586033
research-article2015
LAS0010.1177/0023830915586033Language and SpeechDavis et al.
Language
and Speech
Article
The Time Course for Processing
Vowels and Lexical Tones: Reading
Aloud Thai Words
Language and Speech
1­–23
© The Author(s) 2015
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DOI: 10.1177/0023830915586033
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Chris Davis, Colin Schoknecht, Jeesun Kim and
Denis Burnham
The MARCS Institute, University of Western Sydney, Australia
Abstract
Three naming aloud experiments and a lexical decision (LD) experiment used masked priming
to index the processing of written Thai vowels and tones. Thai allows for manipulation of the
mapping between orthography and phonology not possible in other orthographies, for example,
the use of consonants, vowels and tone markers in both horizontal and vertical orthographic
positions (HOPs and VOPs). Experiment 1 showed that changing a vowel between prime and
target slowed down target naming but changing a tone mark did not. Experiment 1 used an
across item-design and a different number of HOPs in the way vowels and tones were specified.
Experiment 2 used a within-item design and tested vowel and tone changes for both 2-HOP and
3-HOP targets separately. The 3-HOP words showed the same tone and vowel change effect as
Experiment 1, whereas 2-HOP items did not. It was speculated that the 2-HOP result was due
to the variable position of the vowel affecting priming. Experiment 3 employed a more stringent
control over the 2-HOP vowel and tone items and found priming for the tone changes but not for
vowel changes. The final experiment retested the items from Experiment 3 with the LD task and
found no priming for the tone change items, indicating that the tone effect in Experiment 3 was
due to processes involved in naming aloud. In all, the results supported the view that for naming
a word, the development of tone information is slower than vowel information.
Keywords
Masked priming, spoken tone, vowels, word naming, Thai
1 Introduction
The investigation of a range of different languages/writing systems allows tests of whether ideas
gained from one language/writing system apply to others, and also provides the variation needed
Corresponding author:
Chris Davis, The MARCS Institute, University of Western Sydney Locked Bag, 1797, Penrith, NSW 2751, Australia.
Email: [email protected]
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Language and Speech 
for different experimental manipulations. Such investigation makes possible both the discovery of
properties that are unique to particular languages and of properties that are common to them all.
Models of naming written words aloud provide an example where the research base has been
limited to a relatively few languages and writing systems. Typically such models assume that the
process of assembling a phonological code from an orthographic input (orthographic–phonological
conversion) involves the construction of a linear string of phonemes in which the phonological
representation consists simply of an ordered sequence of phonemes (e.g., the nonlexical route of
the DRC model, see Coltheart, Rastle, Perry, Langdon & Ziegler, 2001).
Such a linear phonology might be suitable for processing segmental elements (consonants or
perhaps vowels) but seems less suited to dealing with lexical tone, which, while serving the same
function as consonants and vowels insofar as affecting meaning, consists primarily of pitch variations carried mainly on the vowel but which can extend over several segments. So, it is important
to also investigate the processing of tone information in reading aloud, especially given that tone
languages make up 70% of the world’s languages (Yip, 2002) and are spoken by over half the
world’s population (Fromkin, 1978).
The current study used the Thai language to investigate how text-derived phonology is developed and processed when naming a word aloud. Thai was chosen because it not only has spoken
tone but also because this property is represented in its alphabetic writing system. Written tone
permits a straightforward manipulation of tone by varying only a single feature of the orthographic
input (compare this to, say, Chinese where changing tone means changing the entire character).
The specific focus was whether text-derived phonology develops, and is processed over different
time courses for segmental (vowel) and suprasegmental (tone) based information.
There are already some indications of differences in the way that segments (consonants and
vowel) and tones are processed (Burnham & Mattock, 2007). In particular, Burnham, Kim, Davis,
Ciocca, Schoknecht and Luksaneeyanawin (2011) tested Thai children’s and adults’ awareness of
the odd-one-out of three spoken words when the critical difference was either a tone or a phone
difference. Both phonological and tonological awareness were found to be related to reading ability, however phonological awareness was found to be significantly stronger than tonological
awareness for kindergarten through to Year 6 children. This difference persisted for adults whose
highest education level was primary school, but tonological awareness rose to phonological awareness levels in tertiary-educated adults. Burnham et al. (2011) contend that there is a basic perceptual level superiority of phonological over tonological awareness (see Cutler & Chen, 1997 for a
similar proposal in the auditory domain) that is later ameliorated by orthographic knowledge about
alphabetic markers for phones and tones, and metalinguistic awareness. These conclusions were
supported by parallel studies of phonological/tonological awareness with child and adult Cantonese
speakers (neither phone nor tone explicitly realized in orthography) and English (phone but no
tone), Burnham et al. (2014).
With respect to spelling, Burnham, Luksaneeyanawin, Kantamphan and Reid (2013) analysed
spelling errors of primary school children and adults in a time-limited written recall of a category
member task. Most errors occurred on consonants then vowels then tones, but while consonant
errors decreased over age, those on vowels or tones did not. Comparison of dispensability, the relative occurrence of deletion errors as a proportion of other error types (substitutions, reversals,
additions), revealed that tones and vowels were significantly more dispensable than consonants,
and that there was a tendency for tones to be more dispensable than vowels.
Together these results suggest there may be fundamental differences in perceiving and processing phones and tones, that is, that phones and tones may have a different psycholinguistic status.
This was investigated more specifically here in which the specific proposal that segmental (vowel)
and suprasegmental (tone) based information have different processing time courses were
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Davis et al.
examined, that is, that vowel information is processed before tone information. In addition to the
above indications, this proposal was based on two considerations. The first was that tones and segments are represented at different levels of phonological structure (Chen, Chen &, Dell, 2002; Yip,
2002).1 The second was that aspects of linguistic representation can be reflected in the time-course
of information processing (see Berent & Perfetti, 1995), that is, the representation of vowels and
tones are assembled in cycles that differ in speed. Given these, a testable outcome of this proposal
is that at some point in the development of a phonological representation, words that share vowels
(and consonants) but have different tones would be indistinguishable.
To test this proposal, the masked priming paradigm was used (Forster & Davis, 1984). In this
paradigm, a clearly displayed target (typically in upper case letters) is immediately preceded by a
briefly displayed lower-case prime that is itself immediately preceded by a clearly presented visual
display (typically a series of # marks, which acts as a forward visual mask). The combined actions
of the forward and backward masks (the target) render the prime unavailable for conscious report.
From the participant’s perspective, all that was shown was a forward mask followed by a target
stimulus (on which some task had to be performed).
Although the precise process by which a masked priming effect is generated is still a question
of active research, it is useful to describe how a priming effect can be used to make inferences
about the time-course of processing. The masked priming effect, faster processing of a target when
preceded by a related compared to an unrelated prime, is thought to reflect the savings in processing the target achieves due to the recruitment of processes already set off by the prime (savings
model). In terms of this account, the size of a priming effect will be influenced by the speed of
prime processing (relative to target processing), whether there is common processing of the prime
and target representations, and whether any shared processing is relevant to making a response to
the target (Kim & Davis, 2003). Since the current interest is in the online development and use of
phonology naming aloud as the response task was used, as in this task there is an explicit requirement to develop a phonological code2.
Masked priming has a number of attractive features: it most likely taps relatively early on-line
processing (for priming to occur, interactions between the prime and target must take place before
the response to the target has been executed); and priming effects are made with target items as
their own control, and because primes are masked, it is unlikely that participants notice experimental manipulations and use these strategically. Moreover, when the response task involves naming a
masked primed target aloud, a particular masked priming effect, what Forster and Davis (1991)
called an onset effect, has been identified (see for example, Kim & Davis, 2002; Kinoshita, 2000,
2003; Schiller, 2004). The onset effect refers to the reduction in the time to initiate the naming of
a clearly displayed target item that has been preceded by a rapidly presented masked prime beginning with the same initial letter (e.g., fish-FACT) relative to when preceded by an unrelated control
prime (e.g., more-FACT).
The onset effect appears to involve either the development of a phonological code and/or articulatory planning because priming from a shared initial letter is not robust in other response tasks that do
not require a spoken response (such as the lexical decision task: LDT). Although Forster and Davis
(1991) called this an onset effect, what they manipulated was only the initial letter of the primes and
targets. Subsequent studies have shown that there is a larger priming effect when the prime shares an
initial consonant and the following vowel with the target compared with only the initial consonant (an
‘onset-plus’ effect, see Kim & Davis, 2002; Schiller, 2004).
A priming effect is produced when targets to be named aloud are preceded by masked primes
that share one or more initial letters and is measured with respect to an all letter different (ALD)
baseline. Apart from the ALD baseline, a Repetition prime condition (where the prime and target
are the same word) provides another important baseline with regard to gauging potential vowel and
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Language and Speech 
tone differences. This is because the comparison with the Repetition prime provides a measure of
the cost of changing the prime. If there is no difference between priming from the repetition condition and a form related (onset) prime condition then it would appear that the feature that was altered
in the form prime condition was not processed in time to affect the target.
The use of the ALD and Repetition prime conditions provide a straightforward way of determining the extent to which a form prime has been processed before a target response has been executed. To illustrate this, consider the pattern of response times for the following priming conditions:
form primes that share the first two letters with targets; Repetition primes; and ALD primes. If the
targets in the form prime condition were responded to faster than those in the ALD condition this
would indicate that at least the first letter of the primes had been processed. A finding that responses
to targets in the repetition condition were faster than those in the form priming condition would
indicate that more than the first two prime letters had been processed. If, however, it was found that
there was no difference between the Repetition and form prime conditions, it could be concluded
that no more than two prime letters had been processed. It was by this logic that the time-course of
the development of phonology from text was indexed in the following experiments. Before describing the details of the experimental design and manipulation used in the first experiment, it is important that the relevant features of the Thai writing system are made clear, so that the contrast between
the vowel and tone priming conditions can be appreciated.
Thai is an alphabetic language that represents consonants, vowels, and tones in the orthography.
The Thai alphabet comprises 44 consonants, 32 vowels (18 basic vowel symbols, see Figure 1),
and 4 tone markers. The 32 vowel symbols are made up of 18 monophthongs (nine basic vowels,
each short and long) and 14 diphthongs. Vowels are written above, below, before, or after the consonant they combine with (Figure 1). Thai is a tonal language in which pitch variations on a vowel
or extending over several segments. Spoken Thai has five lexical tones: for example, in Central
Thai /kha/ (mid tone) means ‘to be stuck’, /kha/ (low tone) means ‘galangal’, /kha/ (falling tone)
means ‘to kill’, /kha/ (high tone) means ‘to trade’, and /kha/ (rising tone) means ‘leg’.
These spoken tones are called siang (sound) samane, siang eek, siang tho, siang tri and siang
jattawa. The four tone markers (always positioned above the initial consonant) are called mai
(marker) eek, mai tho, mai tri, and mai jattawa. Despite the connection between the name of the
spoken tones and tone markers, most of the tones and tone markers are feedback inconsistent
(the same spoken tone can be represented by different tone markers) and feedforward inconsistent (the same tone marker can lead to different tone productions). Thai consonant graphemes are
organized into three tone classes (as shown in Table 1). Class membership of the consonant
grapheme (as shown in Table 1) determines the effect of the application of any of the four tone
marks and involves a number of features. That is, class membership specifies how tone is modified when carried on a ‘live’ syllable (ending in a vowel or a continuant) or a ‘dead’ syllable
(ending in a stop) and the consequence of having a long or short vowel. Thus for example, a
syllable that has a low tone maker (_อ̍) will be realized as having a low spoken tone for class 1
and class 2 consonants but a falling tone for class 3 consonants (see Table 1).
A unique feature of the Thai writing system that is used in the current study is that more than
one unit of phonological (or tonological) information can be present in a given serial position (or
horizontal orthographic position (HOP)), since there are four vertical orthographic positions that
can contain different information at any HOP (see Figure 2).
Since Thai allows for more than one unit of phonological (or tonological) information to be
present in a given HOP, whether more than one item of orthographic information in HOP1 can
contribute to the onset priming effect can be tested. Furthermore, this feature of Thai orthography
makes it possible to determine the relative salience and the time-course of assembly of vowel and
tone information presented in HOP1.
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Davis et al.
Figure 1. The 32 Thai vowel forms (written by combining 18 vowel symbols and three consonants) and
their location in relation to initial consonants. Note: Vowels and their components can be positioned
before, after, below or above initial consonant(s) and these positions can also be combined. The consonant
letter อ (in gray) is used as a place-holder to indicate the consonant position; the 3 consonant symbols
used to compose vowels are ย, ว and อ (/j/, /w/, and /ͻ/ respectively. Extra vowel symbols (rare) are
shown in the lower left hand corner.
The following experiments extend the onset priming approach by using primes and targets in
which the onset consonant is fixed (in HOP1) but the relationship of written vowels and tones in
the prime and target is systematically varied. This design was used to investigate the development
of phonological processing in two ways: first, to determine if changes in vowels and tones led to
different sized priming effects (and so by implication have a different processing time-course); and
second, to test whether changes in the vowel’s horizontal position (i.e., HOP2 as compared to
HOP1) would reduce the size of the priming effect even though primes and targets shared an onset
consonant.
2 Experiment 1
In order to investigate the development of vowel and tone phonological information, Experiment
1 was designed to determine the effect that different types of masked primes had on the time it
takes to begin to name target words aloud. If in the development of a naming response the processing of tone information is slower than vowel information, then at some point in time a difference
in a tone mark between the prime and target will have no effect on priming but a difference between
a prime and target vowel will. Of course, it seems unlikely that the typical prime-target interval
used in masked priming (around 50 ms) will just happen to be the ideal duration for distinguishing
a difference between the timing of tone and vowel processing. Indeed, because of variation at the
level of participants and items, it simply may be that no single fixed duration will be entirely adequate for separating the effect that tone and vowel changes have on priming. It is in this regard that
the repetition priming and ALD conditions together may provide additional information concerning the development of tone and vowel information (see above).
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
จ
ch
ฉ

ช
ฌ

ย
ญ

ก
kh
ข
ซ

ค
ฆ
ฅ

ง

ร

ด
ฎ
s
ส
ศ
ษ

ซ

ท
ฑ
ธ
ฒ

ล
ฬ

ต
ฏ
th
ถ
ฐ

ว

ฟ
ฝ
f

บ
*The letter อ is used as a carrier to show the position of the tone marks.
**Realized as High for short vowels.
Class 1 Voiceless
unaspirated Class 2 Voiceless
aspirated Class 3 voiced

น
ณ

พ
ภ
ph
ผ

ป

ม

ฮ
ห
h

อ
M
R
อ
M
Null*
F**
L
อ่
L
may ek
Live syllable (open)
H
F
อ้
F
may
tho
—
—
อ๊
H
may tri
—
—
อ๋
R
may
chattawa
H
L
L
Short
vowel
L
L
F
Long
vowel
Dead syllable
(closed)
Table 1. Shown are the 42 Thai consonant graphemes, organized into three tone classes. Class membership of the consonant grapheme is shown in the
left panel and the realized tone in the right panel: R = rising tone; F = falling tone; H = high tone and M = mid tone (the hyphen indicates a tone/marker
class pairing that does not occur). The realized tone is determined by consonant class, by phonotactic features (whether the syllable is ‘live’ – ending in a
vowel or a continuant – or ‘dead’ – ending in a stop, for which vowel length also becomes a factor), and orthographic features (by the application of any
of the four tone marks – tone marks do not occur with dead syllables). In the current experiments, only the single vowels were used and not the more
complex vowel combinations.
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Language and Speech 
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Davis et al.
Figure 2. Thai words (in the above example, [tʰîː sʊ̀ t], gloss: “-est”, as in biggest) can represent phoneme
and toneme information in three horizontal orthographic positions (HOPs, 1, 2, 3). The figure also shows
that there can be four vertical orthographic positions (subscripts, level -1; on the line, level 0; superscripts,
level 1; above superscript, level 2) possible at any one HOP. Level 0 can take a consonant or specific
before- or after-consonant vowels (see Figure 1), level -1 can only take specific vowels, level-1 can take a
tone marker (if no above-consonant vowel is present) or a vowel, and level-2 can only take a tone marker,
but only when there is a superscript vowel in level-1.
2.1 Method
Participants. Thirty-three native Thai speakers (who were graduate or undergraduate students at the
University of New South Wales) took part in the experiment, 11 participants for each of the three
versions of the experiment (see below).
2.1.1 Materials and design. Ninety monosyllabic target words were selected to form three sets of
materials (30 words per set) such that the graphemic information in HOP1 would consist of: (i) a
∨
t
consonant and vowel, C (Vowel-Only); (ii) a consonant and tone mark, C (Tone-Only); or (iii) a
t
∨
consonant, vowel, and tone mark, C (Vowel plus Tone). This selection of materials allowed for
differences in HOP1 primes and targets to be tested for vowels, tones, and vowels and tones within
each item set. The mean words frequencies of targets within these three sets did not significantly
differ: Vowel-Only, M = 2668; Tone-Only, M = 2114; and Vowel plus Tone, M = 2619, counts per
10 million words (Aroonmanakun, Tansiri, & Nittayanuparp, 2009), F < 1.
In order to determine the effect of changing prime-target HOP1 properties, three sets of nonword primes for each of the three target types (Vowel-Only, Tone-Only and Vowel plus Tone) were
constructed (see Table 2): a Repetition prime-target condition in which all features of primes and
targets were repeated; a set of different conditions in which primes and targets differed in HOP1 by
the vowel (Vowel-Only change), the tone (Tone-Only change), or both (Vowel plus Tone change);
and an ALD prime-target baseline. Three versions of the experiment (lists) were constructed so that
the three prime conditions within each item set could be fully counterbalanced, that is, the same
target words would appear in each of the three prime conditions without being repeated to any
participant. The contrast with the Repetition condition allowed the effect of changing the vowel,
tone, or both to be indexed. The ALD condition enabled the overall size of the effects of each priming condition to be estimated.
The subscript � vowels and ู ◌ู and the superscript vowels _ ◌ิ, _ ◌ี, _◌ึ, _◌ื, were used (see
Figure 1). However, there are constraints on the orthographically permitted combinations of vowel
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Language and Speech 
Table 2. Experiment 1: Mean naming latencies, standard error (SEM) and percentage error rate for target
words for the Vowel-Only, Tone-Only and Vowel plus Tone item sets as a function of prime type.
Design
Condition
Prime
Target
Structure
RT
SEM
Tone-Only Change Set Repetition
น้อง
น้อง
482
9.8
Vowel-Only Change Set Tone-Only
น่อง
น้อง
489
10.8
ALD control
ย่าน
น้อง
534
10.4
Repetition
ดิน
ดิน
489
11.2
Vowel-Only
ดืน
ดิน
500
9.5
ALD control
บีม
ดิน
529
9.9
Repetition
นิ่ม
นิ่ม
496
11.9
Vowel and
Tone
นื้ม
นิ่ม
t
CVC
t
CVC
t
CVC
v
CVC
v
CVC
v
CVC
t
v
CVC
t
515
11.6
542
11.1
Vowel & Tone Change
Set ALD control
ยี้น
นิ่ม
v
CVC
t
v
CVC
%Error
5.5
6.4
6.7
3.9
7.6
3.3
7.0
8.2
8.5
Note: The ‘Structure’ column depicts the arrangement of the consonants (c), vowels (v) and tones (t) in the target.
and final consonants. In particular, ‘sara ee’ (เ–) and ‘sara u’ (� ) do not typically appear with the
final ‘ng’. Where the vowel was different in the prime and target was always paired with (because
of position). Only the tone marks ‘may ek’ and ‘may tho’ were used. The tone marks ‘may tri’ and
‘may chattawa’ are rarer, and occur only in words beginning with mid-class consonants. According
to Haas (1971), these words are either particles (onomatopoetic words, affective words) or loan
words from Chinese or English.
Table 2 shows an example of each of the three sets of materials, and how primes and targets
differed in each condition within a set. It should be noted that (apart from the ALD condition) all
the changes between the primes and the targets occurred in HOP1. Also the majority of the primes
were nonwords (apart from the Repetition condition); however some word primes occurred as a
result of the necessary vowel and tone changes made to the target: for the Vowel-Only set, five
words occurred in the experimental prime condition and seven in the control; for the Tone-Only
set, eight words were in the experimental set and nine in the control; and in the Vowel plus Tone
set, two words were in the experimental prime and two in the control condition. Note the lexical
status of primes does not appear to influence masked priming indexed by target naming (Schiller,
2004). The ALD condition for all three sets consisted of a prime that shared the basic structure of
the target (position of vowel and presence of tone marks) but where the consonant, vowel and tone
marks differed.
The critical condition in each of the three item sets was the ‘change’ condition. In the ‘ToneOnly set’, the change condition consisted of primes and targets that differed only in tone mark (in
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Davis et al.
superscript) in HOP1 (vowels in these items were in HOP2 and written on the mid-line, VOP0, that
is, not super- or sub-scripted). These items had 3 HOPs. In the ‘Vowel-Only’ set, the change condition consisted of primes and targets that differed only in the vowel (in superscript, or subscript,) in
HOP1. As can be seen in Table 2, these Vowel-Only primes and targets were 2 HOPs in length. In
the ‘Vowel plus Tone’ set, the change condition consisted of primes and targets that differed in both
the vowel and the tone mark in HOP1. These words had 2 HOPs.
The visual, orthographic and phonological properties of primes and targets were controlled by
matching the following properties across primes and targets: number of HOPs; vowel length (all
long); tone, syllable length (monosyllabic, almost exclusively CVC), along with the visual envelope or word shape of the prime and target; and font density/style (by having a tone-marker in both
the prime and target, or by having an ascender in the position of the tone-marker).
Unlike English, Thai does not have different letter cases, which means that the usual ‘case
change’ method used to introduce a change of form between the prime and target (i.e., the prime in
lower case letters and the target in upper case) cannot be applied. To overcome this, in this and the
subsequent experiments primes were presented in a font size 68% smaller than that used for the
targets. This is standard practice in conducting masked priming experiments in languages that do
not have case alternation (e.g., Kim & Davis, 2002; Frost, Ahissar, Gotesman, & Tayeb, 2003;
Shen & Forster, 1999).
Finally, it is important to ensure that elements of the prime are properly masked (e.g., by a forward mask), since it is the variation in the patterns of priming that forms the basis of inferences
about processing. Proper masking is especially critical in an experiment in which differences
between primes and targets involve graphical elements that are free floating (e.g., diacritics) since
if these are not properly masked they could be misattributed as being part of the target. In particular, it was found that using the standard forward mask used in studies employing Roman script (a
row of hash marks) did not prevent prime tone marks and superscript vowels from being noticed
by participants.
To avoid prime features becoming apparent, a special forward mask that consisted of two layers
of alpha-numeric character-like elements was constructed such that it was greater both in horizontal and vertical extent than the prime and target (to cover raised vowels and tones). Several versions
of this mask that differed in the density of character constituents were pre-tested. The final version
was chosen based on the prime detection performance of a native Thai speaker; the criterion being
that the participant could not reliably identify the lexical status of the masked prime stimulus at a
prime-target SOA of 57 ms (i.e., detection of performance that did not differ from the chance level
of 50%).
2.1.2 Procedure. Each trial consisted of the following display sequence. Half a second after the
previous trial ended by a response or time limit, a two layered alpha-numeric forward mask
appeared in the centre of the screen for 500 ms. The prime was immediately displayed after the
forward mask and remained displayed for 57 ms. The prime was followed by the target which
remained on the screen for a further 500 ms. Apart from providing the stimulus to be named, the
target also acted as a backward mask for the prime. The targets were, on average, 1.6 cm in length
and 1.1 cm in height (and were viewed from approximately 74 cm).
Participants were randomly allocated to one of the three experimental lists. Participants were
told that a block of alpha-numeric characters would appear as a ‘ready’ signal, followed by a
word that they should say aloud as quickly and accurately as possible. The participants were not
informed about the existence of the prime. In this experiment, the time for a participant to initiate
a naming response was measured by the voice-activated trigger implemented in the DMDX program (Forster & Forster, 2003). The participants’ responses were also monitored on-line by a
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Language and Speech 
native Thai speaker who pressed a button to indicate if the response was valid or not. If the
participant made an error, hesitated, activated the vocal trigger by a lip-smack or other non-relevant response, the data for that trial were not used. The only feedback that was given to participants was if they spoke too quietly to trigger the response key. Eight practice items preceded
each version (list) of the experiment.
Stimulus presentation and response collection were controlled by the DMDX. In this and in
subsequent experiments, all target words were presented in a different pseudorandom order for
each participant.
2.1.3 Data treatment. In this, and in subsequent experiments, data corresponding to incorrect
responses were discarded from the analysis and reaction times more than two standard deviation
units above or below the mean for that participant in all conditions were trimmed to the appropriate
cut-off value to moderate the influence of outliers. To avoid the inclusion of spurious activation of
the voice trigger, reaction times below 200 ms were deemed errors (as per Forster & Davis, 1991).
In the current experiment these treatments affected less than 5% of the data. Any participant who
made more than 15% errors was excluded (this lead to the exclusion of three participants, one in
each version of the experiment).
2.2 Results
Mean naming latencies and error rates for each experimental condition in each of the different
change sets are shown in Table 2. The data were examined using two analyses of variance
(ANOVAs), one for the participant data (collapsed over the different items) and one for the item
data (collapsed over the different participants); note that in the analyses, experimental version
(participant analysis) and item list (item analysis) were included as dummy variables, as this provides a more powerful analysis by accounting for the variance that can result from error associated
with counterbalancing the versions (Pollatsek & Well, 1995).
The first set of analyses examined whether response times to the prime types across the three
different change sets differed. Collapsing across Change set (Vowel-Only, Tone-Only, and Vowel
plus Tone sets), there was a difference in response times for the different priming conditions,
2
2
F1(2, 60) = 141.47, p < .05, η p = 0.83, F2(2, 162) = 122.34, p < .05, η p = 0.58. Collapsing across
prime conditions, there was a difference in response times between the three different change sets
that was significant in the participant analysis F1(2, 60) = 11.92, p < .05, but was not significant in
the item analysis, F2(2, 81) = 2.01, p > 0.05.
The interaction between Change set and Prime Type, was significant in the participant analysis,
2
F1(4, 120) = 3.53, p < .05, η p = 0.11; but was not significant in the item analysis, F2(4, 162) = 2.01,
p = 0.1, ns. The Repetition priming effect did not interact with the Change set (40 ms; 53 and 46
ms for each item set respectively), F1(2, 60) = 2.81, p > 0.05; F2(2, 81) = 1.29, p > 0.05.
A series of planned comparisons was conducted to determine if there were response time differences between the prime types for each of the three change sets. In an effort to keep the number of
comparisons small, only those comparisons critical to examining the effect of changing features in
HOP1 were tested; the size of priming in each of the change conditions was contrasted with the size
of priming in the Repetition condition and the ALD condition.
Tone-Only change: There was no difference between the Repetition and Tone-Only change
conditions, F1(1, 30) = 2.79, p > .05; F2(1, 27) = 3.13, p >.05. There was a priming effect for the
Tone-Only change condition: response times to Tone-Only primed targets were significant faster
2
than those in the ALD condition, F1(1, 30) = 117.89, p < .05, η p = 0.8; F2(1, 27) = 58.39, p < .05,
2
η p = 0.68.
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Davis et al.
Vowel-Only change: There was a significant difference between Repetition and Vowel-Only
2
2
change conditions, F1(1, 30) = 5.20, p < .05, η p = 0.15; F2(1, 27) = 6.04, p < .05, η p = 0.18. There
was a significant priming effect for the Vowel-Only change condition, with targets in this condition
2
being faster than in the ALD condition, F1(1, 30) = 46.12, p < .05, η p = 0.61; F2(1, 27) = 34.62, p <
2
.05, η p = 0.56.
There was a significant difference between Repetition and Vowel plus Tone change conditions,
2
2
F1(1, 30) = 28.26, p < .05, η p = 0.49; F2(1, 27) =17.27, p < .05, η p = 0.39. There was significant
2
priming (Vowel plus Tone vs. ALD condition), F1(1, 30) = 29.66, p < .05, η p = 0.50; F2(1, 27) =
2
14.92, p < .05, η p = 0.36.
The priming effect for the Tone-Only condition (45 ms) was larger than that for the Vowel-Only
condition (29 ms); this difference was significant in the participant analysis, F1(1, 30) = 9.71, p <
2
2
.05, η p = 0.25, and near significant in the item analysis, F2(1, 54) = 3.18, p = 0.07, η p = 0.06. There
was a significant difference for the comparison of the amount of priming for the Tone-Only items
2
(46 ms) vs. the priming effect for the Vowel plus Tone items (27 ms), F1(1, 30) = 9.83, p < .05, η p
2
= 0.25; F2(1, 54) = 6.36, p < .05, η p = 0.11.
2.3 Discussion
The results of Experiment 1 showed that there was no reliable difference in naming times for targets in the Repetition and Tone-Only prime conditions. This suggests that tone information physically present in HOP1 of the prime was not processed in time to affect the target response. It should
be pointed out that this result differs from that reported recently by Winskel and Perea (2013) who
showed that changing a tone mark did reduce priming compared to the Repetition prime condition.
A possible reason for their result is that Winskel and Perea used a series of hash masks as the forward mask. In pilot testing, it was found that a series of hash marks did not adequately mask the
tone mark (see above about the importance of proper masking), and this failure to use an adequate
mask may well explain the tone effect in the Winskel and Perea study.
In contrast to the Tone-Only change case, the current results showed that there was a significant
difference in the naming times of targets in the Repetition and Vowel-Only conditions: changing a
vowel resulted in longer times to begin to pronounce the target word. There was also a significant
difference in the amount of priming (compared to the ALD baseline) for naming targets in the
Tone-Only and Vowel-Only prime conditions, consistent with the proposal that vowel processing
may precede tone processing. That is, primes in the Tone-Only condition shared everything with
their targets except the tone mark; primes in the Vowel-Only condition shared everything but the
vowel.
If a saving model of priming is assumed (see Introduction) and it is also assumed that segments
(vowels) are processed before tone marks, then the changed vowel condition would only share the
processing of the initial consonant with the target, whereas the changed tone condition would share
the processing of the consonant and the vowel (and hence garner larger savings). This indication
that tones may be dealt with late in the processing stream is consistent with the general proposal
that at the phonological level the planning of segments can be separate from tones and with the
processing view of Berent and Perfetti (1995) that different types of phonological information can
develop at different rates.
Another result that potentially indicates the way in which processing unfolds, is that the size of
the Repetition priming effect did not differ across the Vowel-Only, Tone-Only and Vowel plus Tone
∨
t
∨
item sets. This contrast is interesting because in the Vowel-Only ( CC ) and Vowel plus Tone ( C C )
change sets, the vowel was in HOP1, whereas in the Tone-Only change set the vowel was in HOP2
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Language and Speech 
t
( CVC ). If it is assumed that priming in the repetition condition was generated by both consonant
and vowel processing (as the reduced priming in the Vowel-Only change condition would indicate), then this suggests that the vowel is processed in a similar time regardless of whether it was
in HOP1 (superscript) as in the Vowel-Only set or in HOP2 (non-superscript) as in the Tone-Only
set.
The subsequent experiments were designed to follow-up the difference in vowel and tone processing observed in Experiment 1. First, Experiment 2 investigated whether a systematic difference in the vowel and tone items in Experiment 1 might have differently affected the priming
results; then Experiment 3 used a feature of the Thai writing system to elegantly control for any
variation between vowel and tone change items; and Experiment 4 tested the same items in a lexical decision task (to determine whether the effects only held for the naming task).
3 Experiment 2
The critical contrast in Experiment 1 was between primes and targets that differed in HOP1 in
terms of whether a vowel or tone mark was changed. However, in addition to the change at HOP1
there was also another difference between the vowel and the tone items (see Table 2): the Vowel∨
t
∨
Only ( CC ) and Vowel plus Tone ( C C ) conditions had 2 HOPs but the Tone-Only items ( CVC )
had 3 HOPs. Although there is no clear reason why this difference in the number of HOPs would
have produced different vowel and tone priming effects, it is in fact possible to select vowel and
tone change items that do not differ in their number of HOPs, and so it is desirable to re-run this
contrast equating the number of HOPs.
There is an additional benefit in conducting an experiment with such items because these
make it possible to directly contrast the effects of a vowel change in HOP1 with a vowel change
in HOP2. In this way, it can be determined whether processing of the various elements in HOP1
occurs in parallel or sequentially. That is, if processing of all elements in HOP1 begins at the
same time (parallel processing), a changed vowel in HOP1 would be detected sooner than one in
HOP2. Thus, compared to repeated targets, those preceded by HOP1 vowel change primes
should be slower than those preceded by HOP2 ones. In addition, the tone and vowel change
conditions in Experiment 1 had different targets (an across item design); having the same number of HOPs would allow a within item design in which the effect of changing the tone and
vowel could be directly compared.
In summary, Experiment 2 was designed to contrast the effects of changing vowels and tones in
a within item design and also to gauge the effect of vowel changes in different HOPs. The experiment employed two sets of items each with 5 types of primes (the types used in Experiment 1 but
here used with a within-item design so that the same targets appear in every condition). The first
set of items all consisted of 3-HOP items (where vowel changes occurred in HOP2), and the second
set all consisted of 2-HOP items (where vowel changes occurred in HOP1).
t
3.1 Method
3.1.1 Participants. Forty-five native Thai speakers who were graduate and undergraduate students
at the University of New South Wales took part in the experiment (8, 10, 8, 10, 9 participants in
each of the five participant groups respectively). None of these participated in Experiment 1.
3.1.2 Materials and design. The experiment comprised two sets of items, a set of 3-HOP words and
a set of 2-HOP words. The design of the experiment is shown in Table 3. Each of the target word
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Davis et al.
Table 3. Experiment 2: Mean naming latencies, standard error (SEM) and percentage error rate for target
words in the 3-HOP and 2-HOP items sets as a function of prime type.
Design
Condition
Prime
Target
Structure
RT
SEM
%Error
3-HOP items
Repetition
น้อง
น้อง
535
5.5
Tone-Only
น่อง
น้อง
539
4.8
Vowel-Only
น้าง
น้อง
547
5.8
Vowel and
Tone
น่าง
น้อง
t
CVC
t
CVC
t
CVC
t
556
5.8
1.5
4.1
2.9
4.3
ALD control
ย่าน
น้อง
568
5.8
Repetition
ดื่ม
ดื่ม
549
5.5
Tone-Only
ดื้ม
ดื่ม
555
4.8
Vowel-Only
ดึ่ม
ดื่ม
557
5.8
Vowel and
Tone
ดึ้ม
ดื่ม
562
5.7
2-HOP items
ALD control
บี้น
ดื่ม
CVC
t
CVC
t
v
CVC
t
v
CVC
t
v
CVC
t
v
CVC
t
v
CVC
583
5.8
4.9
7.0
6.7
5.8
6.7
6.6
Note: The ‘Structure’ column depicts the arrangement of the consonants (c), vowels (v) and tones (t) in the target.
sets had five prime conditions (Repetition; Vowel-Only change; Tone-Only change; Vowel plus
Tone change; and ALD control). Five versions of the experiment were created such that the five
prime conditions within each item set were fully counterbalanced, that is, the same target items
appeared in each of the five conditions, across five participant groups. Ten targets were selected for
each prime condition, making a total of 100 target words for the participants to pronounce. Eight
practice items preceded each experimental list.
3.1.3 Procedure and data treatment. The procedure, data collection method and data treatment were
the same as that for Experiment 1. Data treatment affected 4.8% of the data and one participant was
excluded due to the error rate criterion being exceeded (thus the data of 44 participants were
analysed).
3.2 Results
Table 3 presents the naming latencies and error rates for both the 2-HOP and 3-HOP stimulus sets
as a function of the various prime conditions. The initial analyses investigated whether there were
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Language and Speech 
differences in response times (and error rates) for the two sets of items and for the prime types. On
average, the 2-HOP words were named more slowly than the 3-HOP ones, this difference was
2
significant in the participant analysis, F1(1, 35) = 33.51, p < .05, η p = 0.49; but not significant
2
(borderline) in the item analysis, F2( 1, 90) = 3.41, p = 0.06, η p = 0.04. There was a difference in
the number of errors each type of item attracted, with the 2-HOP words attracting more errors,
2
2
F1(1, 156) = 7.57, p < .05, η p = 0.16; F2( 1, 90) = 13.25, p < .05, η p = 0.13.
The overall analysis of prime type showed that there were differences in response latencies as a
2
function of prime condition, F1(4, 156) = 28.91, p < .05, η p = 0.43; F2(4, 360) = 23.91, p < .05,
2
η p = 0.21. There was no overall difference in the number of errors made as a function of prime
type, F1 < 1; F2(4, 360) = 1.01, p > 0.05. There was no interaction between the 2-HOP vs. 3-HOP
or the prime type main effects, either in response latency, all Fs < 1; or errors, F1(4, 156) = 1.09,
p > 0.05; F2(4, 360) = 1.01, p > 0.05.
As in Experiment 1, a series of planned comparisons was conducted to determine specific differences across prime types (analyses of errors will not be considered as the main effect of prime
type was not significant). For the 3-HOP words, there was no difference between the Repetition
and Tone-Only conditions, F1 < 1; F2(1, 45) = 1.10, p > 0.05. There was a significant difference
between the Repetition and Vowel-Only conditions, with the repetition condition being faster,
2
2
F1(1, 39) = 8.30, p < .05, η p = 0.18; F2(1, 45) = 8.89, p < .05, η p = 0.17. Finally, the Repetition
2
condition was faster than the Vowel plus Tone condition, F1(1, 39) = 15.53, p < .05, η p = 0.29;
2
F2(1, 45) = 13.49, p < .05, η p = 0.23. The difference between the Vowel-Only and Tone-Only conditions was not significant in the participant analysis, F1(1, 39) = 2.82, p > .05, but was in the item
analysis, F2(1, 45) = 4.85, p < .05. Response latencies in the ALD baseline conditions were slower
2
than in the Vowel plus Tone conditions, F1(1, 39) = 5.65, p < .05, η p = 0.13; F2(1, 45) = 5.38, p <
2
.05, η p = 0.11.
For the 2-HOP words, there was no difference between the Repetition and Tone-Only conditions, F1 < 1; F2(1, 45) = 1.81, p > 0.05. There was also no significant difference between Repetition
and Vowel-Only conditions, F1(1, 39) = 1.84, p > 0.05; F2 < 1. There was, however, a significant
2
difference between the Repetition and Vowel plus Tone conditions, F1(1, 39) = 6.59, p < .05, η p =
2
0.14; F2(1, 45) = 5.02, p < .05, η p = 0.1. The difference between the Vowel-Only and Tone-Only
conditions was not significant, both Fs < 1. Naming latencies in the ALD baseline conditions were
2
slower than in the Vowel plus Tone conditions, F1(1, 39) = 40.87, p < .05, η p = 0.51; F2(1, 45) =
2
12.11, p < .05, η p = 0.21.
3.3 Discussion
Experiment 2 was designed to replicate the vowel and tone contrasts investigated in Experiment
1 separately for the 3-HOP and 2-HOP word types. The 3-HOP items produced the same basic
pattern of results that was found in Experiment 1, that is, compared to the Repetition condition,
changing the tone mark did not affect target response times, whereas changing the vowel made
responses slower.
The 2-HOP words showed a different pattern of priming. Here, there was no effect of changing
prime and target constituents (either vowel or tone) until both the vowel and the tone mark were
changed (the Vowel plus Tone change condition). This difference between item types seems
unlikely to be explained in terms of the timing of the development of prime vowel information for,
∨
if anything, vowels in the 2-HOP primes ( C C ) should have been considered first, as the vowel
change in the 2-HOP items was in the first position (HOP1) but the vowel change in the 3-HOP
t
items was in HOP2 ( CVC ).
t
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Davis et al.
A key difference between 2-HOP and 3-HOP items that could account for why a vowel change
in the 2-HOP words had no impact is that in the 2-HOP items the position of the vowel with respect
to the HOP1 consonant was variable. That is, unlike target vowels in 3-HOP items (that were
always in the same relative position, HOP2), target vowels in 2-HOP items appeared both above
t
∨
( C C ) and below ( C C ) HOP1 consonants (50% each for superscript and subscript, see Figure 2).
v
∨
When a vowel appeared as a superscript ( C ) it could be one of four different types; however only
two vowel types appeared as subscripts ( C ). This may have resulted in a bias to attend more to
∨
spatial locations above HOP1. If so, then some of the time the subscript position vowels in the
prime might not have been attended to. Attention to prime location has been shown to be important
for generating priming. Indeed, Besner, Risko and Sklair (2005) and Lachter, Forster and Ruthruff
(2004) have shown that when the spatial location of primes were not attended to, priming effects
were absent (the simple assumption is that features at an unattended location are either not processed or processed too slowly to affect target processing). Thus the differential pattern of priming
might be due to the way that attention was allocated to the different target types. Support for this
interpretation was found from a post-hoc analysis by dividing the Vowel-Only condition into targets that had superscript vowels and those with subscript vowels. This analysis showed that the
superscript group of items differed from the Repeated condition by 18 ms F1(1, 39) = 7.5, p < .05,
whereas the subscript group did not (there was only a 1 ms difference, F1 < 0).
The above results for the 2-HOP words are interesting because they suggest a role for spatial
attention in lexical processing (see Rayner, 1998) and also because they indicate that variation in
masked priming can have interpretations other than those that strictly relate to linguistic processing. Exploring these non-linguistic differences, however, goes beyond the aim of the current investigation into the development and use of phonological representations (but see Burnham et al.,
2011, regarding the development of phonological and tonological awareness). If only the results
from the 3-HOP targets are considered then the results of Experiment 1 are reinforced. However,
once again, the comparison of vowel and tone changes was not ideal, since this contrast in the
3-HOP items of Experiment 2 involved changes that occurred at different HOPs (tone changes
were in HOP1 but vowel changes in HOP2). In order to more directly establish that vowel and tone
marks are processed differently, it would be best if they had as similar a form as possible. This was
the basis for the design of Experiment 3 where items were selected so that the vowel/tone contrast
would be as similar as possible.
t
4 Experiments 3 and 4
Thai has one aspect of an abugida4 script (Daniels, 1990) in that a vowel does not always need to
be represented orthographically (i.e., an inherent vowel is permitted). This property of the Thai
script provides an extremely elegant way of constructing a set of primes and targets in which the
consonant frame is held constant and tone and vowel change conditions are created by the addition
of a tone or vowel mark respectively above the initial consonant. Table 4 provides an example of
the four priming conditions: The Repeated condition illustrates that when no vowel is explicitly
marked, the value of the implicit vowel (/o/) is realized and in this case a mid-tone is assigned (as
the initial letter is from class 2 (voiceless unaspirated) and it is a ‘live’ syllable because it ends in a
continuant). The same vowel is assigned in the Tone-Only change condition, only in this case, the
prime has a falling tone (as indicated by the tone mark and the initial consonant class). The VowelOnly change condition shows that the addition of a vowel overrides the implicit vowel value and
an /a/ vowel sound is realized. As can be seen the only difference between the Repeated, Tone-Only
and Vowel-Only prime conditions is in the addition or alternation of a diacritic (the vowel or tone
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Language and Speech 
Table 4. The design of Experiment 3.
Condition
Prime
IPA
Target
Repeated
Tone
Vowel
ALD
ตน
ต้น
ตัน
ยึบ
/ton/
/tôn/
/tan/
/jɯb/
ตน
ตน
ตน
ตน
mark), this means that any differences found between the conditions would be likely due to nonlinguistic properties of this change.
One aspect of the above experiments (and in particular Experiment 3) is that the primes and
targets had a high degree of form overlap (consisting of identical characters except for a difference
in the vowel and tone marks). Given this overlap, it might be that the observed facilitation in naming was actually form-priming. In such a case, it has been proposed that priming effects would be
generated by the prime pre-activating the orthographic lexical entry of the target (e.g., the mechanism of form-priming as proposed by Forster, Davis, Schoknecht, & Carter, 1987); in other words,
priming would be a saving in reading out of addressed phonology and not in the development of
the phonological representations themselves. If this were the case however, it would be necessary
to explain why vowel and tone marks were differentially effective in accessing lexical entries.
Furthermore, form-priming effects would also be evident when the response task was a lexical
decision. To examine the extent to which any observed priming was specific to the naming task, an
LDT version of Experiment 3 was constructed for Experiment 4. If the above priming effects were
due to phonological processing then these should not arise with the LDT experiment (Forster &
Davis 1991; Kim & Davis, 2003).
4.1 Method
4.1.1 Participants. Experiment 3, Naming task: Forty Thai graduate and undergraduate students
from Chulalongkorn University, Bangkok, Thailand took part in the experiment. Experiment 4,
Lexical Decision task: Forty-seven Thai graduate and undergraduate students at Chulalongkorn
University took part in the experiment (none of whom had participated in Experiment 3).
4.1.2 Materials and design. Naming: Two sets of word targets were selected, a critical set that consisted of 56 words and a non-critical set of 34 filler targets (both sets had the same consonant–
consonant structure with the implicit vowel /o/). Filler target words were included to provide more
variation to the structure of the target words (e.g., including high tone targets). Four conditions of
primes (14 items per set) were constructed (Repetition; Vowel-Only change; Tone-Only change;
and ALD). Three different vowels were used in the Vowel-Only condition and the tone mark ‘may
tho’ (falling) was always used in the Tone-Only condition. The ALD primes used the same three
vowels marks as used in the Vowel-Only change condition. The realized tone for the critical target
set consisted of 34 items with mid-tone, 11 items with rising tone and 11 items with low tone (conditioned by initial consonant class and syllable type). For the Tone-Only change condition, the
realized tone was falling or high for mid-tone targets, falling for rising tone targets, or high for low
tone targets. The realized tone for the ALD primes was also always different from that of the target
tone (high or low for mid-tone and rising targets and rising for low tone targets).
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Davis et al.
Table 5. Experiments 3 and 4: Mean naming and lexical decision latencies, standard error (SEM) and
error rates as a function of prime condition.
Condition
Prime target
Naming RT (ms)
Error
LDT RT (ms)
Errors
Repeated
Tone Change
Vowel Change
All Letters Different
ตน / ตน
ต้น / ตน
ตัน / ตน
ยึบ / ตน
578 (13.2)
597 (13.5)
608 (13.5)
614 (14.1)
0.7
1.8
1.3
0.6
615 (16.0)
652 (15.1)
638 (15.4)
655 (16.3)
5.3
6.2
6.9
6.6
As in the previous experiments, different versions of the experiment were constructed such that
the four prime conditions within each item set could be fully crossed, that is, the same target items
appeared in each of the four prime conditions, across four participant groups.
Lexical Decision: The same word targets and primes that were used in Experiment 3 were used
in Experiment 4. In addition, 90 pronounceable nonword targets were constructed. The prime conditions for the nonword targets mirrored those of the word targets.
4.1.3 Procedure and data treatment. Naming: The masked priming display parameters and the testing procedures were the same as those for the previous experiments except that in this experiment
due to limitations in available screen refresh rates primes were displayed for 50, not 57 ms; the
procedure and data treatment were the same as that for Experiment 1. In this Experiment eight
practice items preceded each version of the experiment and these were selected to include all of the
prime conditions presented in the experiment. Data treatments affected 4.9% of the data and the
data of one participant were excluded due to exceeding the error rate criterion (leaving the data of
39 participants to be analysed). In this experiment, the participant’s vocalizations were recorded
and the voice-activated trigger times were examined using CheckVocal (Protopapas, 2007); adjustments were made to approximately 1% of the data.
Lexical decision: The procedure was the same as in the naming version except that the task was
lexical decision. Sixteen practice items (consisting of eight word and eight nonword targets) preceded each version of the experiment and these were selected to include all of the prime conditions
presented in the experiment. Data from participants who made more than 15% errors were excluded.
Data treatments affected 5.1% of the data and one participant was excluded due to exceeding the
error rate criterion (leaving the data of 46 participants to be analysed).
4.2 Results
Naming: Mean naming latencies and error rates for each prime condition are shown in Table 5. For
response times, there was a significant difference between the different prime conditions, F1(3, 105)
2
2
= 9.68, p < .05, η p = 2.2; F2(3, 156) = 17.64, p < .05, η p = 0.25. A series of planned sub-analyses
was conducted to examine the specific contrasts of interest. There was a significant difference
2
between the Repeated and Tone-Only conditions, F1(1, 35) = 6.93, p < .05, η p = 0.17; F2(1, 52) =
2
22.26, p < .05, η p = 0.3 and Repeated and Vowel-Only conditions, F1(1, 35) = 14.33, p < .05,
η 2p = 0.29. The difference between the Tone-Only and Vowel-Only conditions was not secure,
F1(1, 36) = 2.68, p > .05; F2(1, 52) = 3.12, p = 0.08. There was a significant difference between the
2
Tone-Only change and the ALD conditions, F1(1, 35) = 7.11, p < .05, η p = 0.16; F2(1, 52) = 6.60,
2
p < .05, η p = 0.11. The difference between the Vowel-Only change and ALD conditions was not
significant, both Fs < 1.
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The same set of analyses was conducted on the error data. There was no overall difference
between the different prime types, F1(3, 105) = 1.65, p > .05; F2(3, 156) = 1.34, p > .05. None of
the sub-analyses were secure, repeated vs. Tone-Only change, both Fs < 1; Tone-Only change vs.
Vowel-Only change, both Fs < 1; Tone-Only change vs. ALD, F1(1, 35) = 2.67, p > .05; F2 (1, 59)
= 2.49, p > .05; finally Vowel-Only change vs. ALD, F1(1, 35) = 1.97, p > .05; F2 (1, 59) = 2.79,
p > .05.
Lexical decision: Response times and error rates for the word targets as a function of prime type
2
are shown in Table 5. There was an overall effect of prime type, F1(3, 126) = 5.34, p < .05, η p =
2
0.11; F2(3, 156) = 5.38, p < .05, η p = 0.10. The difference between the Tone-Only and ALD was
not significant (both Fs < 1); the difference between the Vowel-Only and ALD conditions also was
not significant F1(1, 42) = 1.68, p > 0.05; F2(1, 52) = 1.60, p > 0.05. There was no difference in the
overall analysis of prime conditions in the error rates, F1 < 1; F2(3, 156) = 2.01, p > 0.05. The
analysis of the nonword targets' response time data indicated that there was no main effect of prime
type in the participant analysis, F1(3, 126) = 1.27, p > 0.05; F2(3, 156) = 3.58, p < .05. There was
no difference between the prime conditions in the error data, F1(3, 126) = 1.14, p > 0.05; F2 <1.
4.3 Discussion
The current experiment used unique features of the Thai writing system in order to ensure that the
vowel and tone change conditions were extremely well matched. By and large, the pattern of
results of Experiment 3 was consistent with the previous experiments: Across Experiments 1, 2 and
3 the fastest responses were to targets in the Repetition Condition; next fastest to targets in the
Tone-Only change condition, followed by the Vowel-Only change and then targets in the ALD
baseline condition. Differences across Experiments 1, 2 and 3 emerged when the statistical outcomes were considered.
The first of these differences concerns the Repetition and Tone-Only change conditions. In
Experiment 3 (unlike Experiments 1 and 2) there was a significant difference between the Repetition
and the Tone-Only change conditions. One factor that might explain this discrepant result was that
in the previous experiments the targets themselves all had tone marks and the tone change prime
condition consisted of primes that had different tone marks. In the current case, however, the targets had no tone marks and the tone change primes consisted of primes that had tone marks. Given
that the presence or absence of a tone mark is likely to be perceptually more salient than the distinction between different tone marks, and that the absence of a tone mark is itself important for how
spoken tone is assigned (see Table 1), it seems possible that the first stage of processing might be
to determine whether a tone mark is present or not. If this determination is sufficiently rapid to
affect target processing, then the presence of a tone mark in the prime might interfere with processing a target that did not have one.
This interpretation of interference in the Tone-Only condition is supported by the smaller difference between the Tone-Only condition and the ALD baseline in the current Experiment 3 (17 ms)
compared to Experiment 1 (35 ms) and Experiment 2 (29 ms for the 3-HOP words and 28 ms for
the 2-HOP words). Indeed, interference in the Tone-Only condition would have contributed to the
lack of difference in response times to the Tone-Only and Vowel-Only change conditions.
In summary then, although the contrast between the Vowel-Only and Tone-Only change conditions was not significant it was still the case that priming was found in the changed tone mark but
not in the changed vowel condition. This priming in the Tone-Only change condition did not occur
in the LD version of the task, where there was a repetition priming effect but no priming for the
Tone or Vowel change conditions. This result is consistent with previous studies in which there was
no masked form priming for short word targets (from dense orthographic neighbourhoods), for
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Davis et al.
example, Forster et al. (1987). The lack of priming from the Tone-Only change condition in the
LDT indicates that priming for this condition in Experiment 3 (likewise in Experiments 1 and 2)
was unlikely to be based on pre-activating (or accessing) the lexical entry of the target (and hence
suggests that it was connected to developing a naming response).
5 General discussion
This series of experiments examined how processes involved in naming a written word unfold.
Following Berent and Perfetti’s (1995) proposal that the structures of a phonological representation
determine the manner in which the assembly processes operate, the research focus was on whether
differences in segmental (vowels) and suprasegmental (tones) representation would be reflected in
naming aloud responses (specifically that the processing of tones would be delayed compared to
vowels).
The key idea in mapping representation to process is that the content of the assembled representation changes with processing time, such that tapping the assembled code at different times in the
assembly process will yield different results regarding its content. To index the development of the
phonological representation of vowels and tones, the influence of masked primes on target words
that were identical except for a vowel (Vowel-Only) or tone mark (Tone-Only) change were examined, and these effects were compared with repetition and ALD control primes. If vowel processing
leads more quickly to phonological description than does tone processing, the expectation was that
response to targets preceded by vowel changed primes would be slower than those preceded by
tone changed primes. It is important to note that any difference between the vowel and tone change
conditions would be because of interference in the Vowel-Only change condition that did not occur
in the Tone-Only change condition.
Experiment 1 demonstrated that, compared to the Repetition condition, the degree of priming
was significantly reduced when a vowel was changed but was unaffected by changing the tone
mark. In Experiment 2, the 3-HOP words showed the same results (reduced priming in Vowel-Only
but not Tone-Only changes), whereas in the 2-HOP condition words did not show the Vowel-Only
change difference, but in those items vowel position was variable and this could have affected priming. The Thai writing system permits an elegant manipulation, such that in Experiment 3 the consonant frame for the vowel and tone words could be held constant so that the critical primes only
changed whether a vowel or tone was marked. As measured against the ALD baseline, there was a
significant priming effect for tone change primes but no priming for the vowel change ones. The
results also demonstrated the sensitivity of the effect to small changes in the priming conditions,
with repetition primed targets being faster than both the vowel and tone mark added conditions. The
final experiment showed that there were no form-priming effects in the LDT task. The lack of formpriming in the LDT task suggests that effects shown in the naming task were due to differences in
developing an assembled phonological code.
The evidence for a difference in vowel and tone processing is based on the outcome of contrasts
with the Repetition and ALD baselines, and not on direct comparisons between the vowel and tone
change conditions (none of which were significant). The lack of robustness of these direct comparisons suggests that the time course of processing vowels and tones overlaps considerably.
Overall, however, the differential effect of vowel and tone marks on naming subsequent targets as
measured against the baselines is consistent with the proposition that the development of tone
information lags behind that of the vowel. In Thai spelling tones are more dispensable than consonants, and there is an indication that tones are also more dispensable than vowels (Burnham et al.,
2013). These results are consistent with the conclusion that emerges from the current studies: that
the development of tone information in reading (and in internal representations for spelling) lags
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Language and Speech 
behind that of the vowel (see also Winskall & Iemwanthong, 2010 for a similar finding for reading
aloud errors).
In interpreting their own findings concerning the time course of phonological assembly of consonants and vowels, Berent and Perfetti (1995) argued for distinct mechanisms of assembly that
differed in both when they commenced and the automaticity with which they operated. Although
the current results suggest a difference in when vowel and tone processing begin, they do not in
themselves indicate whether separate processing mechanisms are involved. That is, differences in
the timing of processes do not necessarily require separate types of processing mechanism, as
shown by simulations using parallel distributed processing (PDP) models (e.g., Plaut et al., 1996).
Processing time differences in PDP models typically occur as a consequence of differences in
the consistency of the mapping between network elements. Although the difference in vowel and
tone processing could be due to such differences, two points should be noted: (1) the assignment
of spoken tone from a tone mark is well-governed. So for example, in Experiment 3, the Tone-Only
condition always used the falling tone marker from which spoken tone is realized as either falling
or high depending upon the class of the initial consonant. Given this straightforward mapping, the
distinction between vowels and tones seems unlikely to be due to differences in consistency of the
input to output relationship; and (2) the realization of vowel sounds from vowel forms can also be
complex and can change depending upon whether the syllable is ‘live’ (open) or ‘dead’ (closed).
An issue related to that of the mechanism(s) underlying vowel and tone differences is whether
such is unique to Thai or more universal. If the effect is due to the particularities of the Thai mapping of vowels and tone marks to phonology, then it would be limited to Thai. However, if the
difference reflects a later process than orthography–phonology computation (e.g., one concerned
with speech planning, Kinoshita, 2000), then the differential effect might be more general. In this
regard, the results of Spinks, Liu, Perfetti and Tan (2000) are interesting. Their study used written
Chinese characters in a Stroop procedure and examined the effect of homophones with the same
versus different tones. The results were consistent with the notion that information about segments
is extracted more rapidly than that for tone as it was found that for faster congruent responses,
homophones (regardless of their tone) facilitated colour naming, whereas for the slower incongruent responses, the interference effect was more robust for same tone homophones. In a similar vein,
superior phonological over tonological awareness has been found in both Thai, in which both tones
and segments are represented alphabetically, and in Chinese in which they are not (Burnham et al.,
2011). Thus there is reason to suspect that the precedence of segment (vowel here) over tone processing is: (a) general over at least Thai and Chinese; and (b) manifested in but not peculiar to
orthographic manipulations in the masked priming paradigm. Further tone versus segment processing studies will be valuable in shedding light on how general any differences in the timing may be.
Of course, if the differential effects for vowels and tones are not a consequence of orthographic
to phonological processing but of a later stage of speech planning, then masked priming in a
Chinese character naming aloud task should occur for Tone-Only change character primes but not
for Vowel-Only ones (results from Chen, Lin, & Ferrand, 2003; You, Zhang, & Verdonschot, 2012
have already shown that changing tone produced robust priming effects). Such a result would provide strong confirmation that the difference between vowels and tones is a general one, a difference
possibly reflecting basic differences in the linguistic properties of segments and suprasegments.
Frost (1998) proposed that psycholinguistic research should aim to examine ‘online, step-bystep’ development rather than examining cognitive events well after they have occurred. Given that
estimates of the time taken to activate the visual word-form area are in the order of several hundred
milliseconds (Pammer et al., 2004), naming aloud a written word is a task that can be achieved
remarkably rapidly (in the current experiment average response latencies were about half a second). Thus, indexing step-by-step development will be a difficult task. The results of the current
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Davis et al.
studies show that the development of phonological information occurs not only left-to-right across
horizontal orthographic positions but also occurs at different vertical levels within horizontal
orthographic positions. It is believed that the strategy used in the current investigation is a step in
the right direction, and provides a basic template for future investigations of indexing on-line stepby-step development of phonological processing in visual word recognition.
Acknowledgements
We wish to thank Dr Benjawan Kasisopa for assisting in item selection, compiling lexical statistics and conducting the experiments in Thailand, and Ms Sirithip Tangtulayangkoon for help in conducting the experiments in Australia.
Funding
The experiments in this paper were supported by Australian Research Council grants to the 4th author
(A79601993) to the 4th and 1st authors (A00001283).
Notes
1.
Indeed, autosegmental theories of phonology propose that tone is represented independently of the vowel,
and in a separate phonological tier to consonants and vowels (Clements & Hume, 1995). Furthermore,
on the basis of their analysis of speech errors in Mandarin, Wan and Jaeger (1998) concluded that there
is overwhelming evidence that segments and tones are unlinked and autosegmental, as both segment and
tone errors were almost always independent from each other. Likewise, based on a corpus of approximately 4500 speech errors in Mandarin, Wan (2007) concluded that it was clear that tones and segments
are independent units at the level of phonological representation.
2. The task of reading a word aloud also provides a well-constrained domain within which to examine the
production of a spoken output from a written input. Indeed, modelling the processes involved in converting print to sound have been a primary focus of recent computational models (e.g., Coltheart et al., 2001;
Perry; Zielger & Zorzi, 2007; Plaut, McClelland, Seidenberg & Patterson, 1996).
3. Standard Thai dictionaries list 44 consonant symbols but the third (ฃ) and fifth (ฅ) are obsolete and have
been replaced by the second (ข) and fourth (ค).
4. The terms abjad and abugida were introduced (from Arabic and Ethiopic respectively) to designate types
of writing systems distinct from alphabets and syllabaries. Given that Thai has only a single inherent
vowel it is not clear whether the term abugida is entirely appropriate.
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