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Literature Review

Word frequency effect on the role of phonology and tone activation in visual word recognition in

Chinese reading

Rundi Guo

University of Pittsburgh

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The role of phonology in visual word recognition has been substantially investigated in

reading research on various languages. While it is largely agreed that activation of phonology is

an inevitable process in visual word identification in alphabetic languages, in which

phonological information is often saliently encoded in the visual word forms (Perfetti, Zhang, &

Berent, 1992), debates on the role of phonology emerge as far as the non-alphabetic and non-

transparent Chinese is concerned. Since Chinese separates orthography from phonology, with

almost no grapheme-phoneme correspondence typically seen in phonologically-based alphabetic

systems, a number of researchers have argued that recognition of Chinese characters might

bypass phonology, going directly from orthography to semantics to preserve visual identification

efficiency (e.g. Wong, Wu, & Chen, 2014; Zhang et al., 2012). In other words, as a result of the

lack of direct relatedness between visual forms and phonology as well as the vast amount of

homophones in Chinese, activation of the phonological information of the visual form would be

unjustifiable and could potentially interfere with and thus hurt the semantic retrieval process,

especially in cases of homophony where phonology could elicit multiple and irrelevant semantic

codes since one piece of phonological information maps onto multiple visual forms that envelope

unrelated meanings. As a matter of fact, priming paradigms involving homophones are what

researchers frequently use in their studies on the role of phonology in Chinese word reading. The

underlying principle is that if phonology is automatically activated upon a rapid encounter of one

character, the pronunciation retrieval (i.e. naming) of the homophone would be facilitated as a

result of phonemic priming, whereas the semantic access would be slowed due to the

interference of the previous activation of irrelevant semantic information. If phonology is not

activated, on the other hand, one would not otherwise expect such facilitation or interference

effects of homophones.

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Using such paradigms, much evidence seems to suggest that activation of phonology is

automatic and oftentimes necessary in word recognition in Chinese, supporting a semantic-with-

phonology hypothesis (Tan & Perfetti, 1999; Perfetti & Zhang, 1991; Perfetti & Zhang, 1995;

Ziegler et al., 2000). For example, In a series of experiments, Perfetti and Zhang (1991) found a

facilitation effect of homophonic primes on speed and accuracy of target naming, and that small

phonological priming effect is observed when the prime was exposed for as short as 50 ms. In

terms of semantic processing, phonological similarity have been found to interfere with

judgment on meaning similarity, as reported by Perfetti and Zhang (1995), suggesting the

involvement of phonology in lexical processing. Similarly, Tan and Perfetti (1999) found that

homophonic primes significantly prolonged reaction time in meaning-judgment tasks while

exhibiting a facilitation effect in lexical decision tasks, and that similar pattern is observed in

both one-character and two-character Chinese words. These findings suggest that phonological

recoding might be an automatic and obligatory constituent in word identification in Chinese, and

that phonological information is routinely activated together with semantic information even in

the non-alphabetical Chinese, providing support for a universal principle of phonological

processes in reading. In addition to the utilization of homophony, a large number of studies also

incorporated the classic Stroop task to investigate whether semantically-unrelated homophones

of color words – just like the color words themselves – can elicit interference or facilitation

effect on semantic judgment of the actual color. Using this paradigm, Spinks et al. (2000)

reported interference effect of homophones of color words on color judgment. Similar results

were successfully replicated in many later studies (e.g. Guo, Peng, & Liu, 2005).

Chen and Shu (2001), on the other hand, questioned the universal principle of

phonological activation in reading and argued against early phonological activation in reading

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Chinese. In their priming experiments using semantic, graphic, and homophonic primes at

various stimulus onset asynchrony (SOA), they found facilitation and inhibition effect of

semantic and graphic primes (respectively) on target naming across different SOAs, but only

very weak effect on naming latency in trials with homophonic primes compared to the baseline

unrelated primes, and that such effects only appear at late SOAs. Such findings led them to

conclude that phonological activation, if any, does not occur until a later stage in the recognition

process, only playing an optional role in semantic access. Zhou and Marslen-Wilson (2000)

reached similar conclusion in an investigation of the relative time course of semantic and

phonological activation in word and character reading, in which they measured effects of

semantic and homophonic primes at various SOAs in not only naming tasks but also word-level

and character-level lexical decision tasks. Whereas strong semantic priming effects were

observed across different tasks and different SOAs, The effect of homophonic primes were found

to be either nonexistent or much weaker than the semantic primes in most conditions, indicating

that phonological information, if activated at all, plays no privileged role over semantic

information in visual lexical processing in Chinese. Additionally, in an ERP study involving the

Stroop paradigm, Wang et al. (2010) found a similar pattern of homophone interference effect,

which was relatively weak and only observable in a later time window.

Zhang et al. (2012), among with many others, hold a slightly different view, arguing that

while phonological information is indeed activated rapidly upon encountering a printed form,

such activation is not an essential step in recognizing the printed form resulting from the

simultaneous activation of a more convenient semantic pathway. In their fMRI study on lexical

decision for Chinese words and pronounceable non-words consisting of only legal characters,

Zhang et al. found stronger neural activity in BA (Brodmann’s Area) 44/45 (responsible for

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phonological processing) for non-word trials in not only auditory lexical decision tasks but also

merely visual tasks, suggesting that activation of phonology is necessary at least in non-word

visual spotting tasks. In addition, greater activity in BA 47 (responsible for semantic processing)

was observed in non-word trials compared to real word ones in visual lexical decision tasks only.

It was interpreted to suggest that for visual word processing, although phonology is activated to

some extent, its role is not as essential as it is for speech processing, nor does it serve as a

mediating pathway that links graphemes to semantics, since the co-occurring and even more

prominent activation of the semantic processing pathway could readily and directly lead to the

correct reading, without having to go through an extra step of integrating phonology.

It is noteworthy that none of the aforementioned studies that minimized the role of

phonology controlled for frequency effect, which is generally agreed to have a significant role in

visual word recognition, with evidence from a large number of behavioral as well as brain

imaging studies (Kuo et al., 2003; Su & Weekes, 2007; Zhang et al., 1999). Frequency effect

could have partly contributed to the failure to observe larger homophonic priming effects,

potentially resulting from the possibility that the salience of the facilitation or inhibitory effect

produced by word frequency was so strong that it easily masked the existing but relatively

weaker effect produced by priming, or from the fact that previous studies included mostly highly

frequent words to preserve simplicity of the word recognition tasks, thus failing to capture the

whole picture, in which low frequency words, if incorporated, could likely produce different

results. Indeed, when taking frequency into consideration, multiple studies have been able to

establish strong evidence suggesting a significant role of phonological activation in meaning

retrieval (Zhang, Perfetti, & Yang, 1999; Zhang, Zhang, & Kong, 2009). Specifically, non-

frequent words are found to elicit activation of phonological information more salient and at an

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earlier stage than highly frequent ones. For example, Zhang et al. (2009) found that although

activation of phonology and that of semantic indeed share a similar time course in highly

frequent words, consistent with the previously mentioned findings by Zhou and Marslen-Wilson

(2000) and Zhang et al. (2012), phonological activation occurred nonetheless significantly earlier

than semantic activation in words with low frequency. In addition, Chen et al. (2007) found

neural evidence from their ERP studies on the effect of word frequency on the time course and

the saliency of graphic, semantic, and phonological activation. Combining the behavioral

findings and the ERP recordings, they reached the conclusion that whereas graphic activation

occur in both high- and low frequency words, semantics and phonology are activated only when

the word is low in frequency, and that such activation of phonology is prior to that of semantics.

Moreover, an fMRI study conducted by Peng et al. (2004) showed that when low frequency and

irregular Chinese words are only briefly presented to participants, an automatic activation of the

brain areas that are involved in phonological processing -- such as the bilateral fusiform gyri, the

posterior superior temporal gyrus, and inferior parietal regions – was observed, despite the fact

that the presentation of words were too brief to attend to. This provides evidence for the

existence of an early and automatic phonological activation, at least in processing low frequency

words. Additionally, Ren et al. (2009) investigated the role of phonology in Chinese word

processing within a sentence context. By changing a legitimate sentence-terminal single-

character word into a semantically-incongruent one that is either a homophone or a

phonologically-unrelated character as control, Ren et al. were able to compare ERP

measurements in different sentence-terminal conditions. Homophonic substitutes were found to

systematically show a significantly attenuated N400 as compared to the unrelated control,

regardless of word frequency, which suggests that activation of phonology during word reading

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within a sentence is automatic and independent of word frequency. Taken together, it is perhaps

reasonable to hypothesize that phonology is indeed activated relatively early and does play a role

in semantic access, at least in low frequency Chinese words.

As a matter of fact, one could even reasonably speculate that the difference in the amount

of brain activation in phonology-processing areas previously observed by Zhang et al. (2012)

between real word and non-word reading is also partly attributable to frequency effect, given that

non-words – presumably having the frequency of zero – lie on the lowest end on the word

frequency spectrum. Furthermore, it is important to note that in addition to visual frequency,

phonological frequency (i.e. homophone density) has also been found to play a significant role in

recognition of written words (Ziegler et al., 2000). For example, Tan and Perfetti (1997) have

found modulating effect of homophone density, in that the facilitation effect of homophone

primes on target naming was only salient if the prime had few homophones. In fact, this

phonological frequency effect can serve as fundamental evidence supporting the importance of

phonology in reading Chinese, because if phonology did not play a role, one would not expect

the actually observed difference in word recognition among words differing in phonological

frequency, but only that among those with different orthographic frequencies (Ziegler et al.,

2000).

An additional inquiry that is worth investigating is whether different types of

phonological information are equally activated in reading and equally important to semantic

retrieval. In other words, are certain sub-components of phonology – presumably the more

central “core” components – more saliently activated, thus playing a bigger role in semantic

retrieval than the more peripheral and negligible components, which could be potentially

bypassed in the automatic and rapid phonological activation? This question arises in

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investigating phonological activation in tonal languages such as Chinese, in which different

types (or levels) of phonological information are simultaneously encoded in each individual

orthographical unit (i.e. character). In Chinese, information regarding “pitch and contour” (aka.

tone), without any other types of phonological information, is sufficient in distinguishing

lexicons, as phonological minimal pairs that only differ in tones can oftentimes result in

completely different and unrelated words. The most cited example that elegantly illustrates this

phenomenon might be the four distinct words formed by adding different tones to the same

phonological shape “ma”. Specifically, “ma” in “high flat tone” (1st tone), “high rising tone” (2nd

tone), “dip-and-rise tone” (3rd tone) and “high dropping tone” (4th tone) translates to “mother”,

“hemp”, “horse”, and “to scold”, respectively. Accordingly, one might reasonably argue that

tones, as one type of phonological information in Chinese, do matter in lexical processing, at

least in higher-level lexicon distinguishing processes. On the other hand, however, the fact that

tones are often referred to by linguists as “supra-segmental” features of phonemes could lead to

the implication that they potentially lie on a more peripheral level of the internal structure of a

phonological code than the actual phonemes themselves, which might occupy a more central

position. Such contradictory intuitions lead to the question as to whether the involvement of tone

is as salient as the atonal phonological shape during the phonological recoding process and

whether tone information is critical in meaning retrieval.

In fact, the incorporation of tones in semantic processing has been sporadically

investigated. In a series of priming experiments with manipulation in tones, visual similarity,

semantic relatedness, and interstimulus interval (ISI), Lee (2007) found that although tone

information was readily accessed to disambiguate visually similar minimal tone pairs and play a

role in constraining activation of irrelevant lexicons, such constraining effects does not seem to

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occur at an early stage of lexical activation (i.e. in the short ISI conditions), as suggested by the

observation that when the prime is a semi-homophone with a (not presented) synonym of the

target but the prime itself is not phonologically or semantically related to the target, the

activation of the linking synonym is inhibited at the long ISI but not at the short ISI. Such results

could suggest that tone information might not be a part of the global automatic phonological

activation, only activated at a later stage just in case there are additional demands for resolving

visual ambiguity. Moreover, an interesting investigation on the effects of tones on processing

fluency conducted by Liu et al. (2011) examined how activation of tones could account for the

observed difference in the speed of tone judgment for characters that differed in tones. They

suggest that upon encountering a character, its tonal information is not only activated but such

activation could elicit conscious as well as unconscious subjective experiences, implying the

existence of personal preference for different tones. They argued that such “non-sensory”

affective experiences towards lexical and phonological information on a supra-linguistic level

could have influenced processing of such linguistic information, adding that the contour of

lexical tones, as part of the construct of a whole character, serve as a source of linguistic fluency.

Furthermore, several aforementioned studies involving the homophone paradigms also

included brief examinations on the activation of tones by devising a “semi-homophonic”

condition that enable comparison between the effect of exact homophones and that of minimal

tone pairs, so as to separate out the effect of tones. For example, in the Stroop experiment

conducted by Spinks et al. (2000), it was found that in the incongruent conditions, the

interference effect of semi-homophones is weaker than that of the exact homophones, and that

semi-homophones seem to only affect error rates but not naming latency; in the congruent

conditions, significant facilitation effect was observed in both homophonic and semi-

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homophonic trials, with slightly larger effect seen in homophones than semi-homophones.

Besides, using priming paradigms in a semantic related judgment task, Xu et al. (1999) reported

significant phonological interference effect only in exact homophones but not in semi-

homophones conditions. Such observations that semi-homophones tend to exhibit effects similar

to but weaker than that of exact homophones are consistent with the conjecture that tone

information is incorporated as part of the phonological recoding process. Nevertheless, since

few of the related work placed a primary focus on the investigation of tones per se so as to

directly and comprehensively examined the possible involvement of tone information within the

process of automatic phonology activation in silent word reading, the specific role of tone

activation – its criticality on meaning retrieval, as well as its time course and saliency – still

remains largely unclear.

To sum up, several general key observations from the current literature on Chinese word

recognition are as follows: first and foremost, much evidence support an essential role of

phonological activation in semantic retrieval in Chinese; second, word frequency, both visual

and phonological, are found to modulate the role of phonology on semantic retrieval, in that

phonology is more activated and more influential in lower frequency words, although slightly

discrepant results exist; and third, although evidence has suggested the importance of tones on

semantic processing, consensus on the criticality and the time course of automatic activation of

tones in semantic retrieval is still lacking. Taken these observations together, future research

could investigate more extensively on the interaction of frequency effect and phonological

activation as well as on the activation and importance of tones. To study the effect of tones, in

the aforementioned Stroop type tasks as well as other semantic judgment tasks, besides the semi-

homophone condition in which minimal tone pairs are used, researchers could include further

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tone manipulation in another condition where the prime and the target share nothing but the tone.

In addition, more concentrated investigations on the effect of word frequency on tone activation,

which could potentially explain and / or resolve the discrepancy in findings on the role of tones

by taking word frequency into consideration, might be yet a more specific direction for future

research.

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