Evidence for a global categorical representation of humans by young infants

The representation of pictorial exemplars of humans by young infants was examined. Experiments 1B and 2 demonstrated an asymmetry with respect to the exclusivity of the categorical representations formed by 3- and 4-month-olds for humans and non-human animal species. The categorical representation for humans included novel humans, horses, cats, and fish, but excluded cars; the categorical representation for horses included novel horses, but excluded humans, fish, and cars. Experiment 2 also showed that the categorical representation for humans included exemplar information, whereas the categorical representation for non-human animal species was based on summary information. The asymmetry in categorization of human versus non-human animal species did not extend to the presumed more basic process of discrimination of individual humans versus non-human animals (Experiment 3). The findings suggest that a broad categorical representation of humans may be a cognitive reference point (or region) for young infants.

The emergence of perceptual category representations in young infants: a connectionist analysis

There has been recent interest in the idea that principles governing learning in connectionist networks can form the basis for an alternative understanding of developmental processes (Elman, Bates, Karmiloff-Smith, Johnson, Parisi, & Plunkett, 1996). The present paper can be viewed as a case example of the usefulness (and limitations) of connectionist modeling for the study of infant cognition. Specifically, the paper reports on a series of connectionist models designed to analyze the factors responsible for the emergence of global-level and basic-level category representations in young infants. The models (1) simulated the formation of global-level and basic-level representations, (2) revealed a global-to-basic order of category emergence, (3) uncovered the formation of two distinct global-level representations-an initial "self-organizing" perceptual global level and a subsequently "trained" arbitrary (i.e., nonperceptual) global level, and (4) displayed a gradual transition from perceptual global-level to perceptual basic-level representation with increasing exposure to training stimuli. Hypotheses for empirical investigations of category development in infants that follow from the modeling efforts are discussed.

Perceptual cues that permit categorical differentiation of animal species by infants

Eight experiments were performed to determine the perceptual cues used by 3- and 4-month-old infants to categorically distinguish between perceptually similar natural animal species. These experiments provided evidence that information from the facial and head region, specifically, the internal features of the face and the external contour of the head, give the infant a necessary and sufficient basis to form a categorical representation for cats that excludes dogs. The results are discussed in terms of Johnson and Morton's (1991) theory of facial recognition and more general accounts of the information underlying categorical representations.

Development of exclusivity in perceptually based categories of young infants

The exclusivity of perceptually defined categorical representations for natural animal categories in young infants was investigated. Previously, as well as in Experiment 1, evidence was obtained for a categorical representation for cats in 3- and 4-month-old infants that excluded dogs but included perceptually similar female lions after a number of different familiarization procedures. However, in Experiment 2 both dogs and female lions were found to be excluded when the initial familiarization with cats alone was followed by six pairings of familiar cats and novel lions intermingled with two added pairings of familiar cats. The present results indicate that a categorical representation can attain a high level of exclusivity during early infancy as a consequence of experience with exemplars of the contrasting categories that accents the perceptual similarities among members of a category and the perceptual differences among exemplars from different categories.

Studies on the formation of perceptually based basic-level categories in young infants

A series of experiments examined the abilities of 3- and 4-month-old infants to form categorical representations to exemplars of natural kinds--cats and horses. These experiments also permitted assessment of the relative exclusivity of these representations--the extent to which they exclude exemplars from contrasting basic-level categories from the same superordinate category. We found that categorical representations could be formed for horses that excluded cats, zebras, and giraffes, and for cats that excluded horses and tigers but not female lions. Lions were, however, excluded from the representations of cats in 6- and 7-month-old infants. Evidence was also obtained for 2 a priori preferences for members of one category over another. The discussion examined the roles of similarity between the exemplars of the contrasting categories and those of the tested category on estimates of exclusivity and of spontaneous preferences on the formation and exclusivity of categorical representations.

The categorization of above and below spatial relations by young infants

3 experiments using the familiarization-novelty preference procedure were conducted to investigate whether 3-month-old infants could form categorical representations of the spatial relations above and below. In Experiment 1, one group of infants familiarized with exemplars depicting a dot in different positions above a horizontal bar displayed a subsequent visual preference for a novel category exemplar (dot below bar) that was paired with a familiar category exemplar (dot in novel position above bar). A second group of infants presented with exemplars in which the dot appeared in variable locations below the bar also responded preferentially to a novel category exemplar (dot above bar) when it was paired with a familiar category exemplar (dot in new position below bar). These preferences did not result from the salience of vertical up-down changes in dot position or the encoding of dot positions relative to an internal horizontal midline (Experiment 3) or from an inability to discriminate the members of each category (Experiment 2), but rather would seem to be a consequence of the ability to represent categorically the spatial relations above and below. The data provide evidence for early categorical organization in human spatial memory.

Evidence for representations of perceptually similar natural categories by 3-month-old and 4-month-old infants

The paired-preference procedure was used in a series of experiments to explore the abilities of infants aged 3 and 4 months to categorize photographic exemplars from natural (adult-defined) basic-level categories. The question of whether the categorical representations that were evidenced excluded members of a related, perceptually similar category was also investigated. Experiments 1-3 revealed that infants could form categorical representations for dogs and cats that excluded birds. Experiment 4 showed that the representation for cats also excluded dogs, but that the representation for dogs did not exclude cats. However, a supplementary experiment showed that the representation for dogs did exclude cats when the variability of the dog exemplars was reduced to match that of the cat exemplars. The results are discussed in terms of abilities necessary for the formation of more complex categorical representations.

Feedback effects on sequential ordering in humans

Under various feedback conditions, 38 college undergraduates were asked to rearrange abstract graphic characters on a computer screen, placing them in arbitrarily designated "correct" sequences. Two sets of seven horizontally arrayed stimuli were used. In Experiment 1, subjects in Group 1 learned to arrange the first set under Selection Feedback in which a "+" appeared above each character after it was selected in the correct order and to arrange the second set under Order Feedback in which a correct response produced a copy of the character in its correct ordinal position at the top of the screen. For Group 2 the order of these conditions was reversed. In Experiment 2, for subjects in Group 3, correct responses produced neither of these types of feedback. Subjects in Group 4 received Order Feedback only until the first set was correctly ordered once. Order Feedback was more effective than Selection Feedback during initial acquisition of the first set but not during maintenance; no differences were found for the second set. Only 2 of 9 subjects successfully put the characters in correct sequential order under the No Feedback condition. When, in Experiment 2, Order Feedback was eliminated after the first correctly arranged sequence, the steady-state criteria were met more slowly than in Experiment 1.

Evidence for a general category of oblique orientations in four-month-old infants

Recent work on orientation perception and memory in infants suggest that oblique stimulus orientations are treated as members of a category. The two studies in this report support this hypothesis and extend previous findings by demonstrating that this category includes obliques on either side of vertical even when infants are previously exposed to obliques on only one side.