| The age at which an individual acquires a word,
i.e. age of acquisition (AoA), has been found to significantly
influence lexical processing. AoA effects have been
reported in various processing tasks using normal subjects,
including word naming, picture naming, lexical decision,
word-associate generation and semantic categorization
(see Ghyselinck et al. (2004) for review). Not only
have AoA effects been observed in reaction-time experiments,
they also affect the accuracy of performance and error
production of aphasic individuals in reading aloud,
spelling-to-dictation, oral and written picture naming
(e.g., Hirsh & Ellis, 1994; Nickels & Howard, 1995;
Gerhand & Barry, 2000; Weekes et al., 2003).
Although
the phenomenon of AoA is widely established, its nature
is not yet well understood. One key issue is concerned
with its locus/loci in the lexical system. Brown and
Watson (1987) proposed the phonological completeness
hypothesis stating that AoA effects reside at the phonological
(output) level. Late-acquired words are assumed to
have more segmented phonological representations, compared
with early-acquired words. A more recent account, similarly
maintaining the locus of AoA effects at the lexeme
level, focuses instead on the mapping between input
and output representations (Ellis & Lambon-Ralph, 2000;
Monaghan & Ellis, 2002). It is referred to as the arbitrary
mapping hypothesis. The size of AoA effects is dependent
on the predictability of the orthography-phonology
mappings. AoA effects are prominent for unpredictable
words but reduced in predictable lexical items. Ghyselinck
et al. (2004) put forth an alternative view that the
role of AoA lies in the organization of the semantic
system. This is motivated by their findings of AoA
effects in a semantic categorization task and lexical
decision involving legal nonwords and pseudo-homophones.
The
aim of this study is to investigate into the loci of
AoA effects in Chinese lexical processing through evaluating
the aforementioned hypotheses. Several characteristics
of the Chinese writing system lend itself well to this
purpose. As pointed out in Zevin and Seidenberg (2002),
the relatively high degree of regularity in orthography-to-phonology
mappings in English does not provide a good context
to study AoA effects on reading aloud. In contrast,
the arbitrary relation between Chinese characters and
their pronunciations may constitute better testing
ground. However, for many Chinese characters, namely
phonetic compound characters containing a phonetic
radical component that provides a phonetic cue, the
mapping between written form and sound is not entirely
arbitrary. They vary in terms of predictability of
pronunciation as measured by the degree of consistency
across phonetic compound characters having the same
phonetic radical component (Fang et al., 1986). This
combination of arbitrariness and predictability allows
us to assess the arbitrary mapping hypothesis in reading
aloud. Another characteristic of the Chinese orthography
is its extent of homophony. This affords us a great
opportunity to examine the phonological completeness
hypothesis through contrasting homophonic characters
with early AoAs and late AoAs. Furthermore, the existence
of homographic homophonic morphemes enables us to see
if AoA also plays a role in the semantic system. Homographic
morphemes are characters associated with unrelated
meanings, such as 華 may mean 'Chinese' in 華僑 'overseas
Chinese', or 'beauty' in 華麗'extravagant'. If the different
meanings are acquired at different AoAs, any difference
in the processing speed or accuracy of production of
these characters may be taken as evidence for their
influence at the semantic level.
Although in most previous
studies of AoA word naming and lexical decision tasks
involve orthographic or auditory input and oral output,
a distinction is often not made between spoken and
written AoAs in the AoA estimates. When the distinction
was made in Yamazaki et al. (1997), it was found that
both contribute to naming latencies of Japanese Kanji
characters. These findings imply that AoA effects may
be modality specific. Cantonese is essentially a spoken
language. As such, lexical items may differ in terms
of their availability in spoken, written, or spoken
as well as written forms. For instance, sai3lou6 'child'
is strictly a colloquial form, which has no formal
written representation; hau4zi2 猴子 'monkey' only appears
in text but extremely rarely in spoken language; the
word maa5lou6 馬路 'road' has the same spoken and written
form. We focus on the last two types of words and refer
to the former (the 'monkey' type) as formal words,
and the latter as consistent words (the 'road' type).
Generally speaking, a consistent word is assumed to
have lower spoken AoA than written AoA, whereas a formal
word is believed to have comparable spoken and written
AoAs. In other words, if a formal item and a consistent
item are matched on written AoA, the former is likely
to have a higher spoken AoA. Conversely, if the pair
is matched on spoken AoA, the formal word is likely
to have lower written AoA than the consistent word.
One may take advantage of this characteristic to explore
the issue of modality specific AoA effects through
contrasting visual and auditory lexical decision latencies
of formal and consistent words.
In summary, the proposed
study intends to investigate the locus of AoA effects
in the lexical system and whether the effects are specific
to modality.
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