A comparison of monocular and binocular depth perception in 5- and 7-month-old infants

Monocular depth perception was compared with binocular depth perception in 5- and 7-month-old infants. Reaching was used as the dependent measure. Two objects, identical except in size, were presented simultaneously to each infant. The smaller object was within reach for the infants while the larger object was just beyond reach. The two objects subtended equal visual angles from the infants' observation point. With binocular presentation, 96% of the 7-month-olds' reaches and 89% of the 5-month-olds' reaches were for the nearer object. With monocular presentation, 58% of the 7-month-olds' reaches and 65% of the 5-month-olds' reaches were for the nearer object. The reaching preferences observed in the monocular condition indicated sensitivity to monocular depth information (motion parallax, accommodation, and relative size information were available). Binocular viewing, however, resulted in a far more consistent tendency to reach for the nearer object. This result suggests that the infants' perception of the objects' distances was more veridical in the binocular condition than in the monocular condition.     

Perceptual transparency in 3- to 4-month-old infants

We examined perceptual transparency in infants. In a previous study, Johnson and Aslin (2000 Developmental Psychology 36 808 - 816) found that 4-month-olds could perceive transparency in a moving chromatic display, but not in an achromatic display. In this study, we further examined perceptual transparency in infants using a static achromatic display. Considering the development of figural organisation and contrast sensitivity, we assumed that 3- to 4-month-olds would perceive transparency even in a static achromatic display. We created a transparency and a non-transparent display composed of a partially overlapping circle and square, by switching the colours. Infants aged 3 to 4 months (n = 24) were familiarised with the transparency display (experiment 1) or with the non-transparent display (experiment 2). Then, they were confronted with a uniform colour and a two-colour figure. Infants showed novelty preference for the two-colour figure after they had been familiarised with the transparency display (experiment 1), but not after they had been familiarised with the non-transparent display (experiment 2). These results suggest that 3- to 4-month-old infants can perceive transparency in a static achromatic display.     

Gaze following as a function of affective expression in 3-, 6- and 9-month-old infants

The influence of affective expression on gaze following was investigated in 3-, 6- and 9-month-old infants. Gaze following became more robust at the older ages. There was no strong evidence that infants' gaze following activity was differentially influenced by the adult's affective expression, but rather for a developmental difference in emotion processing.     

Perceptual sensitivity and motoric competence in 5- and 6-month-old infants

The authors explored whether 5- to 6-month-old infants were sensitive to perceptual information and how they used perception as a recognition cue to search for a hidden object. In addition, the authors categorized and examined infant grasp by developmental effectiveness to determine any impact on infant search behaviors. In a within-participants design, 20 infants were presented with a toy in 2 occluder conditions. The toy was hidden under either a thick, camouflaging cloth or a thin, semitransparent cloth. The data revealed significant effects of perceptual sensitivity, age, and motor sophistication on search tasks. The results suggest that motor competence might be a limiting factor in infants' abilities to link motoric responses to notions about an object.     

Face detection in complex visual displays: an eye-tracking study with 3- and 6-month-old infants and adults

The ability to detect and prefer a face when embedded in complex visual displays was investigated in 3- and 6-month-old infants, as well as in adults, through a modified version of the visual search paradigm and the recording of eye movements. Participants (N=43) were shown 32 visual displays that comprised a target face among 3 or 5 heterogeneous objects as distractors. Results demonstrated that faces captured and maintained adults' and 6-month-olds' attention, but not 3-month-olds' attention. Overall, the current study contributes to knowledge of the capacity of social stimuli to attract and maintain visual attention over other complex objects in young infants as well as in adults.     

Speed discrimination in 6- and 10-month-old infants follows Weber's law

The speed of a moving object is a critical variable that factors into actions such as crossing a street and catching a ball. However, it is not clear when the ability to discriminate between different speeds develops. Here, we investigated speed discrimination in 6- and 10-month-old infants using a habituation paradigm showing infants events of a ball rolling at different speeds. The 6-month-olds looked longer at novel speeds that differed by a 1:2 ratio than at the familiar ones but showed no difference in looking time to speeds that differed by a 2:3 ratio. In contrast, the 10-month-olds succeeded at discriminating a 2:3 ratio. For both age groups, discrimination was modulated by the ratio between novel and familiar speeds, suggesting that speed discrimination is subject to Weber's law. These findings show striking parallels to previous results in infants' discrimination of duration, size, and number and suggest a shared system for processing different magnitudes.     

Syllabic pitch perception in 2- to 3-month-old infants

The pitch patterns present in speech addressed to infants may play an important role in perceptual processing by infants. In this study, the high-amplitude sucking procedure was used to assess discrimination by 2- to 3-month-old infants of rising versus falling pitch patterns in 400-msec synthetic [ra] and [la] tokens. The syllables’ intonation contour was modeled on infant-directed speech, and covered a range characteristic of an adult female speaker (180–300 Hz). Group data indicated that the 2- to 3-month-old infants discriminated the pitch contour for both stimuli. Results are discussed with reference to previous studies of syllabic pitch perception.     

The development of preferences for own-race versus other-race faces in 3-, 6- and 9-month-old Caucasian infants

Visual preferences for pairs of African and Caucasian faces were repeatedly assessed in 3-, 6- and 9-month-old Caucasian infants with a preferential looking paradigm. Two different patterns of preference development were found: First, the spontaneous own-race preference at three months reported in the literature tilts to a preference for other-race faces at nine months passing through a null-preference at six months. This replicates the pattern recently reported for Asian infants [Liu et al. (2015). Development of visual preference for own- versus other-race faces in infancy. Developmental Psychology. doi:10.1037/a0038835]. Second, at all three ages fixation time towards Caucasian faces significantly reduces across the consecutive trial presentation. This is a similar effect as in novelty preference studies to occur after a sufficiently long familiarization phase. Both patterns can be explained in terms of an advantaged own-race face processing with the emerging Other-Race-Effect.     

Object individuation and labelling in 6-month-old infants

The ability to determine how many objects are involved in physical events is fundamental for reasoning about the world that surrounds us. Previous studies suggest that infants can fail to individuate objects in ambiguous occlusion events until their first birthday and that learning words for the objects may play a crucial role in the development of this ability. The present eye-tracking study tested whether the classical object individuation experiments underestimate young infants’ ability to individuate objects and the role word learning plays in this process. Three groups of 6-month-old infants (N = 72) saw two opaque boxes side by side on the eye-tracker screen so that the content of the boxes was not visible. During a familiarization phase, two visually identical objects emerged sequentially from one box and two visually different objects from the other box. For one group of infants the familiarization was silent (Visual Only condition). For a second group of infants the objects were accompanied with nonsense words so that objects’ shape and linguistic labels indicated the same number of objects in the two boxes (Visual & Language condition). For the third group of infants, objects’ shape and linguistic labels were in conflict (Visual vs. Language condition). Following the familiarization, it was revealed that both boxes contained the same number of objects (e.g. one or two). In the Visual Only condition, infants looked longer to the box with incorrect number of objects at test, showing that they could individuate objects using visual cues alone. In the Visual & Language condition infants showed the same looking pattern. However, in the Visual vs Language condition infants looked longer to the box with incorrect number of objects according to linguistic labels. The results show that infants can individuate objects in a complex object individuation paradigm considerably earlier than previously thought and that linguistic cues enforce their own preference in object individuation. The results are consistent with the idea that when language and visual information are in conflict, language can exert an influence on how young infants reason about the visual world.     

Large number discrimination in 6-month-old infants

Two experiments with the Stroop paradigm were conducted to investigate the role of phonological codes in access to the meaning of Chinese characters. Subjects named the ink color of viewed characters or color patches. Key items were color characters, their homophones with the same tone, homophones with different tones, and semantic associates. Apart from finding the usual Stroop interference effect, homophones produced significant interference in the incongruent condition, provided that they had the same tone as the color characters. The interference effect from homophones, however, was significantly smaller than that from color characters. Semantic associates generated an interference effect in the incongruent condition, an effect of the same magnitude as the effect from the same-tone homophones. Finally, in the congruent conditions, all the key items yielded facilitations compared to neutral controls, though the facilitation from color characters was larger than the facilitations from other types of characters. These findings suggest that phonological codes in Chinese are activated obligatorily and provide early sources of constraint in access to meaning.     

Neural markers of categorization in 6-month-old infants

Little is known of the neural processes that underlie concept-formation abilities in human infants. We investigated category-learning processes in infants both by using a common behavioral measure and by recording the brain's electrical activity (event-related potentials, or ERPs). ERPs were recorded while 6-month-olds viewed cat images during training, followed by novel cat images interspersed with novel dog images during test. The data indicate that distinct neural signals correspond with learning of a category presented during familiarization, preferential responding to a novel category, and representation of category exemplars at multiple levels of inclusiveness. The results suggest that fundamental components of the neural architecture supporting object categorization are functional within the first half-year of postnatal life, before infants acquire language and young children engage in formal learning of semantic categories. The findings are discussed in terms of their implications for models of category learning and development.     

Hand-use preference for reaching and object manipulation in 6- through 13-month-old infants

Validity, reliability, and stability of separate assessment of hand-use preferences for reaching, object manipulation, and complementary bimanual action were determined for 6 through 13 month-old male and female infants. Only hand-use preferences for complementary bimanual action varied with age. Females had more distinct hand-use preference than males but only for object manipulation. Comparison of hand-use preference among these different sensorimotor skills can provide a richer evaluation of infant handedness status required for systematic study of the development of neuropsychological functions during infancy.     

The still-face response in newborn, 1.5-, and 3-month-old infants

The present study investigated the still-face response to a female stranger in newborn, 1.5-, and 3-month-old infants. The results revealed that 1.5- and 3-month-olds, but not newborns, reliably decreased their visual attention and positive affect when the interaction partner became unresponsive during the still-face period.     

Heart-rate deceleration and smiling in 3-month-old infants

The relation between heart-rate deceleration and the expression of positive affect in infancy is examined by testing the hypothesis that intensity of orienting (as indexed by heart-rate deceleration) is predictive of intensity of positive affect (smile size and duration). A social-stimulation procedure was utilized to elicit smiles in 41 3-month-old infants. The first smile elicited was coded for smile size and duration, and the preceding heart-rate deceleration was coded for magnitude, duration, and slope of deceleration. Slope and duration of heart-rate deceleration proved to be reliable predictors of smile size, but none of the heart-rate measures correlated with smile duration. Results suggest that the steeper and more rapid the deceleration, the larger the ensuing smile. Possible mechanisms for this finding are discussed.     

A cross-sequential assessment of the occurrences of pointing in 3- to 12-month-old human infants

This study presents evidence that a developmental continuity exists between early forms of “pointing” and the later, mature form of social gesturing seen during the latter half of the first year of life. Sixteen infants and their mothers were observed in two different conditions of face-to-face interaction during the first year of life (“mother-alone” and “mother-toy”). The rate (adjusted frequency), proportion (percent of total time), and mean duration of pointing were derived from each infant's videotaped sessions. In addition, the degree of co-occurrence between pointing and selected infant and maternal behaviors was assessed. Significant differences by interactional condition and by hand (right or left) were noted for the proportion and mean duration of pointing; however, none of the tests of co-occurrence were significant. Although there was little indication of a functional continuity between early and later appearing forms of pointing, the general findings indicated a potential morphological continuity that had previously been overlooked. It is suggested that a different developmental approach may be necessary to explain the changes in the structural and functional components of this gesture during the first year of life.     

Diet and gender influences on processing and discrimination of speech sounds in 3- and 6-month-old infants: a developmental ERP study

Early post-natal nutrition influences later development, but there are no studies comparing brain function in healthy infants as a function of dietary intake even though the major infant diets differ significantly in nutrient composition. We studied brain responses (event-related potentials; ERPs) to speech sounds for infants who were fed either breast milk (BF), milk-based formula (MF), or soy formula (SF) during the first 6 months of life. Two syllables presented in an oddball paradigm elicited a late positive wave (P350) from temporal and frontal brain regions involved in language processes. All groups showed significantly greater response amplitudes to the infrequent syllable across sites at 3 months and frontally at 6 months, but significant discrimination at temporal sites was only observed at 6 months in BF infants. Decreases in response amplitudes from 3 to 6 months were greater for the frequently presented syllable, most prominent in BF infants, and greater in females than males. The results indicate greater syllable discrimination in BF than formula-fed infants, but whether this can be attributed to dietary influences alone remains unclear. Feeding method and background factor differences between breastfed and formula-fed infants may also contribute to the observed differences. The general absence of differences between formula-fed groups is notable and suggests that milk-based formula and soy formula equally support brain development and function during the first post-natal 6 months. Finally, the results indicate gender differences in the development of neural and temporal processes involved in sensory discrimination, and suggest that at 6 months these processes are better developed in females.     

Social looking,social referencing and humor perception in 6- and-12-month-old infants

Social referencing refers to infants’ use of caregivers as emotional referents in ambiguous situations (Walden, 1993). Studies of social referencing typically require ambulation, thereby over-looking younger, non-ambulatory infants (i.e., ≤8-months) and resulting in a widespread assumption that young infants do not employ this strategy. Using a novel approach that does not require mobility, we found that when parents provided unsolicited affective cues during an ambiguous-absurd (i.e., humorous) event, 6-month-olds employ one component of social referencing, social looking Additionally, 6-month-olds who did not laugh at the event were significantly more likely to look toward parents than their counterparts who found the event funny. Sequential analyses revealed that, following a reference to a smiling parent, 6-month olds were more likely to smile at the parent, but by 12 months were more likely to smile at the event suggesting that older infants are influenced by parental affect in humorous situations. The developmental implications of these findings are discussed, as well as the usefulness of studying humor for understanding important developmental phenomena.     

Night waking in 6-month-old infants and maternal depressive symptoms

Relations between night waking in infants and depressive symptoms in their mothers at 6 months postpartum were examined using the data from the National Institute for Child Health and Human Development Study of Early Child Care. Although more depressive symptoms were only weakly correlated with a higher frequency of infant waking, longer wake times, and more total time awake, the rate of clinically significant depression scores was about double in mothers of chronically waking infants in comparison with mothers whose infants did not awaken during the night. The value of comparing subgroups to elucidate relations identified through correlations is discussed.