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.     

The role of bottom-up processing in perceptual categorization by 3- to 4-month-old infants: simulations and data

Disentangling bottom-up and top-down processing in adult category learning is notoriously difficult. Studying category learning in infancy provides a simple way of exploring category learning while minimizing the contribution of top-down information. Three- to 4-month-old infants presented with cat or dog images will form a perceptual category representation for cat that excludes dogs and for dog that includes cats. The authors argue that an inclusion relationship in the distribution of features in the images explains the asymmetry. Using computational modeling and behavioral testing, the authors show that the asymmetry can be reversed or removed by using stimulus images that reverse or remove the inclusion relationship. The findings suggest that categorization of nonhuman animal images by young infants is essentially a bottom-up process.     

Development of an abstract category representation for the spatial relation between in 6- to 10-month-old infants

Nine experiments examined the formation of an abstract category representation for the spatial relation between by 6- to 10-month-old infants. The experiments determined that 9- to 10-month-olds, but not 6- to 7-month-olds, could form an abstract category representation for between when performing in an object-variation version of the between categorization task. The results also demonstrated that 6- to 7-month-olds could form category representations for between in the object-variation version of the between categorization task but that such representations were specific to the particular objects presented. The evidence confirms that representations for different spatial relations emerge at different points during development, and suggests that each representation undergoes its own period of development from concrete to abstract.     

Computational approaches to the development of perceptual expertise

Dog experts, ornithologists, radiologists and other specialists are noted for their remarkable abilities at categorizing, identifying and recognizing objects within their domain of expertise. A complete understanding of the development of perceptual expertise requires a combination of thorough empirical research and carefully articulated computational theories that formalize specific hypotheses about the acquisition of expertise. A comprehensive computational theory of the development of perceptual expertise remains elusive, but we can look to existing computational models from the object-recognition, perceptual-categorization, automaticity and related literatures for possible starting points. Arguably, hypotheses about the development of perceptual expertise should first be explored within the context of existing computational models of visual object understanding before considering the creation of highly modularized adaptations for particular domains of perceptual expertise.     

Perceptual categorization of cat and dog silhouettes by 3- to 4-month-old infants

Given evidence that silhouette information can be used by adults to form categorical representations at the basic level, four experiments utilizing the familiarization-novelty preference procedure were performed to examine whether 3- and 4-month-old infants could form categorical representations for cats versus dogs from the perceptual information available in silhouettes (e.g., global shape and external outline). Experiments 1 and 2 showed that infants could form individuated categorical representations for cat and dog silhouettes, whereas Experiments 3 and 4 revealed that infants could use silhouette information from the head, but not the body, to categorically separate the two species. These results indicate that general shape or external contour information that is centered about the head is sufficient for young infants to form individuated categorical representations for cats and dogs. The data thus provide information regarding the nature of the perceptual information that can be used by infants to form category representations for individual animal species and are discussed in terms of domain-general versus domain-specific processing accounts.     

Sensitivity of 5- and 7-month-old infants to pictorial depth information

An Ames (1951, Psychological Monographs, 65(1, Whole No. 324)) static trapezoidal window, under monocular view, was used to test young infants' responsiveness to pictorial depth. When adults view this display monocularly with the smaller side of the window rotated toward them, they report that the orientation of the display becomes ambiguous: When the head is moved, the window may appear to be in the fronto-parallel plane or either side may appear closer. The 7-month-olds we tested appeared to experience a similar ambiguity; they reached to the near side of the rotated trapezoidal window with significantly less consistency or directedness than infants in a control group tested with a rotated object that lacked pictorial depth information. When 5-month-olds were tested, however, they reached with equal consistency to the closer side of the trapezoidal window and of the control display, apparently uninfluenced by the pictorial depth information available in the trapezoidal window. Thus, sensitivity to the pictorial information for depth that is present in the trapezoidal window appears to develop after the age of 22 weeks.     

Choosing the shortest way to Mum: auditory guided rotation in 6- to 9-month-old infants

The purpose of this study was to investigate the use of auditory information for rotation of the shortest way in twelve 6- to 9-month-old sighted infants. Behavior was manipulated by means of an auditory stimulus presented in four different directional angles (90°, 112.5°, 135°, and 157.5°) to the right and to the left behind the infants, and in one non-directional angle (180°). Infants lay in a prone position and had magnetic trackers fastened to the head and body which measured their rotation direction and angular velocity. The results showed that infants not only consistently chose the shortest over the longest way, but also rotated with a higher peak angular velocity as the angle to be covered between themselves and the goal increased. The results did not show significant preferences for one particular rotation direction. The study can contribute to the understanding of the auditory system as a functional listening system where auditory information is used as a perceptual source for prospectively guiding behavior in the environment.     

Global influences on the development of spatial and object perceptual categorization abilities: Evidence from preterm infants

Influences on the development of perceptual categorization were examined by comparing the performance of three groups of infants on spatial and object categorization tasks. The groups consisted of 1) fullterm infants tested at 3 to 4 months of age, 2) healthy preterm infants tested 3 to 4 months from birth (postnatals), and 3) healthy preterm infants tested 3 to 4 months from their due date (postterms). Four experiments showed that fullterms and postterms outperformed postnatals on a spatial categorization task (i.e., ‘above’ vs. ‘below’, and that fullterms outperformed both postnatals and postterms on object categorization tasks (i.e., dogs vs. cats, and cats vs. birds). These results suggest that maturation may be the predominant influence on the early development of the ability to form categorical representations of spatial information, while preterm birth may exert a limiting influence on the development of object categorization abilities.     

Timing strategies used in defensive blinking to optical collisions in 5- to 7-month-old infants

When objects approach on a collision course, young babies will blink to protect their eyes. The timing of the blink is crucial, since it serves to protect the eyes from being injured. The image of a looming virtual object approached infants under different constant velocities and constant accelerations. The youngest infants (5–6 months) blinked when the image of the virtual object reached a threshold visual angle, while older infants (6–7 months) geared their blinks to the image’s time-to-collision. Infants using a strategy based on time coped successfully with all approach conditions, while infants using a strategy based on visual angle had difficulty with the fastest accelerative approach condition. The findings indicate that infants around 6 months of age shift to a more sophisticated strategy based on time, allowing them to deal with more demanding perceptual tasks.     

The development of 3- to 9-month-old infants in two cultural contexts: Bayley longitudinal results for Cameroonian and German infants

Based on the Bayley Scales of Infant Development III, this study provides the results of a longitudinal study on the development of Cameroonian Nso farmer and German middle-class infants. Complete longitudinal data were available for 253 infants (69 from Cameroon and 184 from Germany) with Bayley assessments at 3, 6 and 9 months. The results show large differences between Cameroonian Nso and German infants with regard to gross motor and language development. The developmental sequence within each Bayley scale is more in line with the original Bayley sequence for German than for Cameroonian Nso infants as is indicated by Goodman scalogram analyses. Path analyses show some basic similarities between the developmental paths across ages for Cameroonian Nso and German infants, but more interconnections between the scales in the German sample. The results underline the need to adjust developmental scales to the cultural background of the infants to be tested.     

Rich interpretation vs. deflationary accounts in cognitive development: the case of means-end skills in 7-month-old infants

Seven-month-old infants appear to learn means-end skills, such as pushing a button to retrieve a distant toy (Psychological Review 104 (1997) 686). The present studies tested whether such apparent means-end behaviors are genuine, or simply the repetition of trained behaviors under conditions of greatest arousal, as suggested by a dynamic systems reinterpretation. When infants were trained to repeat behaviors that did not serve as means to retrieving toys (pushing a button to light a set of distant lights), their button-pushing differed significantly from infants for whom button-pushing served as a means for retrieving toys. Further, infants demonstrated means-end skills with behaviors that they had not been trained to repeat. Implications for early means-end abilities and for debates surrounding the interpretation of infant behavior are discussed.     

When cues collide: use of stress and statistical cues to word boundaries by 7- to 9-month-old infants

Prior research suggests that stress cues are particularly important for English-hearing infants' detection of word boundaries. It is unclear, though, how infants learn to attend to stress as a cue to word segmentation. This series of experiments was designed to explore infants' attention to conflicting cues at different ages. Experiment 1 replicated previous findings: When stress and statistical cues indicated different word boundaries, 9-month-old infants used syllable stress as a cue to segmentation while ignoring statistical cues. However, in Experiment 2, 7-month-old infants attended more to statistical cues than to stress cues. These results raise the possibility that infants use their statistical learning abilities to locate words in speech and use those words to discover the regular pattern of stress cues in English. Infants at different ages may deploy different segmentation strategies as a function of their current linguistic experience.     

Dissimilarity is used as evidence of category membership in multidimensional perceptual categorization: a test of the similarity-dissimilarity generalized context model

In exemplar models of categorization, the similarity between an exemplar and category members constitutes evidence that the exemplar belongs to the category. We test the possibility that the dissimilarity to members of competing categories also contributes to this evidence. Data were collected from two 2-dimensional perceptual categorization experiments, one with lines varying in orientation and length and the other with coloured patches varying in saturation and brightness. Model fits of the similarity-dissimilarity generalized context model were used to compare a model where only similarity was used with a model where both similarity and dissimilarity were used. For the majority of participants the similarity-dissimilarity model provided both a significantly better fit and better generalization, suggesting that people do also use dissimilarity as evidence.     

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.     

Learning and retention in 3- and 6-month-old infants: A comparison of different experimental paradigms

Learning and retention effects in 3- and 6-month-old infants were analysed for the habituation, the novelty preference, and the visual expectation paradigm that are assumed to indicate processing speed. A total of 119 infants participated in the study. The tasks related to the different paradigms were presented on three different days within a week and were repeated two weeks later to analyse retention effects. The results showed clear learning effects in all paradigms. The learning effects shown for different tasks were interrelated for 6-month-old infants, thus supporting the assumption of a shared latent dimension like processing speed. Moreover, retention effects over an interval of two weeks could be shown for visual expectation (in both 3- and 6-month-old infants) and for novelty preference (only for 6-month-old infants). The comparably high retention rates especially in the visual expectation paradigm are discussed.     

Evidence of a transition from perceptual to category induction in 3- to 9-year-old children

We examined whether inductive reasoning development is better characterized by accounts assuming an early category bias versus an early perceptual bias. We trained 264 children aged 3 to 9 years to categorize novel insects using a rule that directly pitted category membership against appearance. This was followed by an induction task with perceptual distractors at different levels of featural similarity. An additional 52 children were given the same training followed by an induction task with alternative stimuli. Categorization performance was consistently high; however, we found a gradual transition from a perceptual bias in our youngest children to a category bias around 6 or 7 years of age. In addition, children of all ages were equally distracted by higher levels of featural similarity. The transition is unlikely to be due to an increased ability to inhibit perceptual distractors. Instead, we argue that the transition is driven by a fundamental change in children's understanding of category membership.     

Self-sitting and reaching in 5- to 8-month-old infants: the impact of posture and its development on early eye-hand coordination

The relation between progress in the control of posture (i.e., the achievement of self-sitting posture) and the developmental transition from two-handed to one-handed engagement in infant reaching was investigated. Two groups of 5- to 8-month-old infants, who were either able or yet unable to sit on their own, were videotaped while they reached for objects in four different posture conditions that provided varying amounts of body support. Videotapes of infant reaches were microanalyzed to determine the relative engagement of both hands during reaches. Results demonstrate the interaction between postural development and the morphology of infant reaching. Nonsitting infants displayed symmetrical and synergistic engagement of both arms and hands while reaching in all but the seated posture condition. Sitting infants, by contrast, showed asymmetrical and lateralized (one-handed) reaches in all posture conditions. Results also show that, aside from posture, the perceived spatial arrangement of the object display is a determinant of infant reaching. Combined, these results are discussed as evidence for the interaction between postural and perceptual development in the control of early eye-hand coordination.     

Encoding the goal of an object-directed but uncompleted reaching action in 6- and 9-month-old infants

Infants start to interpret completed human actions as goal-directed in the second half of the first year of life. In a series of three studies, the understanding of a goal-directed but uncompleted action was investigated in 6- and 9-month-old infants using a preferential looking paradigm. Infants saw the video of an actor's reaching movement towards one of two objects. This reaching movement was only presented until the hand passed the midpoint between the starting position and the position of the target object. Subsequently, two final states of the reaching movement were presented simultaneously. In the plausible final state, the hand grasped the object to which the reaching movement was geared; in the implausible final state, the hand grasped the other object. In Studies 1 and 3, infants watched the actor from an allocentric perspective, and in Studies 2 and 3 from an egocentric perspective. Results indicate a discrimination of the two final states if the scene was presented from an allocentric perspective: both 6- and 9-month-olds looked longer at the implausible final state. This was not the case if infants saw the action from an egocentric perspective. The presented findings show that using this paradigm, 6-month-olds are already able to infer the goal of an uncompleted action without seeing the achievement of the goal itself. However, they encoded the goal of the reaching action only when it was presented from an allocentric perspective but not from an egocentric perspective.