Anticipatory Eye Movements Reveal Infants' Auditory and Visual Categories

We introduce a new paradigm for the assessment of auditory and visual categories in 6‐month‐old infants using a 2‐alternative anticipatory eye‐movement response. Infants were trained by 2 different methods to anticipate the location of a visual reinforcer at 1 of 2 spatial locations (right or left) based on the identity of 2 cuing stimuli. After a training phase, infants were presented with a series of generalization trials in which novel (untrained) stimuli served as the cue to the anticipatory eye movement. Four experiments illustrated that infants can learn the 2‐choice discriminative response during training. Infants also showed anticipatory eye movements to novel stimuli, indicating sensitivity to variations along a variety of stimulus dimensions (e.g., color, shape, orientation, spatial frequency, pitch, and duration). In addition, the paradigm can be used to assess categorization in individual infants, thereby revealing the stimulus dimensions to which infants naturally attend.     

Faces Attract Infants' Attention in Complex Displays

Infant's face preferences have previously been assessed in displays containing 1 or 2 faces. Here we present 6‐month‐old infants with a complex visual array containing faces among multiple visual objects. Despite the competing objects, infants direct their first saccade toward faces more frequently than expected by chance (Experiment 1). The attention‐grabbing effect of faces is not selective to upright faces (Experiment 2) but does require the presence of internal facial elements, as faces whose interior has been phase‐scrambled did not attract infants' attention (Experiment 3). On the contrary, when the number of fixations is considered, upright faces are scanned more extensively than both inverted and phase‐scrambled faces. The difference in selectivity between the first look measure and the fixation count measure is discussed in light of a distinction between attention‐grabbing and attention‐holding mechanisms.     

Developmental Changes in Visual Scanning of Dynamic Faces and Abstract Stimuli in Infants: A Longitudinal Study

The characteristics of scanning patterns between the ages of 6 and 26 weeks were investigated through repeated assessments of 10 infants. Eye movements were recorded using a corneal‐reflection system while the infants looked at 2 dynamic stimuli: the naturally moving face of their mother and an abstract stimulus. Results indicated that the way infants scanned these stimuli stabilized only after 18 weeks, which is slightly later than the ages reported in the literature on infants' scanning of static stimuli. This effect was especially prominent for the abstract stimulus. From the 14‐week session on, infants adapted their scanning behavior to the stimulus characteristics. When scanning the video of their mother's face, infants directed their gaze at the mouth and eye region most often. Even at the youngest age, there was no indication of an edge effect.     

Behavioral and Cortical Measures of Infants' Visual Expectations

Features of the habituation paradigm were combined with the visual expectation paradigm to examine behavioral and cortical indexes of infants' visual expectations. Eight 3‐month‐old infants watched an alternating picture sequence while their eye movements were videotaped and their cortical electrophysiological activity (event‐related potential [ERP]) was recorded. Two ERP epochs were examined: a 3,000‐msec stimulus‐locked epoch included 1,000 msec before stimulus onset through 1,000 msec after stimulus offset; and a 1,200‐msec response‐locked epoch included 700 msec before saccade onset through 500 msec after the saccade. All infants anticipated upcoming pictures, and eye movement latencies for pictures that were not anticipated were comparable to saccade latencies reported in other visual expectation studies of infants at this age. Three components were identified in the stimulus‐locked ERP waveform: a slowly developing negativity prior to picture onset, a postonset negative slow wave, and a late negative deflection that peaked about 750 msec after picture onset. All stimulus‐locked components were larger for familiar than for unfamiliar pictures; prestimulus negativity was also greater before anticipated pictures. The response‐locked waveform contained 2 prominent features: a slowly increasing negative shift (NS) that began about 500 msec before saccade onset and a positive presaccadic potential that occurred about 30 to 90 msec before the saccade. Response‐locked components were larger for anticipatory saccades at the frontal scalp site; for reactive saccades, response‐locked components were larger at the vertex. Results are informative about ERPs in infants, cortical control of eye movements, and the development of visual expectations.     

Bimodal Dynamics of Faces and Voices Influence Older Infants' Perception of Emotion

Given the importance of infants' perception of bimodal speech for emerging language and emotion development, this study used eye‐tracking technology to examine infants' attention to face+voice displays differing by emotion (fear, sad, happy) and visual stimulus (dynamic versus static). Peripheral distracters were presented to measure attention disengagement. It was predicted that infants would look longer at and disengage more slowly from dynamic bimodal emotion displays, especially when viewing dynamic fear. However, the results from twenty‐two 10‐month‐olds found significantly greater attention on dynamic versus static trials, independent of emotion. Interestingly, infants looked equally to mouth and eye regions of speakers' faces except when viewing/hearing dynamic fear; in this case, they fixated more on the speakers' mouth region. Average latencies to distracters were longer on dynamic compared to static bimodal stimuli, but not differentiated by emotion. Thus, infants' attention was enhanced (in terms of both elicitation and maintenance) by dynamic, bimodal emotion displays. Results are compared to conflicting findings using static emotion displays, with suggestions for future research using more ecologically relevant dynamic, multimodal displays to gain a richer understanding of infants' processing of emotion.     

Individual Differences in Infants' Recognition of Briefly Presented Visual Stimuli

Infants' recognition memory has been shown to be related to individual differences in look duration and level of heart period variability. This study examined the effect of individual differences in these 2 measures on infants' recognition of briefly presented visual stimuli using a paired‐comparison recognition‐memory paradigm. A sample of 35 full‐term infants was studied longitudinally at 14, 20, and 26 weeks of age. Recognition memory for briefly presented stimuli was tested in 6 experimental conditions, with delays corresponding to different heart‐rate‐defined phases of attention. The 20‐and 26‐week‐old infants, and infants with high levels of heart period variability, generally showed more evidence of recognition memory for briefly presented visual stimuli. Greater evidence of recognition memory was observed when stimuli were presented during sustained attention. Infants with more mature baseline physiological responses show greater evidence of recognition memory, and stimulus and procedural factors may be more important for the study of individual differences in infant visual attention than has previously been suggested.     

Developmental Differences in Infants' Attention to Social and Nonsocial Threats

Research has demonstrated that humans detect threatening stimuli more rapidly than nonthreatening stimuli. Although the literature presumes that biases for threat should be normative, present early in development, evident across multiple forms of threat, and stable across individuals, developmental work in this area is limited. Here, we examine the developmental differences in infants' (4‐ to 24‐month‐olds) attention to social (angry faces) and nonsocial (snakes) threats using a new age‐appropriate dot‐probe task. In Experiment 1, infants' first fixations were more often to snakes than to frogs, and they were faster to fixate probes that appeared in place of snakes vs. frogs. There were no significant age differences, suggesting that a perceptual bias for snakes is present early in life and stable across infancy. In Experiment 2, infants fixated probes more quickly after viewing any trials that contained an angry face compared to trials that contained a happy face. Further, there were age‐related changes in infants' responses to face stimuli, with a general increase in looking time to faces before the probe and an increase in latency to fixate the probe after seeing angry faces. Together, this work suggests that different developmental mechanisms may be responsible for attentional biases for social vs. nonsocial threats.     

The Nature of Infants' Visual Expectations for Event Content

Recent studies have revealed that young infants can form expectations for the spatial location of future visual events. Four experiments examined whether 3‐month‐old infants also form expectations for content features of events, defined as an invariant color combination. Infants viewed a spatially alternating (left–right) sequence of varying pictures in which pictures on one side (invariant colors) always appeared with the same color combination (e.g., red/green), while on the other side (varied colors) the pictures appeared with any of 4 possible color combinations. Results indicated that infants formed a content expectation for the invariant color combination on the invariant side, such that their anticipatory responding was disrupted by a novel color combination event and by a novel pattern event. A dissociation between reactive and anticipatory eye movements in their sensitivity to the content manipulation suggests that infants' expectations for spatial and content information engage somewhat different processes.     

Newborn Infants' Preference for Attractive Faces: The Role of Internal and External Facial Features

Several previous experiments have found that newborn and young infants will spend more time looking at attractive faces when these are shown paired with faces judged by adults to be unattractive. Two experimental conditions are described with the aim of finding whether the “attractiveness effect” results from attention to internal or external facial features, or both. Pairs of attractive and less attractive faces (as judged by adults) were shown to newborn infants (mean age 2 days, 9 hours), where each pair had either identical internal features (and different external features) or identical external features (and different internal features). In the latter, but not the former, condition the infants looked longer at the attractive faces. These findings are clear evidence that newborn infants use information about internal facial features in making preferences based on attractiveness. It is suggested that when newborn (and older) infants are presented with facial stimuli, whether dynamic or static, they are able to attend both to internal and external facial features.     

Infants' ERP Responses to Novel and Familiar Stimuli Change Over Time: Implications for Novelty Detection and Memory

Detection of novelty is an important cognitive ability early in development, when infants must learn a great deal about their world. Work with adults has identified networks of brain areas involved in novelty detection; this study investigated electrophysiological correlates of detection of novelty and recognition of familiarity in 9‐month‐old infants, using event‐related potentials (ERPs). Infants were familiarized with an event in the laboratory, then ERPs were recorded as they viewed repeated presentations of pictures of this familiar event and a novel event, along with single presentations of 30 trial‐unique events. A middle‐latency negative component was sensitive to degree of novelty, differing in amplitude and latency by stimulus condition and across repeated presentations. Long‐latency slow‐wave activity also related to stimulus condition. Findings have implications for our understanding of infants' detection of novel information and the processes that render the novel familiar.     

Infants' Preferences for Familiarity and Novelty During the Course of Visual Processing

At 4 1/2 months, infants were shown a series of brief choice trials between a stimulus that always remained the same and another that was different on every trial. The point when a consistent preference for the novel stimulus commenced was identified for each infant, and their preferences for the familiar and novel stimuli in trials preceding that point were examined. Infants who saw objects or faces as stimuli both exhibited selective attention to the familiar stimulus prior to preferring novel stimuli, although infants shown kaleidoscope patterns did not. These results document a preference for familiarity early in processing with a procedure that is not subject to ambiguities due to individual differences in processing speed or to collapsing data across infants. The results support a nonlinear model for memory formation during infancy and underscore recently voiced concerns that in research on cognitive development, infants' attention to perceptual familiarity‐novelty must be carefully disentangled from conceptual knowledge.     

Infants' Visual Recognition of Pincer Grip Emerges Between 9 and 12 Months of Age

The development of the ability to recognize the whole human body shape has long been investigated in infants, while less is known about their ability to recognize the shape of single body parts, and in particular their biomechanical constraints. This study aimed to explore whether 9‐ and 12‐month‐old infants have knowledge of a hand‐grasping movement (i.e., pincer grip), being able to recognize violations of the hand's anatomical constraints during the observation of that movement. Using a preferential looking paradigm, we showed that 12‐month‐olds discriminate between biomechanically possible and impossible pincer grips, preferring the former over the latter (Experiment 1). This capacity begins to emerge by 9 months of age, modulated by infants' own sensorimotor experience with pincer grip (Experiment 2). Our findings indicate that the ability to visually discriminate between pincer grasps differing in their biomechanical properties develops between 9 and 12 months of age, and that experience with self‐produced hand movements might help infants in building a representation of the hand that encompasses knowledge of the physical constraints of this body part.     

Perceiving the Real World: Infants' Detection of and Memory for Social Information

Research on infants' perception and memory for social information are discussed with respect to the concept of ecological validity. We argue that the use of dynamic, multimodal displays in familiar contexts is critical to understanding infants' developing perception. We also discuss the importance of generalizing appropriately from experimental to real‐world contexts and of using converging methods in the investigation of infants' capabilities.     

An Eye Tracking Investigation of Color–Location Binding in Infants' Visual Short‐Term Memory

Two experiments examined 8‐ and 10‐month‐old infants' (N = 71) binding of object identity (color) and location information in visual short‐term memory (VSTM) using a one‐shot change detection task. Building on previous work using the simultaneous streams change detection task, we confirmed that 8‐ and 10‐month‐old infants are sensitive to changes in binding between identity and location in VSTM. Further, we demonstrated that infants recognize specifically what changed in these events. Thus, infants' VSTM for binding is robust and can be observed in different procedures and with different stimuli.     

Auditory Distress Signals Potentiate Attentional Bias to Fearful Faces: Evidence for Multimodal Facilitation of Spatial Attention by Emotion

Unimodal emotionally salient visual and auditory stimuli capture attention and have been found to do so cross-modally. However, little is known about the combined influences of auditory and visual threat cues on directing spatial attention. In particular, fearful facial expressions signal the presence of danger and capture attention. Yet, it is unknown whether human auditory distress signals that accompany fearful facial expressions potentiate their capture of attention. It was hypothesized that the capture of attention by fearful faces would be enhanced when co-presented with auditory distress signals. To test this hypothesis, we used a modified multimodal dot-probe task where fearful faces were paired with three sound categories: no sound control, non-distressing human vocalizations, and distressing human vocalizations. Fearful faces captured attention across all three sound conditions. In addition, this effect was potentiated when fearful faces were paired with auditory distress signals. The results provide initial evidence suggesting that emotional attention is facilitated by multisensory integration.     

Shake,Rattle, and … One or Two Objects? Young Infants' Use of Auditory Information to Individuate Objects

Most research on object individuation in infants has focused on the visual domain. Yet the problem of object individuation is not unique to the visual system, but shared by other sensory modalities. This research examined 4.5‐month‐old infants' capacity to use auditory information to individuate objects. Infants were presented with events in which they heard 2 distinct sounds, separated by a temporal gap, emanate from behind a wide screen; the screen was then lowered to reveal 1 or 2 objects. Longer looking to the 1‐ than 2‐object display was taken as evidence that the infants (a) interpreted the auditory event as involving 2 objects and (b) found the presence of only 1 object when the screen was lowered unexpected. The results indicated that the infants used sounds produced by rattles, but not sounds produced by an electronic keyboard, as the basis for object individuation (Experiments 1 and 2). Data collected with adult participants revealed that adults are also more sensitive to rattle sounds than electronic tones. A final experiment assessed conditions under which young infants attend to rattle sounds (Experiment 3). Collectively, the outcomes of these experiments suggest that infants and adults are more likely to use some sounds than others as the basis for individuating objects. We propose that these results reflect a processing bias to attend to sounds that reveal something about the physical properties of an object—sounds that are obviously linked to object structure—when determining object identity.     

Toddlers Activate Lexical Semantic Knowledge in the Absence of Visual Referents: Evidence from Auditory Priming

Language learners rapidly acquire extensive semantic knowledge, but the development of this knowledge is difficult to study, in part because it is difficult to assess young children's lexical semantic representations. In our studies, we solved this problem by investigating lexical semantic knowledge in 24‐month‐olds using the Head‐turn Preference Procedure. In Experiment 1, looking times to a repeating spoken word stimulus (e.g., kitty‐kitty‐kitty) were shorter for trials preceded by a semantically related word (e.g., dog‐dog‐dog) than trials preceded by an unrelated word (e.g., juice‐juice‐juice). Experiment 2 yielded similar results using a method in which pairs of words were presented on the same trial. The studies provide evidence that young children activate of lexical semantic knowledge, and critically, that they do so in the absence of visual referents or sentence contexts. Auditory lexical priming is a promising technique for studying the development and structure of semantic knowledge in young children.     

Infants' identification of gender in biological motion displays

Infants' knowledge of social categories, including gender-typed characteristics, is a vital aspect of social cognitive development. In the current study, we examined 9- to 12-month-old infants' understanding of the categories “male” and “female” by testing for gender matching in voices or faces with biological motion depicted in point light displays (PLDs). Infants did not show voice–PLD gender matching spontaneously (Experiment 1) or after “training” with gender-matching voice–PLD pairs (Experiment 2). In Experiment 3, however, infants were trained with gender-matching face–PLD pairs and we found that patterns of visual attention to top regions of PLD stimuli during training predicted gender matching of female faces and PLDs. Prior to the end of the first postnatal year, therefore, infants may begin to identify gender in human walk motions, and perhaps form social categories from biological motion.     

Object Representation in Infants' Coordination of Manipulative Force

This study examined infants' use of object knowledge for scaling the manipulative force of object‐directed actions. Infants 9, 12, and 15 months of age were outfitted with motion‐analysis sensors on their arms and then presented with stimulus objects to examine individually over a series of familiarization trials. Two stimulus objects were used in the familiarization phase, and were identical in size, shape, and material, but different in color and weight. Following familiarization, two test objects that had been hidden from view were presented. The test objects were identical in appearance to the familiarization objects, but their color‐weight correspondence was reversed. Infants' actions on the test objects revealed selective, differential preparation for the specific weights experienced during familiarization. Because the objects were equivalent in their visual affordances for action, the differential preparation and coordination of manipulative force was based on knowledge acquired during the familiarization phase. Infants are capable of utilizing object representations to coordinate manipulative force in object‐directed actions.