once a single word is presented , its orthographically similar words are also partially activated .
coltheart first introduced the concept of orthographic neighborhood of a target word , defined as all words of the same length that can be generated by changing just one letter while preserving letter positions .
for example , cheap , chest , cleat , and wheat are all neighbors of cheat .
grainger and his colleagues pointed out that the printed frequency of a word 's orthographic neighbors played an important role in identification process of this target word , which is termed as neighborhood frequency effect .
the authors indicated that if the frequency of a target word was not the highest among its neighbors , those higher - frequency neighbors ( hfns ) would compete with the target word and , consequently , slow down its processing .
this inhibition was reported in several studies of lexical decision [ 28 ] . in naming tasks , no effect or a facilitatory trend of neighborhood frequency
grainger   gave an explanation to the absence of neighborhood interference based on the analogy theory of word naming [ 10 , 11 ] .
the pronunciations in alphabetic orthographic neighborhoods were of high consistency , a word usually sounded similar with its orthographic neighbors , and then the neighbors with higher frequency would provide support for the component phonology of the target word .
however , there is a close relationship between visual forms and pronunciations in alphabetic words , thus it is still needed to determine whether the hfns affect the target naming during phonological processing or visual / orthographic analysis .
as opposed to alphabetic languages , chinese with a logographic writing system lacks the grapheme - to - phoneme correspondence ( gpc ) rules , in which visual words map onto speech sounds through an addressed way [ 12 , 13 ] .
considering different language characteristics , the definition of orthographic neighbors for alphabetic words is inapplicable for chinese characters .
however , about 85% of chinese characters are semantic - phonetic compounds [ 14 , 15 ] with the phonetic and semantic radicals informing to some extent about the character 's pronunciation and meaning , respectively . by the medium of phonetic or semantic radicals , orthographic neighborhood of chinese characters can be formed .
for instance , characters  ( pronounced / ji1/ , meaning garbage ; the number here refers to chinese tone ; the same below ) ,  ( /ji2/ , draw ) ,  ( /ji2/ , unmitigated ) ,  ( /ji2/ , book ) ,  ( /ji2/ , danger ) ,  ( /ji2/ , class ) ,  ( /xi1/ , absorb ) , and  ( /sa3/ , shoes ) have the same phonetic radical  ( ji2 , and ) and are considered as a phonetic - radical orthographic neighborhood .
moreover , because phonological consistency is much lower in chinese orthographic neighborhoods [ 16 , 17 ] , the higher - frequency neighbors were expected to inhibit the target naming according to analogy theory of word naming , and this has been proved .
li et al . examined the neighborhood frequency effect in chinese character naming , in which neighbors with the highest frequency sounded differently from target characters in the with - hfn condition .
results showed a significantly interference effect of neighborhood frequency , and participants spent longer time and made more errors in with - hfn condition than in without - hfn condition .
and their follow - up fmri study found that naming with - hfn characters induced greater activations than naming without - hfn characters in bilateral inferior frontal gyrus ( bi - ifg ) which was related with the phonological competition and inhibition of extraneous phonological activation .
the above findings revealed that higher - frequency neighbors exerted an inhibitory influence on chinese - character naming , and this inhibition might be linked to the phonological processing . but whether the hfn effect was special to the phonological level was still unclear because of the low temporal resolution of brain imaging , and the event - related potential ( erp ) technique is undoubtedly a valuable way to dissociate the phonological processing from other stages ( e.g. , visual stage ) .  
the bilaterally posterior n1 is usually considered as a visual - orthographic component , with amplitude peak at around 130  ms to 170  ms [ 2026 ] .
the p2 component occurs around 200  ms after stimulus at centrofrontal sites and indexes lexical phonology in chinese reading [ 2729 ] .
a previous study of neighborhood frequency effect using lexical decision found that english words with hfns reliably induced larger amplitude than that without hfns in the 180240  ms time window , while there was no difference between the two conditions at earlier stages , revealing the possible phonological influence of hfns .
however , to our knowledge , there were no erp researches on neighborhood frequency effect in naming tasks .
so , the present study intended to use erps to examine the mechanism of neighborhood frequency effect in chinese - character naming . according to the analogy theory of word naming
, it could be expected that the higher - frequency neighbors would only affect the target processing at phonological stage , exhibiting an effect in p2 component but not n1 component .
all the participants were right - handed native mandarin speakers with normal or corrected - to - normal vision .
there were 48 characters as targets , 24 for with - hfn and without - hfn conditions , respectively ( see table 1 ) .
for the without - hfn characters , a target character had the highest frequency within its neighborhood .
for the with - hfn characters , at least one of its neighbors was of 3 per million higher frequency referred to as a previous study ; meanwhile , the target and its neighbor(s ) with the highest frequency sounded differently from each other .
for example ,  ( pronounced /dan4/ , meaning birth , character frequency being 7.09 occurrences per million ; the same below ) ,  ( /xian2/ , saliva , 0.74 ) ,  ( /yan2/ , wriggly , 0.85 ) , and  ( /yan2/ , feast , 0.65 ) form an orthographic neighborhood .
the target character is  , and its orthographic neighbors all have much lower character frequency , so this target is considered as a without - hfn character .
 ( /di2/ , barbarians , 5.41 ) ,  ( /qiu1/ , autumn , 24.03 ) ,  ( /huo3/ , partner , 28.72 ) , and  ( /huo3/ , holmium , 0.02 ) form another neighborhood , and the target character is . the neighbor  has the highest frequency in this neighborhood , and the difference in frequency between  ( 5.41 ) and  ( 24.03 ) is greater than 3 per million ; meanwhile the two characters sound different from each other , and thus the target  is regarded as a with - hfn character .
the mean number of hfns in one neighborhood was 2 ( range , 1 to 6 ; standard deviation = 1.47 ) .
the irregular character indicates the character whose pronunciation is different from that of its phonetic radical ; for example ,  ( sa3 , shoes ) is an irregular character , because of its phonetic radical  ( ji2 , and ) with a different pronunciation .
the consistency value ( c ) can be calculated from the relative ratio of the number of orthographic neighbors with the same pronunciation ( n ) to the whole neighborhood size ( n ) , c =
n / n . for example in the phonetic - radical neighborhood of  ( ji2 , and ) ,
its neighborhood size is eight , and there are six neighbors with the same pronunciation / ji/ ,  ( /ji1/ , garbage ) ,  ( /ji2/ , draw ) ,  ( /ji2/ , unmitigated ) ,  ( /ji2/ , book ) ,  ( /ji2/ , danger ) , and  ( /ji2/ , class ) , producing a consistency level of /ji / of 0.75 ( c = 6/8 ) . in the present study , the consistency of each target character was below 0.4 .
the target characters were all left - right structure with the phonetic radical on the right side .
moreover , the number of neighbors , character frequency , stroke , and consistency were balanced between conditions ( table 2 ) .
character frequency information was collected from the chinese text computing database ( http://lingua.mtsu.edu/chinese-computing/ ) , and the neighborhood was defined on the basis of li and kang 's statistics .
participants sat in a sound - attenuated room , at a viewing distance of 50  cm from the screen , with a visual angle of 5.7  5.7.
they were instructed to sit comfortably and concentrate on the stimulus avoiding head movements or any other unnecessary movements .
figure 1 displays the presentation format within each trial . a trial consisted of a 500  ms cross - fixation , a 500  ms blank screen , and a 500  ms target character .
the participants were asked to silently name the target . to ensure that the phonology of the target character was accessed , the covert naming was followed with a homophonic decision , in which participants should make a decision on whether the target and the following probe were homophonic and click mouse buttons with their thumbs , with the left button for  different pronunciation  and the right button for  homophony . 
for the compound - character probe , its phonetic radical was always different from that of the paired target .
half of the probes sounded the same with the targets , and the other half sounded different .
the list of the target characters was presented twice so that the number of trials in each condition rose to 48 .
one target was paired up with different probes between the two presentations to reduce practice effects .  
the stimuli were programmed with the stim software and randomly shown on a lenovo monitor .
electroencephalographic ( eeg ) activity was recorded from a 64-channel neuroscan version 4.3 system with a common vertex reference and rereferenced to the average of the left and right mastoids in the offline analysis .
vertical eye movements ( veog ) were recorded by a pair of electrodes placed on the supraorbit and infraorbit of the left eye , and horizontal eye movements ( heog ) were recorded by a pair of electrodes placed beside the outer canthus of both eyes .
eeg signals were recorded and digitized at a bandpass filter of 0.05100  hz , with amplifying at a sample rate of 500  hz .
resistances across all the electrodes were kept below 5  k. the acquired data were corrected for eye movements and blinks and segmented to epochs of 800  ms posttarget interval and 100  ms pretarget baseline .
epochs containing incorrect behavioral responses or with peak - to - peak differences larger than 100  v were rejected , and this led to a rejection rate of 8% over all trials , without statistical difference in the number of rejections between conditions ( p > 0.1 ) .
the remaining epochs were filtered with a low - pass filter of 30  hz ( zero - phase shift mode , 12  db ) and averaged for each condition and participant .
figure 2 displays the erp grand averages time locked to the onset of target characters for neighborhood frequency comparison . as can be seen from the figure , the erps show a negative polarity peaked at around 150  ms over posterior regions and a positive polarity peaked at about 170  ms over frontocentral regions .
the 40  ms time windows were selected centering the n1 and p2 peaks ( n1 : 130170  ms ; p2 : 150190  ms ) . according to topographic mapping in figure 2 ,
the n1 amplitude was output at channels of po5-po6 , po7-po8 , o1-o2 , and the p2 amplitude was recorded at channels of frontal ( f1-f2 , f3-f4 ) , frontocentral ( fc1-fc2 , fc3-fc4 ) , central ( c1-c2 , c3-c4 ) , and centroparietal ( cp1-cp2 , cp3-cp4 ) lobes .
mean erp amplitudes from corresponding time windows were computed for each participant in both conditions .
the n1 amplitude was submitted to a repeated - measure anova with neighborhood frequency ( nf , with / without hfns ) and laterality ( left / right hemisphere ) .
the p2 amplitude was submitted to a repeated - measure anova , with three within - subject variables : neighborhood frequency ( with-/without hfns ) , laterality ( left / right hemispheres ) , and lobe ( frontal / frontocentral / central / centroparietal lobes ) .
the anova on n1 amplitude showed no significant main effect or interaction ( all ps > 0.1 ) .
the anova on p2 amplitude showed a significant main effect of neighborhood frequency ( f(1 , 12 ) = 12.88 , p < 0.01 ) , and erp response to target characters was larger in without - hfn condition than in with - hfn condition ; a significant main effect was also observed for lobe ( f(1 , 12 ) = 8.73 , p < 0.01 ) , and post hoc analysis showed the smallest amplitude in the centroparietal lobe but no differences across other three lobes ; no significant effect was found for laterality ( f(1 , 12 ) < 1 , p = 0.68 ) or any interactions ( all ps > 0.1 ) .
in the present study , there was no effect of neighborhood frequency on bilateral posterior n1 amplitude ; as to the p2 amplitude , naming chinese characters without hfns induced more positive erps than that with hfns .
the current results uncovered the time course of early influence of orthographic neighbors with higher frequency in chinese - character naming .
the absence of neighborhood frequency effect in n1 amplitude revealed that higher - frequency neighbors did not affect visual / orthographic analysis of the target characters , since n1 is usually associated with the visual form processing of written words / characters [ 22 , 26 ] .
the finding was consistent with a previous study using english words , in which there was not hfn effect in the early time window before 180  ms .
moreover , it was reported that the n1 originates predominately from the occipitotemporal regions ; thus the present result was identical with the nonsignificant hfn effect in the occipital areas reported by li et al . .  
the current amplitude difference between with- and without - hfn conditions in the p2 time - window indicated that higher - frequency neighbors exerted an influence on phonological processing of chinese characters .
debruille also reported an hfn effect in english words with the erps response in the posttarget interval ranging from 180  ms to 240  ms .
these findings suggested the universal role of hfns in phonological retrieval of target words / characters across language systems .
however , the current hfn effect was greater p2 amplitude in without - hfn condition than that in with - hfn condition , while the neighborhood frequency effect in debruille   was opposite . the difference might be ascribed to the language characteristics in phonological consistency .
considering the high phonological consistency in alphabetic writing systems , higher - frequency neighbors would provide support for the target phonology , which might correspond with increased brain activity of larger erp amplitude .
whereas the phonological consistency was low in chinese orthographic neighborhoods , different pronunciations of the hfns would be more easily activated because of the lower threshold of activation for these neighbors and compete with the phonological activation of the target characters , resulting in the interference on phonological processing of chinese characters , which may inhibit the relevant brain activity of p2 component .
additionally , the distribution of p2 effect was mainly located in the frontal and centroparietal areas .
neuroimaging studies reported that the left middle frontal gyrus was responsible for the addressed phonology , and the dorsal aspect of the left inferior parietal lobule was thought to be the region specific for phonological storage in chinese ; meanwhile , the right frontal regions were linked to phonological competition and inhibition [ 12 , 19 , 35 , 36 ] .
these results indicated that the higher - frequency neighbors might exhibit a disruptive effect in the lexical route of chinese phonological access .
the present results were consistent with our prediction based on the analogy theory of word naming , revealing that orthographic neighbors with higher frequency might impact on target naming at the phonological level .
proposed that the orthographic neighborhood effect in chinese - character naming may be generated in two phases : orthographic facilitation from visually similar neighbors and phonological inhibition of higher - frequency neighbors .
the current findings provided evidence for the phonological inhibition , suggesting negative influence of higher - frequency neighbors at the phonological retrieval in chinese - character naming .
the present study used erps to separately examine the effect of higher - frequency neighbors at the early orthographic and phonological stages .
results showed amplitude difference between with- and without - hfn conditions in p2 component but not in n1 component , suggesting a special role for the hfns in addressed phonology of chinese characters . the reduced amplitude of p2 for with - hfn characters might reveal the phonological inhibition from the higher - frequency neighbors due to their different phonological representations from the target characters .
 the present study explored the time course of neighborhood frequency effect at the early processing stages , examining whether orthographic neighbors with higher frequency exerted an influence on target processing especially at the phonological stage by using the event - related potential ( erp ) . 
 thirteen undergraduate students were recruited in this study , and they were required to covertly name chinese characters with or without higher - frequency neighbors ( hfns ) ; meanwhile , their brain activity was recorded . 
 results showed that the effect of neighborhood frequency was significant in frontocentral p2 amplitude , with a reduction for naming characters with hfns compared to those without hfns ; while there was no effect in posterior n1 amplitude . 
 the only neighborhood frequency effect in p2 component suggested a special role for the hfns in phonological access of  chinese characters . 
 the decrease in amplitude for naming with - hfn characters might be associated with the phonological interference of higher - frequency neighbors due to their different pronunciations from the target characters . 
1. Introduction
2. Methods
3. Results
4. Discussion
5. Conclusions