Phonological processing during reading aloud

As we have seen, overt speech production and visual processing

of Mandarin tones involve both category-level and sub-phonemic

processing.

Chapters 3 and 4 investigated sub-phonemic pro-

cessing of tonal and segmental information in a different task.

Very few studies have investigated sub-phonemic processing dur-

ing reading aloud. Facilitation has been found in reading aloud

in alphabetic languages, such as Dutch and English, when targets

and primes have the same onset phonemes, compared to those

whose onset phonemes differ (Kinoshita, 2000; Kinoshita & Wool-

lams, 2002; Timmer & Schiller, 2012; Schiller, 2004, 2007). This

may not be surprising, given that these languages use a phonemic

system to represent phonology. However, as shown in Chapter 2

and described above, language processing also involves processing

of sub-phonemic detail, at least during speech production. In two

EEG studies with masked priming, Chapters 3 and 4 investig-

ated two types of sub-phonemic processing during reading aloud.

The first question addressed whether reading aloud involves pro-

cessing of sub-phonemic features in a typologically different lan-

guage, Dutch.

Sub-phonemic feature processing

The first question addressed in Chapter 3 was whether and when

sub-phonemic features are processed in Dutch reading aloud.

Evidence for featural representations comes from a variety of

sources. As early as the 1950s in a consonant identification study,

Miller and Nicely (1955) suggested that speech perception may

involve multiple features. Speech error studies show that substi-

tution of phonemes that differ in only one feature is more likely

than phonemes that differ in more than one feature (Goldrick

& Blumstein, 2006; McMillan & Corley, 2010). Some models of

speech production include a feature level. For example, in Dell

(1986) model, features are activated after word retrieval prior to

articulation. Phonetic features also have been found to play a role

during speech perception and acquisition (Chládková, 2014) and

silent reading (Ashby et al., 2009). So, far the question of whether

features are processed during reading aloud has not been invest-

igated. Further to the question of whether or not features play

a role in reading aloud, a matter of debate in the literature con-

cerns the type of information features represent. One possibility

is that features are relatively abstract contrastive representations

(Chomsky & Halle, 1968; Dell, 1986). Alternatively, they may

consist of articulatory gestures (e.g., Goldstein et al., 2007).

In Dutch, the sound pairs t-d and p-b are produced at the same

place of articulation (alveolar and bilabial, respectively), while the

pairs t-p and d-b match in voicing (voiceless and voiced, respect-

ively).

In this ERP study, participants read aloud real Dutch

words (e.g. huid ‘skin’) from a computer screen. Each target

word was preceded by a brief presentation of a masked non-word

prime in which the final sound matched in voicing (huib), place

of articulation (huit) or mismatched in both voicing and place

(control condition, huip). The best-fit linear mixed effects regres-

sion model revealed that reaction times were significantly faster

when prime and target matched in voicing, than when they did

not. Consistent with this, there was also reduced negativity in the

voice-match condition, compared to the control condition in the

early time window 25-75 ms after presentation of the target word.

These results indicate rapid processing of sub-phonemic voicing

information in Dutch reading aloud. This cannot be due to or-

thographic or phonemic processes, since there was no difference

between the critical and control conditions in terms of either

letters or phonemes: each prime-target pair differed by exactly

one phoneme and one letter. Only when measured at the sub-

phonemic feature level was there greater overlap in congruent

prime-target pairs (voice and place conditions), compared to con-

trols. Both the ERP measures and reaction times provide evid-

ence for processing of sub-phonemic voicing information in reading

aloud. This finding challenges previous assumptions in models of

reading aloud that phonological processing simply involves activ-

ation of strings of phonemic units.

Processing of allophonic variants

In addition to sub-phonemic feature processing, the voice-

congruency effect presented in Chapter 3 and described above also

sheds light on the processing of allophonic variation. In Dutch,

voiced stops have two realisations: a voiced and a voiceless allo-

phonic variant. In word-initial position, voiced stops (e.g. /d/

and /b/) are distinguished from their voiceless counterparts (/t/

and /p/) primarily by voice onset time (VOT). But in word-final

position, the VOT values of voiced and voiceless stops are very

similar. For example, the words hout (‘garden’) and houd (‘to

hold’) are homophones in Dutch. The voiced sounds are described

as devoiced (e.g. [t], [p]). When Dutch listeners were asked to dis-

tinguish between voiceless-devoiced minimal pair words they per-

formed at chance level (Baumann, 1995). This study investigated

the question of whether, when a sound category has more than

one output pattern (i.e. target distribution, or allophone), the

two or more distinct outputs are processed as a single category or

as separate categories.

As described above, response latencies were shorter and the

amplitude of the EEG was reduced with voice-congruent primes,

compared to mismatching control primes. This is a particularly

interesting result, given that final stops are devoiced in Dutch. Ar-

ticulatorily, due to final devoicing, both prime types are voiceless

(and therefore ‘match’ in voicing). However, the voice-congruency

effect indicates that the voicing distinction is retained and pro-

cessed during reading aloud. This suggests that, although the

overt realisation is similar, voiceless and devoiced stops are pro-

cessed as separate categories. This is consistent with the data

presented in Chapter 2 that processing of speech variants dur-

ing speech production and processing of visual words activates

both the speech category and the context-specific allophonic vari-

ant. In the present study, the experiment was not designed to

test for activation of the context-specific allophonic variant, but

it does provide evidence that the voicing distinction is processed

during reading aloud, even for devoiced variants. This seems to

provide support for a fairly abstract representation for features

(e.g., Chomsky & Halle, 1968; Dell, 1986). However, the results

do not rule out processing at the articulatory level. The present

results could also be explained if multi-level processing of the type

seen in Chapter 2 occurs. There may be processing of both a

contrastive feature category (voiced-voiceless) and the context-

specific articulatory gesture. More work is needed to verify this

possibility.