Reaction Timing Research Articles

Fluorescent microplate analysis of amino acids and other primary amines in soils

In studies of soil nitrogen (N) cycling, there is growing demand for accurate high-throughput analyses of amino acids and other small organic N compounds. We adapted an existing fluorometric amino acid method based on o-phthaldialdehyde and β-mercaptoethanol (OPAME) for use in 96-well microplates, and tested it using standards and field samples. While we started with an existing protocol, we made one critical change: instead of using a 1-min incubation period, we used a 1-h incubation period to deal with differences in reaction timing among microplate wells and to reduce interference from ammonium. Our microplate method is similar in sensitivity to existing protocols and able to determine leucine standard concentrations as low as ∼0.5 μM. Finally, we demonstrate that the OPAME reagent fluoresces in the presence of primary amines other than amino acids, such as amino sugars and tyramine. Because of this broad sensitivity to primary amines, descriptions of the measured pool should be revised from total free amino acids (TFAA) to total free primary amines (TFPA).

Effects of Limb Loading on Gait Initiation in Persons with Moderate Hemiparesis

Purpose: To examine the immediate effect of symmetrical weight bearing (SWB) on temporal events of gait initiation (GI) patterns and timing and amplitude of lower distal limb muscles activity during GI in persons with hemiparesis. Method: The study was a within-subjects design. Twelve persons with hemiparesis were recruited from the Veterans Affairs Brain Rehabilitation Research Center at the Malcom Randall Veterans Affairs, Gainesville, Florida. GI trials were performed from 4 beginning limb-loading conditions presented in a randomized order: (1) GI with the paretic limb during natural (asymmetrical) weight bearing (NWB); (2) GI with the nonparetic limb during NWB; (3) GI with the paretic limb during SWB; and (4) GI with the nonparetic limb during SWB. Temporal events of ground reaction forces (GRFs) and timing and amplitude of distal muscles activity were measured during GI trials in a motion analysis laboratory. Results: There were no significant effects of SWB on the temporal events of GRFs and timing and amplitude of distal muscles activity when initiating gait with the paretic limb. Onset of tibilais anterior (TA) muscle was delayed significantly with less amplitude when initiating gait with the paretic limb in both NWB and SWB conditions. However, when initiating gait with the nonparetic limb, TA muscle on the paretic limb was activated normally with greater amplitude in both NWB and SWB conditions. Conclusion: Initiating gait with the nonparetic limb as pregait activity may more effectively challenge the dynamic balance for a symmetrical gait pattern than the standard SWB in persons with hemiparesis.

Reaction progress and timing of retrogression of eclogite-facies rocks, Danmarkshavn, North-East Greenland Caledonides

Eclogites are commonly preserved in the cores of mafic lenses that are surrounded by amphibolite-facies margins. The amphibolites are produced on the retrograde path with the addition of fluid to an otherwise anhydrous assemblage; the fluids are expected to enhance zircon growth. We studied two high-pressure (H P ) mafic/ultramafic lenses from the North-East Greenland eclogite province (a boudinaged garnet-clinopyroxenite and a garnet-websterite) in order to establish the timing of retrogression. We focused on the garnet-clinopyroxenite outcrop to establish the role of the fluid during retrograde metamorphism and to determine the progress of the metamorphic reactions that define the transformation of the H P assemblage to amphibolite. We collected three samples representing different degrees of amphibolitisation, and used them to determine the reaction progress between the different retrograde stages. Reactions (1) and (2) show increasing fluid availability with increasing retrogression: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[3.33 Cpx + 0.56 Grt + 0.105 Plag + 1.17 H_{2}O = 1.17 Amp\] \end{document}(1) \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[2.40 Cpx + 1.99 Grt + 6.33 Qtz + 1.06 Rt + 2.02 H_{2}O = 2.02 Amp + 0.59 Plag + 0.63 Ilm\] \end{document}(2) We determined U-Pb SHRIMP ages and collected zircon trace-element data on metamorphic rims of zircons for both lithologies, from both the H P samples and the surrounding amphibolite rims. These ages and trace elements, combined with chronological and structural data previously published, allow us to interpret the retrograde path for these rocks and the Danmarkshavn area in general. The age of the metamorphic zircon is the same in the center and at the margin of the mafic and ultramafic pods, with ages spanning between 390 and 360 Ma and younger ages (about 330–340 Ma) for the garnet-clinopyroxenite. The oldest Paleozoic ages in the mafic samples likely record the timing of H P metamorphism or initial retrogression. Pegmatite emplacement into strain shadows between mafic boudins was ongoing at 375 Ma. Fluid circulation accompanying deformation and pegmatite emplacement is recorded by the 375 Ma zircon growth in the garnet-websterite. Additional zircon growth is observed both in the garnet-clinopyroxenite and garnet-websterite as well as in a boudin-neck pegmatite at ca . 360 Ma. Continued zircon growth at 340, 330, and 315 Ma is recorded in the garnet-clinopyroxenite, the adjacent boudin-neck pegmatite and the pegmatite dike that cross-cuts amphibolite-facies structural fabrics. All of the younger episodes of zircon growth are interpreted to reflect fluid influx linked to continued retrograde metamorphism, deformation, and pegmatite emplacement in the Carboniferous.

Ab Initio Molecular Dynamics Study on the Initial Chemical Events in Nitramines: Thermal Decomposition of CL-20

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane or HNIW) is a high-energy nitramine explosive. To improve atomistic understanding of the thermal decomposition of CL-20 gas and solid phases, we performed a series of ab initio molecular dynamics simulations. We found that during unimolecular decomposition, unlike other nitramines (e.g., RDX, HMX), CL-20 has only one distinct initial reaction channelhomolysis of the N-NO2 bond. We did not observe any HONO elimination reaction during unimolecular decomposition, whereas the ring-breaking reaction was followed by NO 2 fission. Therefore, in spite of limited sampling, that provides a mostly qualitative picture, we proposed here a scheme of unimolecular decomposition of CL-20. The averaged product population over all trajectories was estimated at four HCN, two to four NO2, two to four NO, one CO, and one OH molecule per one CL-20 molecule. Our simulations provide a detailed description of the chemical processes in the initial stages of thermal decomposition of condensed CL-20, allowing elucidation of key features of such processes as composition of primary reaction products, reaction timing, and Arrhenius behavior of the system. The primary reactions leading to NO2, NO, N 2O, and N2 occur at very early stages. We also estimated potential activation barriers for the formation of NO2, which essentially determines overall decomposition kinetics and effective rate constants for NO2 and N2. The calculated solid-phase decomposition pathways correlate with available condensed-phase experimental data.

Determination of formaldehyde in foodstuffs by flow injection spectrophotometry using phloroglucinol as chromogenic agent

A spectrophotometric method for the determination of formaldehyde in foodstuffs was described by using phloroglucinol as the chromogenic agent. The reaction between formaldehyde and phloroglucinol could occur rapidly at room temperature under mild conditions. The spectrophotometric measurements were conducted at 474 nm of an unstable intermediate orange product of the reaction, which greatly increased the sample throughput. Flow injection technique was used to control the merging and reaction timing of the reagents and sample. A detection limit (3 σ) of 0.023 μg ml −1 was achieved. The relative standard deviation was 0.29% for the determination of 7 μg ml −1 formaldehyde ( n = 11). The proposed method was applied to the analyses of formaldehyde in several preserved foodstuffs and the results were in good agreement with those obtained by a standard method.

Developmental instability and the neural dynamics of the speed–intelligence relationship

Two of the most securely established findings in the biology of intelligence are the relationship between reaction time (RT) and intelligence, and the heritability of intelligence. To investigate why RT may related to intelligence, researchers have used a variety of techniques to subdivide RT into cognitive and motor components. In the current study, magnetoencephalographic (MEG) dipole latencies were used to examine the speed and timing of specific brain processing stages engaged during visually cued simple and choice reaction time tasks. Simple and choice reaction time and timing of MEG sources were considered in relation to fluid intelligence (as measured by the Raven's Advanced Progressive Matrices, RAPM). To address heritability of intelligence, developmental instability (DI) was assessed, measured here as fluctuating asymmetry. DI represents the degree to which an organism is susceptible to developmental stress arising from both environmental and genomic sources. Analyses showed that choice, but not simple reaction time was negatively correlated with RAPM score. MEG revealed a set of complex relationships between the timing of regional brain activations and psychometric intelligence. The neural component associated with integration of sensory and motor information was most associated with RAPM compared to other components. Higher values of fluctuating asymmetry predicted reduced psychometric intelligence, a result suggesting that some part of the variance of the heritability of intelligence reflects DI. Fluctuating asymmetry was significantly and negatively correlated with timing during all components of task completion. These observations suggest that fluid intelligence is primarily related to speed during processing associated with decision time, while fluctuating asymmetry predicted slower processing across all stages of information processing.

Scapulothoracic latent muscle reaction timing comparison between trained overhead throwers and untrained control subjects

This study evaluated select scapulothoracic muscles for training-induced latent muscle reaction timing (LMRT) changes. Comparisons were also made between the dominant and non-dominant upper extremities and between individual muscles. Fifteen male trained overhead throwers (college baseball pitchers) and 15 male untrained, age-matched control subjects participated in this study. Scapulothoracic muscle activation data were collected as subjects attempted to stop a variably timed, sudden glenohumeral joint internal rotation perturbation. Training group differences were not evident for LMRT (P=0.56), however upper extremity dominance (P=0.003) and test muscle (P=0.0002) displayed significant differences. Dominant upper extremity upper trapezius muscle LMRT (72.5+/-26 ms) occurred later than non-dominant upper trapezius muscle LMRT (60.0+/-14.1 ms, P=0.001). Dominant upper extremity middle trapezius-rhomboid muscle LMRT (60.0+/-16.2 ms) occurred later than non-dominant middle trapezius-rhomboid muscle LMRT (50.2+/-12.6 ms, P=0.004). Dominant upper extremity upper trapezius muscle LMRT also occurred later than serratus anterior (55.7+/-16.0 ms, P=0.001) and middle trapezius-rhomboid LMRT (60.2+/-16 ms, P=0.003). Mean overall dominant upper extremity LMRT (62.7+/-19.4 ms) was delayed compared with mean overall non-dominant upper extremity LMRT (53.9+/-12.4 ms, P=0.003). Although training was not found to influence scapulothoracic LMRT, differences were observed between the dominant and non-dominant upper extremities. Consistent LMRT delays at the dominant upper extremity suggest possible neuromuscular timing differences to enable prolonged glenohumeral joint and scapulothoracic articulation acceleration before deceleration through eccentric muscle activation. Both trained and untrained overhead throwers displayed this response. Variable perturbation test velocities, and in-season testing of larger subject groups may be needed to better elucidate the more subtle differences associated with training.

Bioelectrocatalytic signaling from immunosensors with back‐filling immobilization of glucose oxidase on biorecognition surfaces

We report a novel method of electrochemical signaling from antigen-antibody interactions at immunoelectrodes with bioelectrocatalyzed enzymatic signal amplification. For the immunosensing surface construction, a poly(amidoamine) G4-dendrimer was employed not only as a building block for the electrode surface modification but also as a matrix for ligand functionalization. As a model biorecognition reaction, the dinitrophenyl (DNP) antigen-functionalized electrode was fabricated and an anti-DNP antibody was used. Glucose oxidase (GOX) was chosen to amplify electrochemical signal by enzymatic catalysis. The signal amplification strategy introduced in this study is based on the back-filling immobilization of biocatalytic enzyme to the immunosensor surface, circumventing the use of an enzyme-labeled antibody. The non-labeled native antibody was biospecifically bound to the immobilized ligand, and the activated enzyme (periodate-treated GOX) reacted and "back-filled" the remaining surface amine groups on the dendrimer layer by an imine formation reaction. From the bioelectrocatalyzed signal registration with the immobilized GOX, the surface density of biospecifically bound antibody could be estimated. The DNP functionalization reaction was optimized to facilitate the antibody recognition and signaling reactions, and approximately 6% displacement of surface amine to DNP was found to be an optimum. From quartz crystal microbalance measurement, immunosensing reaction timing and the surface inertness to the nonspecific biomolecular binding were tested. By changing the surface functionalization level of DNP in the calibration experiments, immunosensors exhibited different dynamic detection ranges and limits of detection, supporting the capability of parameters modulation for the immunosensors. For the anti-DNP antibody assay, the fabricated immunosensor having 65% functionalization ratio exhibited the linear detection range of 10(-4) to 0.1 g/L protein and a limit of detection around 2 x 10(-5) g/L.

Neural bases of accumulator models

One class of cognitive models, accumulator models (AMs), is a framework to explain cognitive mechanisms of reaction timing. In AMs, an internal signal, which grows linearly with time upon the onset of an external stimulus, is postulated. Reaction time is defined by the time at which the signal reaches a predefined threshold level. Indeed, cortical neurons with activity that grows seemingly linearly with time are largely found, which is consistent with AMs. Here we show that stochastic dynamics of a recurrent network of bistable spiking neurons can produce linear growth of neuronal activity. This suggests possible neural bases of AMs.

Shoulder proprioception: latent muscle reaction times.

The purpose of this study was to identify electromyographic (EMG) differences in the latent muscle reaction timing (LMRT) of the rotator cuff between trained overhead throwers and control subjects in response to sudden internal rotation perturbation (P < or = 0.05). Subjects included 15 trained overhead throwers (male intercollegiate baseball players) and 15 untrained subjects (males not active in competitive throwing sports). Subjects were tested while seated, with their dominant glenohumeral joint positioned in 90 degrees abduction/external rotation (scapular plane), their elbow flexed to 90 degrees, and their forearm placed in the perturbation device. Rotator cuff LMRT was assessed as they tried to decelerate a variably timed, sudden internal rotation force. EMG sampling (2000 Hz, 2-s duration) began immediately before perturbation. Trained throwers had slower infraspinatus (P = 0.011) and teres minor (P = 0.024) LMRT and decreased supraspinatus (P = 0.001) and posterior deltoid (P = 0.0001) muscle activation duration compared with control subjects. These results suggest that the rotator cuff muscles of trained throwers may be downregulated in response to sudden internal rotation perturbation. Although these adaptations would enable greater internal rotation velocities during overhead throwing, they may also contribute to glenohumeral joint pathology. The identification of changes in rotator cuff LMRT in response to sudden internal rotation perturbation suggests an area of acquired neuromuscular imbalance warranting consideration by those involved in the rehabilitation and conditioning of the overhead throwing athlete.

Hardware and software for tachistoscopy: how to make accurate measurements on any PC utilizing the Microsoft Windows operating system.

Methods for automated stimulus display and accurate response time measurement with IBM-compatible PCs are of great importance in cognitive research designs. Accurate measurements of reaction times are required to interpolate other measures, such as speed of mental processing. We present a description of hardware and software that displays stimulus images and performs reaction timing that is not dependent on PC performance characteristics. This is accomplished by electronically bypassing timing errors normally inherent to the operation of the computer. A high-precision external timer measures the time between stimulus onset and a subject's push-button response while a video blanking circuit controls the video presented to the monitor screen. Two options for accurately detecting stimulus onset are presented: (1) A photodetector can be used to sense the actual onset of the stimulus on a secondary video monitor screen; (2) the video blanking circuit can provide a signal coincident with the initiation of video to the monitor. Both methods result in a system timing accuracy of 100 microseconds.

Relationships among age, conditioned stimulus-unconditioned stimulus interval, and neuropsychological test performance.

To evaluate the effect of age at various conditioned stimulus (CS)-unconditioned stimulus (US) intervals, 144 young, middle-aged, and older adults were tested on eyeblink classical conditioning at CS-US intervals of 500, 1,000, or 1,500 ms. Reaction time, response timing, motor learning, declarative memory, and attention were assessed to identify correlates of conditioning at various CS-US intervals. Previously reported middle-aged and older adults were impaired at a 400-ms CS-US interval, but the addition of 100 ms to the CS-US interval in this study enabled equal conditioning in middle-aged and young adults. At a 1,000-ms CS-US interval, older adults remained significantly impaired. It was only at the 1,500-ms CS-US interval that conditioning was equal for the 3 age groups. Measures of reaction time, timing, and motor learning were not correlated systematically with conditioning. Whereas the results of age differences at various CS-US intervals were clear and striking, patterns of relationships among neuropsychological and conditioning variables were not consistent in indicating sources of age differences.

Interference of IgM paraproteins in the olympus AU800 uric acid assay

Introduction: In the Olympus uric acid procedure, uric acid is converted by uricase to allantoin and hydrogen peroxide, which is reacted in a Trinder reaction to produce a chromophore read bichromatically at 520 and 660 nm. Repeated difficulty was encountered in obtaining uric acid results on samples from myeloma patients with known IgM paraproteins. Large absorbances in sample blanks were due to a visible precipitation observed in the reaction cuvettes. Objective: To alter the Olympus method (OM) to eliminate the interference by IgM, and to verify the modified method (MM). Methods: Dilution of the sample blank by saline was substituted for water in the MM, with small alterations in the reaction timing sequence necessary to accommodate the instrument requirements. Results: A comparison of uric acid results obtained from non-myeloma patient samples using the OM and the MM showed a good correlation ( r = 0.970), and no statistical difference between the two means using a paired t-test. A similar comparison performed using the samples containing IgA and IgG paraproteins also revealed a good correlation ( r = 0.981), and no statistical difference between the two means. Results on IgM containing specimens were assessed indirectly because the samples could not be assayed with the OM. First, removal of detectable levels of proteins using a 20% TCA solution did not affect the measurement of uric acid. Second, protein-free supernatants from IgM containing samples were measured by the OM and compared with the corresponding serum samples measured by the MM. There was good correlation between the two methods ( r = 0.945), and no statistical difference between the means using a paired t-test. Conclusion: The modified method is satisfactory for routine analysis of samples, including those with IgM paraproteins.

Simple reaction times and timing of serial reactions of middle-aged and old men.

The timing control of serial reactions in 20 middle-aged (38-43 years) and 20 older men (57-63 years) was examined by using a task of tracking serial-light stimuli with and without the previous learning (Exps. III and II, respectively). In Exp. I, a control group of 20 college students (19-22 years) had significantly faster and less variable mean simple reaction times than the two other groups. For the serial reaction times (Exps. II and III), the control group had significantly faster mean reaction times than the other groups who did not differ. In Exp. III, there was no difference between the serial reaction times and the simple reaction times in the contrasting groups. In Exp. II, however, although the serial reaction times were significantly slower than the simple reaction times in the older group, the serial reaction times did not differ from the simple reaction times in the middle-aged group. The difference between these groups appeared to be due to the task in Exp. II being more difficult than that in Exp. III, suggesting the more complex the movement to be made, the slower the responses of older people. Advancing age seems to have a greater effect on central processing components than on the perceptual and motor output components of serial reactions.

Simple reaction times and timing of serial reactions of adolescents with mental retardation, autism, and Down syndrome.

The purpose of this study was to examine the serial information processing in adolescents with mental retardation, autism, and Down syndrome by using a serially patterned tracking task. Analyses indicated that 7 adolescents with mental retardation, 8 with autism, and 3 with Down syndrome had significantly slower and more variable simple reaction times than did 10 college students. Also, the autistic adolescents had significantly faster mean simple reaction time than those with Down syndrome. On a task of tracking serial light stimulation, mentally retarded adolescents had significantly faster reaction time than college students. The autistic subjects excessively had faster anticipatory reaction time than did the subjects in the other three groups. On the other hand, adolescents with Down syndrome had markedly slower and more variable reaction time than did adolescents with non-Down-syndrome mental retardation. As for motor organization of keystrokes on the tracking task, mentally retarded adolescents responded with six movements, in which these individuals pressed a series of keys 1, 2, 3, 4, 5, and 6, as a chunk, as exhibited by college students. Adolescents with autism and Down syndrome, however, did not produce this movement-output chunking.

Measurement of directional lever response reaction time with the Commodore 64

Routines are described for timing directional lever responses with the Commodore 64 micro-computer. Millisecond reaction timing is carried out with on-board hardware clocks, and lever responses are detected by monitoring the position of a joystick interfaced to a controller port. In a demonstration program, a machine code subroutine is used to measure the reaction times of lever responses in a spatial relations task. In addition, modifications to the demonstration program are suggested to adapt it for use with other tasks.

Selective determination of histamine by flow injection analysis

A flow injection analysis (FIA) method for the determination of histamine is described. Control of reaction timing allows exploitation of a transient, chemical-kinetic increase in selectivity that occurs when o-phthalaldehyde reacts with histamine. The molar fluorescence ratio (selectivity) of histamine/histidine reaches a maximum value of 800 in 32 s, precluding the need for separation of histamine from histidine, spermidine, and other potential interferences in biological samples. On-line dilution prevents matrix effects and affords a linear response up to approximately 4.45 mM histamine, or 500 mg of histamine free base/100 g. Under these conditions the detection limit (3 times peak-to-peak baseline noise) is 5.5 pg (corresponding to 0.60 mg of histamine free base/100 g of sample) and throughput is 60 injections per hour. The high sensitivity and high selectivity of the method allow the rapid determination of histamine in fish with minimal sample conditioning and will find application in the determination of endogenous histamine as well, such as in blood plasma and brain tissue.

Suitability of the IBM XT, AT, and PS/2 keyboard, mouse, and game port as response devices in reaction time paradigms

The IBM PC keyboard is a convenient response panel for subjects in a reaction time task when the stimuli are presented on the same machine. However, there is a mean delay of about 10 msec and a random error of ±7.5 msec (±5 msec on the AT or PS/2). Our analyses show that for typical single response experimental situations, this added variance is acceptable. With mouse buttons, timing resulted in a delay of 31 ±2 msec if the mouse ball was steady but 45 ±15 msec if it was moving, and a 25-msec refractory period before a second response could be detected. With keys connected to the game port, timing was accurate to 1 msec. For timing the interval between two nearly simultaneous responses, only the game port method is recommended. Any research application should provide an external check on reaction timing accuracy and should correct any mean error.

Instabllity of orthophthalaldehyde reagent for amino acid analysis

Determination of amino acids by reversed-phase chromatography of the adduct with orthophthalaldehyde and a thiol is rapid and sensitive. The major recognized adverse feature of this method is the instability of the reaction product, which requires precise control of reaction timing and chromatographic parameters for reliable quantitative application. We report another source of major variability: reagent instability. Deterioration of reagent was noted as low peak heights and peak broadening and was predictable if the premixed reagent was left at room temperature. Restoration of sharp chromatograms was accomplished by addition of mercaptoethanol or sodium metabisulfite. Reagent which was chromatographically inert contained minimal free thiol by direct assay. Free thiol disappearance was markedly slowed by addition of a chelating agent. Excess mercaptoethanol was deleterious. We conclude that reagent deterioration represents oxidation of the thiol, may be reversed by rereduction with minimal thiol or bisulfite, and may be minimized by inclusion of a metal chelator in the reagent.

Using hardware interrupts for timing visual displays and reaction-time key interfacing on the Commodore 64

The use of hardware interrupts for presenting and timing visual displays and for controlling reaction timing on the Commodore 64 is described. The three sources of interrupts discussed are reaction-time keys interfaced through the user port to on-board hardware timers, the alarm of the 60-Hz real-time clocks, and the video raster. In a demonstration program, these interrupts are used to measure display durations, to change screen displays, and to coordinate the onset of reaction timing with the onset of screen changes. In addition, an externally generated interrupt caused by a keypress is used to control reaction timing independently of CPU operations.