Gaze to Objects

Our next set of analyses focused on the frequency with which mothers’ gaze followed

infants’ object directed vocalizations and infants’ gaze followed mothers’ object directed

vocalizations (see Table 2 for a visualization of this variable). We predicted that mothers would

follow their infant’s vocalizations as early as 3 months, but that infants would not follow their

mothers object directed vocalization until later in the first year. As can be seen in Table 20, the

frequency with which both mothers and infants followed their partners’ directed vocalizations with

looks to that location was greater than would be expected by chance, and revealed no effects of

infant age or Risk Status. In fact, counter to our expectations, infant gaze following mothers’ vocalizations was more frequent (β00 = 5.25) than mother gaze following infant vocalizations (β00 = 1.79).

Next, we examined object directed vocalizations following gaze shifts to objects. Again,

we hypothesized that mothers would follow infants’ gaze shifts to an object with an object-directed

vocalization significantly more than expected by chance at 3 months, and that infants would not

be coordinated at 3 months, but would grow in coordination over time. As expected, the frequency

with which mothers followed their infant’s gaze shift to an object with a vocalization in the

direction of that object was significantly greater than would be expected by chance at 3 months.

Mothers also displayed positive, quadratic growth in this variable with a small amount of

deceleration (i.e. flattening) over time. Contrary to our hypothesis, the frequency with which

infants followed their mother’s gaze shift to an object with a vocalization directed to that object

was greater than would be expected by chance and did not show significant change over time.

vocalizations approximately 10 times more than would be expected by chance at 12 months (see

Table 19).

3.4 CONCURRENT RELATIONS AMONG COORDINATION VARIABLES

Our next set of analyses focused on the bivariate relations between the primary

coordination composite variables at each age point (see Table 21). We hypothesized that mother-

infant dyads that were more coordinated in one domain would be more coordinated in other

domains as well. Contrary to our hypothesis, vocal coordination and object gaze coordination

were not related at any age.

Table 21. Concurrent Relations among Coordination Variables Object Gaze

Composite

Mutual Gaze Composite

3 months Vocal Composite 0.01 0.14

Object Gaze Composite -0.11

6 months Vocal Composite -0.15 0.08

Object Gaze Composite -0.14

9 months Vocal Composite -0.03 0.42*

Object Gaze Composite -0.42*

12 months Vocal Composite -0.09 0.37º

Object Gaze Composite -0.41º

In fact, as can be seen in Table 21, the only significant relations between coordination

variables occurred at 9 months, when greater vocal coordination was associated with greater

mutual gaze coordination (r = .42, p = .03), and greater mutual gaze coordination was associated

relations were apparent at 12 months (Vocal & Mutual gaze: r = .37, p = .095; Mutual Gaze &

Object Gaze: r = -.41, p = .06).

3.5 LONGITUDINAL RELATIONS AMONG COORDINATION VARIABLES

Next, we analyzed how coordination variables related to each other across ages. Our first

set of analyses examined how coordination within each domain related from age to age (e.g. how

vocal coordination at 3 months related to vocal coordination at 6 months; see Table 22). To our

surprise, neither vocal coordination nor object gaze coordination composites related from one age

to the next. Only mutual gaze coordination displayed any relation across time, with 6 month

Table 22. Longitudinal Relations among Coordination Variables

6 months 9 months 12 months

Vocal Coordination

3 months -0.09 -0.18 -0.15

6 months 0.12 0.01

12 months 0.17

Mutual Gaze Coordination

3 months -0.02 0.05 0.37

6 months 0.64** -0.13

12 months 0.16

Object Gaze Coordination

3 months 0.40 0.30 -0.32

6 months 0.02 0.10

12 months 0.17

Given the absence of concurrent and longitudinal relations between coordination variables,

we were not surprised to find that our hypothesis that vocal coordination at 3 months would predict

object gaze coordination at later ages was not supported.

3.6 EARLY COORDINATION OF GAZE AND VOCALIZATIONS PREDICTING LATER LANGUAGE

Prior to analyzing the predictive relationships between early coordination variables and

later language development, we examined Risk Status differences in later language. Our dependent

variable was a composite of standardized 18 and 24 month CDI and Mullen scores (Cronbach’s

alpha = .912). Eighteen and/or 24 month language scores were available for 23 (10 HR) of the 30

infants (1 infant did not have an 18 or 24 month visit, 6 infants have not yet turned 18 months).

infants, in contrast with previous research our sample of HR infants did not differ significantly

from the LR sample (MLR = 0.19, SD = 0.80; MHR = -0.22, SD = 0.88; note that these composites

are standardized with a mean of 0).

Previous research has reported predictive relations between aspects of mother-infant vocal

and gaze coordination and later language development. Given the unexpected results regarding

the lack of developmental growth in vocal coordination as well as the absence of concurrent and

predictive relations between coordination variables, the data did not provide clear indications of

which coordination variables to include at which ages. Based on previous research, we decided

to include coordination variables only from the second half of the first year (9 and 12 months) in

this analysis, as these are the ages at which coordination has been shown to be well-established

and predictive of future language (Carpenter et al., 1998; Jasnow & Feldstein, 1986; Tamis-

LeMonda et al., 2001). Thus, vocal coordination composite, object gaze coordination composite,

and multi-modal coordination variables at 9 and 12 months were included in this exploratory

model.

We used a backwards stepwise regression to determine which variables created the best

predictive model. The model begins with all candidate variables included and successively

removes variables based on the significance value of the t-test for each predictor. The predictor

with the lowest significance value is compared to a removal criterion (in this case p = .10), the

predictor is removed if it meets the criterion, and the model is re-estimated with the remaining

predictors. This is continued until no more variables meet the removal criterion, thus leaving only

those variables that make significant contributions to explaining variance in the dependent

variable. This procedure indicated that none of the measures of coordination were significant