Predictors of early vocabulary growth in children born preterm and full term: A study of processing speed and medical complications

Delays in expressive vocabulary may be harbingers of long-term language difficulties. In toddlers born full term (FT), individual differences in language processing speed are associated with variation in expressive vocabulary growth. Children born preterm (PT) are at increased risk for persistent language deficits. Here, we evaluate predictors of early vocabulary growth in PT toddlers in relation to two sources of variability: language processing speed and medical complications of prematurity. Vocabulary growth from 16 to 30 months (adjusted for degree of prematurity) was modeled longitudinally using parent reports in English-speaking FT (n = 63; ≥37 weeks, ≥2495 g) and PT (n = 69; ≤32 weeks, <1800 g) children, matched on sex and socioeconomic status. Children were tested in the “looking-while-listening task” at 18 months to derive a measure of language processing speed. Each PT child was assessed for number of medical complications (13 maximum), based on medical chart reviews. PT and FT children displayed similar vocabulary trajectories; however, birth group disparities began to emerge by 30 months. PT children were slower in language processing speed than FT children. Critically, language processing speed predicted expressive vocabulary size at 30 months; interactions with birth group were not significant (all p > .20). In PT children, faster language processing speed predicted stronger outcomes regardless of number of medical complications; slower processing speed and more medical complications predicted poorer outcomes. Faster processing speed reflected favorable neuropsychological processes associated with faster expressive vocabulary growth that overrode the impact of medical complications on language outcomes in PT children.     

Movement segmentation and visual perturbation increase developmental differences in motor control and learning

We examined the developmental differences in motor control and learning of a two‐segment movement. One hundred and five participants (53 female) were divided into three age groups (7–8 years, 9–10 years and 19–27 years). They performed a two‐segment movement task in four conditions (full vision, fully disturbed vision, disturbed vision in the first movement segment and disturbed vision in the second movement segment). The results for movement accuracy and overall movement time show that children, especially younger children, are more susceptible to visual perturbations than adults. The adults’ movement time in one of the movement segments could be increased by disturbing the vision of the other movement segment. The children's movement time for the second movement segment increased when their vision of the first movement segment was disturbed. Disturbing the vision of the first movement segment decreased the percentage of central control of the second movement in younger children, but not in the other two age groups. The children's normalized jerk was more easily increased by visual perturbations. The children showed greater improvement after practice in the conditions of partial vision disturbance. As the participants’ age increased, practice tended to improve their feedforward motor control rather than their feedback motor control. These results suggest that children's central movement control improves with age and practice. We discuss the theoretical implications and practical significance of the differential effects of visual perturbation and movement segmentation upon motor control and learning from a developmental viewpoint.     

Exploring the beliefs underpinning drivers’ intentions to comply with speed limits

Using the theory of planned behaviour (TPB; [Ajzen, I. (1985). From intentions to actions: A theory of planned behavior. In J. Kuhl, J. Beckmann (Eds.), Action control: From cognition to behavior (pp. 11–39). Berlin: Springer-Verlag.]) as a theoretical framework, the present study was designed to: (a) identify the beliefs underpinning drivers’ intentions to comply with speed limits, and (b) test the expectancy-value theory held to underpin those beliefs. A sample of drivers (N = 598) completed questionnaires designed to measure TPB variables with respect to compliance with speed limits. The results of hierarchical multiple regression analyses provided support for the expectancy-value theory held to underpin each behavioural beliefs (outcome beliefs X outcome evaluations), normative beliefs (referent beliefs X motivation to comply), and control beliefs (control frequency beliefs X control power beliefs). Belief targets for road safety countermeasures that aim persuade drivers to comply with speed limits were also identified by selecting those beliefs that were the statistically significant predictors of direct TPB measures (attitudes, subjective norm, perceived control) and intention. Theoretical and practical implications of the results are discussed.     

Unsignaled delay of reinforcement, relative time, and resistance to change

Two experiments with pigeons examined the effects of unsignaled, nonresetting delays of reinforcement on responding maintained by different reinforcement rates. In Experiment 1, 3-s unsignaled delays were introduced into each component of a multiple variable-interval (VI) 15-s VI 90-s VI 540-s schedule. When considered as a proportion of the preceding immediate reinforcement baseline, responding was decreased similarly for the three multiple-schedule components in both the first six and last six sessions of exposure to the delay. In addition, the relation between response rates and reinforcement rates was altered such that both parameters of the single-response version of the matching law (i.e., k and Re) were decreased. Experiment 2 examined the effects of unsignaled delays ranging from 0.5 s to 8.0 s on responding maintained by a multiple VI 20-s VI 120-s schedule of reinforcement. Response rates in both components increased with brief unsignaled delays and decreased with longer delays. As in Experiment 1, response rates as a proportion of baseline were affected similarly for the two components in both the first six and last six sessions of exposure to the delay. Unlike delays imposed between two stimulus events, the effects of delays between responses and reinforcers do not appear to be attenuated when the average time between reinforcers is longer. In addition, the disruptions produced by unsignaled delays appear to be inconsistent with the general finding that responding maintained by higher rates of reinforcement is less resistant to change.     

Selection of variables in exploratory factor analysis: An empirical comparison of a stepwise and traditional approach

The purpose of this study was to investigate and compare the performance of a stepwise variable selection algorithm to traditional exploratory factor analysis. The Monte Carlo study included six factors in the design; the number of common factors; the number of variables explained by the common factors; the magnitude of factor loadings; the number of variables not explained by the common factors; the type of anomaly evidenced by the poorly explained variables; and sample size. The performance of the methods was evaluated in terms of selection and pattern accuracy, and bias and root mean squared error of the structure coefficients. Results indicate that the stepwise algorithm was generally ineffective at excluding anomalous variables from the factor model. The poor selection accuracy of the stepwise approach suggests that it should be avoided.     

Bouts of responding on variable-interval schedules: effects of deprivation level

Rats obtained food pellets on a variable-interval schedule of reinforcement by nose poking a lighted key. After training to establish baseline performance (with the mean variable interval set at either 60, 120, or 240 s), the rats were given free access to food during the hour just before their daily session. This satiation operation reduced the rate of key poking. Analysis of the interresponse time distributions (log survivor plots) indicated that key poking occurred in bouts. Prefeeding lengthened the pauses between bouts, shortened the length of bouts (less reliably), and had a relatively small decremental effect on the response rate within bouts. That deprivation level affects mainly between-bout pauses has been reported previously with fixed-ratio schedules. Thus, when the focus is on bouts, the performances maintained by variable-interval schedules and fixed-ratio schedules are similarly affected by deprivation.     

Developmental trends in simple and selective inhibition of compatible and incompatible responses

This study examined age-related change in the ability to inhibit responses using two varieties of the stop signal paradigm. Three age groups (29 7-year-olds, 24 10-year-olds, and 28 young adults) performed first on a visual choice reaction task in which the spatial mapping between the go signal and response was varied between blocks. The choice task was then complicated by randomly inserting a visual stop signal on 30% of the trials. In the simple stop signal paradigm, the stop signal required the inhibition of the planned response. In the selective stop signal paradigm, the stop signal required response inhibition only when the stop signal was presented at the same side as the instructed response to the go signal. The results showed that simple stopping was faster than selective stopping and that selective, but not simple, stopping of incompatible responses was slower than stopping of compatible responses. Brinley plot analysis yielded linear functions relating children's latencies to adults' latencies. Analysis of shared variance indicated that developmental change in the speed of selective stopping continued to be significant even when the effect associated with simple stopping was removed. This pattern of findings is discussed vis-à-vis notions of global versus specific developmental trends in the speed of information processing.     

Speed contingencies, number of stimulus presentations, and the nodality effect in equivalence class formation.

Two experiments compared performances on conditional discrimination tasks using single-participant designs with and without speed contingencies. Experiment 1 was a systematic replication of Spencer and Chase (1996). Experiment 2 presented equal numbers of training and testing trials. In each experiment, 2 female undergraduates participated. Each formed three five-member and three seven-member equivalence classes in Experiments 1 and 2, respectively. Response speed was an inverse function of nodal number and relational type in Experiment 1, but only of relational type (i.e., baseline, symmetry, transitivity, and equivalence) in Experiment 2, with and without the speed contingency. Accuracy tended to peak without the speed contingency in both experiments. Adding the speed contingency increased response speeds in both experiments, more so in Experiment 2 with a lower limited hold for I participant. The results of Experiment 2 cast doubt on previous reports of the nodality effect and on the notion of "relatedness" among class members, and they support a reinforcement-contingency, rather than a structural, account of equivalence class formation.     

Variable effects of a behavioral treatment package on the performance of inline roller speed skaters

We investigated the effects of a treatment package on the performance of correct relay tags with 4 inline speed skaters. The treatment package included verbal praise following correct tags, visual feedback of performance data, and instruction for improving performance. Initial gains in the frequency of correct tags were not maintained at 6-month follow-up when baselines were reestablished. Performance on the second intervention phase for the 3 original subjects was variable and differed from the initial phase, whereas the original findings were replicated in the 4th subject. Possible reasons for this variability and implications for future research and behavioral sport interventions are considered.     

Evidence against a constant-difference effect in concurrent-chains schedules

Savastano and Fantino (1996) reported that in concurrent-chains schedules, initial-link choice proportions remained constant as terminal-link durations increased as long as the subtractive difference between the two terminal-link schedules remained constant. Two experiments with pigeons were conducted to examine this constant-difference effect. Both experiments used equal variable-interval schedules as initial links. The terminal links were fixed delays to reinforcement in Experiment 1 and variable delays to reinforcement in Experiment 2. The durations of the terminal links were varied across conditions, but the difference between pairs of terminal links was always 10 s. In both experiments, preference for the shorter terminal link became less extreme as terminal-link durations increased, so a constant-difference effect was not found. It is argued, however, that this choice situation does not provide clear evidence for or against delay-reduction theory versus other theories of choice.