PubMed Health⌕ Search

Biomedical subjects

Anne Giersch

Publications and source records attributed to Anne Giersch.

12 recordsLinked to original sources
PubMed2006

Impairment of contrast sensitivity in long-term lorazepam users.

RATIONALE: Oculomotor balance and contrast sensitivity are known to be impaired after an intake of a single dose of lorazepam. To the best of our knowledge, these effects have not been explored in long-term users of lorazepam, despite the potential importance of such deficits in everyday life. OBJECTIVE: We tested the ophthalmological effects and contrast sensitivity for static stimuli in long-term lorazepam users. MATERIALS AND METHODS: There were 15 lorazepam users and 15 sex-, age- and education level-matched control subjects tested, using a simple blind procedure. RESULTS: The ophthalmological effects were scarce, with a discrete exophoria. Visual acuity was preserved. Contrast sensitivity, however, was more markedly impaired, consistent with the effects of an acute dose of lorazepam. The effects were not correlated with anxiety or sedation. CONCLUSIONS: The results are discussed in terms of their possible impact on everyday life. As visual acuity does not allow the detection of the impairments that are observed in the present study, it is suggested that a more systematic exploration of contrast sensitivity be carried out in long-term users of benzodiazepines.

Adult↗
PubMed2005

Some facilitatory effects of lorazepam on dynamic visual binding.

RATIONALE: The benzodiazepine lorazepam enhances the potential for inhibitory gamma-aminobutyric acid (GABAA) synapses in the cortex to stabilize postsynaptic, excitatory activity by synchronizing discharge rates at frequencies of around 40 Hz. Treatment with lorazepam also affects contour integration processes, suggesting that GABAA-mediated synchronization plays a role in visuospatial organization. This conclusion is supported by other physiological studies that link visual feature integration with neuronal synchronization. OBJECTIVES: One experiment was conducted to assess variations in dynamic figural priming as a result of lorazepam administration. METHODS: Observers were presented a modified version of a figural priming paradigm designed to investigate the effects of dynamic synchronization on visual feature integration. The priming paradigm consisted of premask crosses presented in a square arrangement within the same phase of a multiphase premask matrix oscillating at 40 Hz. Observers responded to a subsequently presented target square. The modification consisted of line elements presented at various distances relative to the unspecified extension of the lines making up the premask crosses. It was expected that priming effects would be enhanced for lines terminating close to the unspecified extension but only following administration of lorazepam. RESULTS: As anticipated, priming was enhanced substantially when the premask crosses flickered around static lines that terminated adjacent to the unspecified extension between the premask crosses. This effect was maximal following treatment with lorazepam. CONCLUSIONS: This finding supports the idea that GABAA-enhanced inhibitory synchronization mediates continuity coding during early visual processing.

Adult↗
PubMed2005

Dissociation between perceptual processing and priming in long-term lorazepam users.

Acute effects of lorazepam on visual information processing, perceptual priming and explicit memory are well established. However, visual processing and perceptual priming have rarely been explored in long-term lorazepam users. By exploring these functions it was possible to test the hypothesis that difficulty in processing visual information may lead to deficiencies in perceptual priming. Using a simple blind procedure, we tested explicit memory, perceptual priming and visual perception in 15 long-term lorazepam users and 15 control subjects individually matched according to sex, age and education level. Explicit memory, perceptual priming, and the identification of fragmented pictures were found to be preserved in long-term lorazepam users, contrary to what is usually observed after an acute drug intake. The processing of visual contour, on the other hand, was still significantly impaired. These results suggest that the effects observed on low-level visual perception are independent of the acute deleterious effects of lorazepam on perceptual priming. A comparison of perceptual priming in subjects with low- vs. high-level identification of new fragmented pictures further suggests that the ability to identify fragmented pictures has no influence on priming. Despite the fact that they were treated with relatively low doses and far from peak plasma concentration, it is noteworthy that in long-term users memory was preserved.

Adult↗
PubMed2005

Focused attention is not enough to activate discontinuities in lines, but scrutiny is.

We distinguish between the roles played by spatial attention and conscious intention in terms of their impact on the processing of segmentation signals, like discontinuities in lines, associated with the act of scrutinizing. We showed previously that the processing of discontinuities in lines can be activated. This is evidenced by an impairment in the detection of a gap between parallel elements when it follows a gap between collinear elements in the same location and orientation. This effect is no longer observed if attention is divided between two gaps in the first stimulus. The results from this study show that focusing attention on a gap between collinear elements is not enough to observe a modulation, consistently with the need to integrate, rather than to separate, collinear elements in usual conditions. The modulation is sensitive to the conscious expectations of subjects, suggesting that an intention can trigger modulations that spatial attention cannot.

Analysis of Variance↗
PubMed2005

Dynamic competition between contour integration and contour segmentation probed with moving stimuli.

Line-ends, corners and junctions are important singularities for form analysis, object recognition, depth ordering or motion processing. In this study, we investigate the extent to which processing the motion of line ends depends on the spatial configuration of their immediate surround. To that aim, we used two vertical collinear line segments, translating clockwise or anti-clockwise along a circular path, together with a direction discrimination task. Direction discrimination was measured independently for outer line-ends--at both segments extremities--and inner line-ends--in between collinear segments--using line segments partially occluded by invisible masks such that the direction of either inner or outer line-ends' motion was restricted to a sinusoidal translation along a horizontal axis, and thus irrelevant for the motion task. Under these conditions, access to the direction of inner line-ends is longer and more difficult than it is for outer line-ends. Subsequent experiments show that these effects depend on the degree of collinearity between line segments. Similar experiments were performed after volunteers took a dose of Lorazepam, a benzodiazepine that facilitates the fixation of GABA on GABAA receptors. The results show that the differences between the processing of inner and outer line-ends is reduced, suggesting that the effect of the surround is modulated by inhibitory mechanisms. Using a simple model, we propose that this effect can be explained by a competition between a segmentation process based on surround suppression and contour integration through long-range horizontal connections, at or prior to motion processing stages.

Adult↗
PubMed2005

What perceptual rules do capuchin monkeys (Cebus apella) follow in completing partly occluded figures?

Capuchin monkeys (Cebus apella) matched a variety of rodlike figures, distinguishable only by their central portions. The monkeys were then tested for perceptual completion rules by examining which comparison figures they would choose as matching the sample with the critical central portion occluded by a horizontal belt. In Experiment 1, the monkeys overwhelmingly chose a straight rod over disconnected rods and rods having irregular shapes at their center, irrespective of the presence-absence of common motion of visible parts of the samples. The monkeys chose a connected rod for relatable rods and disconnected rods for non-relatable ones in Experiment 2. In Experiments 3 and 4, some of the monkeys chose rods specified by the global regularity of the contour, whereas others did not. Experiment 5 showed that humans and capuchin monkeys basically follow similar perceptual rules in completing occluded contours, but the global regularity rule may be stronger in humans.

Adult↗
PubMed2004

Lorazepam strongly prolongs visual information processing.

Lorazepam is a drug that has been widely used for over 30 years. Whereas its therapeutic and amnestic effects are fairly well known, the visuo-perceptual impairments induced by this drug have been studied to a much lesser degree and only little is known about the influence of lorazepam on the time course of visual information processing. To gain a better insight specifically on these temporal characteristics, we used the recently discovered backward masking technique, 'shine-through', in which a vernier target precedes a grating. We tested subjects, treated with lorazepam, diazepam, or a placebo, with masking gratings of various spatial layouts. Our experiments reveal surprising results. First, for the unmasked vernier target, lorazepam induced a strong deterioration of performance compared to both diazepam and placebo. Performance deteriorated even more significantly if a masking grating was presented following the vernier. We observed that vernier discrimination could be completely abolished even if the grating appeared 400 ms after the vernier presentation. Such long time intervals are beyond usual visual masking effects. When performing the task under placebo, the participants perceived the vernier target and the masking grating as two independent time events rather than as a single event. It appears that lorazepam prolongs dramatically the processing of visual targets. The masking effects revealed here are specific to the type of grating and are much stronger under lorazepam than under diazepam.

Adult↗
PubMed2003

Abnormal sequencing of motor actions in patients with schizophrenia: evidence from grip force adjustments during object manipulation.

OBJECTIVE: During object manipulation, grip force must be adjusted in anticipation of destabilizing load forces to prevent the object from slipping. This study used three gripping tasks to assess whether schizophrenia affects the predictive mechanisms required for the scaling, timing, and/or sequencing of motor actions. METHOD: Sixteen patients with schizophrenia and 16 comparison subjects matched for age, sex, and educational level 1) lifted objects of various mass and texture (lift task) and 2) used a manipulandum to hit (hit task) or resist (resist task) impacts produced by a collision with a pendulum. For an optimized performance, all tasks demanded a predictive increase in grip force and the timing of external events. The fluid sequencing of finger and hand submovements was required for the lift and the hit tasks but not for the resist task. RESULTS: Patients were impaired in the smooth execution of both the lift and the hit tasks but not in the performance of the resist task. In all three tasks, the scaling of grip force was similar for patients and comparison subjects. CONCLUSIONS: Schizophrenia is associated with a specific deficit in the sequencing of motor actions rather than with an overall problem in the predictive control of movement.

Adolescent↗
PubMed2002

A deficit in the adjustment of grip force responses in schizophrenia.

Delusions of control in schizophrenia may be due to a deficit in the generation of an efference copy, used to distinguish between self generated and externally imposed changes in the environment. This hypothesis was tested using a framework that differentiated automatic and controlled levels of motor behavior. Subjects resisted collisions that were either self or externally imposed. The grip to load force correlation (response accuracy) and the overall grip force level used (response efficiency) were measured. Controls improved both accuracy and efficiency of their grip force responses in self compared to externally imposed collisions. Patients improved accuracy but not efficiency of motor response. There was no difference between patients with and without delusions of control. These results refute the hypothesis of a perturbed efference copy in patients with delusions of control. We rather propose that schizophrenia globally preserves the automatic level but affects the controlled, more voluntary level of motor behavior.

Adult↗
PubMed2002

Reduced or increased influence of non-pertinent information in patients with schizophrenia?

We tested the ability of 18 patients with schizophrenia and 18 matched controls to filter non-pertinent information in orientation matching tasks. The non-pertinent information consisted of pictures conveying semantic information. The pertinent information consisted of oriented line-segments drawn inside pictures or was represented by the overall orientation of the picture itself. The results showed that non-pertinent information interfered with performance of control subjects in all tasks. In contrast, non-pertinent information interfered with the performance of patients with schizophrenia to the same extent as that of matched controls only when non-pertinent and pertinent information was physically mingled, but not when they were separated. Yet, patients processed non-pertinent information in all experiments, as shown by reversed interference effects when non-pertinent and pertinent information was physically separated. These results suggest a deficit at linking physically distinct visual information in patients with schizophrenia. Additionally, performance was more impaired in patients with schizophrenia than in control subjects when the amount of displayed information increased. The results suggest the coexistence, and a possible relationship between attentional deficits and impairments at linking distinct visual information in patients with schizophrenia.

Adult↗
PubMed2002

Modulations of the processing of line discontinuities under selective attention conditions?

We examined whether the processing of discontinuities involved in figure-ground segmentation, like line ends, can be modulated under selective attention conditions. Subjects decided whether a gap in collinear or parallel lines was located to the right or left. Two stimuli were displayed in immediate succession. When the gaps were on the same side, reaction times (RTs) for the second stimulus increased when collinear lines followed parallel lines, or the reverse, but only when the two stimuli shared the same orientation and location. The effect did not depend on the global form of the stimuli or on the relative orientation of the gaps. A frame drawn around collinear elements affected the results, suggesting a crucial role of the "amodal" orthogonal lines produced when line ends are aligned. Including several gaps in the first stimulus also eliminated RT variations. By contrast, RT variations remained stable across several experimental blocks and were significant for interstimulus intervals from 50 to 600 msec between the two stimuli. These results are interpreted in terms of a modulation of the processing of line ends or the production of amodal lines, arising when attention is selectively drawn to a gap.

Attention↗