Because we cannot ask babies what they know or what they think about, we have to find clever ways in in which we can figure it out.

For example, from how much attention babies pay to something we can infer a lot about how babies process information.

Looking times: The duration of babies’ looking tells us about their attention process: the longer they look at something, the more attention they pay, the more they need to process,  and vice versa, shorter looking indicates less attention and less processing demand. We often show babies images or short animations and can then compare which image or animation elicits longer looking. These measures can inform us about babies’ expectations.

Eye movements: For this type of research we use an apparatus called an Eye-tracker. This is a monitor with built-in cameras and infrared lights. Due to the reflection of the harmless infrared lights on the eyes, the device can precisely measure where exactly babies are looking at on the monitor. With the help of the eye-tracker we can thus determine which aspect of an image or a movie is relevant or salient for the babies, how they process what they see, and whether they show anticipatory eye-movements when for example they expect something to happen.

Pupil Dilation: When we use the Eye-tracker, it can also measure how wide the pupils are during watching the presentation of an image or a movie. We know that when pupils are wider more processing is going on, this measure is therefore can help us to determine how “hard” a baby has to think when watching a picture or a movie.


For research on language development of babies, we try to let one-and-a-half years old babies to say a few words. For example, they get to see pictures of well-known objects or we ask them to repeat some words. A recording is be made of the speech which will be later analyzed.

Behavioral observation & Interactions

We can also study the behavior of the babies during play sessions. This way we can get more insight into the emotional processes and behavioral strategies of babies. We can also learn more about their social- cognitive development. Every play session is different. In some sessions the baby plays with familiar toys together with his/her parent or a lab assistant, in other sessions these toys can be unfamiliar and interesting for the baby. In some sessions we show the baby how they can play with an interesting object and try to encourage them to imitate us.

Brain activity (EEG)

In some of our studies, we use EEG (electro-encephalography) measures. With EEG, the brain activity of the baby can be measured. In these studies the babies get to wear a cap or a net (see picture) with sensors which we can register the brainwaves. In this way we can directly measure what happens in babies’ brains while they explore the world around them. Babies sit on their parent’s lap while listen to sounds or watch pictures or movies on a monitor.

Optical imaging (fNIRS)

NIRS (near infra-red spectroscopy) is another safe and baby-friendly way to measure brain activity. Using NIRS we can assess which part in the baby brain the activity takes place exactly. Babies  wear a headband or a cap (see picture) with tiny LED-lights and detectors. The light shines on the outer part of the brain (the cortex). Part of the light is absorbed in the cortex by hemoglobin molecules (a protein in the blood) while the rest is picked up by the detectors in the cap. We can measure the difference between the intensity of light that goes in and comes out. When a brain area is active the blood flow in that area increases together with the concentration of the hemoglobin molecules which results in more light absorption in that area.

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