Acta Psychologma North-Holland
73 (1990) 131-143
131
PROCESSING DOMINANCE OF GLOBAL AND LOCAL INFORMATION IN VISUAL PATIERNS * D. LUNA,
J.M. MERINO
and R. MARCOS-RUIZ
Unrversrdad Nacronal de Educacrbn a Dtstancra, Madrrd, Spain Accepted
May 1989
The processmg dommance of global and local levels of visual patterns was studied using two tasks: speeded classtfication and tdentification Sttmuh were presented with spattal certamty and controlled eccentncity. The results with both procedures showed global advantage RTs to global level were faster than those to local level. In the same way, the Interference effect was btdnectional between the global and local levels, the amount of interference bemg larger from the global level to the local one than vice versa
Introduction The processing of the global and local levels of visual patterns has become, in the last few years, a hotly contested issue. First Navon (1977) formulated the global precedence hypothesis, according to which global information is processed before local information. The results of his experiments showed global dominance: RTs to global information were shorter than those to local information and RTs to global information were immune to interference from variations in local information. These results were soon put into question by research that showed several limitations to the global dominance effect. Global dominance could be affected by stimulus uarzables such as size (Kinchla and Wolfe * Part of thts study was presented at the Second Meeting of the European Society for Cogmttve Psychology; Madrid, September 1987 This research was supported by a grant (PB86-0519) of the Dtrecctbn General de Investtgacion Ctentlfica y Tecmca to the authors. The authors wish to thank Michael Kubovy, Pto Tudela, and Ana J. Garriga for thetr helpful suggestions. Anonymous referees gave valuable comments on earher drafts Mailing address. D Luna, Departamento de Pstcologla B&ma, Facultad de Pstcologia, Umversidad National de Educactbn a Dtstancra, 28040-Madnd, Spam.
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D Luna et al / Protessrng dotmnance of global and local vformat~on
1979) the sparsity of local elements (Martm 1979), and the quality of the form (Hoffman 1980). It could also be affected by experzmental variables such as spatial uncertainty and peripheral presentation of the stimuli (Pomerantz 1983; Grice et al. 1983). These factors can make selective attention to local level more difficult (Johnston and Dark 1986), and thus bias processing toward global information. Navon (1983) replied to Martin’s work, using the results of an experiment in which the size and sparsity between the local elements were manipulated. The data showed that the effect of sparsity on global dominance depends on the geometric figure used as stimulus. Navon and Norman (1983) replied to Kmchla and Wolfe’s objections with experiments in which stimuli were presented m the center of the screen, with complete spatial certainty; visual angle was manipulated and the eccentricity of the global and local levels was equated. Generally speaking, global dominance was found. But Navon and Norman’s (1983) results are still inconsistent with those of Grice et al. (1983) and Pomerantz (1983). Both experimenters presented their stimuli foveally and with spatial certainty. They obtained equal RTs to global and local information and a symmetric interference effect. In order to explain these discrepancies, Navon drew attention to the kind of stimuli used in the maJority of studies on processing dominance: they usually consisted of large letters made up of small letters (generally, Hs and Ss). In such stimuli there are large differences in eccentricity between the global and local information. The greater proximity of some local elements to the fovea is likely to facilitate their identification (Eriksen and Schultz 1977), and could bias processing toward the local level. When Navon and Norman (1983) equated the eccentricity of global and local information, global dominance persisted. Ward (1983) suggested that the Navon (1977, 1981b, 1983) and Pomerantz (1983) approaches are not incompatible because they address different aspects of global/ local processing dominance. Navon focussed on the temporal priority of global information in the microgenesis of percepts, whereas Pomerantz focussed on the effects of differential discriminability on global/ local processing dominance. They used remarkably different experimental procedures: Navon used a tachistoscopic identification task with brief masked stimuli. In contrast, Pomerantz used a speeded classification task and each stimulus stayed on until the SubJect responded.
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According to the global precedence hypothesis (Navon 1977, 1981a, b), limiting exposure duration degrades the processing of local information more than the processing of global information. Thus, when brief masked stimuli are presented, we expect global dominance: faster RTs to global than to local information and asymmetric interference. On the other hand, according to Navon, when exposure duration is unlimited, we expect neither global nor local dominance. Bearing Ward’s (1983) suggestions in mind, our first aim was to determine whether the two types of procedures have differential effects on processing dominance. We used two tasks: speeded classification (experiment 1) and identification (experiment 2). The same stimuli, with controlled eccentricity and spatial certainty, were presented in both tasks, so the biases attributed to the majority of the previous studies were removed. In the speeded classification task, the stimuli were not masked and were terminated by subject response. In the identification task, the stimuli were masked and presented briefly (140 msec). The second aim of our study was to explore the effect of similarity between the stimuli on processing dominance. The questions asked were the following: First, whether the degree of similarity between stimuli affects the processing of global and local levels. It could be expected that the more different the stimuli were the more easily the global and local levels were discriminated. Second, whether the inter-
Fig 1 The sttmuh m sets A, B and C, were generated from the orthogonal combtnatlon of two levels global and local StIrnull 1 and 2 present congnuty between the global and local levels Stlmuh 3 and 4 present mcongrulty between the global and local levels The A, B, and C sets differ from each other m the degree of slmrlanty between the stlmuh Smnlanty was mampulated using the cntenon of symmetry axes. Set A presents low slmllanty, set B presents mtermedlate smulanty and set C presents htgh smulanty.
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D Luna et al / Processrng domnance
ofglobal
and local rnformatlon
ference effect is affected by the degree of similarity. It could be expected that the more similar the stimuli the greater the interference between the global and local levels. To accomplish this aim, similarity was manipulated at three levels (see fig. 1). In the first two experiments, low and intermediate degrees of similarity were compared. In the third experiment, low and high degrees of similarity were compared.
Experiment 1 This expenment examines the effects of unhmtted exposure duration and similarity between stimuli (low and intermediate simtlanty) on processmg dommance. Method SubJects Sixteen sublects, subjects had normal
eight males and eight females, or corrected-to-normal vision.
aged
22-33,
participated.
All
Stlmuh and apparatus The stimuli consisted of figures belongmg to sets A and B of figure 1, drawn on white poster-board cards. The diameter of the global circles, the side of the global squares, and the height of the global triangles was 7 cm (about 5” at a distance of 0.8 m). The base of the global triangles was 5.5 cm (4O ). The diameter of the local circles, the side of the local squares, and the height of the local triangles was 6 mm (0.4O). The base of the local triangles was 5 mm (0.36 o ) The sttmuh were presented m a TKK (DP-6) tachistoscope, controlled by an Apple IIe mtcrocomputer through a programmable interface (Merino et al 1987). The nncrocomputer also controlled the course of the experiment, Including the randomtzatton of stimulus sequences and the analysis of data. Two response keys and a Lafayette 54417-A digital counter were used for response and time registration. Design and procedure The experimental design conststed of four factors: smular~ty, relevant level, congrurty, and condltzons (all within subjects except the first). The stimuh are shown m fig. 1. There are two levels of srmrlarlty low (stimulus set A) and rntermedrate (stimulus set B). In all tasks selective attention was required. There are two levels to which the sublect’s attention could be directed: global and local Thus the relevant level factor has two levels. Sttmuh can be congruous or mcongruous: if the parts and the whole have the same shape, the stimulus is congruous, if the parts and the whole have a different shape, the stimulus is rncoflgruous.
D Luna et al / Processmg domrnanceof global and local rnformatlon
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The condrtlons factor has two levels Control and Fdtenng condrttons. In the Control condttton, strmuh only varied with respect to one level whrle the other level was held constant. In the Ftltermg condttion, stimuh vaned with respect to both levels. Subjects were tested mdtvtdually To famrhanze the sublects with the strmuh, the sesston began by showing them the four sttmuh correspondmg to the A or B sets (depending upon the expenmental group to which they belonged). SubJects responded by pressing one of two keys. Both speed and accuracy were emphasized. There were SIX blocks corresponding to each expenmental condttron Each block had 80 trials, the first 16 of whtch were considered as practice trials. There were 480 tnals. The order of the condttrons was counterbalanced across subjects by means of a Latin square Etght subjects were presented with the sttmuh m set A and eight with the sttmuh m set B. Subjects fixated the center of the screen, where the stimuli were presented, thus msurmg spatial certamty. No fixation point was provided, but subjects were told to attend to the center of the screen. The task of the subJect was to respond to the presence of a sttmulus (for example, circle) m the relevant level (global or local) by pressing the nght-hand key, and to the presence of the other sttmulus (for example, triangle) by pressing the left-hand key, accordmg to the specific requirements corresponding to the described condttrons. The eccentrtcrty of global and local levels was controlled. Global and local levels fell within the mtermedtate regron of the retma (0.5 o to 8” of eccentncrty). On the other hand none of the local elements fell wrthm the central fovea (0.5 o of eccentncrty) m which visual acuity IS maxtmal (Polyak 1941). Each tnal started with a 500 msec tone, followed by the presentation of the strmulus, which remained on the screen until the response was made. The inter-trial interval was 2 set The expenmental session lasted about 1 hour and 40 minutes. Results and D~scusslon The mean RTs and error rates are presented analyzed separately by two ANOVAs mvolvmg level X congrutty X condrtrons).
m table 1. RTs and error rates were four factors. strmulus set X (relevant
Global domrnance was found. The effect of the relevant level was significant (F(l, 14) = 33.2, p < 0.001). RTs when local level was relevant (530 msec) averaged 44 msec longer than when global level was relevant (486 msec). Blhrectlonal Stroop interference was found The effect of congruity was significant (F(1, 14) = 32.0, p < 0.001). RTs to mcongruous sttmuh (522 msec) averaged 28 msec longer than those to the congruous sttmuh (494 msec). Bidlrectronal Garner interference was found The effect of condtttons was significant (F(l, 14) = 38.5, p < 0.001) RTs m the filtering condtttons (532 msec) averaged 48 msec longer than RTs m the control condtttons (484 msec). The effect of strmulus set was not srgmfrcant (F(1, 14) = 3.4, p < 0.08). Stroop interference was greater when local level was relevant than when global level was relevant. The mteractton between relevant level and congrutty was stgmftcant (F(1, 14) = 12 5, p < 0.003). The difference m Stroop interference was 26 msec
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D Luna et al / Processrng domrnance
Table 1 Mean response ment 1 Stimulus
set
times (m msec) and error
Relevant
rates (percentages)
Qrcle - square Congruous RT % Incongruous RT % Stroop mterf
local tnformatton
for the four condltlons
of expen-
level
Local
Cwcle- mangle Congruous RT B Incongruous RT s Stroop mterf.
ofglobaland
Global
Control
Fdtenng
478 45
502 4.7
486 47 8
Gamer mterf.
Control
Fdtenng
Gamer mterf.
24
440 45
469 5.1
29
555 4.7 53
69
443 41 3
493 4.3 24
51
511 49
545 55
34
492 3.3
511 31
30
522 63 11
640 3.9 95
118
499 47 7
538 47 27
40
Garner tnterjerence was greater when local level was relevant than when global level was relevant The Interaction between relevant level and condrttons was stgmfrcant (F(1, 14) = 4 9, p < 0.04). The difference m Garner interference was 24 msec. Stroop interference was greater rn the jdtenng condrttons than tn the control condltlons: The mteractron between condmons and congrmty was significant (F(1, 14) = 24.2, p < 0.002). The difference m Stroop interference was 43 msec Stroop and Garner Interference were greater when local level was relevant than when global level was relevant The three-way mteractton between globahty, condtttons and congruity was sigmftcant (F(1, 14) = 10.0, p < 0.006) mdlcatmg a stronger mteractton between the Stroop and Gamer interference effect when local level was relevant than when global level was relevant. The analysis of error rates, conducted on folded-log transformatrons of error proportions (Tukey 1977) showed a stgniftcant mam effect of the relevant level (F&14) = 29.3, p < 0.001). Error rates when local level was relevant were greater than when global level was relevant These results suggested no speed-accuracy trade-off: correlatron between RTs and error rates (folded-log) was posmve (r = 0.36, n.s.). The results did not support our hypothesis that neither global nor local dommance were presented when exposure duration IS unhnuted. The fact that global dommance was presented could be due to the eccentrtctty whtch favors the low spatial frequencies corresponding to the global level.
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These results are drscrepant from those of Pomerantz (1983: expenment 2) and Gnce et al. (experiments 1 and 2). In these expenments, fovea1 presentation of sttmuli and spatial certainty was used. The results showed equal RTs to both levels and the same amount of interference. This discrepancy could be explained by the fact that the eccentnctttes of both the global and local level m our expenment were more stmtlar (Fig. 1) than they were m the sttmuh used m the experiments mentioned above (Hs and Ss) The greater proxumty of some local elements to the fovea m thts kmd of sttmuh, could bias processmg toward the local level.
Experiment 2 In experiment 1 global dominance was found, using a speeded classtftcatton task and a presentation of stimuli with unlimited exposure duration. Given that experiments showing the same effect have usually presented masked sttmuh with hmtted exposure duration and used an tdentification task (Navon 1977, 1981b; Navon and Norman 1983), the purpose of the second experiment was to replicate the results found in experiment 1 under condttions of limited exposure duration and using an tdentification task. Method Subjects Nine sublects, four males and five females whose ages ranged from 25-30, ticipated in this expenment. All reported normal or corrected-to-normal vtsion
par-
Strmub and apparatus The sttmuh and apparatus were the same as those described in experiment 1. Design and procedure The expenmental design consisted of three factors (all w&m subjects). srmllanty, attention condrtlons and congrurty. There are two levels of srmrlanty: low (sttmulus set A) and intermediate (sttmulus set B) (see fig. 1) Stimuli can be congruous or mcongruous: if the parts and the whole have the same shape, the stimulus is congruous; tf the parts and the whole have a different shape, the stimulus is incongruous. The attention condrtlons factor has three levels. global attention, local attention and drvrded attention. In the global attention condltron, sublects were instructed to attend selectively to the global level while ignoring the local one. In the local attention condrtlon, subjects had to selectively attend to the local level whtle tgnonng the global one. In the dwrded attention condrtron, subjects were mstructed to attend simultaneously to both levels. The sublects were tested mdtvidually and received the same mstructtons as m experiment 1.
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Each subject carried out the task correspondmg to the described condttrons wtth two stimulus sets, A and B. The presentation order was A-B for half of the subjects and B-A for the other half. There were three blocked condrtlons for each stimulus set. Each block had 80 trials, the ftrst 16 of which were considered as practice trials. There were 480 tnals. The order of the condttrons was counterbalanced for each subject according to a Latin square design. Sttmulus presentation order was randonnzed. Strmuh were presented with spatial certainty and controlled eccentrlclty as m expertment 1 A 500 msec tone indicated the begmnmg of each trial. Immediately afterwards, the strmulus was presented durmg 140 msec and then a mask was presented. The mask was a square formed by a random black strokes, about 20% longer than stimulus size. It disappeared when SubJeCts made a response. Once sequence was fmtshed, a new trial began. The experimental session lasted about 1 hour and 30 mmutes.
Results and Discussion
The mean RTs and error rates are presented analyzed separately by two ANOVAs mvolvmg condmons X congruity).
Table 2 Mean response ment 2 Stnnulus
set
Circle - trrangle Congruous RT x Incongruous RT % Stroop mterf Cwcle - square Congruous RT I% Incongruous RT % Stroop mterf Overall
mterf
times (m msec) and error
Attention
m table 2. RTs and error rates were three factors (stimulus set X attention
rates (percentages)
for the three condltlons
condltlons
Global
Local
Divided
462 26
476 43
616 83
494 56 32
535 94 59
715 6.7 99
472 5.7
507 5.4
600 7
507 64 35
560 5 53
694 64 94
33
56
96
of expen-
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139
The sigmflcant effect of attent~n condemns (F(2, 16) = 96.052, p < 0.001) shows that It zseasier to pay attention to a smgle level than to two. Shorter RTs were observed m the selective attention conditions (502 msec for global and local combined) than m the divided attention condltlon (656 msec) This result 1s consistent with Navon and Norman (1983: expenment 1) and Pomerantz (1983. experiments 1 and 2). Our results showed global dommance. RTs m the local attention condltlon (520 msec) were longer than those in the global attention condition (484 msec). A significant effect of congrurty (F(1, 8) = 91 1, p < 0.001) indicated Stroop rnterference. RTs to the congruous stimuli (522 msec) were shorter than those to the incongruous stimuli (584 msec). A slgmflcant Interaction between attention condltlons and congruity (F(2, 16) = 9.372, p < 0.002) Indicated that the difference between the congruous and mcongruous stimuli m the divided attention condition was greater (by 96 msec) than m the selective attention condltlons (by 44 msec for the global and local combined). Although there was a bidlrectlonal Stroop interference effect, it was greater m the local attention condition (56 msec) than m the global attention condltlon (33 msec). The ANOVA on error rates was carried out takmg as data the folded-log transformations on the error proportions. Neither mam effects nor interaction effects were slgmficant, although the trend shown by the analysis of error rates was m agreement with that pomted out by the RTs data. This analysis suggested no speed-accuracy trade-off. correlation between RTs and error rates (folded log) was positive (r = 0 66, p i 0.01). The results confirm our hypothesis that global dommance would appear when stimuli were presented with short and hrmted exposure duration. At the same time, the results are compatible with the global precedence hypothesis (Navon 1977, 1981a, b) These results are generally in line with Navon and Norman (1983. experiment 2) However, they found a umdlrectional interference effect with small stimuli and a symmetnc interference effect with large ones. These differences m the results may be due to the Size of the stimuli we used, which were halfway between the sizes used by Navon and Norman.
Experiment 3
In the two previous expenments no effect on processing dommance was found due to the mampulation of similarity between stimuli. In both expenments a stimulus set of low slmdanty (set A m fig. 1) was compared with a stimulus set of mtermedlate snmlanty (set B in fig. 1). It is possible that the slmdanty between stimuli of set A were not different enough from the snndanty between stimuli of set B. In the present expenment, set A was compared with a new stimulus set m which the similarity between stimuli was maxlrmzed (set C in fig. 1). Thus the differences m between-stlmuh srmrlarrty of the two stimulus sets was increased.
D Luna et al / Processrng domrnnnce of global
140
and
local rnformatron
Method SubJects Twelve sublects, seven males and five females participated m thts experiment. All reported normal
whose ages ranged or corrected-to-normal
from 27-40, vision.
Strmulr and apparatus The stimuli were those included in sets A and C (fig. 1). The size of the global and local levels were those described m experiments 1 and 2. The size and eccentncrty of dtamonds were the same as those Indicated for squares The apparatus was the same as that used m expenment 2. Design and procedure They were the same as m the expenment
2.
Results and D~scussron The mean RTs and error rates for thts experiment are shown in table 3. These data were analyzed separately by two ANOVAS mvolving three factors (sttmulus set X attention condtttons X congruity).
Table 3 Mean response ment 3
times (m msec) and error
Strmulus set
Circle- mangle Congruous RT %J Incongruous RT % Stroop mterf Square - dramond Congruous RT !% Incongruous RT % Stroop mterf Overall
mterf
Attention
rates (percentages)
for the three condltlons
condltlons
Global
Local
Dvnded
404 47
453 55
639 96
423 7 19
487 6.6 34
712 89 13
440
547 62
719 13 5
443 72 3
618 10 71
787 69 68
11
52
70
62
of expen-
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141
The effect of stun&.x set was slgmflcant (F(1, 11) = 18.5, p < 0.001). The mean RTs were longer when sundanty between stimuli was high (592 msec) than when sirmlanty was low (519 msec). The significant effect of attentton cond~ons (F(2, 22) = 69.2, p < 0.001) shows that I? LScaster topay attention to a single level than to two. Shorter RTs were observed m the selective attention condltlons (690 msec for global and local combined) than m the divided attention condltlon (714 msec). Global domrnance was found: RTs m the local attention condition (527 msec) were longer than those m the global attention condltlon (427 msec). A slgmficant effect of congruity (F(1, 11) = 24 36, p -C 0.001) indicated Stroop Interference RTs to congruous stimuli (533 msec were shorter than those to the mcongruous stimuli (578 msec). A significant interaction between attention condrtrons and congrurty (F(2, 22) = 5.3, p < 0.001, indicated that the difference between the congruous stimuli m the dlvlded attention condition was greater (by 70 msec) than m the selective attention condltlons (by 31 msec for the global and local combined). Although there was a bldirectlonal Stroop interference effect, it was greater m the local attention condition (52 msec) than m the global attention condltlon (11 msec). ANOVA on error rates was conducted on folded-log transformations of error proportions. Neither mam effects nor interaction effects were significant, although the trend shown by the analysis of error rates was m agreement with that pointed out by the RT data. Thus analysis suggested no speed-accuracy trade-off: correlation between RTs and error rates (folded-log) was positive (r = 0.60, p < 0 03) In summary, the results of experiment 3 showed the followmg effects. on the one hand, RTs to global and local dimensions were shorter when stimuli were more different than when they were more slmdar. However, the absence of interaction between slrmlanty and attention condltlons or between slrmlarlty and congnuty showed that this factor had no Influence on processmg dommance On the other hand, the results on global dommance and the interference effect replicate those presented in the former expenment and they are compatible with the global precedence hypothesis (Navon 1977, 1981a, b).
Conclusion The first aim of our study was to examine the effects of two different procedures on processing dominance, using stimuli which were presented with spatial certainty and controlled eccentricity. The results from the three experiments showed that with both procedures global dominance was found. RTs to global level were shorter than RTs to local level. In the same way, the interference effect was bidirectional, although it was larger from the global level onto the local one, than vice versa. The results of the three experiments could not be attributed to the influence of the bias factor mentioned in the previous study. The
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of global and local mformatlon
bias concerning a greater facility to selectively attend to the global level with spatial uncertainty was removed presenting stimuli with spatial certainty. The factor that could influence the faster identification of the global level and its greater amount of interference on the local level, is the eccentricity which favors the low spatial frequencies (Navon and Norman 1983). Concerning this suggestion, the Shulman et al. (1986) studies, analyzing the role of the spatial frequency channels, showed that the RTs to the low frequency channels were shorter than the RTs to the high frequency channels. On the other hand, Hughes et al. (1984) suggested that the channels tuned in to the low frequencies inhibit those tuned in to the high frequencies to a greater extent than vice versa. The second aim of our study was to analyze the possible effects of the similarity between stimuli on processing dominance. The expertmental results indicated that the RTs were shorter when similarity between stimuli was low than when similarity was high. This effect was only significant in experiment 3. However, manipulation of differences m similarity does not influence the processing dominance. In summary, the results obtained in the three experiments showed global dominance, even its presence does not seem to depend on similarity and the two procedures used. Global dominance seems to be related to eccentricity. Since this factor was maintained constant in our work it could be responsible for global dominance.
References Enksen, Ch W. and W.D. Schultz, 1977. Retmal locus and acuity m visual mformatlon processmg. Bulletm of the Psychonormc Society 9, 81-84. Gnce, G.R., L. Canham and J M. Boroughs, 1983 Forest before trees? It depends on where you look. Perceptlon & Psychophyslcs 33, 121-128 Hoffman, J E., 1980. InteractIon between global and local levels of a form Journal of Expenmental Psychology. Human PerceptIon and Performance 6, 222-234 Hughes, H.C , M. Layton, J C. Brurd and L S Lester, 1984. Global precedence m visual pattern recogmtlon. PerceptIon & PsychophysIcs 35, 361-371 Johnston, WA. and V.J Dark, 1966 Selective attention. Annual Review of Psychology 37, 43-75 Kmchla, R A and J M Wolfe, 1979. The order of visual processmg: Top-down, bottom-up or nuddle-out PerceptIon and PsychophysIcs 35, 225-231. Martm, M., 1979 Local and global processmg. The role of sparslty Memory & Cogmtlon 7, 476-484 Menno, J M, M. Paddla and L Hemindez, 1987 Interface programable para el control expenmental y la recogda de datos en el laboratono de pslcologia. Pslcologca 8, 97-103.
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Navon, D , 1977 Forest before the trees The precedence of global features in visual perceptlon Cogmtlve Psychology 9, 353-383 Navon, D., 1981a Do attention and declslon follow perceptIon Comment on Mdler Journal of Expenmental Psychology Human PerceptIon and Performance 7, 1175-1182 Navon, D., 1981b The forest revIsIted More on global precedence Psycholo@cal Research 43, l-32 Navon, D , 1983 How many trees does It take to make a forest? Perception 12, 239-254 Navon, D and J. Norman, 1983 Does global precedence really depend on visual angle? Journal of Expenmental Psychology- Human PerceptIon and Performance 9, 955-965 Polyak, S.L., 1941 The retma. Chicago, IL: University of Chicago Press. Pomerantz, R., 1983 Global and local precedence. Selective attention m form and motion perception Journal of Expenmental Psychology General 112, 516-540. Shulman, G L , MA. Sulhvan, K Glsh and WA. Sakoda, 1986 The role of spatial-frequency channels m the perception of local and global structure. PerceptIon 15, 259-273 Tukey, J., 1977 Exploratory data analysis London Addison Wesley Ward, L M., 1983 On processmg dommance Comment on Pomerantz. Journal of Expenmental Psychology General 112, 541-546
73 (1990) 131-143
131
PROCESSING DOMINANCE OF GLOBAL AND LOCAL INFORMATION IN VISUAL PATIERNS * D. LUNA,
J.M. MERINO
and R. MARCOS-RUIZ
Unrversrdad Nacronal de Educacrbn a Dtstancra, Madrrd, Spain Accepted
May 1989
The processmg dommance of global and local levels of visual patterns was studied using two tasks: speeded classtfication and tdentification Sttmuh were presented with spattal certamty and controlled eccentncity. The results with both procedures showed global advantage RTs to global level were faster than those to local level. In the same way, the Interference effect was btdnectional between the global and local levels, the amount of interference bemg larger from the global level to the local one than vice versa
Introduction The processing of the global and local levels of visual patterns has become, in the last few years, a hotly contested issue. First Navon (1977) formulated the global precedence hypothesis, according to which global information is processed before local information. The results of his experiments showed global dominance: RTs to global information were shorter than those to local information and RTs to global information were immune to interference from variations in local information. These results were soon put into question by research that showed several limitations to the global dominance effect. Global dominance could be affected by stimulus uarzables such as size (Kinchla and Wolfe * Part of thts study was presented at the Second Meeting of the European Society for Cogmttve Psychology; Madrid, September 1987 This research was supported by a grant (PB86-0519) of the Dtrecctbn General de Investtgacion Ctentlfica y Tecmca to the authors. The authors wish to thank Michael Kubovy, Pto Tudela, and Ana J. Garriga for thetr helpful suggestions. Anonymous referees gave valuable comments on earher drafts Mailing address. D Luna, Departamento de Pstcologla B&ma, Facultad de Pstcologia, Umversidad National de Educactbn a Dtstancra, 28040-Madnd, Spam.
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1979) the sparsity of local elements (Martm 1979), and the quality of the form (Hoffman 1980). It could also be affected by experzmental variables such as spatial uncertainty and peripheral presentation of the stimuli (Pomerantz 1983; Grice et al. 1983). These factors can make selective attention to local level more difficult (Johnston and Dark 1986), and thus bias processing toward global information. Navon (1983) replied to Martin’s work, using the results of an experiment in which the size and sparsity between the local elements were manipulated. The data showed that the effect of sparsity on global dominance depends on the geometric figure used as stimulus. Navon and Norman (1983) replied to Kmchla and Wolfe’s objections with experiments in which stimuli were presented m the center of the screen, with complete spatial certainty; visual angle was manipulated and the eccentricity of the global and local levels was equated. Generally speaking, global dominance was found. But Navon and Norman’s (1983) results are still inconsistent with those of Grice et al. (1983) and Pomerantz (1983). Both experimenters presented their stimuli foveally and with spatial certainty. They obtained equal RTs to global and local information and a symmetric interference effect. In order to explain these discrepancies, Navon drew attention to the kind of stimuli used in the maJority of studies on processing dominance: they usually consisted of large letters made up of small letters (generally, Hs and Ss). In such stimuli there are large differences in eccentricity between the global and local information. The greater proximity of some local elements to the fovea is likely to facilitate their identification (Eriksen and Schultz 1977), and could bias processing toward the local level. When Navon and Norman (1983) equated the eccentricity of global and local information, global dominance persisted. Ward (1983) suggested that the Navon (1977, 1981b, 1983) and Pomerantz (1983) approaches are not incompatible because they address different aspects of global/ local processing dominance. Navon focussed on the temporal priority of global information in the microgenesis of percepts, whereas Pomerantz focussed on the effects of differential discriminability on global/ local processing dominance. They used remarkably different experimental procedures: Navon used a tachistoscopic identification task with brief masked stimuli. In contrast, Pomerantz used a speeded classification task and each stimulus stayed on until the SubJect responded.
D Luna et al / Processrng dommance of global and local mformatlon
133
According to the global precedence hypothesis (Navon 1977, 1981a, b), limiting exposure duration degrades the processing of local information more than the processing of global information. Thus, when brief masked stimuli are presented, we expect global dominance: faster RTs to global than to local information and asymmetric interference. On the other hand, according to Navon, when exposure duration is unlimited, we expect neither global nor local dominance. Bearing Ward’s (1983) suggestions in mind, our first aim was to determine whether the two types of procedures have differential effects on processing dominance. We used two tasks: speeded classification (experiment 1) and identification (experiment 2). The same stimuli, with controlled eccentricity and spatial certainty, were presented in both tasks, so the biases attributed to the majority of the previous studies were removed. In the speeded classification task, the stimuli were not masked and were terminated by subject response. In the identification task, the stimuli were masked and presented briefly (140 msec). The second aim of our study was to explore the effect of similarity between the stimuli on processing dominance. The questions asked were the following: First, whether the degree of similarity between stimuli affects the processing of global and local levels. It could be expected that the more different the stimuli were the more easily the global and local levels were discriminated. Second, whether the inter-
Fig 1 The sttmuh m sets A, B and C, were generated from the orthogonal combtnatlon of two levels global and local StIrnull 1 and 2 present congnuty between the global and local levels Stlmuh 3 and 4 present mcongrulty between the global and local levels The A, B, and C sets differ from each other m the degree of slmrlanty between the stlmuh Smnlanty was mampulated using the cntenon of symmetry axes. Set A presents low slmllanty, set B presents mtermedlate smulanty and set C presents htgh smulanty.
134
D Luna et al / Processrng domnance
ofglobal
and local rnformatlon
ference effect is affected by the degree of similarity. It could be expected that the more similar the stimuli the greater the interference between the global and local levels. To accomplish this aim, similarity was manipulated at three levels (see fig. 1). In the first two experiments, low and intermediate degrees of similarity were compared. In the third experiment, low and high degrees of similarity were compared.
Experiment 1 This expenment examines the effects of unhmtted exposure duration and similarity between stimuli (low and intermediate simtlanty) on processmg dommance. Method SubJects Sixteen sublects, subjects had normal
eight males and eight females, or corrected-to-normal vision.
aged
22-33,
participated.
All
Stlmuh and apparatus The stimuli consisted of figures belongmg to sets A and B of figure 1, drawn on white poster-board cards. The diameter of the global circles, the side of the global squares, and the height of the global triangles was 7 cm (about 5” at a distance of 0.8 m). The base of the global triangles was 5.5 cm (4O ). The diameter of the local circles, the side of the local squares, and the height of the local triangles was 6 mm (0.4O). The base of the local triangles was 5 mm (0.36 o ) The sttmuh were presented m a TKK (DP-6) tachistoscope, controlled by an Apple IIe mtcrocomputer through a programmable interface (Merino et al 1987). The nncrocomputer also controlled the course of the experiment, Including the randomtzatton of stimulus sequences and the analysis of data. Two response keys and a Lafayette 54417-A digital counter were used for response and time registration. Design and procedure The experimental design conststed of four factors: smular~ty, relevant level, congrurty, and condltzons (all within subjects except the first). The stimuh are shown m fig. 1. There are two levels of srmrlarlty low (stimulus set A) and rntermedrate (stimulus set B). In all tasks selective attention was required. There are two levels to which the sublect’s attention could be directed: global and local Thus the relevant level factor has two levels. Sttmuh can be congruous or mcongruous: if the parts and the whole have the same shape, the stimulus is congruous, if the parts and the whole have a different shape, the stimulus is rncoflgruous.
D Luna et al / Processmg domrnanceof global and local rnformatlon
135
The condrtlons factor has two levels Control and Fdtenng condrttons. In the Control condttton, strmuh only varied with respect to one level whrle the other level was held constant. In the Ftltermg condttion, stimuh vaned with respect to both levels. Subjects were tested mdtvtdually To famrhanze the sublects with the strmuh, the sesston began by showing them the four sttmuh correspondmg to the A or B sets (depending upon the expenmental group to which they belonged). SubJects responded by pressing one of two keys. Both speed and accuracy were emphasized. There were SIX blocks corresponding to each expenmental condttron Each block had 80 trials, the first 16 of whtch were considered as practice trials. There were 480 tnals. The order of the condttrons was counterbalanced across subjects by means of a Latin square Etght subjects were presented with the sttmuh m set A and eight with the sttmuh m set B. Subjects fixated the center of the screen, where the stimuli were presented, thus msurmg spatial certamty. No fixation point was provided, but subjects were told to attend to the center of the screen. The task of the subJect was to respond to the presence of a sttmulus (for example, circle) m the relevant level (global or local) by pressing the nght-hand key, and to the presence of the other sttmulus (for example, triangle) by pressing the left-hand key, accordmg to the specific requirements corresponding to the described condttrons. The eccentrtcrty of global and local levels was controlled. Global and local levels fell within the mtermedtate regron of the retma (0.5 o to 8” of eccentncrty). On the other hand none of the local elements fell wrthm the central fovea (0.5 o of eccentncrty) m which visual acuity IS maxtmal (Polyak 1941). Each tnal started with a 500 msec tone, followed by the presentation of the strmulus, which remained on the screen until the response was made. The inter-trial interval was 2 set The expenmental session lasted about 1 hour and 40 minutes. Results and D~scusslon The mean RTs and error rates are presented analyzed separately by two ANOVAs mvolvmg level X congrutty X condrtrons).
m table 1. RTs and error rates were four factors. strmulus set X (relevant
Global domrnance was found. The effect of the relevant level was significant (F(l, 14) = 33.2, p < 0.001). RTs when local level was relevant (530 msec) averaged 44 msec longer than when global level was relevant (486 msec). Blhrectlonal Stroop interference was found The effect of congruity was significant (F(1, 14) = 32.0, p < 0.001). RTs to mcongruous sttmuh (522 msec) averaged 28 msec longer than those to the congruous sttmuh (494 msec). Bidlrectronal Garner interference was found The effect of condtttons was significant (F(l, 14) = 38.5, p < 0.001) RTs m the filtering condtttons (532 msec) averaged 48 msec longer than RTs m the control condtttons (484 msec). The effect of strmulus set was not srgmfrcant (F(1, 14) = 3.4, p < 0.08). Stroop interference was greater when local level was relevant than when global level was relevant. The mteractton between relevant level and congrutty was stgmftcant (F(1, 14) = 12 5, p < 0.003). The difference m Stroop interference was 26 msec
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D Luna et al / Processrng domrnance
Table 1 Mean response ment 1 Stimulus
set
times (m msec) and error
Relevant
rates (percentages)
Qrcle - square Congruous RT % Incongruous RT % Stroop mterf
local tnformatton
for the four condltlons
of expen-
level
Local
Cwcle- mangle Congruous RT B Incongruous RT s Stroop mterf.
ofglobaland
Global
Control
Fdtenng
478 45
502 4.7
486 47 8
Gamer mterf.
Control
Fdtenng
Gamer mterf.
24
440 45
469 5.1
29
555 4.7 53
69
443 41 3
493 4.3 24
51
511 49
545 55
34
492 3.3
511 31
30
522 63 11
640 3.9 95
118
499 47 7
538 47 27
40
Garner tnterjerence was greater when local level was relevant than when global level was relevant The Interaction between relevant level and condrttons was stgmfrcant (F(1, 14) = 4 9, p < 0.04). The difference m Garner interference was 24 msec. Stroop interference was greater rn the jdtenng condrttons than tn the control condltlons: The mteractron between condmons and congrmty was significant (F(1, 14) = 24.2, p < 0.002). The difference m Stroop interference was 43 msec Stroop and Garner Interference were greater when local level was relevant than when global level was relevant The three-way mteractton between globahty, condtttons and congruity was sigmftcant (F(1, 14) = 10.0, p < 0.006) mdlcatmg a stronger mteractton between the Stroop and Gamer interference effect when local level was relevant than when global level was relevant. The analysis of error rates, conducted on folded-log transformatrons of error proportions (Tukey 1977) showed a stgniftcant mam effect of the relevant level (F&14) = 29.3, p < 0.001). Error rates when local level was relevant were greater than when global level was relevant These results suggested no speed-accuracy trade-off: correlatron between RTs and error rates (folded-log) was posmve (r = 0.36, n.s.). The results did not support our hypothesis that neither global nor local dommance were presented when exposure duration IS unhnuted. The fact that global dommance was presented could be due to the eccentrtctty whtch favors the low spatial frequencies corresponding to the global level.
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137
These results are drscrepant from those of Pomerantz (1983: expenment 2) and Gnce et al. (experiments 1 and 2). In these expenments, fovea1 presentation of sttmuli and spatial certainty was used. The results showed equal RTs to both levels and the same amount of interference. This discrepancy could be explained by the fact that the eccentnctttes of both the global and local level m our expenment were more stmtlar (Fig. 1) than they were m the sttmuh used m the experiments mentioned above (Hs and Ss) The greater proxumty of some local elements to the fovea m thts kmd of sttmuh, could bias processmg toward the local level.
Experiment 2 In experiment 1 global dominance was found, using a speeded classtftcatton task and a presentation of stimuli with unlimited exposure duration. Given that experiments showing the same effect have usually presented masked sttmuh with hmtted exposure duration and used an tdentification task (Navon 1977, 1981b; Navon and Norman 1983), the purpose of the second experiment was to replicate the results found in experiment 1 under condttions of limited exposure duration and using an tdentification task. Method Subjects Nine sublects, four males and five females whose ages ranged from 25-30, ticipated in this expenment. All reported normal or corrected-to-normal vtsion
par-
Strmub and apparatus The sttmuh and apparatus were the same as those described in experiment 1. Design and procedure The expenmental design consisted of three factors (all w&m subjects). srmllanty, attention condrtlons and congrurty. There are two levels of srmrlanty: low (sttmulus set A) and intermediate (sttmulus set B) (see fig. 1) Stimuli can be congruous or mcongruous: if the parts and the whole have the same shape, the stimulus is congruous; tf the parts and the whole have a different shape, the stimulus is incongruous. The attention condrtlons factor has three levels. global attention, local attention and drvrded attention. In the global attention condltron, sublects were instructed to attend selectively to the global level while ignoring the local one. In the local attention condrtlon, subjects had to selectively attend to the local level whtle tgnonng the global one. In the dwrded attention condrtron, subjects were mstructed to attend simultaneously to both levels. The sublects were tested mdtvidually and received the same mstructtons as m experiment 1.
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D Lunn et al / Processrng domrnance of global and local rnformairon
Each subject carried out the task correspondmg to the described condttrons wtth two stimulus sets, A and B. The presentation order was A-B for half of the subjects and B-A for the other half. There were three blocked condrtlons for each stimulus set. Each block had 80 trials, the ftrst 16 of which were considered as practice trials. There were 480 tnals. The order of the condttrons was counterbalanced for each subject according to a Latin square design. Sttmulus presentation order was randonnzed. Strmuh were presented with spatial certainty and controlled eccentrlclty as m expertment 1 A 500 msec tone indicated the begmnmg of each trial. Immediately afterwards, the strmulus was presented durmg 140 msec and then a mask was presented. The mask was a square formed by a random black strokes, about 20% longer than stimulus size. It disappeared when SubJeCts made a response. Once sequence was fmtshed, a new trial began. The experimental session lasted about 1 hour and 30 mmutes.
Results and Discussion
The mean RTs and error rates are presented analyzed separately by two ANOVAs mvolvmg condmons X congruity).
Table 2 Mean response ment 2 Stnnulus
set
Circle - trrangle Congruous RT x Incongruous RT % Stroop mterf Cwcle - square Congruous RT I% Incongruous RT % Stroop mterf Overall
mterf
times (m msec) and error
Attention
m table 2. RTs and error rates were three factors (stimulus set X attention
rates (percentages)
for the three condltlons
condltlons
Global
Local
Divided
462 26
476 43
616 83
494 56 32
535 94 59
715 6.7 99
472 5.7
507 5.4
600 7
507 64 35
560 5 53
694 64 94
33
56
96
of expen-
D Luna et al / Processrngdomrnanceof global and local mformatron
139
The sigmflcant effect of attent~n condemns (F(2, 16) = 96.052, p < 0.001) shows that It zseasier to pay attention to a smgle level than to two. Shorter RTs were observed m the selective attention conditions (502 msec for global and local combined) than m the divided attention condltlon (656 msec) This result 1s consistent with Navon and Norman (1983: expenment 1) and Pomerantz (1983. experiments 1 and 2). Our results showed global dommance. RTs m the local attention condltlon (520 msec) were longer than those in the global attention condition (484 msec). A significant effect of congrurty (F(1, 8) = 91 1, p < 0.001) indicated Stroop rnterference. RTs to the congruous stimuli (522 msec) were shorter than those to the incongruous stimuli (584 msec). A slgmflcant Interaction between attention condltlons and congruity (F(2, 16) = 9.372, p < 0.002) Indicated that the difference between the congruous and mcongruous stimuli m the divided attention condition was greater (by 96 msec) than m the selective attention condltlons (by 44 msec for the global and local combined). Although there was a bidlrectlonal Stroop interference effect, it was greater m the local attention condition (56 msec) than m the global attention condltlon (33 msec). The ANOVA on error rates was carried out takmg as data the folded-log transformations on the error proportions. Neither mam effects nor interaction effects were slgmficant, although the trend shown by the analysis of error rates was m agreement with that pomted out by the RTs data. This analysis suggested no speed-accuracy trade-off. correlation between RTs and error rates (folded log) was positive (r = 0 66, p i 0.01). The results confirm our hypothesis that global dommance would appear when stimuli were presented with short and hrmted exposure duration. At the same time, the results are compatible with the global precedence hypothesis (Navon 1977, 1981a, b) These results are generally in line with Navon and Norman (1983. experiment 2) However, they found a umdlrectional interference effect with small stimuli and a symmetnc interference effect with large ones. These differences m the results may be due to the Size of the stimuli we used, which were halfway between the sizes used by Navon and Norman.
Experiment 3
In the two previous expenments no effect on processing dommance was found due to the mampulation of similarity between stimuli. In both expenments a stimulus set of low slmdanty (set A m fig. 1) was compared with a stimulus set of mtermedlate snmlanty (set B in fig. 1). It is possible that the slmdanty between stimuli of set A were not different enough from the snndanty between stimuli of set B. In the present expenment, set A was compared with a new stimulus set m which the similarity between stimuli was maxlrmzed (set C in fig. 1). Thus the differences m between-stlmuh srmrlarrty of the two stimulus sets was increased.
D Luna et al / Processrng domrnnnce of global
140
and
local rnformatron
Method SubJects Twelve sublects, seven males and five females participated m thts experiment. All reported normal
whose ages ranged or corrected-to-normal
from 27-40, vision.
Strmulr and apparatus The stimuli were those included in sets A and C (fig. 1). The size of the global and local levels were those described m experiments 1 and 2. The size and eccentncrty of dtamonds were the same as those Indicated for squares The apparatus was the same as that used m expenment 2. Design and procedure They were the same as m the expenment
2.
Results and D~scussron The mean RTs and error rates for thts experiment are shown in table 3. These data were analyzed separately by two ANOVAS mvolving three factors (sttmulus set X attention condtttons X congruity).
Table 3 Mean response ment 3
times (m msec) and error
Strmulus set
Circle- mangle Congruous RT %J Incongruous RT % Stroop mterf Square - dramond Congruous RT !% Incongruous RT % Stroop mterf Overall
mterf
Attention
rates (percentages)
for the three condltlons
condltlons
Global
Local
Dvnded
404 47
453 55
639 96
423 7 19
487 6.6 34
712 89 13
440
547 62
719 13 5
443 72 3
618 10 71
787 69 68
11
52
70
62
of expen-
D Luna et al / Processrng domrnance of global and local mformatlon
141
The effect of stun&.x set was slgmflcant (F(1, 11) = 18.5, p < 0.001). The mean RTs were longer when sundanty between stimuli was high (592 msec) than when sirmlanty was low (519 msec). The significant effect of attentton cond~ons (F(2, 22) = 69.2, p < 0.001) shows that I? LScaster topay attention to a single level than to two. Shorter RTs were observed m the selective attention condltlons (690 msec for global and local combined) than m the divided attention condltlon (714 msec). Global domrnance was found: RTs m the local attention condition (527 msec) were longer than those m the global attention condltlon (427 msec). A slgmficant effect of congruity (F(1, 11) = 24 36, p -C 0.001) indicated Stroop Interference RTs to congruous stimuli (533 msec were shorter than those to the mcongruous stimuli (578 msec). A significant interaction between attention condrtrons and congrurty (F(2, 22) = 5.3, p < 0.001, indicated that the difference between the congruous stimuli m the dlvlded attention condition was greater (by 70 msec) than m the selective attention condltlons (by 31 msec for the global and local combined). Although there was a bldirectlonal Stroop interference effect, it was greater m the local attention condition (52 msec) than m the global attention condltlon (11 msec). ANOVA on error rates was conducted on folded-log transformations of error proportions. Neither mam effects nor interaction effects were significant, although the trend shown by the analysis of error rates was m agreement with that pointed out by the RT data. Thus analysis suggested no speed-accuracy trade-off: correlation between RTs and error rates (folded-log) was positive (r = 0.60, p < 0 03) In summary, the results of experiment 3 showed the followmg effects. on the one hand, RTs to global and local dimensions were shorter when stimuli were more different than when they were more slmdar. However, the absence of interaction between slrmlanty and attention condltlons or between slrmlarlty and congnuty showed that this factor had no Influence on processmg dommance On the other hand, the results on global dommance and the interference effect replicate those presented in the former expenment and they are compatible with the global precedence hypothesis (Navon 1977, 1981a, b).
Conclusion The first aim of our study was to examine the effects of two different procedures on processing dominance, using stimuli which were presented with spatial certainty and controlled eccentricity. The results from the three experiments showed that with both procedures global dominance was found. RTs to global level were shorter than RTs to local level. In the same way, the interference effect was bidirectional, although it was larger from the global level onto the local one, than vice versa. The results of the three experiments could not be attributed to the influence of the bias factor mentioned in the previous study. The
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D Luno et al / Processrng domrnonce
of global and local mformatlon
bias concerning a greater facility to selectively attend to the global level with spatial uncertainty was removed presenting stimuli with spatial certainty. The factor that could influence the faster identification of the global level and its greater amount of interference on the local level, is the eccentricity which favors the low spatial frequencies (Navon and Norman 1983). Concerning this suggestion, the Shulman et al. (1986) studies, analyzing the role of the spatial frequency channels, showed that the RTs to the low frequency channels were shorter than the RTs to the high frequency channels. On the other hand, Hughes et al. (1984) suggested that the channels tuned in to the low frequencies inhibit those tuned in to the high frequencies to a greater extent than vice versa. The second aim of our study was to analyze the possible effects of the similarity between stimuli on processing dominance. The expertmental results indicated that the RTs were shorter when similarity between stimuli was low than when similarity was high. This effect was only significant in experiment 3. However, manipulation of differences m similarity does not influence the processing dominance. In summary, the results obtained in the three experiments showed global dominance, even its presence does not seem to depend on similarity and the two procedures used. Global dominance seems to be related to eccentricity. Since this factor was maintained constant in our work it could be responsible for global dominance.
References Enksen, Ch W. and W.D. Schultz, 1977. Retmal locus and acuity m visual mformatlon processmg. Bulletm of the Psychonormc Society 9, 81-84. Gnce, G.R., L. Canham and J M. Boroughs, 1983 Forest before trees? It depends on where you look. Perceptlon & Psychophyslcs 33, 121-128 Hoffman, J E., 1980. InteractIon between global and local levels of a form Journal of Expenmental Psychology. Human PerceptIon and Performance 6, 222-234 Hughes, H.C , M. Layton, J C. Brurd and L S Lester, 1984. Global precedence m visual pattern recogmtlon. PerceptIon & PsychophysIcs 35, 361-371 Johnston, WA. and V.J Dark, 1966 Selective attention. Annual Review of Psychology 37, 43-75 Kmchla, R A and J M Wolfe, 1979. The order of visual processmg: Top-down, bottom-up or nuddle-out PerceptIon and PsychophysIcs 35, 225-231. Martm, M., 1979 Local and global processmg. The role of sparslty Memory & Cogmtlon 7, 476-484 Menno, J M, M. Paddla and L Hemindez, 1987 Interface programable para el control expenmental y la recogda de datos en el laboratono de pslcologia. Pslcologca 8, 97-103.
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Navon, D , 1977 Forest before the trees The precedence of global features in visual perceptlon Cogmtlve Psychology 9, 353-383 Navon, D., 1981a Do attention and declslon follow perceptIon Comment on Mdler Journal of Expenmental Psychology Human PerceptIon and Performance 7, 1175-1182 Navon, D., 1981b The forest revIsIted More on global precedence Psycholo@cal Research 43, l-32 Navon, D , 1983 How many trees does It take to make a forest? Perception 12, 239-254 Navon, D and J. Norman, 1983 Does global precedence really depend on visual angle? Journal of Expenmental Psychology- Human PerceptIon and Performance 9, 955-965 Polyak, S.L., 1941 The retma. Chicago, IL: University of Chicago Press. Pomerantz, R., 1983 Global and local precedence. Selective attention m form and motion perception Journal of Expenmental Psychology General 112, 516-540. Shulman, G L , MA. Sulhvan, K Glsh and WA. Sakoda, 1986 The role of spatial-frequency channels m the perception of local and global structure. PerceptIon 15, 259-273 Tukey, J., 1977 Exploratory data analysis London Addison Wesley Ward, L M., 1983 On processmg dommance Comment on Pomerantz. Journal of Expenmental Psychology General 112, 541-546
