A high-density EEG study into the control of
prospective eye movements in
adults and infants
Magnus Holth, Audrey van der Meer & Ruud van der Weel
NU-LAB
Psykologisk Institutt
BACKGROUND
•
Tracking with the head and eyes a moving object that temporarily disappears
behind an occluder requires perception of object permanence (Kaufman, Csibra & Johnson,
2003) and the ability to estimate and predict the trajectory of the moving object
(Rosander & Von Hofsten, 2004). This, in turn, requires prospective control of eye
movements.
•
The perception of visual motion and control of eye movement is mainly related to
the middle temporal (MT) and medial superior temporal (MST) brain areas,
located adjacent at the occipital-temporal-parietal junction (Leigh & Zee, 2006).
•
These signals are passed on to frontal areas in the cortex, the frontal eye field
(FEF), which are believed to play an important role in controlling prospective eye
movements (Leigh & Zee, 2006), and the development of this control (Canfield & Kirkham,
2001).
•
How is the initiation of prospective eye movements timed, and do infants and
adults show different brain activity time-locked to this behaviour?
METHOD
•
Six infants (mean age 35 weeks) and six adults (mean age 23 years) visually
tracked a fast-moving car that was projected on a screen, while their brain activity
was being measured with high-density EEG.
•
Eye movements were measured with the child-friendly Tobii infra-red eyetracker
which allowed for investigating when the eye movement catches up with the
stimulus, and time-lock the EEG recordings to this event.
The car travelled under three different decelerations,
10% deceleration (FAST), 50% deceleration (Medium) and
90% deceleration (Slow). The start speed of the car was
1.0 px/ms for adults, and 0.5 px/ms for infant.
The experimental situation
with the mother and an assistant nearby.
RESULTS
EYE DATA
Eye data (↑ position and → time) from a typical trial with
“Medium” speed for an adult subject.
The grey area represents the occluders.
= Stimulus, • = Left eye, and • = Right eye
Eye data (↑ position and → time) from a typical trial with
“Medium” speed for an infant subject.
The grey area represents the occluders.
= Stimulus, • = Left eye, and • = Right eye
•
The marker indicates the catch-up event for each trial, and can be defined as the
moment at which the horizontal eye velocity approximately equals the velocity of the
car in the interval [100; 800] ms.
•
There was no main effect of speed (F(2,20)=.614, ns) indicating that the catch-up
event occurred at approximately the same time, but infants had overall longer
latencies for the catch-up event than adults (F(1,10)=79.26, p<.05).
EEG DATA
•
The EEG recordings were analysed with the software program Brain Electrical Source
Analysis (BESA). For the source analysis we used a standard source model to map the
brain activity in different areas (Scherg, Ille, Bornfleth & Berg, 2002).
The figure describes regional sources which reflect all source activities in the related brain regions.
•
The EEG analysis show a high burst in activity in both left and right FEF that
coincides with the catch-up event in the adult group, but not in the infant group.
The figure describes regional sources which reflect all source activities in the related brain regions.
•
Analysis of areas in the visual cortex shows mainly a higher activity in the infant
group than in the adult group, especially in the left secondary visual cortex. This
activity seems to be time-locked to the catch-up event as well.
•
The EEG recordings show no clear or stable differences between the speed conditions.
SUMMARY OF RESULTS
•
The EEG data indicate an increase in activity around the catch-up event, and a
possible developmental difference. This increase seems also to be clearer when the
EEG data is time-locked to the catch-up event.
•
Neither the eye data nor the EEG data showed a main effect of speed.
•
The interpretations of these results are not conclusive, and there are different
explanations and questions related to these topics.
CONCLUSION
•
The present findings suggest that time-locking EEG recordings to a behaviourdefined onset such as the catch-up event, provides a promising method for
analysing brain activity. Possible developmental differences will be investigated
further by using this method.
REFERENCES
Canfield, R.L., & Kirkham, N.Z. (2001). Infant cortical development and the prospective control of saccadic eye movements,
Infancy, 2, 2, 197-211.
Kaufman, J., Csibra, G., & Johnson, M.H. (2003). Representing occluded objects in the human infant brain, Proc. R. Soc. Lond. B
(Suppl.), Biology Letters, 270/S2, 140-143.
Leigh, R.J., & Zee, D.S. (2006). The Neurology of Eye Movements. 4th. Ed., Oxford University Press.
Rosander, R., & Von Hofsten, C. (2004). Infants' emerging ability to represent occluded object motion, Cognition, 91, 1-22.
Scherg, M., Ille, N., Bornfleth, H., & Berg, P. (2002). Advanced tools for digital EEG review: Virtual source montages, whole
head mapping, correlation, and phase analysis, Journal of Clinical Neurophysiology, 19, 2, 91-112.