The dynamics of development on the Dimensional Change Card Sorting task

A widely used paradigm to study cognitive flexibility in preschoolers is the Dimensional Change Card Sorting (DCCS) task. The developmental dynamics of DCCS performance was studied in a cross-sectional design (N = 93, 3 to 5 years of age) using a computerized version of the standard DCCS task. A model-based analysis of the data showed that development on the DCCS task is best described as a discontinuous change in performance on the post-switch phase of the task. In addition to a perseveration group and a switch group, a transitional group that showed shifts between perseverating and switching during the post-switch trials could be distinguished. Computational models of performance and development on the DCCS task cannot, in their current forms, explain these results. We discuss how a catastrophe model of the developmental changes in task performance could be used to generate specific hypotheses about the variables that control development of DCCS performance.     

Is auditory discrimination mature by middle childhood? A study using time‐frequency analysis of mismatch responses from 7 years to adulthood

Behavioural and electrophysiological studies give differing impressions of when auditory discrimination is mature. Ability to discriminate frequency and speech contrasts reaches adult levels only around 12 years of age, yet an electrophysiological index of auditory discrimination, the mismatch negativity (MMN), is reported to be as large in children as in adults. Auditory ERPs were measured in 30 children (7 to 12 years), 23 teenagers (13 to 16 years) and 32 adults (35 to 56 years) in an oddball paradigm with tone or syllable stimuli. For each stimulus type, a standard stimulus (1000 Hz tone or syllable [ba]) occurred on 70% of trials, and one of two deviants (1030 or 1200 Hz tone, or syllables [da] or [bi]) equiprobably on the remaining trials. For the traditional MMN interval of 100–250 ms post-onset, size of mismatch responses increased with age, whereas the opposite trend was seen for an interval from 300 to 550 ms post-onset, corresponding to the late discriminative negativity (LDN). Time-frequency analysis of single trials revealed that the MMN resulted from phase-synchronization of oscillations in the theta (4–7 Hz) range, with greater synchronization in adults than children. Furthermore, the amount of synchronization was significantly correlated with frequency discrimination threshold. These results show that neurophysiological processes underlying auditory discrimination continue to develop through childhood and adolescence. Previous reports of adult-like MMN amplitudes in children may be artefactual results of using peak measurements when comparing groups that differ in variance.     

Comparing responses of four ungulate species to playbacks of baboon alarm calls

A growing body of evidence suggests that a wide range of animals can recognize and respond appropriately to calls produced by other species. Social learning has been implicated as a possible mechanism by which heterospecific call recognition might develop. To examine whether familiarity and/or shared vulnerability with the calling species might influence the ability of sympatric species to distinguish heterospecific alarm calls, we tested whether four ungulate species (impala: Aepyceros melampus; tsessebe: Damaliscus lunatus; zebra: Equus burchelli; wildebeest: Connochaetes taurinus) could distinguish baboon (Papio hamadryas ursinus) alarm calls from other loud baboon calls produced during intra-specific aggressive interactions (‘contest’ calls). Overall, subjects’ responses were stronger following playback of alarm calls than contest calls. Of the species tested, impala showed the strongest responses and the greatest difference in composite response scores, suggesting they were best able to differentiate call types. Compared with the other ungulate species, impala are the most frequent associates of baboons. Moreover, like baboons, they are susceptible to both lion and leopard attacks, whereas leopards rarely take the larger ungulates. Although it seems possible that high rates of association and/or shared vulnerability may influence impala’s greater ability to distinguish among baboon call types, our results point to a stronger influence of familiarity. Ours is the first study to compare such abilities among several community members with variable natural histories, and we discuss future experiments that would more systematically examine development of these skills in young ungulates.     

Executive function and theory of mind: stability and prediction from ages 2 to 3

Several studies have demonstrated a relation between executive functioning (EF) and theory of mind (ToM) in preschoolers, yet the developmental course of this relation remains unknown. Longitudinal stability and EF-ToM relations were examined in 81 children at 24 and 39 months. At Time 1, EF was unrelated to behavioral measures of ToM but was significantly related to parent report of children's internal-state language, independent of vocabulary size. At Time 2, behavioral batteries of EF and ToM were significantly related (r=.50, p<.01). Furthermore, EF (Time 1) significantly predicted ToM (Time 2), independent of several controls. A reciprocal relation (internal-state language --> EF at Time 2) was nonsignificant with the controls included. Individual differences in EF were relatively stable.     

In focus. Has patient autonomy gone to far? Geneticists' views in 36 nations

We surveyed genetics professionals, patients, and the public about rights to information, to requested services, and to parenthood, posing difficult cases found in practice. In all, 2906 genetics professionals (63%), 499 primary care physicians (59%), 476 North American genetics patients (67%), 394 French patients (51%), 593 German patients (65%), and 988 members of the American public (99%) returned anonymous questionnaires. Results suggest a trend toward increased respect for patient autonomy since an earlier survey in 1985; in most nations more would perform prenatal diagnosis for a couple with 4 daughters who desire a son. A minority (35% in U.S., 14% elsewhere) would perform PND for a deaf couple who want a deaf child, but most (94% in U.S., 62% elsewhere) would do prenatal paternity testing in the absence of rape or incest. About half (51%) would support a woman with fragile X who wants children. The trend to respect patient autonomy was greatest in the U.S. and was least evident in China and India. In general, responses to these cases illustrate a shift away from population or eugenic concerns to a model of genetics focused on the individual.     

Presupposition and Implication of Truth: Linguistic Deficits following Early Brain Lesions

Twenty-four children (4–17 years) with unilateral left (N = 14) or right (N = 10) hemisphere damage and 24 age-matched controls were tested on their ability to presuppose the truth of factive sentences e.g., “Max knew that he locked the door,” and to infer the truth or falsity of implicative sentences “Max remembered to lock the door.” Experimental sentence types varied according to the type of inference, the semantic features of the verb (factive vs. implicative), the presence and type of negation (lexical or syntactic), and the syntax of the complement (tensed or infinitive). Relative to age-matched controls, left lesion subjects were deficient in both their presupposition and implication performance, particularly when such inferences required the computation of negation scope. Right lesion subjects exhibited a somewhat more selective deficit; one limited to implication, but not presupposition, and one limited to lexical but not syntactic forms of negation.