Habituation: Studying Infants Before They Can Talk

Recruit a number of 6-month-old infants. Participants should be healthy, have no history of developmental disorders, and have normal hearing and vision. Because infants of this age can be uncooperative or fussy (e.g., refuse to watch a demonstration or fall asleep during testing) and will need to meet the habituation criterion, extra participants need to be recruited in order to obtain sufficient data.

1. Data collection

1. Habituation Phase
   1. Place a chair in front of a large monitor in a quiet room.
   2. Instruct parents to hold their babies and remain as quiet as possible while looking at a point just above the center of the screen.
      1. Many studies of infant cognition require parents to be blindfolded or fitted with noise-cancelling headphones in order to make certain they don’t consciously or unconsciously influence their infant’s looking behaviors. However, having a parent wear a blindfold or headphones can alone be distracting to a baby. Therefore, some researchers simply instruct parents not to influence their babies and then review the videos after the fact to ensure that there were no issues.
   3. Observe the infant from another room, using a camera positioned below the monitor. This camera focuses on the infant’s face, so you can see whether the baby is looking at the monitor or away from it, not the images shown to the infant. Film the infant throughout the experiment.
   4. Present the stimuli in the habituation trials.
      1. First, an attention-getting stimulus is presented on the monitor to ensure that the infant is paying attention to the monitor prior to each trial.
      2. When the infant is looking at the monitor, press a key to present the stimulus assigned for habituation, in this case a blue circle.
      3. Simultaneously record the infant's looking time for each trial by holding down a key that tracks time. If the infant looks away from the monitor, release the key. If the baby’s attention returns to the monitor, then press the key and the stimuli remains on the screen. If the baby looks away from the monitor for more than 1.0 s at any time or looks for the maximum length of the trial (20 s), the image disappears from the screen and the attention-getting stimulus returns. This procedure is repeated for every trial throughout both phases of the experiment.
   5. As infants generally look longest during the first few trials of habituation and considerably less in later trials, use the first three trials in this phase to set the criteria for determining if an infant's visual attention has decreased enough to be considered habituated. In this case, this is when their average looking time on on three sequential habituation trials is 50% or less than their average looking time on the first three habituation trials observed.
   6. Continue this phase of the study until the infant reaches criteria for habituation. The number of trials required to reach habituation varies between babies.
2. Test Phase
   1. Once the infant has been habituated, begin the test phase. This phase only differs from the habituation phase in that different stimuli are presented.
   2. Show the infant either the habituation stimulus, in this case the blue circle, or a novel stimulus—a blue square. The procedure for measuring infants' looking remains the same.
   3. All babies will see both stimuli: counterbalance the presentation order of the test stimuli so that half see the habituation stimulus first, while the other half see the novel stimulus first.
   4. Following the test trials, end the session by thanking the parent and infant for participating.

2. Analysis

1. Because of the placement of the video camera, experimenters are unaware of the stimuli shown to the infant. If this is not the case, have two independent raters who are blind to the stimuli shown code the video recordings. Alternatively, many modern labs also use eye-tracking equipment that allows them to identify exactly where the infants are looking at any time during the experiment.
2. Omit data from those infants who do not meet habituation criteria.
3. Note the dependent variable, which is how long the infant spent looking at the novel test stimuli relative to the familiar habituated test stimulus.