Affect is an important feature of infant-directed speech (IDS). IDS towards infants during the first year of life varies in degree of affect. In Australian English (AuE), positive affect in mothers’ IDS increases over age from birth to twelve months, with a dip at nine months (Kitamura & Burnham, 2003).

This study investigates whether affect in Swedish (Swe) mothers’ IDS towards their infants develops in a similar pattern compared to the Australian English data. It also introduces a cross-linguistic perspective of affect perception in IDS as Swedish native speakers rate both the Swe and AuE IDS samples.

The adult raters (N=16; 8 female, mean age 36.4 years; SD = 10.1) assessed affect polarity and affect degree in low-pass filtered IDS samples on a scale from -4 to +4 (highly negative to highly positive). The 25 s long samples were cut from interactions between mothers and their infants at three, six, nine and twelve months and low-pass filtered. The Australian material was sampled from the same dataset as used in Kitamura and Burnham (2003); the Swedish material was recorded at Stockholm Babylab (Gerholm et al., 2015).

Separate repeated measures ANOVAs were conducted on the mean affect ratings of AuE and Swe IDS, with infant age as within-subject factor, followed up with polynomial contrasts. For AuE IDS, a significant main effect was found for age (F(45,3)=10.356; p<.001), with a linear (F(15,1)=20.542; p<.001) and a cubic trend (F(15,1)=7.780; p=.014). For Swe IDS, a significant main effect was found for age (F(45,3)=4.186; p=.011), with a linear (F(15,1)=10.993; p=.005) and a quadratic trend (F(15,1)=6.124; p=.026). In both languages, positive affect decreases over age.

While cross-linguistic affect perception of AuE IDS is still similar to the original, Kitamura and Burnham’s data show a more pronounced cubic trend and a general increase of affect in IDS over the first year. In this study, affect development in AuE IDS shows a steep increase from three to six months, followed by a decrease from six to nine months and a slight recovery from nine to twelve months. Affect in Swe IDS follows a different developmental trajectory, as it decreases from three to nine months to recover with an increase from nine to twelve months. This is a first indication for language-specific differences in IDS affect over the first year. Future ratings of the same material with AuE native speakers will show if the difference in the AuE results is an effect of rater language.