Presentations

Abstract

The relationship between lexical and grammatical knowledge in young children is
impressively strong. Indeed, the correlation between productive vocabulary and
grammar (r = .84) is larger than that between productive and receptive vocabulary (r =
.63) when measured with the commonly used Communicative Development
Inventories (CDIs). This correlation fits cleanly with usage-based theories of language,
which assume no clear distinction between the lexicon and grammar (Tomasello,
2003). However, it could also reflect separate systems that are mutually causally
related (mutualism); initially uncorrelated domains can gradually become so correlated
as to be statistically indistinguishable when they are mutually causally related (Van der
Maas et al 2006). Disentangling these accounts is complicated by the non-linear
relationship between true and measured grammatical/lexical knowledge, which is not
accounted for in traditional regression-based approaches. Here we present a new
approach to disentangling these accounts which overcomes these measurement
challenges. We examined the dimensional structure of item-level data from CDI data
on Wordbank (Frank et al. 2017) using item-response theory and the DETECT method
(Stout et al. 1996). We first considered all non-longitudinal data from the American
English subsample of Wordbank. A DETECT analysis found evidence of moderate
multidimensionality with vocabulary and grammar items clustering separately, contra
some usage-based accounts which assume no distinction between grammatical and
lexical knowledge. Given that mutualism predicts that two domains become
increasingly correlated with age, we next ran a similar analysis in separate sets of
younger (~18 months) and older (~28 months) children. These data were
unidimensional at 18 months and multidimensional at 28 months. In sum, our results did not strongly support either account described above and are most consistent with
an initially integrated lexico-grammatical system that becomes decoupled between the second and third year.

Abstract

Infant-directed speech (IDS) is typically slower, higher-pitched with greater pitch
modulation and larger vowel space than adult-directed speech (ADS) (Saint-Georges et
al., 2013). IDS may aid development of infant attention (Senju & Csibra, 2008), emotion
(Fernald, 1992) and language (Golinkoff et al., 2015), though IDS quantity (Cristia et al.,
2019) and acoustic features vary across languages and cultures (Moser et al., 2020).
One proposed source of cross-cultural variability is the time that caregivers have infant
body-contact (Falk, 2004). However, most studies involve small samples from WEIRD
populations, so cultural variability is poorly estimated. We focused on free play and
mother-infant interactions in Uganda and the UK to assess cross-cultural differences in
IDS quantity and acoustic features and test the body-contact hypothesis. In Study 1,
we calculated the proportion of free play mothers spent producing IDS and/or were in
body contact with their infant (3-9 months). In Study 2 we recorded mothers speaking
to their infant (3-6 months) and an adult experimenter, including naming objects to
elicit the corner vowels /i, u, a/. We extracted mean pitch, pitch modulation, speech
rate and vowel space measures. In contrast to the body-contact hypothesis, mothers
in Uganda and the UK produced comparable amounts of IDS, despite Ugandan mothers
spending significantly more time in body contact with their infant. Study 2 showed that
IDS was higher in mean pitch and pitch modulation than ADS in both Uganda and the
UK, but this difference was more pronounced in the UK. Speech rate for IDS was
significantly slower than ADS in Uganda, but not the UK. We found no evidence of
group level vowel-hyper articulation in either population. We discuss possible drivers
of this cultural variation in acoustic features of IDS and highlight the importance of
future work probing downstream effects of this variation on infant behaviour.

Abstract

It is unknown whether modality affects the efficiency with which we learn novel word forms and their meanings. In this study, 60 participants were trained on 24 pseudowords, each paired with a pictorial meaning (novel object). Following a 20 minute filler task participants were tested on their ability to identify the picture-word form pairs on which they were trained when presented amongst foils. Word forms were presented in either their written or spoken form, with exposure to the written form equal to the speech duration of the spoken form. The between subjects design generated four participant groups 1) written training, written test; 2) written training, spoken test; 3) spoken training, written test; 4) spoken training, spoken test. Our results show a written training advantage: participants trained on written words were more accurate on the matching task. An ongoing follow-up experiment tests whether the written advantage is caused by additional time with the full word form, given that words can be read faster than the time taken for the spoken form to unfold. To test this, in training, written words were presented with sufficient time for participants to read, yet maximally half the duration of the spoken form in experiment 1.

Abstract

It is unknown whether modality affects the efficiency with which humans learn novel word forms and their meanings, with previous studies reporting both written and auditory advantages. The current study implements controls whose absence in previous work likely offers explanation for such contradictory findings. In two novel word learning experiments, participants were trained and tested on pseudoword - novel object pairs, with controls on: modality of test, modality of meaning, duration of exposure and transparency of word form. In both experiments word forms were presented in either their written or spoken form, each paired with a pictorial meaning (novel object). Following a 20-minute filler task, participants were tested on their ability to identify the picture-word form pairs on which they were trained. A between subjects design generated four participant groups per experiment 1) written training, written test; 2) written training, spoken test; 3) spoken training, written test; 4) spoken training, spoken test. In Experiment 1 the written stimulus was presented for a time period equal to the duration of the spoken form. Results showed that when the duration of exposure was equal, participants displayed a written training benefit. Given words can be read faster than the time taken for the spoken form to unfold, in Experiment 2 the written form was presented for 300 ms, sufficient time to read the word yet 65% shorter than the duration of the spoken form. No modality effect was observed under these conditions, when exposure to the word form was equivalent. These results demonstrate, at least for proficient readers, that when exposure to the word form is controlled across modalities the efficiency with which word form-meaning associations are learnt does not differ. Our results therefore suggest that, although we typically begin as aural-only word learners, we ultimately converge on developing learning mechanisms that learn equally efficiently from both written and spoken materials.