The future of infant categorization research: a process-oriented approach.

We call for a shift from a content-oriented approach to a process-oriented approach to the study of categorization in infancy. Although gains have been made in our understanding of infant categorization by evaluating the categories to which infants respond, further understanding of infant categorization, and how categorization changes with development, requires that we more directly assess infants' category formation. We argue that two directions for future research will continue to enhance our understanding of categorization in infancy (and beyond). First, contextual variations (e.g., the effects of task, stimuli, and other factors) on infants' categorization must be better understood. Second, we must more directly evaluate the kinds of information infants use when forming categories, as well as how their use of such information changes with age, task, and so forth. We argue that these two foci will provide clearer understanding of the origins and early development of categorization.

By land or by sea: the role of perceptual similarity in infants' categorization of animals.

In 3 experiments, the authors used an object-examining task to investigate the role of perceptual similarity in infants' categorization. In Experiment 1, infants were familiarized with a set of either perceptually similar or perceptually variable exemplars from 1 category and tested with novel exemplars from both categories. Ten-month-olds did not respond to the category in either condition, and 13-month-olds responded categorically in both conditions but somewhat differently in the 2 conditions. Experiment 2 showed that when 10-month-olds were familiarized with similar exemplars but not with variable exemplars, they responded to the categorical distinction when given tests with typical exemplars. Experiment 3 established that 10-month-olds could differentiate among the exemplars. These results suggest that the perceptual similarity of the exemplars influences infants' recognition of categorical distinctions.

Distractibility in infancy: the effects of distractor characteristics and type of attention.

Two experiments investigated the role of distractor characteristics and type of object-directed attention on infants' distraction latencies during object exploration. In Experiment 1, 7- and 10-month-old infants' distraction latency was a function of both attention and the characteristics of the distractors. Infants took longer to turn toward distractors during focused object-directed attention than when engaged in more casual attention. In addition, their latencies were longer regardless of attention type when the distractors were unimodal (e.g., consisting of only a visual or an auditory component) than when they were bimodal (e.g., consisting of both auditory and visual components). Experiment 2 demonstrated that infants exhibit shorter distraction latencies toward complex than simple bimodal distractors. These results are discussed in the context of Allport's (1989) model of attention and suggest that infants' allocation of attentional resources, as measured by distraction latencies, is influenced both by the characteristics of the distractor and by the type of infants' object-directed attention.

Effects of gentamicin, neomycin and tobramycin on renal calcium and magnesium handling in two rat strains.

1. Standard renal clearance techniques were used to compare the acute effects of gentamicin, neomycin and tobramycin on renal calcium and magnesium handling in Sprague-Dawley and Fischer 344 rats. 2. Significant hypercalciuric and hypermagnesiuric responses to all three drugs (P < 0.01) were apparent within 30 min of the onset of drug infusion. 3. The magnitude of the acute hypercalciuric and hypermagnesiuric response to the three aminoglycosides was comparable. This contrasts with their nephrotoxic action where neomycin >> gentamicin > tobramycin. The magnitude of the acute physiological responses to these drugs do not therefore reflect their nephrotoxic potential. 4. Sprague-Dawley rats were at least as responsive as Fischer rats in their acute renal responses to gentamicin. If Fischer rats are more sensitive to aminoglycoside nephrotoxicity than Sprague-Dawley rats, this is not reflected in their acute responses to gentamicin.