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.     

Infants' perception of goal-directed actions: development through cue-based bootstrapping

It is now widely accepted that sensitivity to goal-directed actions emerges during the first year of life. However, controversy still surrounds the question of how this sensitivity emerges and develops. One set of views emphasizes the role of observing behavioral cues, while another emphasizes the role of experience with producing own action. In a series of four experiments we contrast these two views. In Experiment 1, it was shown that infants as young as 6 months old can interpret an unfamiliar human action as goal-directed when the action involves equifinal variations. Experiments 2 and 3 demonstrated that 12- and 9-month-olds are also able to attribute goals to an inanimate action if it displays behavioral cues such as self-propelledness and an action-effect. In Experiment 4, we found that even 6-months-olds can encode the goal object of an inanimate action if all three cues, equifinality, self-propelledness and an action-effect, were present. These findings suggest that the ability to ascribe goal-directedness does not necessarily emerge from hands-on experience with particular actions and that it is independent from the specific appearance of the actor as long as sufficient behavioral cues are available. We propose a cue-based bootstrapping model in which an initial sensitivity to behavioral cues leads to learning about further cues. The further cues in turn inform about different kinds of goal-directed agents and about different types of actions. By uniting an innate base with a learning process, cue-based bootstrapping can help reconcile divergent views on the emergence of infants' ability to understand actions as goal-directed.     

Infants' understanding of actions performed by mechanical devices

Recent research suggests that 9-month-old infants tested in a modified version of the A-not-B search task covertly imitate actions performed by the experimenter. The current study examines whether infants also simulate actions performed by mechanical devices, and whether this varies with whether or not they have been familiarized with the devices and their function. In Experiment 1, infants observed hiding and retrieving actions performed by a pair of mechanical claws on the A-trials, and then searched for the hidden toy on the B-trial. In Experiment 2, infants were first familiarized with the experimenter and the claws but not their function. In Experiment 3, infants were familiarized with the function of the claws. The results revealed that search errors were at chance levels in Experiments 1 and 2, but a significant proportion of the infants showed the A-not-B error in Experiment 3. These results suggest that 9-month-old infants are less likely to simulate observed actions performed by mechanical devices than by human agents, unless they are familiarized with the function of the devices so that their actions are perceived as goal-directed.     

Infants' discrimination of number vs. continuous extent

Seven studies explored the empirical basis for claims that infants represent cardinal values of small sets of objects. Many studies investigating numerical ability did not properly control for continuous stimulus properties such as surface area, volume, contour length, or dimensions that correlate with these properties. Experiment 1 extended the standard habituation/dishabituation paradigm to a 1 vs 2 comparison with three-dimensional objects and confirmed that when number and total front surface area are confounded, infants discriminate the arrays. Experiment 2 revealed that infants dishabituated to a change in front surface area but not to a change in number when the two variables were pitted against each other. Experiments 3 through 5 revealed no sensitivity to number when front surface area was controlled, and Experiments 6 and 7 extended this pattern of findings to the Wynn (1992) transformation task. Infants' lack of a response to number, combined with their demonstrated sensitivity to one or more dimensions of continuous extent, supports the hypothesis that the representations subserving object-based attention, rather than those subserving enumeration, underlie performance in the above tasks.     

Infants' association of linguistic labels with causal actions

Six experiments examined infants' ability to associate nonsense words with 2 causal actions: pushing and pulling. Although Experiment 1 found that 14-month-olds failed to form word-action associations, 18-month-olds in Experiment 2 provided reliable evidence of doing so. Additional experiments explored why 14-month-olds may not have formed such an association. Experiment 3 examined 14-month-olds' ability to discriminate a change in either the action or the label when the other element was held constant. Infants discriminated the change in label but not the change in action. When the language labels were replaced with music (Experiments 4-6), 14-month-old infants responded in terms of and discriminated between pushing and pulling. These results, in comparison with those from Experiments 1 and 3, suggest that for 14 month-olds, attempting to associate labels with actions may interfere with their discrimination of similar actions.     

Infants' goal anticipation during failed and successful reaching actions

The ability to interpret and predict the actions of others is crucial to social interaction and to social, cognitive, and linguistic development. The current study provided a strong test of this predictive ability by assessing (1) whether infants are capable of prospectively processing actions that fail to achieve their intended outcome, and (2) how infants respond to events in which their initial predictions are not confirmed. Using eye tracking, 8‐month‐olds, 10‐month‐olds, and adults watched an actor repeatedly reach over a barrier to either successfully or unsuccessfully retrieve a ball. Ten‐month‐olds and adults produced anticipatory looks to the ball, even when the action was unsuccessful and the actor never achieved his goal. Moreover, they revised their initial predictions in response to accumulating evidence of the actor's failure. Eight‐month‐olds showed anticipatory looking only after seeing the actor successfully grasp and retrieve the ball. Results support a flexible, prospective social information processing ability that emerges during the first year of life.     

Infants' imitation of goal-directed actions: the role of movements and action effects

This paper reviews studies on infants' imitation of goal-directed actions in the first two years of life. Special emphasis is given to the role of the two observable components of an action, that is, the movement and the action effects, on infants' replication of target actions. The reviewed studies provide evidence that infants benefit most from a full demonstration of both movements and effects. If movements are demonstrated in isolation, infants may encode this information, but they preferentially reproduce actions that lead to salient effects. If action effects are presented in isolation, infants younger than 19 months usually fail to emulate the unseen movements that would be necessary to produce these effects. Infants' ability to predict action effects or to infer unseen movements from incomplete demonstrations improves substantially at the end of the second year of life. It is concluded that the capability to learn relations between movements and action effects by observation, and the knowledge about movement-effect relations acquired so far, may be important factors underlying the developmental changes in infants' imitation of goal-directed actions.     

Infants' discrimination of faces by using biological motion cues

We report two experiments in which we used animated averaged faces to examine infants' ability to perceive and discriminate facial motion. The faces were generated by using the motion recorded from the faces of volunteers while they spoke. We tested infants aged 4-8 months to assess their ability to discriminate facial motion sequences (condition 1) and discriminate the faces of individuals (condition 2). Infants were habituated to one sequence with the motion of one actor speaking one phrase. Following habituation, infants were presented with the same sequence together with motion from a different actor (condition 1), or a new sequence from the same actor coupled with a new sequence from a new actor (condition 2). Infants demonstrated a significant preference for the novel actor in both experiments. These findings suggest that infants can not only discriminate complex and subtle biological motion cues but also detect invariants in such displays.     

Infants' symbolic comprehension of actions modeled with toy replicas

While very young children's understanding of objects as symbols for other entities has been the focus of much investigation, very little is known concerning the emergence of comprehension for symbolic relations among actions modeled with toy replicas and their real counterparts. We used videotaped depictions of real actions in a preferential looking task to assess toddlers' ability to comprehend such connections for action categories aligned with familiar object concepts. Across two experiments, 16- and 18-month-olds provided no evidence of understanding such relations, even when action categories were highlighted with verbal prompts. Among 24- and 26-month-olds, comprehension of relations between certain actions modeled with toys and videos of their real-world counterparts began to emerge, independent of expressive vocabulary size. Implications of our results for theoretical conclusions drawn from use of the generalized imitation procedure to study early conceptual development are discussed.     

Infants' perception of goal‐directed actions on video

Imitation studies and object search studies show that infants have difficulties using action information presented on video to guide their own behaviour. The present study investigated whether infants also have problems interpreting information shown on video relative to real live information. It was examined whether 6‐month‐olds interpret an action with a salient action effect as goal‐directed when it is performed by an actor on a video‐screen and when it is performed by a live actor. A video presentation of a goal‐directed action display was presented to one group of infants, and another group received the same action display, matched in all details, live on a stage. Results indicate that 6‐month‐olds in the video group as well as in the live group interpreted the human action as goal‐directed. Moreover, comparison across both groups revealed no difference in the overall looking pattern between the video and the live presentation group. Thus, our findings show that infants as young as 6 months of age can take important information from video clips and interpret televised actions in meaningful ways that is equivalent to their interpretation of live actions.     

Infants' use of material properties to guide their actions with differently weighted objects

Two studies with 9‐, 11‐ and 13‐month‐old infants were conducted to investigate infants' ability to use an object's material properties to guide their object‐directed actions. In study 1, 9‐ and 11‐month‐old infants played in an exploration phase with two objects made of different materials, one very heavy and the other one light and playable. Subsequently, when given the choice between both objects in a preferential reaching task, only the 11‐month‐olds' used the object's material information to remember and choose the lighter object. In study 2, 11‐ and 13‐month‐old infants underwent the same exploration phase. In the test phase, novel objects made of the same materials were offered. The 13‐ but not the 11‐month‐olds chose the objects made from the same material as the lighter object in the exploration phase. Additionally, infants' performances in the reaching task were positively correlated with their exploratory behaviour during the exploration phase. Altogether, the studies show a developmental progression in the use of an object's material information to guide infants' action. The results are discussed in respect to infants' perception of object properties and their implications for the development of physical knowledge. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient versus flexible mentalizing in complex social settings: Exploring signature limits

Wu, Sheppard, and Mitchell (Br. J. Psychol., 2016; 107, 1–22) investigate in a fascinating study the fact that adults can detect empathic traits in others after only briefly watching or listening to a person. In this commentary, we highlight how the processes of an efficient, implicit, but inflexible mentalizing system are likely to operate in such situations. Further, we specify how testing signature limits over time‐, attribute‐, and protagonist‐restrictions can help distinguish whether an efficient‐implicit or flexible‐explicit mentalizing system is of relevance when processing complex social settings.     

Infants' mu suppression during the observation of real and mimicked goal‐directed actions

Since their discovery in the early 1990s, mirror neurons have been proposed to be related to many social‐communicative abilities, such as imitation. However, research into the early manifestations of the putative neural mirroring system and its role in early social development is still inconclusive. In the current EEG study, mu suppression, generally thought to reflect activity in neural mirroring systems was investigated in 18‐ to 30‐month‐olds during the observation of object manipulations as well as mimicked actions. EEG power data recorded from frontal, central, and parietal electrodes were analysed. As predicted, based on previous research, mu wave suppression was found over central electrodes during action observation and execution. In addition, a similar suppression was found during the observation of intransitive, mimicked hand movements. To a lesser extent, the results also showed mu suppression at parietal electrode sites, over all three conditions. Mu wave suppression during the observation of hand movements and during the execution of actions was significantly correlated with quality of imitation, but not with age or language level.     

Speed limits: orientation and semantic context interactions constrain natural scene discrimination dynamics

The visual system rapidly extracts information about objects from the cluttered natural environment. In 5 experiments, the authors quantified the influence of orientation and semantics on the classification speed of objects in natural scenes, particularly with regard to object-context interactions. Natural scene photographs were presented in an object-discrimination task and pattern masked with various scene-to-mask stimulus-onset asynchronies (SOAs). Full psychometric functions and reaction times (RTs) were measured. The authors found that (a) rotating the full scenes increased threshold SOA at intermediate rotation angles but not for inversion; (b) rotating object or context degraded classification performance in a similar manner; (c) semantically congruent contexts had negligible facilitatory effects on object classification compared with meaningless baseline contexts with a matching contrast structure, but incongruent contexts severely degraded performance; (d) any object-context incongruence (orientation or semantic) increased RTs at longer SOAs, indicating dependent processing of object and context; and (e) facilitatory effects of context emerged only when the context shortly preceded the object. The authors conclude that the effects of natural scene context on object classification are primarily inhibitory and discuss possible reasons.     

Behavioral limits of auditory temporal resolution in the rat: amplitude modulation and duration discrimination

Thresholds for detecting the presence of amplitude modulation in a noise carrier were determined for rats using conditioned avoidance procedures. There was a progressive increase in threshold with modulation rates between 5 Hz and 2 kHz. Further tests were conducted to determine difference thresholds for detecting an increase in modulation rate for standard rates of 10, 50, and 100 Hz. The size of the difference threshold increased progressively as the standard rate increased. In addition, thresholds for detecting an increase in the duration of a noise burst were determined for various standard durations. The difference thresholds were constant for values between 10 and 50 ms but increased progressively, with standard durations between 0.1 and 1.0 s.     

Infant discrimination of faces in naturalistic events: actions are more salient than faces

Despite the fact that faces are typically seen in the context of dynamic events, there is little research on infants' perception of moving faces. L. E. Bahrick, L. J. Gogate, and I. Ruiz (2002) demonstrated that 5-month-old infants discriminate and remember repetitive actions but not the faces of the women performing the actions. The present research tested an attentional salience explanation for these findings: that dynamic faces are discriminable to infants, but more salient actions compete for attention. Results demonstrated that 5-month-old infants discriminated faces in the context of actions when they had longer familiarization time (Experiment 1) and following habituation to a single person performing 3 different activities (Experiment 2). Further, 7-month-old infants who have had more experience with social events also discriminated faces in the context of actions. Overall, however, discrimination of actions was more robust and occurred earlier in processing time than discrimination of dynamic faces. These findings support an attentional salience hypothesis and indicate that faces are not special in the context of actions in early infancy.     

Core knowledge and its limits: The domain of food

Adults, preschool children, and nonhuman primates detect and categorize food objects according to substance information, conveyed primarily by color and texture. In contrast, they perceive and categorize artifacts primarily by shape and rigidity. The present experiments investigated the origins of this distinction. Using a looking time procedure, Experiment 1 extended previous findings that rhesus macaques (Macaca mulatta) generalize learning about novel food objects by color over changes in shape. Six additional experiments then investigated whether human infants show the same signature patterns of perception and generalization. Nine-month-old infants failed to detect food objects in accord with their intrinsic properties, in contrast to rhesus monkeys tested in previous research with identical displays. Eight-month-old infants did not privilege substance information over other features when categorizing foods, even though they detected and remembered this information. Moreover, infants showed the same property generalization patterns when presented with foods and tools. The category-specific patterns of perception and categorization shown by human adults, children, and adult monkeys therefore were not found in human infants, providing evidence for limits to infants’ domains of knowledge.