Compensatory Tracking Research Articles

P.6.a.010 Cognitive disorders among alcoholics: relevance of the Montreal Cognitive Assessment

Acetaldehyde, the first product of ethanol metabolization, is a biologically active compound, but the behavioral properties of acetaldehyde in humans are largely undefined. We investigated the acute effects of both alcohol and acetaldehyde on psychomotor functions related to automobile driving skills.Twenty-four men were selected through genotyping; one-half had the ALDH2*1/*1 (active form) genotype and one-half had the ALDH2*1/*2 (inactive form) genotype. In a double-blind placebo-controlled crossover design, each subject was administered one of the following doses of alcohol: .25 g/kg, .5 g/kg, or .75 g/kg or a placebo in four trials that took place at 1-week intervals. Blood ethanol concentration (BEC) and blood acetaldehyde concentration (BAAC) were measured nine times, and psychomotor function tests (critical flicker fusion threshold, choice reaction time, compensatory tracking task, and digit symbol substitution test) were assessed seven times in total over 4 hours after study drug ingestion.After the consumption of alcohol, BEC was comparable in the two subject groups, whereas BAAC was significantly higher in subjects with ALDH2 *1/*2 than in those with ALDH2 *1/*1. The psychomotor performance of subjects with ALDH2*1/*2 was significantly poorer than that of subjects with ALDH2*1/*1. Significant correlations between psychomotor performance and both BEC and BAAC were observed. However, in the linear regression analysis, BAAC significantly predicted poorer psychomotor performance, whereas BEC was not associated with any measure of psychomotor function.Acetaldehyde might be more important than alcohol in determining the effects on human psychomotor function and skills.

Caffeine counteracts impairments in task-oriented psychomotor performance induced by chlorpheniramine: a double-blind placebo-controlled crossover study

This study aimed to evaluate the effects of chlorpheniramine on psychomotor performance and the counteracting effects of caffeine on those sedative antihistamine actions. Sixteen healthy young men participated in this study. Using a double-blind placebo-controlled crossover design, each subject was administered one of the following conditions in a random order with a one-week interval: 'placebo-placebo', '4 mg of chlorpheniramine-placebo', 'placebo-200 mg of caffeine' or '4 mg of chlorpheniramine-200 mg of caffeine'. Before and after the treatments, psychomotor functions were assessed using a battery of tests. Additionally, subjective responses were assessed using a visual analogue scale (VAS). Psychomotor performance changed over time in different ways according to the combination of study medications. In the 'chlorpheniramine-placebo' condition, reaction times of the compensatory tracking task were significantly impaired compared with the other three conditions. In addition, the number of omission errors of the continuous performance test were significantly greater compared with the 'placebo-caffeine' condition. However, the response pattern of the 'chlorpheniramine-caffeine' condition was not significantly different from that of the 'placebo-placebo' condition. Changes of VAS for sleepiness were significantly greater in the 'chlorpheniramine-placebo' condition compared with the other three conditions. In conclusion, chlorpheniramine significantly increases subjective sleepiness and objectively impairs psychomotor performance. However, caffeine counteracts these sedative effects and psychomotor impairments.

Effects of single therapeutic doses of promethazine, fexofenadine and olopatadine on psychomotor function and histamine-induced wheal- and flare-responses: a randomized double-blind, placebo-controlled study in healthy volunteers

Since most first-generation antihistamines have undesirable sedative effects on the central nervous systems (CNS), newer (second-generation) antihistamines have been developed to improve patients’ quality of life. However, there are few reports that directly compare the antihistaminic efficacy and impairment of psychomotor functions. We designed a double-blind, placebo controlled, crossover study to concurrently compare the clinical effectiveness of promethazine, a first-generation antihistamine, and fexofenadine and olopatadine, second-generation antihistamines, by measuring their potency as peripheral inhibitors of histamine-induced wheal and flare. Further, we investigated their sedative effects on the CNS using a battery of psychomotor tests. When single therapeutic doses of fexofenadine (60 mg), olopatadine (5 mg) and promethazine (25 mg) were given in a double-blind manner to 24 healthy volunteers, all antihistamines produced a significant reduction in the wheal and flare responses induced by histamine. In the comparison among antihistamines, olopatadine showed a rapid inhibitory effect compared with fexofenadine and promethazine, and had a potent effect compared with promethazine. In a battery of psychomotor assessments using critical flicker fusion, choice reaction time, compensatory tracking, rapid visual information processing and a line analogue rating scale as a subjective assessment of sedation, promethazine significantly impaired psychomotor function. Fexofenadine and olopatadine had no significant effect in any of the psychomotor tests. Promethazine, fexofenadine and olopatadine did not affect behavioral activity, as measured by wrist actigraphy. These results suggest that olopatadine at a therapeutic dose has greater antihistaminergic activity than promethazine, and olopatadine and fexofenadine did not cause cognitive or psychomotor impairment.

Absence of neuropsychological impairment in hyperammonaemia in healthy young adults; possible synergism in development of hepatic encephalopathy (HE) symptoms?

The aetiology of minimal hepatic encephalopathy (mHE) remains unclear. It is generally accepted that hyperammonaemia plays a major role, however there are a multitude of metabolic perturbations present. To determine the contribution of hyperammonaemia to mHE symptom development, ten healthy males (Age:25 ± 5yrs, BM:76.3 ± 7.1kg, Height:178.6 ± 4.5cm, mean ± SD) received two 4h intravenous infusions of either a 2% ammonium chloride solution (AMM) or a placebo (PLA;0.9% sodium chloride) using a double blind cross-over design. Sensations of fatigue were measured at baseline, 2 and 4h using the Multidimensional Fatigue Symptom Inventory-Short Form (MFSI-SF) questionnaire. Learning & memory, motor control and cognition were assessed using Rey's Auditory Verbal Learning Test (AVL), Continuous Compensatory Tracking (COMPTRACK) Task and Inhibitory Control Test (ICT) respectively. Arterialised venous blood samples were collected every hour, and analysed for ammonia concentration. There was a significantly higher plasma ammonia concentration in the AMM trial than the PLA trial at every time point during the infusion, peaking at 2h (57 ± 4μmol/L PLA, 225 ± 14μmol/L AMM; p < 0.05). At 2h there were significantly higher sensations of general fatigue (Z = -2.527, p = 0.008, 2 tailed) and physical fatigue (Z = -2.156, p = 0.027, 2 tailed), and lower sensations of vigour (Z = -2.456, p = 0.012, 2 tailed) for the AMM trial. There were no significant effects on the performance of the psychological tasks. These results demonstrate that hyperammonaemia in the absence of other complications induces significant sensations of fatigue but does not cause the typically observed performance impairment in individuals with mHE. Supporting the hypothesis for synergism between ammonia and other co-factors in mHE.

One versus Two-Handed Six Degree-of-Freedom Compensatory Tracking in 3D and the Effects of Practice

Three-dimensional displays and input devices are now widely available. While research has investigated 3D input devices for a variety of applications, much research describes custom-made devices. There are also limited guidelines on the use of 3D input devices. A previous study investigating six degree-of-freedom (DOF) compensatory tracking performance found that novice users with little practice performed the task very poorly. This study investigates the effects of practice on performance. Subjects performed a compensatory tracking task using off-the-shelf six-DOF input devices with one device in one hand, or two devices, one in each hand splitting translation (X, Y, Z axis) and rotation (Heading, Pitch, Roll) control between hands. Examining Root Mean Square Error for each axis indicated that the tracking task was difficult to perform. Regression results and slopes indicated there was greater improvement over time for translation movements for the two hand condition, but performance for translation was better when using one hand. Research is needed to determine appropriate settings for the 3D mouse based on task type.

Design of Forcing Functions for the Identification of Human Control Behavior

Human control behavior, as exercised during vehicle or aircraft control, can be identified by applying forcing functions with a specific frequency content to excite the human control system. The presence of these forcing functions may affect human control behavior as well, an effect which is not well-understood and might considerably affect the result of experiments. Common metrics, such as spectral shape and bandwidth, have been shown to be insufficient in predicting the forcing function's effect on human control behavior. This paper investigates the effect of forcing function phase on the control behavior, as well as the effect of the forcing function frequencies at which power is present, within a fixed spectral shape. These effects were tested in a human-in-the-loop compensatory tracking experiment. Our experiment showed that the effects ofthe frequencies were substantial. For this reason, a new metric was proposed to better predict the effects of forcing functions on the human control behavior, and to allow comparison between forcing functions with different spectral shapes and frequency contents. The metric considers the variance of the signal's derivatives. To test the validity of the metric, forcing functions with equal derivative variances were used in a compensatory tracking experiment. The outcome of the experiment reveals that the resulting behavior indeed can be considered equal when the variances are equal, even when the forcing function spectral shapes are considerably different.

Age-related performance differences in compensatory tracking under a dual task condition

Due to demographic changes and a higher age of retirement, an increasing number of older people will maintain mobility in car traffic. At the same time the extent of technical equipment, e.g. driver assistance systems in motor vehicles, increases as well. Such assistent systems should provide additional and supportive information during driving. However, they can also result in distraction and disturb driving performance especially in older drivers. In order to investigate this, young and older participants performed a simulated driving task under a dual task condition: a visuo-motor tracking task and a visual attention task. An age-related slowing of response speed was observed in the visual attention task. Independent of age, both groups showed comparable error proportions and were able to improve their performance with time on task. In the tracking task, older participants showed a generally impaired performance compared to the young group which could not be improved with time on task. Particularly after relevant targets in the visual attention task, the tracking performance of both groups was decreased; this was more pronounced for the older group. The results may have relevant implications for the presentation of information by driver assistance systems especially for older drivers.

Slower Visuomotor Corrections with Unchanged Latency are Consistent with Optimal Adaptation to Increased Endogenous Noise in the Elderly

We analyzed age-related changes in motor response in a visuomotor compensatory tracking task. Subjects used a manipulandum to attempt to keep a displayed cursor at the center of a screen despite random perturbations to its location. Cross-correlation analysis of the perturbation and the subject response showed no age-related increase in latency until the onset of response to the perturbation, but substantial slowing of the response itself. Results are consistent with age-related deterioration in the ratio of signal to noise in visuomotor response. The task is such that it is tractable to use Bayesian and quadratic optimality assumptions to construct a model for behavior. This model assumes that behavior resembles an optimal controller subject to noise, and parametrizes response in terms of latency, willingness to expend effort, noise intensity, and noise bandwidth. The model is consistent with the data for all young (n = 12, age 20–30) and most elderly (n = 12, age 65–92) subjects. The model reproduces the latency result from the cross-correlation method. When presented with increased noise, the computational model reproduces the experimentally observed age-related slowing and the observed lack of increased latency. The model provides a precise way to quantitatively formulate the long-standing hypothesis that age-related slowing is an adaptation to increased noise.

The Role of Acetaldehyde in Human Psychomotor Function: A Double-Blind Placebo-Controlled Crossover Study

Acetaldehyde, the first product of ethanol metabolization, is a biologically active compound, but the behavioral properties of acetaldehyde in humans are largely undefined. We investigated the acute effects of both alcohol and acetaldehyde on psychomotor functions related to automobile driving skills. Twenty-four men were selected through genotyping; one-half had the ALDH2*1/*1 (active form) genotype and one-half had the ALDH2*1/*2 (inactive form) genotype. In a double-blind placebo-controlled crossover design, each subject was administered one of the following doses of alcohol: .25 g/kg, .5 g/kg, or .75 g/kg or a placebo in four trials that took place at 1-week intervals. Blood ethanol concentration (BEC) and blood acetaldehyde concentration (BAAC) were measured nine times, and psychomotor function tests (critical flicker fusion threshold, choice reaction time, compensatory tracking task, and digit symbol substitution test) were assessed seven times in total over 4 hours after study drug ingestion. After the consumption of alcohol, BEC was comparable in the two subject groups, whereas BAAC was significantly higher in subjects with ALDH2 *1/*2 than in those with ALDH2 *1/*1. The psychomotor performance of subjects with ALDH2*1/*2 was significantly poorer than that of subjects with ALDH2*1/*1. Significant correlations between psychomotor performance and both BEC and BAAC were observed. However, in the linear regression analysis, BAAC significantly predicted poorer psychomotor performance, whereas BEC was not associated with any measure of psychomotor function. Acetaldehyde might be more important than alcohol in determining the effects on human psychomotor function and skills.

Investigation into Crossover Regression in Compensatory Manual Tracking Tasks

This paper investigates the crossover-regression phenomenon in compensatory manual-control tasks. The adjustment, between-subject variation, and accuracy of linear human-operator models are analyzed in detail. A theoretical investigation into closed-loop error minimization will be presented. Our main hypothesis was that crossover regression is caused by an operator's inability to sufficiently decrease the time delays required to limit forcing-function resonance. To test the hypothesis and explore the use of linear-operator models in regressed conditions, an experiment very similar to McRuer's landmark 1965 experiment was conducted. A comparison between regressive and nonregressive conditions revealed that crossover regression is indeed a strategy to reduce forcing-function resonance. The bandwidth of the forcing-function signal at which participants regressed their crossover frequency was found to vary considerably between participants. In regressed conditions, the between-subject variability in frequency-domain performance increased. Additionally, the operator control behavior became increasingly nonlinear, resulting in larger uncertainties and a higher between-subject variability in the linear-model parameter estimates.

MT Neurons Combine Visual Motion with a Smooth Eye Movement Signal to Code Depth-Sign from Motion Parallax

The capacity to perceive depth is critical for an observer to interact with his or her surroundings. During observer movement, information about depth can be extracted from the resulting patterns of image motion on the retina (motion parallax). Without extraretinal signals related to observer movement, however, depth-sign (near versus far) from motion parallax can be ambiguous. We previously demonstrated that MT neurons combine visual motion with extraretinal signals to code depth-sign from motion parallax in the absence of other depth cues. In that study, head translations were always accompanied by compensatory tracking eye movements, allowing at least two potential sources of extraretinal input. We now show that smooth eye movement signals provide the critical extraretinal input to MT neurons for computing depth-sign from motion parallax. Our findings demonstrate a powerful modulation of MT activity by eye movements, as predicted by human studies of depth perception from motion parallax.

Visual control of stable and unstable loads: what is the feedback delay and extent of linear time‐invariant control?

Human balance is commonly described using linear-time-invariant (LTI) models. The feedback time delay determines the position of balance in the motor-control hierarchy. The extent of LTI control illuminates the automaticity of the control process. Using non-parametric analysis, we measured the feedback delay, extent of LTI control and visuo-motor transfer function in six randomly disturbed, visuo-manual compensatory tracking tasks analogous to standing with small mechanical perturbations and purely visual information. The delay depended primarily on load order (2nd: 220+/-30 ms, 1st: 124+/-20 ms), and secondarily on visual magnification (extent 2nd: 34 ms, 1st: 8 ms) and was unaffected by load stability. LTI control explained 1st order and stable loads relatively well. For unstable (85% passive stabilisation) 2nd order loads, LTI control accounted for 40% of manual output at 0.1 Hz decreasing below 10% as frequency increased through the important 1-3 Hz region where manual power and visuo-motor gain are high. Visual control of unstable 2nd order loads incurs substantial feedback delays and the control process will not be LTI. These features do not result from exclusive use of visual inputs because we found much shorter delays and a greater degree of LTI control when subjects visually controlled a 1st order load. Rather, these results suggest that delay and variability are inevitable when more flexible, intentional mechanisms are required to control 2nd order unstable loads. The high variability of quiet standing, and movement generally, may be indicative of flexible, variable delay, intentional mechanisms rather than the automatic LTI responses usually reported in response to large perturbations.

Next‐day residual effects of gaboxadol and flurazepam administered at bedtime: a randomized double‐blind study in healthy elderly subjects

To evaluate the next-day residual effects of the novel hypnotic, gaboxadol, following bedtime dosing in healthy elderly subjects. Healthy women (N = 15) and men (N = 10) aged 65-79 years received a single bedtime (22:00 h) dose of gaboxadol 10 mg, flurazepam 30 mg (positive control), and placebo in a randomized, double-blind, crossover study. Measures of information processing and psychomotor performance (choice reaction time, critical flicker fusion, digit symbol substitution, compensatory tracking, body sway), memory (immediate and delayed word recall), and daytime sleepiness (Multiple Sleep Latency Test), as well as subjective ratings (line analog rating scales, Leeds Sleep Evaluation Questionnaire), were obtained starting at 07:00 h the following morning. Adverse events were recorded. Gaboxadol did not show next-day impairments versus placebo on any pharmacodynamic measures whereas the positive control, flurazepam, did show impairments versus placebo on most measures. Gaboxadol showed improvements versus placebo on some measures including subjective rating of next-day alertness/clumsiness on the Leeds Sleep Evaluation Questionnaire. Gaboxadol was generally well-tolerated; there were no serious adverse experiences and no subjects discontinued due to an adverse experience. A single oral bedtime dose of gaboxadol 10 mg did not have next-day residual effects in healthy elderly subjects, as measured by a range of pharmacodynamic assessments, in contrast to the clear impairments produced by flurazepam 30 mg.

The Effects of Infrasound on Rhesus Monkey Performance of a Continuous Compensatory Tracking Task

Background: Potential bio-behavioral effects of infrasonic energy (&lt;20 Hz) have generally been considered to be due to extra-aural (non-hearing) mechanisms. Since systems that deliver acoustic energy, including infrasound, are being considered for use as non-lethal weapons, it is important to elucidate the possible aural and extra-aural effects of such energy. Methods: Subjects (5 adult male rhesus monkeys) engaged in a continuous compensatory tracking task. The effect of short-term exposure to high-intensity infrasound (160 dB), using a custom-made system, on tracking task performance was measured. The effects of the infrasound exposure on auditory measures (otoacoustic emissions and auditory brainstem evoked potentials) were also examined. Results: Tracking behavior of the subjects was substantially disrupted by exposure to 10-Hz infrasound at 160 dB. There was no evidence of any post-exposure alterations in tympanometry, distortion product otoacoustic emissions, or in auditory brainstem evoked potentials. Conclusions: Although the present experiments showed significant effects on performance, further experiments using larger working volumes would have to be undertaken to address the potential uses of such a device.

Tonic and phasic electroencephalographic dynamics during continuous compensatory tracking

Tonic and phasic dynamics of electroencephalographic (EEG) activities during a continuous compensatory tracking task (CTT) were analyzed using time–frequency analysis of EEG sources identified by independent component analysis (ICA). In 1-hour sessions, 70-channel EEG data were recorded while participants attempted to use frequent compensatory trackball movements to maintain a drifting disc close to a bulls-eye at screen center. Disc trajectories were converted into two moving-average performance measures, root mean square distance of the disc from screen center in 4-s (‘local’) and in 20-s (‘global’) moving time windows. Maximally independent EEG processes and their equivalent dipole source locations were obtained using the EEGLAB toolbox ( http://sccn.ucsd.edu/eeglab). Across subjects and sessions, independent EEG processes in occipital, somatomotor, and supplementary motor cortices exhibited tonic power increases during periods of high tracking error, plus additional phasic power increases in several frequency bands before and after trackball movements following disc ‘perigees’ (moments at which the disc began to drift away from the bulls-eye). These phasic activity increases, which were larger during high-error periods, reveal an intimate relation between EEG dynamics and top–down recognition of responding to threatening events. Thus during a continuous tracking task without impulsive stimulus onsets, sub-second scale EEG dynamics related to visuomotor task could be dissociated from slower spectral modulations linked to changes in performance and arousal. We tentatively interpret the observed EEG signal increases as indexing tonic and phasic modulations of the levels of task attention and engagement required to maintain visuomotor performance during sustained performance.

Neural substrates of visuomotor learning based on improved feedback control and prediction

Motor skills emerge from learning feedforward commands as well as improvements in feedback control. These two components of learning were investigated in a compensatory visuomotor tracking task on a trial-by-trial basis. Between-trial learning was characterized with a state–space model to provide smoothed estimates of feedforward and feedback learning, separable from random fluctuations in motor performance and error. The resultant parameters were correlated with brain activity using magnetic resonance imaging. Learning related to the generation of a feedforward command correlated with activity in dorsal premotor cortex, inferior parietal lobule, supplementary motor area and cingulate motor area, supporting a role of these areas in retrieving and executing a predictive motor command. Modulation of feedback control was associated with activity in bilateral posterior superior parietal lobule as well as right ventral premotor cortex. Performance error correlated with activity in a widespread cortical and subcortical network including bilateral parietal, premotor and rostral anterior cingulate cortex as well as the cerebellar cortex. Finally, trial-by-trial changes of kinematics, as measured by mean absolute hand acceleration, correlated with activity in motor cortex and anterior cerebellum. The results demonstrate that incremental, learning-dependent changes can be modeled on a trial-by-trial basis and neural substrates for feedforward control of novel motor programs are localized to secondary motor areas.

Effects of Long Audio Communication Delays on Team Performance

Mediated communication in sociotechnical systems is quite common but the effects of long audio delays remain unexplored. In the current study, two-person teams (N=67) completed a modified NASA Multi-Attribute Task Battery with closed-loop audio communication delays 0 to 16 seconds in length. In addition to a joint fuel management task, each team member had simultaneous responsibility for either a compensatory tracking or a system monitoring task. As communication delay increased, performance on the joint task degraded in a cubic fashion while individual tasks were unaffected. These results imply that audio communication delay degrades team performance in a non-linear fashion while simultaneous tasks not requiring communication are unaffected. Implications for the design of sociotechnical systems with long audio communication delays are discussed.

Wireless Magnetic Motion Capture System—Compensatory Tracking of Positional Error Caused by Mutual Inductance

A wireless magnetic motion capture system using an LC resonant magnetic marker was developed and has been studied. The positional error of the system caused by mutual inductance between the exciting coil and the LC marker was examined. It has been found that the impedance change of the exciting coil due to a resonance of the LC marker perturbs the strength of the magnetic field which is used for marker excitation. The more a marker approaches the exciting coil, the larger it becomes. This fluctuation induces an error in the marker signal which is measured by the pickup coils and is necessary for positional calculation. Then, the compensatory process in consideration of the mutual inductance has been employed for positional calculation in order to improve the positional accuracy. From the compensation, the absolute positional accuracy is less than 2 mm within 140 mm of the pickup coil array

Procedure and Dynamic Display Relocation on Performance in a Multitask Environment

In this paper, the responses of experienced professional pilots to change in interface configuration and differing automated invocation procedures were examined using a simulated flight-task environment. Performance was evaluated on three subtasks: two-dimensional compensatory tracking; fuel management; and systems monitoring. The status of automation, which was available for tracking and fuel management only, was conveyed by a change in display configuration represented by either a reduction in the size of the relevant display or by a reduction in size accompanied by its displacement to a peripheral spatial location. Combined with these interface-configuration changes were two forms of automation invocation procedure, which were pilot-initiated automation and system-initiated automation. Each was compared to a standard manual-control condition. Results indicated several response asymmetries. While tracking showed no effect for the location of the automated fuel-management display, fuel-management performance did reveal a significant effect, which favored the peripheral location of the automated tracking display. This display-location effect is thought to result from a general requirement for pilots to change their visual-scan pattern. The converse effect does not appear for fuel management and represents the continued primacy given by the pilots to tracking performance. System-initiated automation of fuel management, as a set condition, resulted in significantly better tracking performance, in both mean and variability measures, when compared to pilot-initiated automation. In the converse situation, involving the automation of the tracking subtask, a significant difference was also evident, but only in the variance measure of the fuel-management performance. The fuel-management variance for the pilot-initiated automation of tracking was significantly lower than that for the condition where the automation was enacted by the system. These results indicate that the automation-initiation process itself influences subsequent multitask performance. The present results support a general contention that the operator should initiate automation, except in circumstances in which the operator is for some reason incapacitated

A Double-blind, Placebo- and Flurazepam-controlled Investigation of the Residual Psychomotor and Cognitive Effects of Modified Release Zolpidem in Young Healthy Volunteers

Short-acting hypnotic drugs, such as zolpidem, have minimal residual effects but may not provide optimal efficacy throughout the night for all insomnia patients. A modified-release formulation of zolpidem, zolpidem-MR, has been developed to overcome this limitation. This was a phase I, double-blind, 3-way crossover, placebo-controlled study to investigate the residual psychomotor and cognitive effects of a single oral dose of zolpidem-MR 12.5 mg in 18 healthy young adults. Flurazepam 30 mg was used as a positive control. No comparison with standard immediate-release zolpidem was made. Five neuropsychological tests and 2 subjective tests were performed 8 hours after dosing. The safety of zolpidem-MR was also investigated. Performance on the Critical Flicker Fusion Frequency test, Choice Reaction Time, Immediate and Delayed Word Recall, and the Compensatory Tracking Task was significantly impaired by flurazepam but not by zolpidem-MR (with the exception of the Compensatory Tracking Task) or placebo. No significant effects were observed on the Digit Symbol Substitution Test. The Leeds Sleep Evaluation Questionnaire showed that both drugs improved the ease of getting to sleep and perceived quality of sleep, whereas only flurazepam significantly impaired the ease of awakening. Neither drug scored significantly better than placebo on the Bond and Lader contentedness scale, but both induced a significant difference in calmness; only flurazepam significantly reduced alertness. The safety profile of zolpidem-MR was comparable to placebo. In conclusion, the study showed the good tolerance of zolpidem-MR in terms of residual neuropsychological effects as well as a beneficial effect on sleep quality in young healthy adults.