It is commonly believed that first-learned words correspond with first-learned categories (both described as ‘basic level’) leading to the belief that language acquisition is a reasonably good indicator of early cognition. However, toddlers often overextend their first words. Do these errors reflect their comprehension? Two experiments were conducted in order to examine two-year-olds' production and comprehension of basic-level terms. The results showed overextensions both in production (e.g. children labelled a rocket ‘airplane’) and comprehension (e.g. they pointed to a rocket when airplane was requested). One reason toddlers extend labels to a wider conceptual domain is because they have not clearly differentiated basic-level concepts from related conceptual categories.

Thelen and her colleagues' model overemphasizes the role of action in cognitive development. Recent research has shown that infants do not have to be trained to reach for a hidden object. By 7.5 months of age, infants can recall the location of a hidden object with no practice trials. Thelen at al.'s goal to design a parsimonious account of A-not-B behaviors was successful, but at the expense of focusing primarily on implicit and ignoring explicit memory.

Two experiments were conducted to evaluate symbolic-deficit andmemory-deficit hypotheses to account for the cognitive problems seenin children with autism. Experiment 1 tested imitation, in immediateand deferred conditions, of familiar actions with different sets ofobjects representing the developmental progression from functional tosymbolic play. The results showed that the autism group and both theirreceptive language and nonverbal IQ-matched controls imitated familiaractions with realistic objects (evidence for functional play) andplaceholder objects (evidence for symbolic play) after delays rangingfrom 24 hr to 3 weeks. Experiment 2 tested familiar three-step eventsequences in which a placeholder object was substituted for the secondstep in half the events. The results showed that the autism groupremembered as many of the actions with the placeholder objects astheir language-matched controls and as many correctly orderedsequences, a finding that supports a symbolic-delay (rather thandeficit) hypothesis. These results were obtained in highly structuredtest situations and sharply contrast with the impairments seen inchildren with autism who are observed in naturalistic settings. Twointerpretations of these findings are offered. First, structured testsettings minimize distractions that typically occur in naturalisticsettings that may interfere or disrupt symbolic play in children withautism. Second, the results are consistent with an executive functiondeficit in that the autistic group demonstrated more knowledge in thetest settings than they demonstrate spontaneously in naturalisticones.