Infants Discriminate the Affective Expressions of their Peers: The Roles of Age and Familiarization Time.

Research examining infants' discrimination of affect often uses unfamiliar faces and voices of adults. Recently, research has examined infant discrimination of affect in familiar faces and voices. In much of this research, infants were habituated to the affective expressions using a "standard" 50% habituation criterion. We extend this line of research by examining infants' discrimination of unfamiliar peers', that is, 4-month-olds, dynamic, facial, and vocal affective expressions and assessing how discrimination is affected by changing the habituation criterion. In two experiments, using an infant-controlled habituation design, we explored 3- and 5-month-olds' discrimination of their peers' dynamic audiovisual displays of positive and negative expressions of affect. Results of Experiment 1, using a 50% habituation criterion, revealed that 5-month-olds, but not 3-month-olds discriminated the affective expressions of their peers. In Experiment 2, we examined whether 3-month-olds' lack of discrimination in Experiment 1 was a result of insufficient habituation (i.e., familiarization). Specifically, 3-month-olds were habituated using a 70% habituation criterion, providing them with longer familiarization time. Results revealed that using the more stringent habituation criterion, 3-month-olds showed longer habituation times, that is increased familiarization, and discriminated their peers' affective expressions. Results are discussed in terms of infants' discrimination of affect, the role of familiarization time, and limitations of the 50% habituation criterion.

Dynamics of infant habituation: infants' discrimination of musical excerpts.

Schöner and Thelen (2006) summarized the results of many habituation studies as a set of generalizations about the emergence of novelty preferences in infancy. One is that novelty preferences emerge after fewer trials for older than for younger infants. Yet in habituation studies using an infant-controlled procedure, the standard criterion of habituation is a 50% decrement in looking regardless of he ages of the participants. If younger infants require more looking to habituate than do older infants, it might follow that novelty preferences will emerge for younger infants when a more stringent criterion is imposed, e.g., a 70% decrement in looking. Our earlier investigation of infants' discrimination of musical excerpts provides a basis and an opportunity for assessing this idea. Flom et al. (2008) found that 9-month-olds, but not younger infants, unambiguously discriminate "happy" and "sad" musical excerpts. The purpose of the current study was to examine younger infants' discrimination of happy and sad musical excerpts using a more stringent, 70% habituation criterion. In Experiment 1, 5- and 7-month olds were habituated to three musical excerpts rated as happy or sad. Following habituation infants were presented with two musical excerpts from the other affect group. Infants at both ages showed significant discrimination. In Experiment 2, 5- and 7-month-olds were presented with two new excerpts from the same affective group as the habituation excerpts. The infants did not discriminate these novel, yet affectively similar excerpts. In Experiment 3, 5- and 7-month-olds discriminated individual happy and sad excerpts. These results replicate those for the older, 9-month-olds in the previous investigation. The results are important as they demonstrate that whether infants show discrimination using an infant-controlled procedure is affected by the researchers' chosen criterion of habituation.

To Grasp or Not to Grasp: Infants' Actions Toward Objects and Pictures.

We conducted two experiments to address questions over whether 9-month-old infants believe that objects depicted in realistic photographs can be picked up. In Experiment 1, we presented 9-month-old infants with realistic color photographs of objects, colored outlines of objects, abstract colored "blobs," and blank pages. Infants most commonly rubbed or patted depictions of all types. They also showed significantly more grasps toward the realistic photographs than toward the colored outlines, blobs, and blank pages, but only 24% of infants directed grasping exclusively at the photographs. In Experiment 2, we further explored infants' actions toward objects and pictures while controlling for tactile information. We presented 9-month-old infants with objects and pictures of objects under a glass cover in a false-bottom table. Although there were no significant differences between the proportion of rubs and pats infants directed toward the objects versus the photographs, infants exhibited significantly more grasping toward the objects than the photographs. Together, these findings show that 9-month-old infants largely direct appropriate actions toward realistic photographs and real objects, indicating that they perceive different affordances for pictures and objects.

Infants' discrimination of happy and sad music.

Infants can detect information specifying affect in infant- and adult-directed speech, familiar and unfamiliar facial expressions, and in point-light displays of facial expressions. We examined 3-, 5-, 7-, and 9-month-olds' discrimination of musical excerpts judged by adults and preschoolers as happy and sad. In Experiment 1, using an infant-controlled habituation procedure, 3-, 5-, 7-, and 9-month-olds heard three musical excerpts that were rated as either happy or sad. Following habituation, infants were presented with two new musical excerpts from the other affect group. Nine-month-olds discriminated the musical excerpts rated as affectively different. Five- and seven-month-olds discriminated the happy and sad excerpts when they were habituated to sad excerpts but not when they were habituated to happy excerpts. Three-month-olds showed no evidence of discriminating the sad and happy excerpts. In Experiment 2, 5-, 7-, and 9-month-olds were presented with two new musical excerpts from the same affective group as the habituation excerpts. At no age did infants discriminate these novel, yet affectively similar, musical excerpts. In Experiment 3, we examined 5-, 7-, and 9-month-olds' discrimination of individual excerpts rated as affectively similar. Only the 9-month-olds discriminated the affectively similar individual excerpts. Results are discussed in terms of infants' ability to discriminate affect across a variety of events and its relevance for later social-communicative development.

Experimenter Affective Expression and Gaze Following in 7-Month-Olds.

The study of gaze following in infants younger than 12 months of age has emphasized the effects of gesture, type of target, and its position or placement. This experiment extends this literature by examining the effects of adults' affective expression on 7-month-olds' gaze following. The effects of 3 affective expressions-happy, sad, and neutral-on 7-month-olds' frequency of gaze following were examined. The results indicated that infants more frequently followed the gaze of an adult posing a neutral expression than that of an adult posing either a happy or a sad expression. The infants also looked proportionately longer toward the indicated target when the adult's expression was neutral. The results are interpreted in terms of infants' flexibility of attention.

Matching and naming objects by shape or function: age and context effects in preschool children.

Three experiments tested preschoolers' use of abstract principles to classify and label objects by shape or function. Three- and 4-year-olds were instructed to match objects by shape or function. Four-year-olds readily adopted either rule, but 3-year-olds followed only the shape rule. Without a rule, 4-year-olds tended to match by shape unless object function was shown during matching (Experiment 2). Three-year-olds' ability to use a function rule was tested in several conditions (re-presenting functions; reminders to "use the rule"; repeating rule on every trial). None induced consistent function matching (Experiment 3). Supplemental memory and verbal tasks showed that 3-year-olds have trouble using function as an abstract basis of comparison. Naming data, however, show that preschoolers are learning that object labels are based on function. The results show preschoolers' growing flexibility in adopting abstract generalization rules and growing knowledge of conventions for extending words.