Top-Down Effects of Syntax
Supplemental Materials
Top-Down Effects of Syntactic Sentential Context on Phonetic Processing
by N. P. Fox & S. E. Blumstein, 2015, JEP: Human Perception and Performance
http://dx.doi.org/10.1037/a0039965
Supplementary Materials A: Complete Results and Discussion of Experiment 1
A.1. Details of Analysis Procedures
Because subjects’ responses were categorical (/p/ vs. /b/), the data were analyzed using
mixed effects logistic regression (Baayen, Davidson & Bates, 2008; Jaeger, 2008), implemented
using the lme4 package (Bates, Maechler, Bolker & Walker, 2014) in R (R Core Team, 2014).
Factorial main effects (CONTEXT, CONTINUUM, BIAS, and SPEED) were deviation-coded
(contrasts: 0.5, -0.5; positive contrasts corresponded to noun-biased, buy–pie, /p/-congruent, and
fast trials). VOT was a centered, continuous fixed effect. Since the design was fully withinsubjects and within-items (an item corresponded to a main verb; e.g., hated), the maximal
random effects structure (Barr, Levy, Scheepers & Tily, 2013) for this design included all
random intercepts, slopes and interactions for every subject and item. In order to achieve
convergence while minimizing the risk of inferential bias (Barr et al., 2013), random correlations
were excluded.
A.2. Supplementary Results/Discussion
Besides the two critical findings discussed in the main text (CONTEXT × CONTINUUM and
BIAS × SPEED
interactions), our results provided evidence that several other factors influence
subjects’ responses. Most are attributable to phonetic factors in our stimuli and well-established
observations about how context effects interact with phonetic factors in speech perception.
1
Top-Down Effects of Syntax
A.2.1. Analysis 1a (omnibus): CONTEXT × CONTINUUM × VOT
In addition to the crucial CONTEXT × CONTINUUM interaction in Experiment 1, there was
a main effect of VOT (β = 0.42, SE = 0.04, |z| = 11.70, p < 0.001) such that tokens with longer
VOTs were more often labeled as beginning with /p/, as expected given that VOT is the primary
cue distinguishing the /b/ and /p/ categories in English (Liberman, Harris, Kinney & Lane, 1961).
A significant VOT × CONTEXT interaction (β = 0.10, SE = 0.03, |z| = 3.58, p < 0.001)
replicates previous work showing that the size of a top-down bias depends on the acoustic
ambiguity of the stimuli (Burton, Baum & Blumstein, 1989; Ganong, 1980; McQueen, 1991; Pitt
& Samuel, 1993; Tuinman et al, 2014; van Alphen & McQueen, 2001). As Figure 1 suggests, the
closer a token’s mean rate of /p/-responses was to the phoneme category boundary (the VOT at
which one would expect to see 50% /b/-responses and 50% /p/-responses), the larger the
difference between subjects’ /p/-response rates at the two levels of CONTEXT appears to be.
VOT
interacted with CONTINUUM (β = 0.18, SE = 0.03, |z| = 6.30, p < 0.001), suggesting a
somewhat stronger influence of VOT in the buy–pie continuum than in the bay–pay continuum.
Although the exact source of this asymmetry is not immediately obvious, one should not
necessarily expect the effect of VOT to pattern identically in the bay–pay and buy–pie continua,
because VOT is only one of many cues to the identity of phonetically ambiguous (between /b/
and /p/) stimuli. Burst amplitude (Repp, 1984), subsequent vowel duration (Miller & Dexter,
1988; Summerfield, 1981), vowel identity (Klatt, 1975; Stevens & Klatt, 1974), and the lexical
frequency of continuum endpoints (Fox, 1984) can all influence voicing decisions about
phonetically ambiguous stimuli, and although it is not clear which of these (if any) contributed to
this asymmetry in Experiment 1, it is unclear how any of these factors could account for the
theoretically important CONTEXT × CONTINUUM interaction.
2
Top-Down Effects of Syntax
Finally, a significant main effect of CONTEXT (β = -0.36, SE = 0.12, |z| = 2.89, p < 0.004)
such that subjects were more likely to make /p/-responses after verb-biasing sentences than after
noun-biasing sentences reflected the fact that the simple effect of CONTEXT was stronger in the
bay–pay continuum (β = -1.37; /p/-responses to ambiguous tokens: 44.4% in noun-biased
contexts vs. 65.5% in verb-biased contexts) than in the buy–pie continuum (β = 0.95; /p/responses to ambiguous tokens: 58.4% in noun-biased contexts vs. 38.5% in verb-biased
contexts). Further research would be necessary to identify the specific source of this asymmetry,
but one possibility is that the syntactic manipulation was more efficacious in the bay–pay
continuum because the specific items in the experiment (e.g., Brett hated to...) created stronger
preferences when judging between bay and pay than between buy and pie. Importantly, though,
no matter the cause of this or any of the other ancillary effects discussed here, the prediction that
CONTEXT
would have robust, contrasting effects in the two continua was borne out by the data.
A.2.2. Analysis 1b (follow-up tests): CONTEXT × VOT
In addition to the reported simple effects of CONTEXT in the by-continuum follow-up
tests, both analyses, as in the omnibus analysis, revealed simple effects of VOT (bay–pay: β =
0.33, SE = 0.03, |z| = 11.58, p < 0.001; buy–pie: β = 0.50, SE = 0.04, |z| = 13.74, p < 0.001) in the
expected direction. Finally, there was a significant interaction between CONTEXT and VOT in the
bay–pay continuum (β = 0.12, SE = 0.03, |z| = 3.48, p < 0.001) and marginal interaction in the
buy–pie continuum (β = 0.07, SE = 0.04, |z| = 1.80, p = 0.07), suggesting that ambiguous tokens
were differentially impacted by CONTEXT in both continua (see Supplementary Materials A.2.1
for discussion).
A.2.3. Analysis 2: BIAS × SPEED × VOT
3
Top-Down Effects of Syntax
In addition to the BIAS × SPEED interaction, the results revealed a main effect of VOT (β = 0.36,
SE = 0.03, |z| = 12.47, p < 0.001) and a main effect of BIAS (β = 0.99, SE = 0.14, |z| = 7.21, p <
0.001), such that /p/-responses were more likely when targets had longer VOTs and in trials for
which the CONTEXT and CONTINUUM jointly made /p/ the congruent response. There was also a
significant VOT × SPEED interaction (β = 0.09, SE = 0.03, |z| = 3.12, p < 0.002), suggesting that
slower responses to a token were less influenced by that token’s VOT.
4
Top-Down Effects of Syntax
Supplementary Materials B: Complete Results and Discussion of Experiment 2
B.1. Details of Analysis Procedures
Analyses followed the same approach as Experiment 1’s. When occasional convergence
failures occurred, the random effects structure was simplified by removing random slopes for
factors involving the VOT factor. In all cases, this simplification allowed for convergence, and
the pattern of results (i.e., which fixed effects reached significance) was identical to the results of
the unconverged models with all of the random effects.
B.2. Supplementary Results/Discussion
Besides the two critical findings of Experiment 2 discussed in the main text (CONTEXT ×
CONTINUUM
interaction, but no BIAS × SPEED interaction), there was evidence that several other
effects influenced subjects’ responses, including effects replicating most patterns seen in
Experiment 1 (see Supplementary Materials A). However, aside from differing in the presence
of a BIAS × SPEED interaction, Experiments 1 and 2 differed in a few other ways. In particular,
the critical tokens were, on the whole, less often identified as /p/ in Experiment 2 than in
Experiment 1, even for the /p/-endpoint tokens (pay-endpoint: 96.0% vs. 77.0% /p/-responses in
Experiment 1 vs. 2; pie-endpoint: 86.8% vs. 76.5%). Such a pattern is consistent with earlier
studies showing that the distributional statistics of acoustic-phonetic cues (e.g., VOTs) within an
experimental context can produce range effects in the perception of phonetic category structure
(Clayards, Tanenhaus, Aslin & Jacobs, 2008). An analysis of the VOTs of the ten naturally
produced /p/-initial filler targets showed that these fillers had a mean VOT of 90 ms (with the
shortest VOT being 71 ms), in contrast to 35 and 34 ms VOTs for the two critical /p/-endpoint
stimuli. Thus, it appears that the longer VOTs of the filler targets affected the perception of
5
Top-Down Effects of Syntax
voicing in the critical target stimuli such that the boundary between the /p/ and /b/ stimuli was
now skewed towards fewer /p/ and more /b/ responses, consistent with range effects (Brady &
Darwin, 1978).
B.2.1. Analysis 1a (omnibus): CONTEXT × CONTINUUM × VOT
In addition to the crucial CONTEXT × CONTINUUM interaction in Experiment 2, main
effects of CONTEXT (β = -0.67, SE = 0.20, |z| = 3.28, p < 0.002) and VOT (β = 0.22, SE = 0.05, |z|
= 4.91, p < 0.001) emerged in Experiment 2, both matching patterns observed in Experiment 1.
B.2.2. Analysis 1b (follow-up tests): CONTEXT × VOT
Follow-up tests in each continuum revealed significant simple effects of CONTEXT (see
main text), as well as simple effects of VOT (bay–pay: β = 0.21, SE = 0.04, |z| = 5.75, p < 0.001;
buy–pie: β = 0.21, SE = 0.05, |z| = 4.65, p < 0.001).
B.2.3. Analysis 2: BIAS × SPEED × VOT
Although there was no evidence for a BIAS × SPEED interaction, the results showed a main effect
of BIAS (β = 1.01, SE = 0.21, |z| = 4.73, p < 0.001) which corresponds to the CONTEXT ×
CONTINUUM
interaction in the primary analysis, and a main effect of VOT (β = 0.18, SE = 0.03,
|z| = 5.40, p < 0.001).
6