Development of sensitivity to information for impending collision

Infants were tested in three experiments to study the development of sensitivity to information for impending collision and to investigate the hypothesis that postural changes of very young infants in response to an approaching object are of a tracking rather than of a defensive nature. Experiment 1 involved the presentation of three types of shadow projection displays, specifying (1) collision, (2) noncollision, and (3) a nonexpanding rising contour, to infants from 1 to 9 months of age. Avoidance of collision appears to be absent in 1- to 2-month-olds, begins to develop in 4- to 6-month-olds, and is present in 8- to 9-month-old infants. In Experiment 2, 1- to 2-month-old infants were presented with optical expansion patterns which specified collision and noncollision. The top contour of these displays stayed at eye level. No significant difference was observed between reaction to the collision and the noncollision displays, suggesting that the young infants were tracking the displays and not attempting to avoid collision. Experiment 3 was designed to determine whether an approaching real object might elicit an avoidance response in infants not sensitive to an optical display specifying collision. No evidence of avoidance behavior was observed in the 1- to 2-month-olds; however, avoidance, as indexed by blinking, does appear to be present at 4 months of age.     

Exploring early developmental changes in face scanning patterns during the perception of audiovisual mismatch of speech cues

Young infants are capable of integrating auditory and visual information and their speech perception can be influenced by visual cues, while 5-month-olds detect mismatch between mouth articulations and speech sounds. From 6 months of age, infants gradually shift their attention away from eyes and towards the mouth in articulating faces, potentially to benefit from intersensory redundancy of audiovisual (AV) cues. Using eye tracking, we investigated whether 6- to 9-month-olds showed a similar age-related increase of looking to the mouth, while observing congruent and/or redundant versus mismatched and non-redundant speech cues. Participants distinguished between congruent and incongruent AV cues as reflected by the amount of looking to the mouth. They showed an age-related increase in attention to the mouth, but only for non-redundant, mismatched AV speech cues. Our results highlight the role of intersensory redundancy and audiovisual mismatch mechanisms in facilitating the development of speech processing in infants under 12 months of age.     

The development of infants' preference for motherese

Generally, infants prefer infant-directed (ID) to adult-directed (AD) speech. Mostly, researchers have used unfamiliar female voices in these studies. We investigated preferences for maternal ID speech in 1- and 4-month-olds. Using a procedure in which infants controlled access to voices by fixating a visual display, infants listened to recordings of natural female ID and AD speech. In Experiment 1, 1-month-olds heard recordings of maternal ID and AD speech, but these infants showed no preference for maternal ID speech. In Experiment 2, 1-month-olds heard the same ID and AD speech tapes but were not familiar with the speakers. Contrary to Experiment 1, these infants preferred ID speech. In Experiment 3, 4-month-olds heard recordings of maternal ID and AD speech and showed a significant preference for ID speech. Collectively, these results suggest that infant attention to ID speech depends on both speaker-general and speaker-specific characteristics, with interesting developmental changes occuring during early infancy.     

Development of infant ear asymmetries for speech and music

Groups of 2-, 3-, and 4-month olds were tested for dichotic ear differences in memory-based phonetic and music timbre discriminations. A right-ear advantage for speech and a left-ear advantage (LEA) for music were found in the 3- and 4-month-olds. However, the 2-month-olds showed only the music LEA, with no reliable evidence of memory-based speech discrimination by either hemisphere. Thus, the responses of all groups to speech contrasts were different from those to music contrasts, but the pattern of the response dichotomy in the youngest group deviated from that found in the older infants. It is suggested that the quality or use of lefthemisphere phonetic memory may change between 2 and 3 months, and that the engagement of right-hemisphere specialized memory for musical timbre may precede that for left-hemisphere phonetic memory. Several directions for future research are suggested to determine whether infant short-term memory asymmetries for speech and music are attributable to acoustic factors, to different modes or strategies in perception, or to structural and dynamic properties of natural sound sources.     

Infants’ sensitivity to the depth cue of shading

Five- and 7-month-old infants were tested for sensitivity to the depth cue of shading. Infants were presented with two displays: a surface in which a convexity and a concavity were molded and a photograph in which shading specified a convexity and a concavity. Each display was presented under both monocular and binocular viewing conditions. Reaching was observed as the dependent measure. Infants in both age groups reached preferentially for the actual convexity in both the monocular and binocular viewing conditions. In the monocular photograph condition, the 7-month-olds reached preferentially for the apparent convexity specified by shading, indicating that they perceived it to be an actual convexity. These infants showed no significant reaching preference in the binocular photograph condition. This finding rules out interpretations of the infants’ reaching not based on perceived depth. The results therefore suggest that the 7-month-olds perceived depth from shading. The 5-month-olds showed no significant reaching preferences when viewing the photograph; thus, they showed no evidence of depth perception from shading. These findings are consistent with the results of a number of studies that have investigated infants’ sensitivity to pictorial depth cues. Together, these studies suggest that the ability to perceive depth from pictorial cues may first develop between 5 and 7 months of age.     

The cocktail party effect in infants revisited: listening to one's name in noise

This study examined infants' abilities to separate speech from different talkers and to recognize a familiar word (the infant's own name) in the context of noise. In 4 experiments, infants heard repetitions of either their names or unfamiliar names in the presence of background babble. Five-month-old infants listened longer to their names when the target voice was 10 dB, but not 5 dB, more intense than the background. Nine-month-olds likewise failed to identify their names at a 5-dB signal-to-noise ratio, but 13-month-olds succeeded. Thus, by 5 months, infants possess some capacity to selectively attend to an interesting voice in the context of competing distractor voices. However, this ability is quite limited and develops further when infants near 1 year of age.     

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).     

Changes in infants' ability to switch visual attention in the first three months of life.

The abilities of 1-month-old and 3-month-old infants to shift their gaze from a central target to a peripheral target were compared in four experiments. In experiment 1 targets matched in mean luminance to the background were presented to infants in the periphery at varying levels of contrast. The contrast thresholds for target detection were found to be significantly different for 1-month-olds compared with 3-month-olds. With targets set close to these contrast thresholds, correct refixations and the latency for shifting attention were examined in experiment 2. Two conditions were used: a peripheral target was presented against a homogeneous background (noncompetition); and in the second condition, the patterned target appeared at one of two lighter peripheral windows set against a darker background (competition). Although there was no difference between the two age groups in the latency for shifting visual attention, 1-month-olds were found to make more directional errors in the competition condition. The competition effect of two potential targets on latencies was examined in experiment 3. In the competition condition, two identical peripheral patterned targets were presented to the infants. The 3-month-olds refixated more quickly to one of the double targets in the competition condition than to a single peripheral target, whereas 1-month-olds were slowed down by a double target display. Finally, in experiment 4 the ability of the infants to process and disengage from a central stimulus and to refixate towards a similar peripheral target was examined. This type of competition disrupted both the direction of the first eye movement and the latency to shift attention in both age groups. However, the effect was significantly greater for the 1-month-olds. Taken together, the results of these experiments demonstrate the greater disruption of fixation-shift behaviour in 1-month-olds compared with 3-month-olds when competing visual stimuli are used. This developmental change is explained in terms of maturation of executive cortical orienting systems over the first months of life.     

Development of the functional visual field

Andries Sanders' dissertation examined selective mechanisms in the functional visual field, and much of his work since has been concerned with the stages that underlie visual information processing particularly while making saccades. We argue that the study of orienting in the functional visual field is timely because it deals with the relation of covert attention shifts, eye movements and head movements to their underlying neurology. In our paper we develop a method to study learning of sequences at all ages from infants to adults. Our studies focus on how learning influences anticipatory eye movements. We examined the learning of unambiguous and context dependent sequences by 4-, 10-, and 18-month-old infants and undergraduates. We found clear learning of unambiguous sequences at 4 months, but learning of context dependent associations was found only in 18-month-olds and in adults. We hypothesize that the learning of unambiguous sequences by 4-month-olds reflects maturation of a basal ganglia-parietal circuit related to adult implicit learning, while the learning of context dependent sequences requires development of frontal structures underlying more general attentional abilities.     

Rapid Gains in Speed of Verbal Processing by Infants in the 2nd Year

Infants improve substantially in language ability during their 2nd year. Research on the early development of speech production shows that vocabulary begins to expand rapidly around the age of 18 months. During this period, infants also make impressive gains in understanding spoken language. We examined the time course of word recognition in infants from ages 15 to 24 months, tracking their eye movements as they looked at pictures in response to familiar spoken words. The speed and efficiency of verbal processing increased dramatically over the 2nd year. Although 15-month-old infants did not orient to the correct picture until after the target word was spoken, 24-month-olds were significantly faster, shifting their gaze to the correct picture before the end of the spoken word. By 2 years of age, children are progressing toward the highly efficient performance of adults, making decisions about words based on incomplete acoustic information.     

Language development at 18 months is related to multimodal communicative strategies at 12 months

The present study investigated the degree to which an infants’ use of simultaneous gesture–speech combinations during controlled social interactions predicts later language development. Nineteen infants participated in a declarative pointing task involving three different social conditions: two experimental conditions (a) available, when the adult was visually attending to the infant but did not attend to the object of reference jointly with the child, and (b) unavailable, when the adult was not visually attending to neither the infant nor the object; and (c) a baseline condition, when the adult jointly engaged with the infant's object of reference. At 12 months of age measures related to infants’ speech-only productions, pointing-only gestures, and simultaneous pointing–speech combinations were obtained in each of the three social conditions. Each child's lexical and grammatical output was assessed at 18 months of age through parental report. Results revealed a significant interaction between social condition and type of communicative production. Specifically, only simultaneous pointing–speech combinations increased in frequency during the available condition compared to baseline, while no differences were found for speech-only and pointing-only productions. Moreover, simultaneous pointing–speech combinations in the available condition at 12 months positively correlated with lexical and grammatical development at 18 months of age. The ability to selectively use this multimodal communicative strategy to engage the adult in joint attention by drawing his attention toward an unseen event or object reveals 12-month-olds’ clear understanding of referential cues that are relevant for language development. This strategy to successfully initiate and maintain joint attention is related to language development as it increases learning opportunities from social interactions.     

Infants' sensitivity to allophonic cues for word segmentation

A series of four experiments was conducted to determine whether English-learning infants can use allophonic cues to word boundaries to segment words from fluent speech. Infants were familiarized with a pair of two-syllable items, such as nitrates and night rates and then were tested on their ability to detect these same words in fluent speech passages. The presence of allophonic cues to word boundaries did not help 9-month-olds to distinguish one of the familiarized words from an acoustically similar foil. Infants familiarized with nitrates were just as likely to listen to a passage about night rates as they were to listen to one about nitrates. Nevertheless, when the passages contained distributional cues that favored the extraction of the familiarized targets, 9-month-olds were able to segment these items from fluent speech. By the age of 10.5 months, infants were able to rely solely on allophonic cues to locate the familiarized target words in passages. We consider what implications these findings have for understanding how word segmentation skills develop.     

Explanation-based learning in infancy

In explanation-based learning (EBL), domain knowledge is leveraged in order to learn general rules from few examples. An explanation is constructed for initial exemplars and is then generalized into a candidate rule that uses only the relevant features specified in the explanation; if the rule proves accurate for a few additional exemplars, it is adopted. EBL is thus highly efficient because it combines both analytic and empirical evidence. EBL has been proposed as one of the mechanisms that help infants acquire and revise their physical rules. To evaluate this proposal, 11- and 12-month-olds (n?=?260) were taught to replace their current support rule (that an object is stable when half or more of its bottom surface is supported) with a more sophisticated rule (that an object is stable when half or more of the entire object is supported). Infants saw teaching events in which asymmetrical objects were placed on a base, followed by static test displays involving a novel asymmetrical object and a novel base. When the teaching events were designed to facilitate EBL, infants learned the new rule with as few as two (12-month-olds) or three (11-month-olds) exemplars. When the teaching events were designed to impede EBL, however, infants failed to learn the rule. Together, these results demonstrate that even infants, with their limited knowledge about the world, benefit from the knowledge-based approach of EBL.     

The attribution of attention: 9-month-olds' interpretation of gaze as goal-directed action

The current study distinguishes between attributions of goal-directed perception (i.e. attention) and non-goal-directed perception to examine 9-month-olds' interpretation of others' head and eye turns. In a looking time task, 9-month-olds encoded the relationship between an actor's head and eye turns and a target object if the head and eye turns were embedded in a sequence of multiple, variable actions with equifinal outcomes, but not otherwise. This evidence supports the claim that infants of this age may attribute perception, at least goal-directed perception, to others and undermines arguments that gaze-following at this age consists only of uninterpreted reflexes. The evidence also suggests alternative interpretations of the typical errors infants make in standard gaze-following procedures. Implications for infants' understanding of perception and attention in both human and non-human agents are discussed.     

Memory Processing of a Serial List By Young Infants

Serial list learning is thought to be beyond the capabilities of infants before the end of their 1st year. In separate experiments with 3- and 6-month-olds, we studied infants' memory for a serial list using a modified serial probe recognition procedure that was originally developed for monkeys and a precuing procedure that was previously used with human adults. Infants were trained with a three-item list. One day later, they were precued with one list member and tested for recognition of another. When the precue specified valid order information, infants of both ages recognized the test item; when the precue specified invalid order information, infants of neither age did. These findings reveal that even very young infants can learn and remember the order of items on a serial list.     

Phonotactic cues for segmentation of fluent speech by infants

There is growing evidence that infants become sensitive to the probabilistic phonotactics of their ambient language sometime during the second half of their first year. The present study investigates whether 9-month-olds make use of phonotactic cues to segment words from fluent speech. Using the Headturn Preference Procedure, we found that infants listened to a CVC stimulus longer when the stimulus previously appeared in a sentential context with good phonotactic cues than when it appeared in one without such cues. The goodness of the phonotactic cues was estimated from the frequency with which the C.C clusters at the onset and offset of a CVC test stimulus (i.e. C.CVC.C) are found within and between words in child-directed speech, with high between-word probability associated with good cues to word boundaries. A similar segmentation result emerged when good phonotactic cues occurred only at the onset (i.e. C.CVC.C) or the offset (i.e. C.CVC.C) of the target words in the utterances. Together, the results suggest that 9-month-olds use probabilistic phonotactics to segment speech into words and that high-probability between-word clusters are interpreted as both word onsets and word offsets.     

Infants’ responsiveness to pictorial depth cues in preferential-reaching studies: A meta-analysis

The findings of numerous preferential-reaching studies suggest that infants first respond to pictorial depth cues between 5 and 7 months of age. However, three recent preferential-reaching studies have found evidence of responsiveness to pictorial depth cues in 5-month-olds. We investigated these apparently contradictory results by conducting meta-analyses of the data from 5-month-olds who participated in preferential-reaching studies. The data from 16 samples, comprising 475 infants 5–5.5 months of age, were integrated. The results showed that the infants responded more consistently to depth relationships specified by pictorial cues under monocular than under binocular viewing conditions (p < .001), indicating that 5-month-old infants respond to pictorial depth cues. This effect remained significant (p < .001) when the individual experiments that had found significant results were omitted from the analysis. Although the majority of experiments were unable to find evidence of pictorial depth perception individually, this ability was clearly revealed when their results were combined.     

Learning perceptual organization in infancy

It has been demonstrated that older infants (6- to 7-month-olds), but not younger infants (3- to 4-month-olds), use form similarity to organize stimuli consisting of X and O elements. We investigated whether utilization of form similarity is governed by maturation or experience by contrasting how infants perform when familiarized with a single exemplar versus multiple exemplars depicting a particular organization. In Experiment 1, 3- to 4-month-olds failed to organize alternating columns or rows of squares and diamonds or Hs and Is, respectively. In Experiment 2, same-aged infants familiarized with all three patterns (X-O, square-diamond, H-I) displayed evidence of organization. The results suggest that 3- to 4-month-olds can use form similarity to organize visual patterns in a concept-formation task. The findings imply that perceptual organization based on form similarity is learned through experience with multiple patterns depicting a common arrangement, rather than immediately apprehended in an individual pattern.     

Infants’ sensitivity to allophonic cues for word segmentation

A series of four experiments was conducted to determine whether English-learning infants can use allophonic cues to word boundaries to segment words from fluent speech. Infants were familiarized with a pair of two-syllable items, such asnitrates andnight rates and then were tested on their ability to detect these same words in fluent speech passages. The presence of allophonic cues to word bound-aries did not help 9-month-olds to distinguish one of the familiarized words from an acoustically similar foil. Infants familiarized withnitrates were just as likely to listen to a passage aboutnight rates as they were to listen to one aboutnitrates. Nevertheless, when the passages contained distributional cues that favored the extraction of the familiarized targets, 9-month-olds were able to segment these items from fluent speech. By the age of 10.5 months, infants were able to rely solely on allophonic cues to locate the familiarized target words in passages. We consider what implications these findings have for understanding how word segmentation skills develop.

     

An investigation of young infants' perceptual representations of speech sounds

The present study examined the ability of newborns and 2-month-olds to detect phonetic differences between syllables. By relying on the modified high-amplitude sucking procedure, which did not permit the infants to use a simple same-different response, the present experiments tapped the perceptual representations of the speech sounds. Infants as young as a few days old displayed some capacity to represent differences in a set of syllables varying in their phonetic composition, although there was no convincing evidence that their representations were structured in terms of phonetic segments. Finally, evidence of developmental changes in speech processing were noted for the first time with infants in this age range. The change noted was a tendency from global toward more specific representations on the part of the older infants.