Human infants are capable of learning and developing at an incredible speed in the first few years of life. Within two years of birth, infants grow from being entirely helpless and dependent on their caregivers to toddlers who can begin to explore the world around them. Considering the amazing amount of information acquired by infants in such a brief period of time, many researchers are interested in discovering more about what infants know, as well as when and how they learn certain skills.
However, conducting research with infants comes with its fair share of challenges. Young infants are not yet verbal, making it impossible for researchers to ask infants questions about what they do or don’t know. Additionally, young infants have limited motor skills, making it challenging to provide them with objects to move or manipulate to demonstrate their knowledge.
So, how do researchers assess what infants do and do not understand? For decades now, researchers have utilized infant looking behavior to address this. Infants are born with the ability to see light and motion, and to detect large shapes. Given that they are born with the ability to see various aspects of the world around them, researchers often measure what infants choose to look at in order to elucidate infant preferences and understanding.
Some of the earliest looking time research aimed to determine if infants preferred complex or simple visual stimuli (Fantz, 1958). Infants were shown a more complex stimulus (such as a checkerboard design) on one side of their visual field, and a simpler design (a design with only one color) on the other side. The researchers observed the infants and pressed two different buttons to determine how much time the infants spent looking at each of the two types of stimuli. Across numerous infants, they found a significant preference for the more complex design, indicating that infants can tell the difference between such complex and simple stimuli, and prefer to look at something more complex.
Over time, with technological improvements, looking time studies have become more common in infant research, and have also become more precise. Eye tracking studies are now commonly used to assess infant looking time. In such studies, infants are shown various stimuli on a computer monitor or television screen, and an eye tracker is used to measure specifically where on the screen an infant is looking at any given point in time. This offers significantly more precision and accuracy, and removes potential experimenter bias from looking time studies.
So, how exactly does eye tracking work? Typically, an infant is placed in front of a computer monitor or television screen, which will display something for the infant to look at. Mounted near the screen (usually either directly above or below) is the eye tracker. The eye tracker emits a small amount of near-infrared light, which reflects off the cornea of the eye. The eye tracker then tracks these reflections, and uses this information to identify the direction of the eye’s gaze. In this way, the eye tracker can determine where an infant is looking on the screen at any given point in time.
Using eye tracking in this way allows us to assess multiple facets of infant comprehension and understanding. One type of eye tracking design that can be used is a “preferential looking paradigm”. In this type of design, infants are shown two different stimuli side-by-side on a screen. If, across many trials with many infants, the infants consistently look more to one type of stimulus than another, then we can determine that the infants discriminated the two stimuli and preferred one over the other. If we are interested, instead, in determining whether infants can recognize what belongs in a particular category, we can use a “habituation paradigm”. In this type of design, infants view many different examples of a category (such as many different dogs) one at a time. After the infants see many examples of different dogs, we expect them to become a little bored and look less at the dogs, suggesting that they show some understanding that all the prior images belonged to the same category. When something from a different category is shown (perhaps a cat, in this case), if the infants begin looking more to the screen (e.g. to the cat), we can determine that the infants recognized the category switch and perceive dogs and cats as separate categories of stimuli.
Ultimately, we can use these eye tracking designs for many different types of studies. Researchers can investigate infant social development by showing them faces, social categories, or even social situations. Based on how the infants respond, we can determine what types of social stimuli infants can discriminate or categorize. We can also investigate cognitive development using eye tracking. Researchers can explore whether infants understand that some objects should be solid, certain words are used to refer to specific objects, or that moving objects have a specific trajectory (e.g. Johnson et al., 2003). Using eye tracking, we can learn more about how and when infants learn these important concepts.
Another advantage to eye tracking is that it can be used with people of all ages. Although eye tracking is particularly helpful with infants, we can also use eye tracking with children, adolescents, and adults. This offers the ability to explore how patterns of looking change across development. Ultimately, this gives us the opportunity to see how certain aspects of social and cognitive development change from infancy into adulthood.
Overall, eye tracking is a useful method for learning about the immense amount of development that occurs in infancy. Even though infants can’t verbally respond to questions asked of them and have limited mobility, we can use eye tracking to better understand how they make sense of the world around them, and how this understanding may change as they get older.
References:
Fantz, R. L. (1958). Pattern vision in young infants. The Psychological Record, 8, 43-47.
Johnson, S. P., Bremner, G., Slater, A., Mason, U., Foster, K., & Cheshire, A. (2003). Infants’ perception of object trajectories. Child Development, 74, 94-108.