Age Differences in Frontal EEG Activation in Response to Attractive and
Unattractive Faces: A Study of 6- and 10-Month-Old Infants
Background and Aims: Infants selectively attend to social stimuli in their environment, but
motivation underlying selective attention is difficult to study across the first year. Six-month-
olds look longer at attractive than unattractive faces suggesting visual preference, but 9- and
12-month-olds do not look significantly longer at attractive or unattractive faces (e.g.
Langlois et al., 1987). By 12-month, infants show more approach behaviors toward attractive
strangers and more withdrawal behaviors toward unattractive strangers (Langlois et al.,
1990)—clearly indicating social preferences through behavior. We studied frontal EEG
hemispheric activation to assess of approach/withdrawal motivation in response to attractive
and unattractive faces before 12-months. Greater relative left EEG activation correlates to
approach motivation, whereas greater right EEG asymmetry correlates to withdrawal
motivation (Fox, 1991).
Method: Nineteen 6-month-olds and twenty 10-month-olds viewed images of 5 attractive
and 5 unattractive female faces presented for 20 seconds each while EEG was acquired
from electrodes at left (F3) and right (F4) mid-frontal regions of the scalp. Following
EEG data reduction, we calculated raw power density for the 6 to 9 Hz frequency band
and the EEG asymmetry index as the difference between the log-transformed alpha
power density form the right and left sites [Ln(F4) – Ln(F3)]. Power and activation are
inversely related—negative scores indicate greater activation on the right while positive
scores indicate greater activation on the left.
Results: A 2 (Face Type) X 2 (Age) repeated measures ANOVA using EEG asymmetry
as the within subjects variable showed a main effect for face type but no age effect.
Infants showed greater left asymmetry when viewing attractive faces (M = .07; SD = .36)
compared to unattractive faces (M = -.02; SD = .36), F(1,37) = 7.58, p < .01.
A 2 (Face Type) X 2 (Age) X 2 (Hemisphere) repeated measures using EEG raw power
as the within subject variable showed a Face Type X Age interaction, F(1,37) = 6.63, p =
.01 and a Face Type X Hemisphere interaction, F(1,37) = 5.52, p = .02.
Conclusion: Supporting our hypothesis, both age groups showed EEG asymmetry
suggesting greater motivation to approach attractive than unattractive faces. The relative
contributions of left and right hemispheric activation to these asymmetry indices differed
by age. Older infants showed differences in left activation between conditions suggesting
greater motivation to approach attractive than unattractive faces. Younger infants showed
differences in right activation suggesting more motivation to withdraw from unattractive
than attractive faces.