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Attention can operate onsemantic objects defined byindividual Chinese charactersJie Yuanab & Shimin Fua

a Department of Psychology, School of Social Sciences,Tsinghua University, Beijing, Chinab Department of Biomedical Engineering, School ofMedicine, Tsinghua University, Beijing, ChinaPublished online: 03 Jun 2014.

To cite this article: Jie Yuan & Shimin Fu (2014): Attention can operate onsemantic objects defined by individual Chinese characters, Visual Cognition, DOI:10.1080/13506285.2014.916772

To link to this article: http://dx.doi.org/10.1080/13506285.2014.916772

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Attention can operate on semantic objects defined byindividual Chinese characters

Jie Yuan1,2 and Shimin Fu1

1Department of Psychology, School of Social Sciences, TsinghuaUniversity, Beijing, China2Department of Biomedical Engineering, School of Medicine, TsinghuaUniversity, Beijing, China

(Received 19 February 2013; accepted 15 April 2014)

Attention can select perceptual objects, but it is less clear whether attention can operateon objects defined by higher level cognition, such as semantic associations. Recentstudies have shown that attention may be based on objects defined by Chinese two-character compound words, suggesting that attention can operate on semantic objects. Inthe present study, object-based attention (OBA) effect was investigated at the level ofindividual Chinese characters, and the role of character structure and radical order inOBAwas explored by using a spatial cueing paradigm. In Experiment 1, we found OBAeffect for conditions that had legal radical order, but not for other conditions in whichthe radical order information was disrupted. Character structure, however, had noinfluence on the OBA effect. In Experiment 2, we observed OBA effect for allconditions after enhancing the radical order and character structure information byadding perceptual cues. The results extend previous findings of a “semantic object”-based attention effect from the two-character word level to the individual character level.Moreover, we found that radical order but not character structure was important forthis semantic OBA effect. We conclude that visual attention can be based on semanticobjects at the level of individual characters, and that the development of semanticobjects is affected by the perceptual grouping of the radicals.

Keywords: Object-based attention; Chinese characters; Semantic object; Characterstructure; Radical order.

Please address all correspondence to Shimin Fu, Department of Psychology, Tsinghua University,Beijing, 100084, China. E-mail: sfu@mail.tsinghua.edu.cn

We are grateful to Dr. Raja Parasuraman andDr. Danling Peng for helpful comments on this manuscript.We thank Hailing Wang, Shichun Guo and Jian Chen for preparing stimuli for the present study.

This research was supported by the National Natural Science Foundation of China (NSFC,31371142), the Initiative Scientific Research Program, Tsinghua University, China (2011Z02177), andthe Scientific Research Foundation for the ReturnedOverseas Chinese Scholars, State EducationMinistry.

© 2014 Taylor & Francis

Visual Cognition, 2014http://dx.doi.org/10.1080/13506285.2014.916772

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Visual selective attention in the absence of eye movements can be space-, part-and object-based. Metaphors for space-based attention (SBA) include a spotlight(e.g., Eriksen & Eriksen, 1974; Posner, 1980), zoom lens (e.g., Eriksen &St. James, 1986; Eriksen & Yeh, 1985), or a gradient (e.g., Downing & Pinker,1985), with the core idea that attention enhances information processing at theattended location or space. Part-based attention selects features of a single partmore efficiently than features of different parts (e.g., Barenholtz, & Feldman,2003; Vecera, Behrmann, & Filapek, 2001; Vecera, Behrmann, & McGoldrick,2000). In contrast, object-based attention (OBA) proposes that attention canoperate on stimuli that occupy multiple spatial locations, if those stimuli form asingle perceptual object. Evidence in support of object-based selection comesfrom studies using both divided-attention (e.g., Awh, Dhaliwal, Christensen, &Matsukura, 2001; Duncan, 1984; Vecera & Farah, 1994) and spatial cueingparadigms (e.g., Egly, Driver, & Rafal, 1994; Moore, Yantis, & Vaughan, 1998;Pratt & Sekuler, 2001; Vecera, 1994). A two-rectangle spatial cueing paradigmintroduced by Egly et al. (1994) has been extensively used in a number of laterstudies of OBA (e.g., He, Fan, Zhou, & Chen, 2004; Ho & Yeh, 2009; Li &Logan, 2008; Liu, Wang, & Zhou, 2011).

BOTTOM-UP AND TOP-DOWN OBJECT-BASED ATTENTION

In most studies of OBA, including Egly et al. (1994), object was defined byGestalt principles in a bottom-up manner, as a perceptual object (e.g., Driver &Baylis, 1989; Kahneman & Henik, 1981; Kramer & Jacobson, 1991; Logan,1996). A few studies have indicated that top-down factors such as instruction,experience and subjects’ knowledge of lexical organization can also modulatethe perception of objects and therefore affect attention deployment (e.g., Chen,1998; Li & Logan, 2008; Zemel, Behrmann, Mozer, & Bavelier, 2002). Forexample, Li and Logan (2008) investigated whether objects defined by lexicalinformation of Chinese two-character compound words could constrain attentiondeployment just like the bottom-up objects did. They used a paradigm similar toEgly et al., but with some crucial variations. Four Chinese characters whichcould constitute two different compound words horizontally or vertically werepresented in a 2 by 2 matrix to replace the two rectangles used by Egly et al.From a bottom-up perspective, the four characters could be defined as fourindividual perceptual objects, or one large object based on the Gestalt groupingprinciple. In contrast, from a top-down perspective, they were two compoundwords for skilled Chinese readers and thus could be defined as two semanticobjects. Importantly, Li and Logan (2008) found that RTs were shorter when thecue character and the target character constituted a compound word (i.e., thewithin condition) than when they did not (i.e., the between condition), underthe invalid cueing conditions that had the same distance between the cue and the

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target. This OBA effect elucidated that attention deployment can be affected byobjects defined in a top-down manner, based on lexical knowledge. This findingof semantic OBA effect was replicated by a recent study, in which lexical- andperceptual-based objects were jointly manipulated (Liu et al., 2011).

Note that the concepts of “bottom-up” and “top-down” are a little ambiguousand only rarely defined in the psychology and neuroscience literature (Li &Logan, 2008; Rauss & Pourtois, 2013). On the one hand, top-down can meananything that is not purely perceptual, so lexical knowledge should be consideredas a top-down factor. On the other hand, top-down may also mean voluntary, inwhich case lexical knowledge, if applied automatically, should be considered asbottom-up but not top-down. Consistent with previous studies on semantic OBAeffect (Li & Logan, 2008; Liu et al., 2011), we used the former definition of top-down factor in the present study.

CHINESE CHARACTERS

As mentioned by Li and Logan (2008), “words are the basic lexical units inChinese”. Moreover, most words in Chinese are compound words consisting oftwo or more characters, and two-character compound words are of the highestfrequency among these words. Meanwhile, it is generally agreed that charactersare the basic writing unit in Chinese (e.g., Chou, 1929; Han & Bi, 2009;Wang, 1973).

A Chinese character can be constituted by a single radical alone, or more thantwo radicals. The latter is the so-called compound character, and about 80% ofcharacters are of this kind (Li & Kang, 1993). For example, the character “蝗”(locust) is a compound character comprising two radicals (“虫” and “皇”) abreasthorizontally and closely in distance, whereas both the left and right radical of thischaracter can also become individual characters when they stand alone. Amongcompound characters, there are several structures by which radicals can becombined into a two-dimensional character or “a perfect square”: left–right (e.g.,“蝗”), up–down (e.g., “皇”), or surrounding structures (e.g., “圈”) (Chou, 1929).The left–right arrangement is most common for Chinese characters, and thus wechose it for the stimuli used in the present study. Up–down-structured charactersare the second most common, but we did not choose them because there are notenough characters for the experimental manipulation and more crucially, some ofthem are not suitable to be segmented into two parts because of theconnectedness of the upper and lower radical’s border (e.g., “男”, “舌”, “表”,and “县”).

Compared to alphabetic scripts (such as English) that are linearly unfolding inonly one dimension, Chinese characters have a two-dimensional square form andhave several distinct spatial structures (Sun, Yang, Desroches, Liu, & Peng,2011). If Chinese characters lose their crucial spatial structure or are written in an

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incorrect structure, would these new arranged symbols be viewed as “objects”?In addition, the radical order of the left–right-structured Chinese characters isanother factor that might affect the perception of Chinese characters as objects.Similarly, we all know that the two-letter English word “no” becomes anotherword “on” when the order of letters is reversed. It is therefore interesting toexamine whether the manipulation of character structure and radical order affectattention deployment.

OBJECT-BASED ATTENTION TO CHINESE CHARACTERS?

On the basis of OBA effect found on two-character words by Li and Logan(2008), the present study aimed to investigate whether this effect on two-character words could be extended to the level of single characters. That is, weasked whether the separately presented radicals of a Chinese character could bedefined as a top-down object in the same way as the two characters of acompound word. This is of important theoretical significance for two reasons.First, if there is OBA effect based on single Chinese character level, then theexistence of semantic-objects is further confirmed, and the basic concept ofsemantic-object is extended from compound words to single characters. Second,the existence of OBA effect for single character would support the notion that,relative to the two-character compound words, single Chinese characters aremore basic as a unit for meaning.

EXPERIMENT 1

In this experiment, we aimed to examine whether the OBA effect on two-character words could be extended to the level of single characters. Meanwhile,we investigated the role of character structure and radical order in this process. Inthe present experiment, the structure manipulation was denoted S+ for left–right-structured and S− for up–down-structured characters. Similarly, the radical orderwas denoted O+ for normal and O− for reversed order. Thus, the combinationof these two factors were S+O+, S+O−, S−O+, and S−O−. As illustrated inFigure 1, the characters were displayed in correct character structure and incorrect radical order (S+O+), in reversed character structure and in correctradical order (S−O+), in correct character structure but in reversed radical order(S+O−), or in reversed character structure and in reversed radical order (S−O−).These four conditions can be illustrated by using the English letter conditionsof “T” and “O”, in which S+O+ is the designation for the word “TO”, S+O−

for “OT”, S−O+ for “ TO”, and S−O− for “O

T”.

Overall, semantic object condition (between or within) that indexed OBAeffect, together with character structure and radical order described earlier,

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constituted a 2 (character structure: S+, S−) × 2 (radical order: O+, O−) × 2(semantic object: between, within) within-subject factorial design in the presentexperiment.

Method

Participants. Twenty-eight (14 males, aged between 18 and 26 years, M =21.5 ± 2.38) college students were paid to participate in this experiment.Participants were native Mandarin Chinese speakers, right-handed, with normalor corrected-to-normal vision. Informed consent was obtained from all partici-pants prior to the experiment according to the research protocol approved byDepartment of Psychology, Tsinghua University.

Stimuli. Four radicals from two paired left–right-structured compoundcharacters were displayed in two rows and two columns in each trial (seeFigure 2). The 2 by 2 stimuli matrices were shown in black on a whitebackground at the centre of the screen. The radicals could not form other newcharacters in the diagonal direction. The mean usage frequencies of these 800

Figure 1. Illustration of a 2 (character structure: S+, S–) × 2 (radical order: O+, O–) factorial design. Inpractice, there were four radicals that could form two characters in each trial; here only two radicals weredisplayed for illustration. For example, left–right character “酿” (brew) was constituted by radicals “酉” and“良” abreast. Under the S+O+ condition, two radicals were displayed horizontally and in correct order.Under the S–O+ condition, radicals were displayed vertically and in correct order (from top to bottom).Under the S+O– condition, radicals were displayed horizontally but in reversed order. Under the S–O–condition, radicals were displayed vertically and in reversed order. The stimuli used in Experiment 1 wereshowed in grey shades that were not shown in the real experiment; the stimuli that surrounded by framesand arrows were used in Experiment 2.

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left–right-structured characters (200 per condition) were 276 per million (Cai &Brysbaert, 2010), and there were no significant differences in frequency andnumber of strokes of the radicals between the two rows or columns in eachcondition (all ps > .05). Each radical was shown in a 1 cm × 1 cm square (whichsubtended about 0.8° visual angle), with a gap of 1 cm between rows andcolumns. Because we used only left–right-structured characters, the horizontallengths of radicals varied and were less than 1 cm, whereas the vertical lengthswere almost the same and close to 1 cm.

The experiment was run on a desktop PC using an E-Prime script. Participantswere seated in a chair with a back, with a viewing distance of approximately71 cm.

Procedure and task. There were 400 experimental trials in total and eachcondition consisted of 100 trials (equally mixed into four blocks). In each trial,participants were shown the four-radical array for 2500 ms first. Participantswere encouraged to group the radicals into two left–right-structured charactersmentally as possible as they could during this period. Then a black cross fixationappeared at the centre of the four radicals. Participants were asked to fixate thiscross until the end of the trial. As shown in Figure 3, after 300 ms the cue radicalturned to green for 100 ms, randomly at the four radical locations. Then, the cuedradical turned back to black for 100 ms, after which the target radical turned tored in 288 of 400 trials (72 of 100 trials per condition). Participants were

Figure 2. The modified version of spatial-cueing paradigm that used in the present study had only invalidtarget but no valid target. The grey shades that did not appear in the experiment indicated that the twostimuli within a shade could form a character. (a) Left–right-structured characters “醋” (vinegar) and “胶”(glue) displayed horizontally, producing the S+O+ condition. (b) Left–right-structured characters “幅”(range) and “杆” (pole) displayed vertically, producing the S–O+ condition. There were two types of invalidconditions: between and within. The cue was displayed in green, and the target was displayed in red. Toview this figure in colour, please see the online issue of the Journal.

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instructed to respond as quickly and accurately as possible by pressing a button(“H”) on the keyboard with their right index finger when a radical turned to red.The target screen was on until participants made a response. Participants werealso instructed to withhold their response when they did not perceive the targetradicals (catch trials, 28 of 100 trials per condition), and in this case the targetscreen would disappear automatically after 2000 ms.

The target was presented equally often in the same character as the cuedradical (within, 36 out of 100 trials for each condition) and in the othercharacters (between, 36 out of 100 trials for each condition) in a locationequidistant from the cued radical (see Figures 2 and 3). The target radicalsappeared at the four radical locations equally often and were never diagonal tothe cued radicals. All characters were used only once in this experiment.

There were 25 practice trials prior to the formal experiment. The order oftrials for each condition was randomized within a block and the order of blockswas counterbalanced across participants. After the practice session and after eachblock of 100 trials, there was a short break.

Memory-test task. In order to urge participants to group characters withradicals mentally at the first 2500 ms period of each trial, they were given amemory-test task after one fourth of randomly selected trials (25 trials wereselected per block and per condition). During each memory-test trial, theparticipants were shown a left–right-structured character and were asked to press“H” on keyboard when they had actually grouped that character in the just-ended

Figure 3. The procedures of Experiment 1 and Experiment 2. Besides frames and arrows being addedaround the stimuli displayed during the 2500 ms exposure period in Experiment 2, the rest were identical inboth experiments. To view this figure in colour, please see the online issue of the Journal.

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trial and withhold their response when they saw a novel character. In half of theselected memory trials, the characters presented to participants were these theyhad grouped in the just-ended trials; in the other half, the characters werecompletely new. Participants were instructed that accuracy was more importantthan RTs in this memory-test task.

Results and discussion

Only target-present trials with correct responses were included in the analysis.RTs shorter than 150 ms or longer than three standard deviations (SD) from themean were excluded. Altogether, 2.5% target-present trials with correctresponses were excluded.

Mean RT and accuracy of main task. For the target detection task, theoverall accuracy was 98.5%. The false alarm was 4.6%, and the missing rate was0.3%. Since the missing rate of target-present trials was extremely low (and thehit rate was extremely high accordingly), the accuracy data was not sent forfurther analysis.

We first conducted a three-way repeated-measure ANOVA on RTs withfactors of character structure, radical order, and semantic object. This three-wayANOVA revealed significant main effects for radical order, F(1, 27) = 16.864,p < .001, g2p ¼ :384, and semantic object, F(1, 27) = 6.531, p = .017, g2p ¼ :195,but no main effect for character structure, F(1, 27) = 0.388, p = .539, g2p ¼ :014.These effects reflected that mean RT for conditions with legal radical order (430ms) was significantly shorter than that with illegal radical order (446 ms). Moreimportantly, mean RT for within conditions (433 ms) was shorter than that forbetween conditions (442 ms). This result indexed the existence of object-basedattention effect on the level of individual Chinese character. However, the meanRTs of conditions with legal character structure (439 ms) and illegal structure(437 ms) showed no significant difference. The three-way interaction amongthese three factors was not significant, F(1, 27) = 0.179, p = .676, g2p ¼ :007, butthe two-way interaction of radical order by semantic object was marginallysignificant, F(1, 27) = 3.553, p = .07, g2p ¼ :116. No other interactions reachedsignificance (all ps > .3).

As the marginally significant interaction of radical order by semantic object,we further conducted simple effects analysis. This analysis showed that mean RTon within trials (422 ms) was significantly shorter than that on between trials inthe O+ condition (437 ms), F(1, 27) = 23.674, p < .001, g2p ¼ :467. In contrast,in the O− condition, mean RT on within trials (444 ms) showed no significantdifference with that on between trials (447 ms), F(1, 27) = 0.238, p = .63, g2p ¼:009 (see Figure 4). These results suggest that the OBA effect existed inthe condition with legal radical order (both S+O+ and S−O+ conditions)but vanished in the condition with illegal radical order (both S+O− and S−O−

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conditions), confirming again the role of radical order in the OBA effect. Incontrast, the absence of significant main effect of character structure and itsrelated interactions indicated that it had no influence on the presence or absenceof the OBA effect on character.

Accuracy of the memory-test task. The overall accuracy rate of the fellow-upmemory-test task was 96.5%. Then, to assess the performance of groupingcharacter during the first 2500 ms exposure period under four conditions, weconducted a two-way ANOVA on accuracy with factors of character structureand radical order. This ANOVA revealed significant main effect for radical order,F(1, 27) = 5.929, p = .022, g2p ¼ :18, but no main effect for character structure,F(1, 27) = 0.26, p = .615, g2p ¼ :01. As can be seen in Figure 5, there was also asignificant interaction between character structure and radical order, F(1, 27) =16.953, p < .001, g2p ¼ :386

These accuracy results of the memory-test task were consistent with andprovided evidence for the findings on RT data in target detection task. Becausethe time interval from the first 2500 ms exposure period to the follow-upmemory-test task was constant under four conditions, the differences of accuracyof the memory-test task indexed the performance of grouping character duringexposure period but not additional factor, such as memory. Although theaccuracy of memory-test task under four conditions were fairly high (all above

Figure 4. Reaction times of the two invalid cueing (between and within) under the O+ and O– conditionsin Experiment 1. The error bars indicate 95% within-subjects confidence intervals computed on between vs.within comparisons for each condition. ***p < .001. n.s. = not significant.

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94%), the significant accuracy gap between legal and illegal radical ordercondition indicated that it was more difficult for participants to form “semanticobject” (characters) mentally when the correct radical order informant wasdeprived, and further supported that it was also more difficult to deploy attentionfor radical conditions when the correct radical was reversed. As a result, it wasn’table to generate a significant OBA effect in the illegal radical order condition(see Figure 4). As for character structure, the nonsignificant difference ofaccuracy between the legal and illegal level of this factor was also consistentwith the conclusion described above that character structure had no influence onthe OBA effect on character level.

In sum, in Experiment 1, we found the object-based attention effect on thelevel of individual character, and extended this effect from two-charactercompound word to individual character. Moreover, we further discovered thatradical order but not character structure had an important role in the effect. Notethat, in Experiment 1, we found the role of radical order in the object-basedattention effect by depriving the correct radical order information and comparingbetween the illegal and legal conditions. In contrast, in Experiment 2, weenhanced the character structure and radical order information by addingperceptual cues (frames and arrows) around the stimuli accordingly to investigate(1) whether the OBA effect could be replicated under the legal radical order (i.e.,

Figure 5. Accuracy of the four conditions in the memory-test task in Experiment 1. The error bars indicate95% within-subjects confidence intervals computed on between vs. within comparisons for each condition.***p < .001. n. s. = not significant.

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S+O+, and S−O+) conditions, and (2) whether the OBA effect could beobserved under the illegal radical order (i.e., S+O−, and S−O−) conditions.

EXPERIMENT 2

We combined the paradigm of Experiment 1 with that used in studies examiningOBA effect with bottom-up rectangular objects defined by the Gestalt principle(e.g., Egly et al., 1994; He et al., 2004). First, we used two horizontal andvertical line-drawing rectangle frames to “patch up” the structure informationthat was disrupted in Experiment 1. Second, we used arrows with differentdirections (left, right, upward, and downward) to indicate whether the radicalorder was normal or reversed for each trial.

Method

Another 29 (15 males, aged between 19 and 27 years, M = 22.45 ± 1.79) collegestudents who had not took part in Experiment 1 were paid to participate inExperiment 2.

The experimental settings were the same as that in Experiment 1, except thatduring the 2500 ms exposure period two parallel rectangle frames and fourarrows on the four long sides of rectangles were added around the stimuli (seeFigure 3). The frame indicated that the two radicals inside could constitute a left–right-structured character. Because we used only left–right-structured characters,the horizontal frame indexed that the two horizontal radicals could constitute acharacter (S+ condition), and the vertical frame indexed that the two verticalradicals could constitute a character (S− condition). The direction of the fourarrows on the middle of long sides of frames indicated which conditions thestimuli belonged to: Right arrows and down arrows indexed the radical order ofstimuli was normal (O+ condition), and left arrows and up arrows indexed theradical order of stimuli was reversed (O− condition). The probabilities fornormal and reversed order were equal. Note that, unlike the manipulation of Liuet al. (2011) who displayed rectangles during the entire trial with characterstimuli to investigate the competition between objects defined by top-down andbottom-up factors, we only presented the stimuli with frames and arrows duringthe 2500 ms exposure period. In short, the bottom-up information provided byframes and arrows was used as perceptual cues to help patch up the top-downinformation of character structure and radical order that was disrupted inExperiment 1.

Like previous studies that found local object structure influences overall OBAeffect (e.g., Hecht & Vecera, 2007; Matsukura & Vecera, 2006), the presentstudy hypothesized that semantic OBA effect can be influenced by perceptualcues around the radical stimuli in Experiment 2. Specifically, since the radical

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order information under the O+ condition were not disrupted in both Experi-ments 1 and 2 and sufficient enough for participants to group characters, wepredicted replication of the OBA effects but with little or no benefit from theseperceptual cues under the O+ (S+O+ and S−O+) conditions. In contrast, wepredicted that the O− (S+O− and S−O−) conditions might benefit more fromthe perceptual cues by retrieving the correct radical order information relative tothat in Experiment 1.

Results and discussion

As with the criterion in Experiment 1, only target-present trials with correctresponses were included in the analysis. RTs that were shorter than 150 ms orlonger than three standard deviations from the mean RT were excluded.Altogether, 2.2% target-present trials with correct responses were excluded.

Mean RT and accuracy of main task. For the target detection task, theoverall accuracy was 99.2%. The false alarm was 2.4%, and the missing rate was0.1%. The accuracy data was again not sent for further analysis, as withExperiment 1.

The same three-way repeated-measure ANOVA on RTs that applied inExperiment 1 was utilized in Experiment 2. This three-way ANOVA revealedsignificant main effect for semantic object (Mwithin = 396 ms; Mbetween = 411 ms),F(1, 28) = 34.059, p < .001, g2p ¼ :549, and marginally significant main effectfor radical order (MO+ = 401 ms; MO− = 405 ms), F(1, 28) = 4.045, p = .054,g2p ¼ :126, but no main effect for character structure (MS+ = 402 ms; MS− = 405ms), F(1, 28) = 1.008, p = .324, g2p ¼ :035. The significant main effect ofsemantic object indexed a top-down organization of the displays into “semanticobjects” defined by single Chinese characters. These patterns on main effectswere almost identical with those in Experiment 1 except for one small difference—the main effect for radical order that reached significance in Experiment 1 wasmarginally significant in Experiment 2. There were no significant two-way or three-way interactions (all ps > .1). Importantly, the two-way interaction of radical orderby semantic object, which reached marginal significance in Experiment 1, was notsignificant in Experiment 2.

As in Experiment 1, in order to further characterize these results and the vitaldifference, we calculated same simple effects analysis. This analysis showed thatmean RT on within trials (393 ms) was significantly shorter than that on betweentrials (409 ms) in the O+ condition, F(1, 28) = 29.97, p < .001, g2p ¼ :517; and inthe O− condition, mean RT on within trials (398 ms) was also significantlyshorter than that on between trials (413 ms), F(1, 28) = 20.627, p < .001, g2p ¼:424 (see Figure 6). These results indicated that the conditions with illegal radicalorder information could also deploy attention as the legal conditions did whenthe perceptual cues were introduced to help participants to pick up the correct

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radical order information. Importantly, this further confirms the role of radicalorder in the OBA effect on individual character level, but from a reversed pointof view as compared to Experiment 1. That is, disrupting the radical order inExperiment 1 (S+O− and S−O− conditions) resulted in no OBA effect, whereasenhancing the radical order information for these two conditions in Experiment 2generated significant OBA effects. As in Experiment 1, neither the main effectnor any related interactions of character structure were significant. These resultsconfirmed that character structure was not essential in the OBA effect on thelevel of individual character.

Accuracy of the memory-test task. The overall accuracy rate of the follow-up memory-test task was 97.8%. Like in Experiment 1, we conducted a two-wayANOVA on accuracy with factors character structure and radical order. The maineffects for radical order and character structure were not significant, F(1, 28) =1.34, p = .257, g2p ¼ :046, and F(1, 28) = 1.582, p = .219, g2p ¼ :053,respectively. There was also no significant interaction between characterstructure and radical order, F(1, 28) = 2.061, p = .162, g2p ¼ :069 (see Figure 7).These results indicated that, with the help from perceptual cues, participantscould group radical combinations of the O− condition into correct characters,i.e., the semantic objects, almost as well as in the O+ condition. As inExperiment 1, the nonsignificant difference of accuracy between the legal and

Figure 6. Reaction times of the two invalid cueing (between and within) under the O+ and O– conditionsin Experiment 2. The error bars indicate 95% within-subjects confidence intervals computed on between vs.within comparisons for each condition. ***p < .001.

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illegal character structure is consistent with the conclusion that characterstructure had no influence on the OBA effect.

GENERAL DISCUSSION

We investigated whether the semantic-OBA effect on the level of two-charactercompound word exists at the single character level and whether this OBA effectcan be affected by character structure and radical order in two experiments. Weinvestigated the roles of character structure and radical order on semantic OBAeffect at the individual character level, when the spatial information wasdisrupted (Experiment 1) or enhanced by perceptual cues (Experiment 2). First,we found that attentional shift within two radicals was faster relative to shiftbetween two radicals, suggesting that the top-down “semantic object” can bedefined not only at two-character compound word level, as has been reportedpreviously (Li & Logan, 2008; Liu et al., 2011), but also at single character level.To our knowledge, this is the first study that extended the concept of “semanticobject” from the two-character compound word level to the single characterlevel, and supported the notion that, relative to the two-character compoundwords, single Chinese characters are more basic as a unit for meaning. Second,the present study demonstrated that radical order information but not characterstructure information played an important role in the semantic-object-based

Figure 7. Accuracy of the four conditions in the memory-test task in Experiment 2. The error bars indicate95% within-subjects confidence intervals computed on between vs. within comparisons for each condition.n. s. = not significant.

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attention. In Experiment 1, the OBA effect found in the O+ condition (S+O+ andS−O+) vanished when we deprived correct radical order information in the O−condition (S+O− and S−O−). In contrast, in Experiment 2, the OBA effectappeared when we introduced correct radical order information with the helpfrom perceptual cues. We also manipulated the factor character structure in thesame way we did on radical order, but the OBA effect was not affected by thisfactor. In addition, the results of the accuracy of the memory-test task wereconsistent with the results based on RT data.

How can these results in Experiments 1 and 2, which significant OBA effectexhibited in both S+O+ and S−O+ conditions (O+ condition) but not only in theformer condition, be interpreted? After all, only the S+O+ condition shares legalcharacter structure (displayed horizontally) and radical order (from left to right)information with real left–right-structured characters that Chinese readers read indaily life. In the S−O+ condition, however, the radicals of left–right-structuredcharacters were displayed vertically and illegally from top to bottom. Theseseemingly puzzling results can be explained as the influence from reading/writing system of Chinese. Different from alphabetic scripts (such as English)that readers read in a left-to-right directionality, Chinese readers can read andwrite in two distinct directionalities—besides the left-to-right directionality aswith English, there is also a top-to-bottom directionality (such as in calligraphy,Chinese painting work, spine titles of book, and antithetical couplets). These twokinds of reading/writing directionality coexist in Chinese culture with thefollowing characteristics that the left-to-right directionality was predominant inMainland China, whereas the top-to-bottom directionality was predominant inTaiwan (Chou, 1929; Hung, Hung, Tzeng, & Wu, 2008). That is, Chineseparticipants with these two kinds of reading/writing directionality experiencecould form semantic objects (and then deploy OBA) in the S+O+ condition withthe left-to-right directionality, and form semantic objects in the S−O+ conditionwith the top-to-bottom directionality. In addition, it is worth mentioning that tworelated previous studies on OBA effect using Chinese characters as stimuli alsoemploy these two reading directionalities (Li & Logan, 2008; Liu et al., 2011).

In the O− condition (both S+O− and S−O− conditions), the perceptual cues(frames and arrows around the stimuli accordingly) in Experiment 2—the onlydifference of manipulation between Experiments 1 and 2—could explain whyOBA effects of the O− condition turn from nonsignificant in Experiment 1 tosignificant in Experiment 2. Participants in Experiment 2 could use theseperceptual cues to help them to form semantic objects in these conditions withillegal radical orders in Experiment 1. To be specific, the frames show clearlythat every two radicals inside each frame could form a character, and the arrowson the middle of long sides of frames index the correct radical order. As a result,Experiment 2 verifies the important role of radical order in OBA effect found inExperiment 1.

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One possible argument could be that the significant OBA effects observed inall four conditions in Experiment 2 might be confounded by the perceptualeffects generated by the perceptual cues. This argument seems unlikely, becausethe perceptual cues are displayed only during the first 2500 ms exposure periodand perceptually disappeared long before the target frame. Consistent with this,another recent study finds no OBA effect when the perceptual objects(rectangles) disappear from view in the last target frame no matter the likelihoodof the rectangles disappearing (Ho & Yeh, 2009). Therefore, we argue that theperceptual cues in Experiment 2 just help participants to form charactersmentally but have no influence on the semantic-OBA effect that we observed.

Compared to the original experimental design of a previous study (Li &Logan, 2008), the present study had some variations. First, the duration of four-radical array was longer (2500 vs. 1500 ms) than that of the four-character arrayin Li and Logan (2008). This is because radicals were less familiar thancharacters in daily life for participants and some participants in our pilotexperiment also self-reported that the duration of 1500 ms was not long enoughto generate two characters. Second, we used cues of 0% validity (relative to 75%cue validity used by the Li & Logan study) to abnegate the space-based attentioneffect and focused on the OBA effect. The advantage of using 0% cue validity inthe present study was that it helped us to save trials and to focus on the OBAeffect that of our research interest. However, one big concern is that thissignificant change of cue validity from above 50% to 0% may have changed thenature of attentional employment elicited by the cues. For example, one couldargue that the 0% of cue validity may lead participants not to take the cueseriously and cannot attract attention. As a consequence, participants’ attentionalemployment might be randomized on possible target locations. However, thisargument is not supported for several reasons. First, there is evidence suggestingthat stimulus onset can attract attention automatically (Yantis et al., 1990), evenunder conditions of 0% cue validity (Muller & Rabbitt, 1989). Second,decreasing the cue validity actually increases the OBA effect (He et al., 2004).Finally, the significant OBA effect due to a semantic object in the present studyalso suggests that randomized attentional employment by cue onset was unlikely,because randomized attentional employment for cues would predict no suchobject-based effect. A more straightforward and parsimonious account is thatparticipants attended to the cued location first and then switch their attention tothe target location in the present 0% cue validity condition, the same processes asin the previous 50% cue validity conditions. Therefore, we argue that the presentOBA effect is generated by the same processes as in previous studies usinghigher cue validity and can be compared across these studies.

One could also argue that the four radicals with only 1 cm distance betweenthem might be able to form two perceptual characters. That is, the so-calledsemantic-object-based attention effect could be simply due to the bottom-upperceptual objects rather than the top-down “semantic objects”. First, this

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argument is unlikely, because a recent study has shown that, during a lexicaldecision task, participants’ RTs were longer and error rates were higher for the0.75 space and the 1.5 space conditions relative to the 0 space original condition(Sun et al., 2011). The present manipulation of inserting one space between tworadicals under the S+O+ condition could effectively degrade the intactness of thecharacter and therefore minimize the possibility of forming a bottom-upperceptual object. Second, and more importantly, this argument can hardlyexplain the OBA effect observed under the S−O+ condition, in which no correctperceptual objects can be formed. As such, the object-based attention effectobserved in the present study was more likely due to the top-down “semanticobject” developed mentally during the 2500 ms exposure period.

CONCLUSION

In conclusion, we had several novel findings in this study. First, we extended thesemantic-OBA effect from two-character words in previous studies to singlecharacters. Second, we found that radical order, but not character structure, iscrucial for the development of semantic objects at the single character level.Finally, we demonstrated that the development of semantic object at the singlecharacter level can be influenced by bottom-up perceptual cues by retrieving thecorrect radical order information. Therefore, attention can operate on semanticobjects developed from individual characters—the more basic writing units ofChinese characters relative to two-character compound words.

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