Object individuation: infants' use of shape, size, pattern, and color.

Recent research indicates that when an event-monitoring paradigm is used, infants as young as 4.5 months of age demonstrate the ability to use featural information to individuate objects involved in occlusion events (Wilcox & Baillargeon, 1998a, Object individuation in infancy: The use of featural information in reasoning about occlusion events. Cognitive Psychology 37, 97-155; Wilcox & Baillargeon, 1998b, Object individuation in young infants: Further evidence with an event monitoring task. Developmental Science 1, 127-142). For example, in one experiment (Wilcox & Baillargeon, 1998b, Object individuation in young infants: Further evidence with an event monitoring task. Developmental Science 1, 127-142) 4.5-month-old infants saw a test event in which a green ball with colored dots disappeared behind one edge of a narrow or wide screen, and a red box with silver thumbtacks appeared at the other edge; the narrow screen was too narrow to hide both objects simultaneously, whereas the wide screen was sufficiently wide to hide both objects at the same time. The infants looked reliably longer at the narrow- than at the wide-screen test event. These and control results suggested that the infants had: (a) used the featural differences between the ball and box to conclude that two objects were involved in the event; (b) judged that both objects could fit simultaneously behind the wide but not the narrow screen; and hence (c) were surprised by the narrow-screen event. The present experiments build on these initial findings by investigating the features to which infants are most sensitive. Four experiments were conducted with infants 4.5-11.5 months of age using the same procedure, except that only one feature was manipulated at a time: shape, size, pattern, or color. The results indicated that 4.5-month-olds use both shape and size features to individuate objects involved in occlusion events. However, it is not until 7.5 months that infants use pattern, and 11.5 months that infants use color, to reason about object identity. It is suggested that these results reflect biases in the kind of information that infants attend to when reasoning about occlusion events. Possible sources of bias are discussed.     

Priming infants to attend to color and pattern information in an individuation task

Wilcox (Cognition 72 (1999) 125) reported that infants are more sensitive to form than surface features when individuating objects in occlusion events: it is not until 7.5 months that infants spontaneously use pattern information, and 11.5 months that they spontaneously use color information, as the basis for object individuation. The present research assessed the extent to which infants' sensitivity to surface features could be increased under more supportive conditions. More specifically, we examined whether younger infants could be primed to draw on color and pattern features in an individuation task if they were first shown the functional value of attending to color and pattern information (i.e. the color or the pattern of an object predicted the function it would engage in). Five experiments were conducted with infants 4.5 to 9.5 months of age. The main findings were that 9.5- and 7.5-month-olds could be primed to use color information, and 5.5- and 4.5-month-olds could be primed to attend to pattern information, after viewing the function events. The results are discussed in terms of the kinds of experiences that can lead to increased sensitivity to surface features and the mechanisms that support feature priming in young infants.     

Electrophysiological responses to auditory novelty in temperamentally different 9‐month‐old infants

Behavioral reactivity to novel stimuli in the first half‐year of life has been identified as a key aspect of early temperament and a significant precursor of approach and withdrawal tendencies to novelty in later infancy and early childhood. The current study examines the neural signatures of reactivity to novel auditory stimuli in 9‐month‐old infants in relation to prior temperamental reactivity. On the basis of the assessment of behavioral reactivity scores at 4 months of age, infants were classified into groups of high negatively reactive and high positively reactive infants. Along with an unselected control group, these groups of temperamentally different infants were given a three‐stimulus auditory oddball task at 9 months of age which employed frequent standard and infrequent deviant tones as well as a set of complex novel sounds. In comparison to high positively reactive and control infants, high negatively reactive infants displayed increased amplitude of a positive slow wave in the ERP response to deviant tones compared to standard tones. In contrast, high positively reactive infants showed a larger novelty P3 to the complex novel sounds. Results are discussed in terms of optimal levels of novelty for temperamentally different infants.     

Object individuation in young infants: Further evidence with an event-monitoring paradigm

Recent results indicate that, when tested with an event-monitoring task, 7.5- and 9.5-month-olds give evidence that they can individuate objects in different-objects occlusion events – events in which two distinct objects appear successively on either side of an occluder (Wilcox and Baillargeon, in press). The present research sought to confirm and extend these findings. The experiments examined 7.5- and 4.5-month-olds’ ability to correctly interpret a different-objects (ball-box condition) and a same-object (ball-ball condition) occlusion event. The infants in the ball-box condition saw a test event in which a ball disappeared behind the left edge of a screen; after a pause, a box emerged from behind the screen's right edge. For half of the infants (wide-screen event), the screen was wide and could occlude the ball and box simultaneously; for the other infants (narrow-screen event), the screen was narrow and should not have been able to occlude the ball and box at the same time. The infants in the ball-ball condition saw identical wide- and narrow-screen events except that the ball appeared on both sides of the screen. The infants in the ball-box condition looked reliably longer at the narrow- than at the wide-screen event, whereas those in the ball-ball condition tended to look equally at the events. These results suggest that the ball-box infants (a) were led by the featural differences between the ball and box to view them as distinct objects; (b) judged that the ball and box could both be occluded by the wide but not the narrow screen; and (c) were surprised in the narrow-screen event when this judgment was violated. In contrast, the ball-ball infants (a) assumed, based on the featural similarities of the balls that appeared on either side of the screen, that they were one and the same ball, and (b) realized that the ball could be occluded by either the wide or the narrow screen. These results indicate that, by 4.5 months of age, infants are able to use featural information to correctly interpret different-objects and same-object occlusion events. These findings are discussed in the context of the newly-drawn distinction between event-monitoring and event-mapping paradigms (Wilcox and Baillargeon, in press).     

Twelve-month-olds privilege words over other linguistic sounds in an associative learning task

We examined whether 12-month-old infants privilege words over other linguistic stimuli in an associative learning task. Sixty-four infants were presented with sets of either word–object, communicative sound–object, or consonantal sound–object pairings until they habituated. They were then tested on a ‘switch’ in the sound to determine whether they were able to associate the word and/or sound with the novel objects. Infants associated words, but not communicative sounds or consonantal sounds, with novel objects. The results demonstrate that infants exhibit a preference for words over other linguistic stimuli in an associative word learning task. This suggests that by 12 months of age, infants have developed knowledge about the nature of an appropriate sound form for an object label and will privilege this form as an object label.     

Multisensory exploration and object individuation in infancy

Recent research indicates that by 4.5 months, infants use shape and size information as the basis for individuating objects but that it is not until 11.5 months that they use color information for this purpose. The present experiments investigated the extent to which infants' sensitivity to color information could be increased through select experiences. Five experiments were conducted with 10.5- and 9.5-month-olds. The results revealed that multimodal (visual and tactile), but not unimodal (visual only), exploration of the objects prior to the individuation task increased 10.5-month-olds' sensitivity to color differences. These results suggest that multisensory experience with objects facilitates infants' use of color information when individuating objects. In contrast, 9.5-month-olds did not benefit from the multisensory procedure; possible explanations for this finding are explored. Together, these results reveal how an everyday experience--combined visual and tactile exploration of objects--can promote infants' use of color information as the basis for individuating objects. More broadly, these results shed light on the nature of infants' object representations and the cognitive mechanisms that support infants' changing sensitivity to color differences.     

The human first hypothesis: identification of conspecifics and individuation of objects in the young infant

How do infants individuate and track objects, and among them objects belonging to their species, when they can only rely on information about the properties of those objects? We propose the Human First Hypothesis (HFH), which posits that infants possess information about their conspecifics and use it to identify and count objects. F. Xu and S. Carey [Cognitive Psychology, 30(2), 111-153, 1996] argued that before the age of 1 year, infants fail to use property information. To explain their results, Xu and Carey proposed the Object First Hypothesis (OFH), according to which infants under 1 year of age have only the general concept of physical object to identify and count objects. We show that infants have a more extensive knowledge of sortals than that claimed by the OFH. When 10-month-olds see one humanlike and one non-humanlike object, they successfully identify and count them by using the contrast in their properties, as predicted by the HFH. We also show that infants succeed even when they make a decision based on differences between two close basic-level categories such as humanlike objects and doglike objects, but fail when they have to use differences within the human category. Thus, infants treat "human" as a basic sortal, as predicted by the HFH. We argue that our results cannot be accounted for by general purpose mechanisms. Neither the strong version of the OFH and its explanation in terms of object indexing mechanisms [A. M. Leslie, F. Xu, P. Tremoulet, & B. J. Scholl, Trends in Cognitive Sciences, 2(1), 10-18, 1998] nor explanations in terms of task demands [T. Wilcox & R. Baillargeon, Cognitive Psychology, 37(2), 97-155, 1998] are sufficient to explain our results.     

Tuned to the signal: the privileged status of speech for young infants

Do young infants treat speech as a special signal, compared with structurally similar non‐speech sounds? We presented 2‐ to 7‐month‐old infants with nonsense speech sounds and complex non‐speech analogues. The non‐speech analogues retain many of the spectral and temporal properties of the speech signal, including the pitch contour information which is known to be salient to young listeners, and thus provide a stringent test for a potential listening bias for speech. Our results show that infants as young as 2 months of age listened longer to speech sounds. This listening selectivity indicates that early‐functioning biases direct infants’ attention to speech, granting speech a special status in relation to other sounds.     

Delayed development of phonological constancy in toddlers at family risk for dyslexia

Phonological constancy refers to infants’ ability to disregard variations in the phonetic realisation of speech sounds that do not indicate lexical contrast, e.g., when listening to accented speech. In typically-developing infants, this ability develops between 15- and 19-months of age, coinciding with the consolidation of infants’ native phonological competence and vocabulary growth. Here we investigated the developmental time course of phonological constancy in infants at family risk for developmental dyslexia, using a longitudinal design. Developmental dyslexia is a disorder affecting the acquisition of reading and spelling skills, and it also affects early auditory processing, speech perception, and lexical acquisition. Infants at-risk and not at-risk for dyslexia, based on a family history of dyslexia, participated when they were 15-, 19-, and 26-months of age. Phonological constancy was indexed by comparing at-risk and not at-risk infants’ ability to recognise familiar words in two preferential looking tasks: (1) a task using words presented in their native accent, and (2) a task using words presented in a non-native accent. We expected a delay in phonological constancy for the at-risk infants. As predicted, in the non-native accent task, not at-risk infants recognised familiar words by 19 months, but at-risk infants did not. The control infants thus exhibited phonological constancy. By 26 months, at-risk toddlers did show successful word recognition in the native accent task. However, for the non-native accent task at 26 months, neither at-risk nor control infants showed familiar word recognition. These findings are discussed in terms of the impact of family risk for dyslexia on toddlers’ consolidation of early phonological and lexical skills.     

Infants' ability to categorise on the basis of rhyme

Two experiments are described, which investigated 7 - to 13-month-old infants' abilities to categorise syllables according to their ending sounds, or rhymes. Using the Conditioned Headturn (CHT) Procedure, infants were conditioned to turn their head when one set of rhyming CVCs changed to another set of rhyming CVCs. Even the 7 -month-old infants demonstrated an ability to categorise according to rimes. The infants could be separated into three different groups: those who conditioned but did not succeed in a rhyming task; those who succeeded at one rhyming task but not a second; and those infants who succeeded on two rhyming tasks. The infants in the second group were showing an early sensitivity to rhyme. However, they appeared to be learning a very specific rule, listening only for one category of rhyme. The third group of infants was able to extend the initial rule they learned to include new rhymes. This group learned not only to highlight one particular rhyme, but were also able to abstract the previously learned rule to new rhymes, thereby demonstrating a higher level of sophistication in their categorisation of rhymes. These results are discussed in relation to the ontogeny of language learning, and work demonstrating a relationship between rhyming ability and competence in reading and writing.     

The role of language in acquiring object kind concepts in infancy

Four experiments investigated whether 9-month-old infants could use the presence of labels to help them establish a representation of two distinct objects in a complex object individuation task. We found that the presence of two distinct labels facilitated object individuation, but the presence of one label for both objects, two distinct tones, two distinct sounds, or two distinct emotional expressions did not. These findings suggest that language may play an important role in the acquisition of sortal/object kind concepts in infancy: words may serve as "essence placeholders". Implications for the relationship between language and conceptual development are discussed.     

6- to 9-Month old infants discriminate vowel durations in variable speech contexts

Discriminating temporal relationships in speech is crucial for speech and language development. However, temporal variation of vowels is difficult to perceive for young infants when it is determined by surrounding speech sounds. Using a familiarization-discrimination paradigm, we show that English-learning 6- to 9-month-olds are capable of discriminating non-native acoustic vowel duration differences that systematically vary with subsequent consonantal durations. Furthermore, temporal regularity of stimulus presentation potentially makes the task easier for infants. These findings show that young infants can process fine-grained temporal aspects of speech sounds, a capacity that lays the foundation for building a phonological system of their ambient language(s).     

Comparing infants' use of featural and spatiotemporal information in an object individuation task using a new event-monitoring design

Discussions have recently taken place on whether spatiotemporal information is more important than featural information when infants attempt to individuate objects. Hitherto, spatiotemporal and featural information have only been compared directly by using cognitively demanding 'event-mapping designs' (e.g. Xu & Carey, 1996), whereas the simpler event-monitoring designs (e.g. the 'wide-screen/narrow-screen' by Wilcox and colleagues) have not been employed for such a comparison. The present research offers a new event-monitoring design, the rotating screen design, that allows for such a direct comparison. Three experiments in which 9.5-, 8.0-, and 6.5-month-old infants attempt to individuate objects by spatiotemporal and featural information are reported. The results showed that whereas the 9.5-month-old infants were able to individuate objects by spatiotemporal as well as featural information, the infants of the younger age groups only successfully individuated objects when provided with spatiotemporal information, but not with featural information.     

Basic-level category discriminations by 7- and 9-month-olds in an object examination task

This study examines 7- and 9-month-olds' ability to categorize cats as separate from dogs, and dogs as separate from cats in an object examination task. In Experiment 1, 7- and 9-month-olds (N = 30) familiarized with toy cat replicas were found to form a category of cat that included novel cats but excluded a dog and an eagle. In Experiment 2, 7- and 9-month-olds (N = 30) familiarized with toy dog replicas were found to form a category of dog that included a novel dogs and a novel cat but excluded an eagle. These results mirror those of 3- to 4-month-olds tested with visual preference methods and stand in contrast to previously reported object examination results. Analyses of the distribution of features in the exemplars used to familiarize infants suggest that, like the 3- to 4-month-olds, the 7- and 9-month-olds in these studies form categories within the task, and on the basis of feature distributions.     

Perceptual narrowing towards adult faces is a cross‐cultural phenomenon in infancy: a behavioral and near‐infrared spectroscopy study with Japanese infants

Recent data showed that, in Caucasian infants, perceptual narrowing occurs for own‐race adult faces between 3 and 9 months of age, possibly as a consequence of the extensive amount of social and perceptual experience accumulated with caregivers and/or other adult individuals of the same race of the caregiver. The neural correlates of this developmental process remain unexplored, and it is currently unknown whether perceptual tuning towards adult faces can be extended to other cultures. To this end, in the current study we tested the ability of 3‐ and 9‐month‐old Japanese infants to discriminate among adult and infant Asian faces in a visual familiarization task (Experiment 1), and compared 9‐month‐olds’ cerebral hemodynamic responses to adult and infant faces as measured by near‐infrared spectroscopy (NIRS) (Experiment 2). Results showed that 3‐month‐olds exhibit above‐chance discrimination of adult and infant faces, whereas 9‐month‐olds discriminate adult faces but not infant faces (Experiment 1). Moreover, adult faces, but not infant faces, induced significant increases in hemodynamic responses in the right temporal areas of 9‐month‐old infants. Overall, our data suggest that perceptual narrowing towards adult faces is a cross‐cultural phenomenon occurring between 3 and 9 months of age, and translates by 9 months of age into a right‐hemispheric specialization in the processing of adult faces.     

Distraction and facilitation--two faces of the same coin?

Unexpected and task-irrelevant sounds can capture our attention and may cause distraction effects reflected by impaired performance in a primary task unrelated to the perturbing sound. The present auditory-visual oddball study examines the effect of the informational content of a sound on the performance in a visual discrimination task. The informational content was modulated by varying the sound-target interval and the probability of target occurrence. Effects of informational content were examined with two types of distractors: a burst of white noise (deviant) and environmental sounds (novel). Behavioral results reveal the following. (1) Novel and deviant sounds do not necessarily cause behavioral distraction effects when they are uninformative with respect to both time and probability of occurrence of a visual target. (2) Novel, but not deviant, sounds cause an unspecific bias toward facilitation. (3) The informational content of task-irrelevant sounds speeds reaction times, indicating the use of information not directly related to the task for enhancing performance. (4) It is suggested that performance in deviant and novel trials is the sum of the costs of attentional orienting and benefits of information as well as benefits of unspecific activation for novels.     

Cognitive development in 7- to 24-month-old extremely/very-to-moderately/late preterm and full-term born infants: The mediating role of focused attention

The present study analyzed the links between prematurity, attention, and global cognitive performance in infancy and early childhood. At 7 months, focused attention (FA) was examined with an object examination task in 93 preterm infants (39 of them born extremely/very preterm, 54 born moderately/late preterm, and 38 infants born full-term). Global cognition was assessed at 7 and 24 months with the Bayley-II cognitive scale. Groups did not differ with respect to global cognitive performance but FA of infants born extremely/very preterm was significantly lower than in infants born moderately/late preterm. FA correlated significantly with both prematurity and cognitive performance at 7 months of age but not with global cognition in childhood. Findings point to a subtle adverse effect of prematurity on early attention and reveal evidence for the mediating role of FA on the effect of prematurity on cognition.     

Evidence of rapid correlation‐based perceptual category learning by 4‐month‐olds

Young infants are very sensitive to feature distribution information in the environment. However, existing work suggests that they do not make use of correlation information to form certain perceptual categories until at least 7 months of age. We suggest that the failure to use correlation information is a by‐product of familiarization procedures that encourage infants to over encode individual exemplars rather than relations across exemplars. By changing the exemplar presentation regime to one in which exemplars are rapidly (2 s durations) and repeatedly presented we find that 4‐month‐olds can form perceptual categories on the basis of feature correlation information. In addition, this ability emerges rapidly between 114 and 134 days. We argue that the ability to process correlation information is present very early on but that the demonstration of that ability in categorization tasks is mediated by the demands of the task the infant is tested with. Copyright © 2005 John Wiley & Sons, Ltd.     

Visual experience enhances infants' use of task-relevant information in an action task

Four experiments examined whether infants' use of task-relevant information in an action task could be facilitated by visual experience in the laboratory. Twelve- but not 9-month-old infants spontaneously used height information and chose an appropriate (taller) cover in search of a hidden tall toy. After watching examples of covering events in a teaching session, 9-month-old infants succeeded in an action task that involved the same event category; learning was not generalized to events from a different category. The present results demonstrate that learning through visual experience can be transferred to infants' subsequent actions. These findings shed light on the link between perception and action in infancy.