when addressing the right hemisphere. For local stimuli, the time of response upon stimuli presentation to the left or right fields of vision did not differ significantly; while for global stimuli the time of response was differ ent (р = 0.0001 according to Fisher’s test), with smaller values when addressing stimuli to the left hemisphere. Analysis of the strategies of stimuli comparison performed for this part of the experiments similar to the first part also demonstrated the domination of a global strategy (in 62.4% of cases) without any signifi cant differences in the preferences between men and women. DISCUSSION The results obtained in the part of the study con cerning the selection of hierarchic stimuli at the global and local levels coincide with the effect detected ini tially by Navon, and then also in several subsequent studies [4, 7, 12, 13]: the time of response to a global stimulus is smaller than to a local one, and the right hemisphere dominates during the processing of global

140 (a) Number of correct answers 8.0 7.8 7.6 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 5.8 RH LH Response time, ms (b) 900

RAZUMNIKOVA, VOLF

global

local

IP

850 800 local 750 700 650

global

600 550 Fig. 3. (a) The number of correct answers and (b) the response time in the experiments in the comparison of glo bal and local stimuli addressed to the right (RH), the left (LH), and both (IP) hemispheres.

properties of the stimulus. Good agreement was also obtained upon comparison of individual preference of the global or local strategy of perception of hierarchic visual stimuli in our study and the study by Machin skaya et al. (67.2 and 68.8%, respectively) [8]. This allows us to conclude that there are common, sexindependent, principles of processing complex visual stimuli. Few studies in which special attention was paid to the analysis of specific features of the selection of hier archic stimuli at the global and local levels inherent to men or women yield contradictory results [14–16]. In one case, it was shown that women respond more rap idly to local stimuli than men, while in men, there are no differences in the rate of response to hierarchic stimuli [16]. However, in other studies, no sexrelated differences of this kind were revealed; moreover, women, on the reverse, perform local classification of stimuli slower, though more accurately [14, 15]. In our study, sexrelated differences concerned mainly the perception of the global characteristics of letters: men more rapidly than women recognized these target stimuli, and, for men, hemispheric spe

cialization was typical during the perception of hierar chically organized stimuli, with the domination of the right hemisphere for the global level of selection, and of the left, for the local stimulus. It is known that dif ferences in the rate of recognition of hierarchic visual stimuli are determined by the interference and conflict of their local and global properties and are determined by specific features of the topdown regulation of the cortex of the left and right hemispheres [17]. The results obtained by us indicate a pronounced lateral ization of these functions in men and a stable domina tion of the global strategy of the right hemisphere dur ing both the perception of hierarchically organized letters and their comparison. In women, the strategy of perception of such stim uli differs at the expense of a wider use of selective pro cesses of the local level, as compared to men, which finally leads to a great diversity in the individual vari ants of processing visual information. This is shown by the results of analysis of the response time in the case of intentional selection of a signal at its local or global level: a comparatively greater preference by women of the local and mixed strategies of recognition of letters and also the fact that they provided more correct answers when addressing local stimuli to the right hemisphere. This effect can be explained by the fact of a closer hemispheric interaction in women than in men [18, 19]. So, the right hemisphere offers advan tages as a result of the rapid transfer of additional information from the left hemisphere associated with the detailed processing [3]. Note that the final result of activity, i.e., the total number of correct answers, does not differ in men and women for either global or local stimuli. Thus, we obtained additional proof of sex related differences in the mechanisms of brain activity per se, without such differences at the behavioral level shown previously in different models of study of cog nitive functions in men and women [1, 2, 5, 9, 20, 21]. In the experimental situation of comparisons of hierarchic stimuli, sexrelated differences also involved the difference in correct responses in the case of the comparison of the global and local levels of the processed information, with preference of the former in men and the absence of this effect in women. Since no significant sexrelated differences in the total num ber of correct answers were found under these condi tions either, we may conclude that, at the same effi ciency in the selection of visual hierarchic stimuli at the behavioral level, men to a greater extent rely on the righthemispheric global strategy, and women, on the lefthemispheric local strategy. Hence, the results obtained support our working hypothesis of the study based on the published evidence on sexrelated differ ences in information processes [3, 22]. In correspondence with the theory of regulation foci, individual preferences of perception of hierarchic stimuli at a global level are related to the promotion strategy for the search for progressive activity while the preference of a local level indicates a prevention strat HUMAN PHYSIOLOGY

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egy focused on protection [23, 24]. Sexrelated differ ences in the preference of a global or local level of selection of visual hierarchic stimuli found here agree with this theory and the known postulates of a more pronounced strategy of prevention and hemispheric asymmetry associated with development of depressive states in women [25−27]. CONCLUSIONS (1) In the case of a conflict of information at the global and local levels, the time of response to a global stimulus is faster than to a local stimulus, and the right hemisphere dominates during the processing of global properties of a stimulus. (2) Sexrelated differences in the perception of visual hierarchic stimuli are greater than in the case of comparison and consist of men to a greater extent pre ferring a righthemispheric global strategy of informa tion selection, and women preferring a lefthemi spheric local. (3) Domination, in men, of the global strategy in the perception of visual hierarchic stimuli and, in women, of local and mixed strategies, in the absence of sexrelated differences in the total number of correct responses, indicates the possibility of achieving equal efficiency in cognitive activity in different ways. ACKNOWLEDGMENTS The study was supported by the grant of the Rus sian Foundation for the Humanities “The Role of Selective Processes in the Formation of Strategies of Creative Thinking” (project no. 080600615a). REFERENCES 1. Volf, N.V., Tarasova, I.V., and Razumnikova, O.M., Sexrelated Differences in Changes of Coherence of Brain Cortex Biopotentials at Image Creative Think ing: Relation to Activity Efficiency, Zh. Vyssh. Nervn. Deyat. im. I.P. Pavlova, 2009, vol. 59, no. 4, p. 429. 2. Razumnikova, O.M., Vol’f, N.V., and Tarasova, I.V., Strategy and Results: Sex Differences in Electrographic Correlates of Verbal and Figural Creativity, Fiziol. Chel., 2009, vol. 35, no. 3, p. 31 [Human Physiol. (Engl. Transl.), vol. 35, no. 3, p. 285]. 3. MeyerLevy J. Gender differences in information pro cessing: A selectivity interpretation. Cognitive and Affective Responses to Advertising. Eds. P. Cafferata, A. Tybout., MA: Lexington, 1989, p. 219. 4. Volberg, G. and Hübner, R., Hemispheric Differences for the Integration of Stimulus Levels and Their Con tents: Evidence from Bilateral Presentations, Percep tion Psychophys., 2006, vol. 68, p. 1274. 5. Vol’f, N.V., Razumnikova, O.M., Bryzgalov, A.O., Mashukova, A.V., et al., Neurophysiological Bases of SexRelated Differences in the Hemispheric Organiza tion of Selective Attention and Verbal Memory, Byull. Sib. Otd. Ross. Akad. Med. Nauk, 2004, no. 2, p. 83. HUMAN PHYSIOLOGY

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