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.

Object recognition and object segregation in infancy: historical perspective, theoretical significance, "kinds" of knowledge, and relation to object categorization.

Needham (2001, this issue) reports that 4.5-month-old infants can use a short-term familiarization experience with a single object to facilitate the segregation of a visual display consisting of a configurally similar object and a configurally dissimilar adjacent object. We reflect on this finding in the larger context of Needham's systematic research on the development of object perception, a program that has included (1) a series of empirical studies designed to identify the different cues that infants use for object segregation and (2) a theoretical framework in which infants are presumed to integrate these cues to form interpretations of complex visual displays.

Perceptual reference points for form and orientation in young infants: anchors or magnets?

In some domains, certain stimuli are especially salient and efficiently encoded and are referred to as reference points. One current issue concerns whether reference points are associated with regions of increased or decreased discriminability and function as either perceptual anchors or magnets. In two experiments utilizing the familiarization/novelty-preference procedure, the question of whether 3- to 4-month-old infants' representations of form and orientation information are structured by perceptual reference points and whether such reference points serve as anchors or magnets is examined. In Experiment 1, infants displayed above-chance discrimination performance for pairs of form stimuli that were equivalently distinct on a physical basis, but only when one member of each pair was a "good" form (i.e., diamond, square, or triangle). In Experiment 2, infants displayed above-chance discrimination performance for pairs of stimuli differing by 7.5 degrees of orientation, but only when one member of each pair was either horizontal or vertical. The combined results from the two experiments suggest that "simple" gestalts and main axes (i.e., horizontal and vertical) serve as perceptual anchors in young infants' representations of form and orientation information.

Identification of gender in domestic-cat faces with and without training: perceptual learning of a natural categorization task.

Three experiments were conducted to determine whether human observers could identify the gender of 40 domestic cats (20 female, 20 male) depicted in individual color photographs. In experiment 1a, observers performed at chance for photographs depicting whole cats, cat heads (bodies occluded), and cat bodies (heads occluded). Experiment 1b showed that chance performance was also obtained when the photographs were full-face close-ups of the cats. Experiment 2a revealed that even with gender-identification training on 30 (15 female, 15 male) of the 40 face close-ups, observers were unable to generalize their training to reliably identify the gender of the 10 remaining test faces (5 female, 5 male). However, experiment 2b showed that gender-identification training with the 14 most accurately identified faces from experiment 1b (7 female, 7 male) was successful in raising gender identification of the 10 test faces above chance. Experiments 3a and 3b extended this facilitative effect of gender-identification training to a population of animal-care workers. The findings indicate that, with appropriate training, human observers can identify the gender of cat faces at an above-chance level. A perceptual category learning account emphasizing the on-line formation of differentiated male versus female prototypes during training is offered as an explanation of the findings.

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.

Comparing the effects of two correction procedures on human acquisition of sequential behavior patterns.

Thirty-one college undergraduates learned to touch abstract stimuli on a computer screen in arbitrarily designated "correct" sequential orders. Four sets of seven stimuli were used; the stimuli were arrayed horizontally on the screen in random sequences. A correct response (i.e., touching first the stimulus designated as first) resulted in that stimulus appearing near the top of the screen in its correct sequential position (left to right), and remaining there until the end of the trial. Incorrect responses (i.e., touching a stimulus out of sequence) terminated the trial. New trials displayed either the same sequence as the one on which an error had occurred (same-order correction procedure), or a new random sequence (new-order correction procedure). Whenever all responses occurred in the correct sequence, the next trial displayed a new random sequence. Each phase ended when five consecutive correct response sequences occurred. Initially, the same-order correction procedure increased control by the position as well as by the shape of the stimuli; also, it produced more errors, more total trials, more trials to mastery, and more individual patterns of reacquisition than were produced by the new-order procedure.

Delayed recognition memory for orientation by human infants.

The familiarization/novelty preference paradigm was employed to study the effect of a delay (between the end of the familiarization phase and the beginning of the test phase) on discrimination of the orientation of square-wave gratings by 2- and 3-month-old human infants. Three stimulus pairs were studied: horizontal-vertical, non-mirror-image obliques, and mirror-image obliques. The data indicate that the members of the oblique-oblique stimulus pairs are confused in memory to a greater extent than the members of the horizontal-vertical stimulus pair. These findings are consistent with P.C. Bomba's (1984, Journal of Experimental Child Psychology, 37, 609-636) recent report that infants respond to the orientation of a visual stimulus in a categorical-like manner.