The developmental pattern of stimulus and response interference in a color-object Stroop task: an ERP study

Background

Several studies have shown that Stroop interference is stronger in children than in adults. However, in a standard Stroop paradigm, stimulus interference and response interference are confounded. The purpose of the present study was to determine whether interference at the stimulus level and the response level are subject to distinct maturational patterns across childhood. Three groups of children (6–7 year-olds, 8–9 year-olds, and 10–12 year-olds) and a group of adults performed a manual Color-Object Stroop designed to disentangle stimulus interference and response interference. This was accomplished by comparing three trial types. In congruent (C) trials there was no interference. In stimulus incongruent (SI) trials there was only stimulus interference. In response incongruent (RI) trials there was stimulus interference and response interference. Stimulus interference and response interference were measured by a comparison of SI with C, and RI with SI trials, respectively. Event-related potentials (ERPs) were measured to study the temporal dynamics of these processes of interference.

Results

There was no behavioral evidence for stimulus interference in any of the groups, but in 6–7 year-old children ERPs in the SI condition in comparison with the C condition showed an occipital P1-reduction (80–140 ms) and a widely distributed amplitude enhancement of a negative component followed by an amplitude reduction of a positive component (400–560 ms). For response interference, all groups showed a comparable reaction time (RT) delay, but children made more errors than adults. ERPs in the RI condition in comparison with the SI condition showed an amplitude reduction of a positive component over lateral parietal (-occipital) sites in 10–12 year-olds and adults (300–540 ms), and a widely distributed amplitude enhancement of a positive component in all age groups (680–960 ms). The size of the enhancement correlated positively with the RT response interference effect.

Conclusion

Although processes of stimulus interference control as measured with the color-object Stroop task seem to reach mature levels relatively early in childhood (6–7 years), development of response interference control appears to continue into late adolescence as 10–12 year-olds were still more susceptible to errors of response interference than adults.     

Ab initio SCF MO calculation of ionisation energies and charge distributions of TCNQ and its mono- and divalent anions

Ab initio SCF MO calculations using a contracted double zeta basis set of 168 gaussian type functions were performed on TCNQ⁺, TCNQ, TCNQ^? and TCNQ^2?. The ionisation potentials obtained from total energy differences are generally 0.25-0.50 eV higher than the corresponding negative orbital energies from the TCNQ calculation and in satisfactory agreement with experimental results. The energy of the disproportionation reaction 2TCNQ^?-TCNQ+TCNQ^2? is calculated to be 4.62 eV. The charge distributions as measured by the gross atomic populations generally deviate from those obtained in earlier π-electron calculations as a consequence of taking the σ-electron distribution into account. The atomic charges are in good agreement with the limited experimental data available.     

One-way optoelectronic switching of photochromic molecules on gold

We investigate photochromic molecular switches that are self-assembled on gold. We use two experimental techniques; namely, the mechanically controllable break-junction technique to measure electronic transport, and UV/Vis spectroscopy to measure absorption. We observe switching of the molecules from the conducting to the insulating state when illuminated with visible light (lambda=546 nm), in spite of the gold surface plasmon absorption present around this wavelength. However, we fail to observe the reverse process which should occur upon illumination with UV light (lambda=313 nm). We attribute this to quenching of the excited state of the molecule in the open form by the presence of gold.     

Iron nanoparticles grown in a carbon arc discharge

Summary Iron particles, encapsulated by graphite layers, were produced by means of the Kratschmer arc discharge method in an iron pentacarbonyl atmosphere. The M?ssbauer effect is dominated by the vibration of the particles as a whole. Superparamegnetism is dominant for iron oxide particles. No endohedral iron fullerenes were observed, contrary to a previous report. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Rational experimental design for bioanalytical methods validation illustration using an assay method for total captopril in plasma

Generally, bioanalytical chromatographic methods are validated according to a predefined programme and distinguish a pre-validation phase, a main validation phase and a follow-up validation phase. In this paper, a rational, total performance evaluation programme for chromatographic methods is presented. The design was developed in particular for the pre-validation and main validation phases. The entire experimental design can be performed within six analytical runs. The first run (pre-validation phase) is used to assess the validity of the expected concentration-response relationship (lack of fit, goodness of fit), to assess the specificity of the method and to assess the stability of processed samples in the autosampler for 30 h (benchtop stability). The latter experiment is performed to justify overnight analyses. Following approval of the method after the pre-validation phase, the next five runs (main validation phase) are performed to evaluate method precision and accuracy, recovery, freezing and thawing stability and over-curve control /dilution. The design is nested, i.e., many experimental results are used for the evaluation of several performance characteristics. Analysis of variance (ANOVA) is used for the evaluation of lack of fit and goodness of fit, precision and accuracy, freezing and thawing stability and over-curve control/ dilution. Regression analysis is used to evaluate benchtop stability. For over-curve control/ dilution, additional to ANOVA, also a paired comparison is applied. As a consequence, the recommended design combines the performance of as few independent validation experiments as possible with modern statistical methods, resulting in optimum use of information. A demonstration of the entire validation programme is given for an HPLC method for the determination of total captopril in human plasma.