Experimental design & pre-analyses

5.4.2.1.1 Material

16 triplets of English minimal pairs (e.g. bat–bet–bit) were selected as prime items. Each of the 48 test primes was a monosyllabic noun with a short vowel, conforming to the syllable structures CVC, CCVC, CVCC or CCVCC.

The targets were selected as semantic relatives of the test-primes containing the root vowel [æ], (e.g.

club for bat). Semantically rather than associatively related words were used, for two reasons: First, only semantically related words can actually tap into the meaning of the corresponding prime (Perea and Rosa, 2002). The nature of the indirect semantic priming design crucially hinges on semantic activation, rather than on associative (co)-activation. Furthermore, Perea and Rosa (2002:188) showed that in the time course of a lexical decision task, purely semantic relations decay faster than associative or mixed relations. That is, by using only semantically related targets, priming between test-pairs or test-pairs and fillers can be kept to minimum, if it is not avoided altogether.

The semantically related targets were chosen according to WebsterÊs dictionary of synonyms (Gove, 1968) and verified by WordNet (Miller, 2003). For the majority of primes containing <a>, the semantic relative was a (near)-synonym. No semantic relative of the <a>-primes had an associative or semantic relation to the <e>- and <i>-words of the same triplet, i.e. the target for bat was club and had no (obvious) relation to bet or bit. Otherwise, one could counter that bit may have facilitated the recognition of club by virtue of a semantic or associative connection between the two words.

Semantically related and unrelated word pairs were tested in an offline judgement study. 8 subjects (4 male) from a New Zealand English origin (mean age 25) had to rate the similarity in meaning between the two words in either a semantically related or in a control pair condition. Similarity ratings were given on a scale from 1 (very similar) to 5 (very different).

- 193 - Results. The ANOVA with JUDGEMENT as dependent variable used the independent variables

SUBJECT (as random factor), ITEM (related to the test pair) and RELATION (semantic, control). The factor

RELATION showed a strong effect (F[1,203]=691.01, p<0.001), indicating that subjects judged the semantically related items as more similar than the unrelated items (median 2 for related, median 5 for unrelated pairs).

Targets were also approximately matched to the frequency of their primes (48 per million [targets]

vs. 49 per million [primes], based on Cobuild Spoken Word Frequency, taken from CELEX (Baayen et al., 1993))⁷⁴.

The experimental design involved three test conditions and one control condition. The appropriate prime occurred in the direct semantic condition (batÆclub), the inappropriate primes occurred in the indirect semantic conditions (betÆclub; bitÆclub) and the unrelated prime was used in the control condition (campÆclub).

All four conditions were distributed over four subject groups in a Latin Square design, such that group 1 had the appropriate (baseline) prime for club, group 2 the inappropriate <e>-prime, group 3 the

<i>-prime and group 4 the unrelated (control) prime. For the next test target, group 1 had the inappropriate <e>-prime and group 2 the <i>-prime etc.

Between prime-target pairs, word and nonword fillers were included. A short script in PASCAL ensured a pseudo-randomised distribution of 5-8 intervening fillers (3-4 prime-target pairs) and also determined the necessary number of fillers, which was 104. 68 of these fillers were nonwords. Primes were always words. The total number of items per group was 136. There were as many words as nonwords. Nonwords were derived from existing English monosyllabic nouns by changing one or more segments. All nonwords conformed to the English phonology and the CV-structure of the test items and were cross-checked by a native NZE speaker for their validity. The experimental items were read by a native speaker of NZE with phonetic training. The recording was done with a Sony Stereo microphone (ECMMS957) and stored on a DAT-tape. Subsequently, the material was digitised with the sound editing application Cool Edit Pro (Hain, 2003) with a sampling rate of 44.1 kHz (16 bit, mono). The cutting was done at zero-crossings.

5.4.2.1.2 Acoustic analysis of test stimuli

Prior to the acoustic analysis, the experimental stimuli were down-sampled to 11 kHz using Cool Edit Pro (Hain, 2003). Formant values (F1, F2, F3; cf. Table 54) were calculated using KAYÊs Multi-Speech (KAY, 2002). They stemmed from a LPC analysis at the midpoint of each vowel. The analysis involved a (full) Hanning-window with a frame length of 20 ms. The filter order was 12, using the auto-correlation method. Pre-emphasis was set to 0.9.

In a subsequent ANOVA with the factors ITEM (nested under VOWEL), FORMANT (F1, F2, F3),

VOWEL (<i>, <e>, <a>), and the interaction term VOWEL X FORMANT,the factor FORMANT was significant (F[2,40]=1926.23, p<0.001) as well as the factor VOWEL (F[3,40]=19.83, p<0.001). The interaction of

FORMANTXVOWEL was significant, too (FORMANT X VOWEL: F[2,40]=16.79, p<0.001). For the purpose of

74 A comparison of the Cobuild Spoken Word Frequency with both the Wellington Corpus of Spoken New Zealand English and the Canterbury Corpus revealed approximately the same frequency distribution for the test stimuli.

this study, it was crucial to determine the differences in the perceived vowel height as indicated by the F1 values⁷⁵ across the three vowels. Therefore, a planned comparison for the first formant was calculated. The F1 difference between <a> and <e> as well as the difference between <e> and <i> was significant (F1 <a>-<e>: t=3.10, p<0.003; F1 <e>-<i>: t=2.55, p<0.02), although the difference between <a>

and <i> was not (F1 <a>-<i>: t=0.55, p=0.58).

Table 54: Formant values of the primes in experiment 1 and 2.

VOWEL FORMANT FREQUENCY [Hz]

<a> F1 530

F2 1843

F3 2507

<e> F1 349

F2 2077

F3 2645

<i> F1 498

F2 1571

F3 2381

The vowels <a> and <i> were still distinguishable, though, on the basis of their F2 values which differed significantly in a post-hoc analysis (F2 <a>-<i>: t=4.66, p<0.001). Furthermore, <i> differs from the other two vowels in its F3 value (t=3.86, p<0.001). Together with its lower F2 values, this indicates that its realisation is in fact rounded.

Euclidian distances between all three vowels also differed significantly. Euclidian distances were calculated in the [F2-F1]/[F1] vowel space and a single-factor ANOVA was applied subsequently. The factor was DISTANCE TYPE (<a>-<i> <a>-<e> <e>-<i>). All three distances differed significantly from each other (F[2,45]=18.13, p<0.001, cf. Table 55).

Table 55: Euclidian distances of the vowels in the test stimuli.

DISTANCE TYPE DISTANCE [Hz]

<a>-<e> 456

<a>-<i> 293

<e>-<i> 673

The acoustic analysis showed two important points. First, all three vowels of the test items could be distinguished by their formant values. Furthermore, all their Euclidian distances differed. Second, the F1 frequency of <e> is always lower than that of <i>, supporting the findings elsewhere that in NZE, <e>

is realised as a front, high vowel, while <i> is a more centralised mid and rounded vowel. From an acoustic point of view, it is thereby guaranteed that the primes included both high front and mid central vowels (cf. Figure 38).

75 cf. Ladefoged, 2001 and references therein; see also Pfitzinger, 2003, and Kingston, 1991.

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Realisations of the Stimuli Vowel (Experiment 1 and 2)

300

Figure 38: Realisations of the test stimuli stem vowels in the F2-F1/F1 space for the indirect semantic priming experiments 1 and 2. The formant values represent the average

across experimental items (primes) and are based on a LPC analysis at the vowelsÊ midpoints.