1. Stimulus Visibility and Motion Coherence Sensitivity in Early Infancy
Induni A. Wickramasinghe, Emily J. Blumenthal, Karen R. Dobkins
Introduction Methods Results
• The perception of global motion over large areas is made possible by
neurons that combine input from many neurons with small receptive
fields in the striate cortex
• Global motion sensitivity emerges early in infants (around 6-8
weeks) but there is much disagreement about when this ability
becomes adult-like, with some reports saying as late as 12
years of age (Mason et. al., 2003)
• One theory is that local motion signals are available to the infant, but
higher brain areas that integrate them are slower to develop
• However, an alternative, not addressed in the literature, could be that
the global motion mechanism matures very early, but awaits stronger,
more detectible local motion input from subcortical mechanisms
• In the current study, we test 2 possible explanations for protracted
global motion sensitivity development:
• 1) Global motion sensitivity takes a long time to develop
• 2) Global motion sensitivity matures early but the input it
needs takes time to develop
• To test these hypotheses, we:
• First assessed each infant’s ability to detect the stimulus
• Then we tested motion sensitivity, making the stimuli equally
detectable across all ages tested
-In doing so, we are able to plot the trajectory of global
motion development controlling for detectability
Methods
Subjects
• 45 typically developing infants
• Age groups from 3-7 months
• n=9 in each age group
• 8 adults with normal or
corrected-to-normal vision
Procedure
• Subjects were show random dot kinetograms (see image)
• An experimenter judged the direction of the subject’s eye movements
as the subject visually tracked the moving dots
• How much of the development of contrast and coherence is
determined by brain maturation vs. environmental experience?
• We can compare preterm babies (who started receiving visual
input when their brains were less mature) with full term babies
• We may be able to determine the role of neural development vs.
visual experience in the maturation of these two mechanisms
• Do infants at risk for autism spectrum disorders show any difference
in contrast/coherence sensitivity?
• If any differences are found, it could potentially serve as criteria
for early detection and intervention
• Could individuals with anorexia nervosa show differences in
contrast/coherence sensitivity?
• Research has shown individuals with anorexia nervosa have
deficiencies in central coherence processing. Could this apply to
contrast/motion coherence processing as well?
Part 1 – Contrast
• Dots were presented at different contrast levels
• A measure of each infant’s contrast sensitivity was obtained
• That is, how bright the dots needed to be for the baby to be
able to see it
Part 2 – Coherence
• Tested coherence sensitivity on a second day
• Stimuli were run at 2.5 time the infant’s own contrast sensitivity
• This is critical; it is a level at which we know the babies can see
• A measure of each infant’s coherence sensitivity was obtained
• The percentage of dots that needed to be moving together for
the baby to see them as a coherent whole moving in one
direction
Adults
• Adults were tested in nearly identical conditions. The only difference was
that stimuli were presented for a limited duration (400 ms)
Table: Age Distribution of Infant Subjects
Age (months) Mean Age
(SEM)
3 3.10 (0.04)
4 4.10 (0.10)
5 4.97 (0.06)
6 6.06 (0.10)
7 6.90 (0.08) .
low contrast high contrast
less coherent more coherent
Random dot kinetogram. Each arrow represents the direction
in which the dot is moving.
For contrast testing, all dots in a trial moved in one direction
Results
• Contrast showed
a significant
increase in
sensitivity from
3-7 months, and
between infancy
and adulthood
• There was no
significant difference in
coherence sensitivity
across infancy
• Statistical analysis
showed no significant
difference in coherence
sensitivity when
infants’ data were
compared to adults.
Discussion
• This data gives us insight into how the two levels of motion
processing and their respective neural “streams” develop
• We found a developmental change in infant contrast sensitivity. This
is consistent with the literature (Mason et al., 2003)
• Coherence sensitivity did not change across ages and was
statistically no different than adult data
• This suggests coherence processing may be mature from
an earlier age
• It also suggests coherence processing is somewhat dependent on
contrast processing
• Although it may be mature at an earlier age, it needs to
“wait” for contrast processing to develop in order to
become useful
Future Directions
Contact Information: Induni Wickramasinghe
Email: iwickram@ucsd.edu
F(4,40)=6.09
p<.001
ηp
2=.40
F(4,40)=0.84
ns