Denise Free and Dr. Ross Flom, Department of Psychology

Although we arguably know very little about the actual process of infant habituation, in assessing infant conditioning, controlled habituation is the procedure used most often. It may be that how infants habituate could vary as a function of their age. In addition a perceived “inability” at one age may reflect instead an incomplete period of familiarization or habituation. Most studies have used the same criterion for infants of different ages, and it may be more appropriate to vary the criterion of habituation or familiarization as a function of infant age.

In earlier research Flom, Gentile, and Pick (2008) established that nine-month old infants were able to discriminate “sad” and “happy” musical excerpts with a habituation criterion set at 50% decrement from initial look time. Like most other infant-controlled procedure studies, the criterion for habituation was the same for all the infant age ranges. It was found that the younger, 5- and 7-month old infants in the same study failed to show reliable discrimination.

The purpose of our current study was to look at the effect of changing criterion for habituation to a more conservative 70% from the “standard” 50% for 5- and 7-month old infants.

For the two experiments, we recruited 5- and 7- month olds from a list of birth records for Utah County. Their parents were called and asked if they were willing to bring their babies to the BYU Infant Development Lab to participate in infant research.

Upon arrival at the lab, and after the purpose of the experiment was explained to the parent, the infant was placed in an infant seat facing a television screen. We played musical excerpts rated as either “happy” or “sad” by adults. While playing the music we paired an image of a still and neutral face. Infant looking to the static face was used to assess infantsʼ listening to the auditory events, since the pairing of a static, unrelated image with an auditory event is typically how infantsʼ discrimination of auditory events is assessed. Two researchers observed each infant during the procedure. Observers recorded infantsʼ looking behavior, using a button box connected to a computer. Infantsʼ looking behavior is the dependent variable and was used to calculate the baseline (initial looking). The computer program used preset habituation criterion to indicate when habituation was reached, and then controlled the presentation of the test stimuli (change in music for sad to happy or vice versa depending on condition).

Experiment 1: For half of the infants the criterion for habituation was set at 70% decrement from initial look time.

The result was that the 5- and 7-month-olds no longer showed the asymmetrical pattern of discrimination that characterized Flom et al.’s (2008) Experiment 1. In using the 70% habituation criterion infants discriminated happy and sad musical excerpts when habituated to sad music and heard happy music during the test trials as well as when habituated to happy music and heard sad music during the test trials.

Experiment 2: For the remaining half of the infants the criterion of habituation was set at 50% decrement from initial look time.

In Experiment 2 7-month-olds showed discrimination of individual happy and individual sad excerpts whereas 5- and 7-month-olds in Flom et al.’s (2008) third experiment failed to show any evidence of discriminating individual happy or sad excerpts. In Experiment 2, the 5-month olds overall looking was greater than the looking time of the 7-month olds. A break down showed that the 5 month olds looking during baseline and the post habituation trials was greater than that of the 7-month olds, but the 5-month olds did not differ in looking times during the test trials from the 7-month olds.

Both of these experiments when compared with the three done by Flom et al., (2008) show evidence that discrimination of sad or happy musical excerpts is not just affected by the infants’ age, development, or perceptual ability, it is also affected by the criterion that is used to define habituation.

This is important because as researchers continue to use controlled habituation to assess infant conditioning, they must be aware of the variables affecting outcomes. In future research habituation criterion may be adjusted by age, perhaps giving a more accurate picture of the abilities of infants to discriminate at different ages.

Developing a more accurate picture of how early infants are able to understand and discriminate between objects and events is foundational to our understanding of child development, and I feel privileged that I was able to contribute in small part to that understanding.

Being able to participate in this important research has been a valuable asset in my learning experience here at BYU. I am hoping to continue on to do more research in different areas within psychology, and I believe that having the opportunity to work with Dr. Flom has been invaluable in my progress. I am very appreciative for the opportunities that he has created for myself and many other students, as well as for the ORCA grant that made my participation in this particular research possible