Publications (45) View all
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Article: Low time resolution in schizophrenia Lengthened windows of simultaneity for visual, auditory and bimodal stimuli.
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ABSTRACT: The guarantee of perceptual coherence for events through everyday life situations depends upon the capacity to correctly integrate series of multi-sensory experiences. Patients with schizophrenia have been shown to reveal a deficit in integrating, i.e., "binding", perceptual information together. However, results in the literature have also suggested the reverse effect. Indeed, in certain paradigms patients have revealed more binding phenomenon than healthy controls and reported experiencing two distinct events as occurring "together". This finding suggests that patients may require longer time intervals between two distinct events before being able to perceive them as "one-after-the-other". The question here was to test whether this perceptual binding abnormality in schizophrenia is confined to events within the same modality or whether it is also present across sensory modalities. Thirty patients with schizophrenia were compared with 33 normal controls using a simultaneity judgement paradigm. There were two uni-modal conditions in which stimuli were presented in the same modality (visual or auditory) and one bimodal condition (audio-visual). Participants were presented with stimuli varying across a range of inter-stimulus intervals (ISI). They were required to judge whether they experienced two stimuli as occurring "together" or "one-after-the-other". Compared to controls and in all conditions, patients needed larger ISI to experience two stimuli as "one-after-the-other" (all ISI x Group interactions p<5 x 10(-5)). These abnormalities correlated with the disorganization dimension but not with the dosage of chlorpromazine equivalent. The increase of the time interval needed to perceive two stimuli as "one-after-the-other", reflect an abnormally low time resolution in patients with schizophrenia. We discuss the possible involvement of anatomical disconnectivity in schizophrenia which would specifically affect the time integration properties of neural assemblies.Schizophrenia Research 01/2008; 97(1-3):118-27. · 4.75 Impact Factor -
Article: A two-stage account of computing and binding occluded and visible contours: Evidence from visual agnosia and effects of lorazepam.
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ABSTRACT: Previous work has shown that HJA, a patient suffering from visual agnosia, can complete occluded contours whilst being impaired at assigning contours to foreground and background figures (Giersch, Humphreys, Boucart, & Kovacs, 2000). Here we tested whether completed contours are automatically bound with visible contours, after being derived from them. HJA, lorazepam-treated and nontreated healthy participants were asked to match a first reference line with an equal or longer line of identical orientation included in one of two lateral figures. The target line was in the foreground or the background of the figures. The distractor picture included two short collinear line-segments belonging to two different figures, so that participants had to process the occluded parts to discriminate the target from the distractor line. When the target line was in the background, both HJA and lorazepam-treated participants were faster when the length of the reference line corresponded to the length of the occluded part of the target line, relative to when it corresponded to the length of the occluded part plus a visible contour. In contrast, control participants tended to show an advantage for matching a reference line whose length was the same as the visible contours plus the occluded part. However, when the stimuli were displayed for 50 ms only and then masked, controls showed the same results as HJA. These results suggest that responses in the matching tasks are biased by the existence of an early completed occluded line that remains isolated from real contours.Cognitive Neuropsychology 01/2006; 23(2):261-77. · 2.13 Impact Factor -
Article: Lorazepam, sedation, and conscious recollection: a dose-response study with healthy volunteers.
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ABSTRACT: The role of sedation in the benzodiazepine-induced impairment of conscious recollection is still subject to debate. The aim of this study was to investigate further the role of sedation using the Remember-Know procedure and a physiological measure of sedation based on pupillography in addition to standard measures of sedation and attention (digit-symbol substitution task, symbol cancellation task, self-rated sedation). Twelve subjects were tested after the intake of placebo, lorazepam 0.026 mg/kg and lorazepam 0.038 mg/kg, administered in a randomized order, with a minimum interval of 8 days between each administration. On a recognition memory task, they were asked to give 'Remember', 'Know' or 'Guess' responses to items that were recognized on the basis of conscious recollection, familiarity, or guessing, respectively. Lorazepam selectively impaired recognition based on 'Remember' responses. This impairment was greater in the lorazepam 0.038 mg/kg than in the lorazepam 0.026 mg/kg groups. Measures of sedation were not correlated with the proportion of 'Remember' responses. These results suggest that sedation alone cannot account for the impairment of conscious recollection induced by lorazepam.International Clinical Psychopharmacology 02/2002; 17(1):19-26. · 2.92 Impact Factor -
Article: Different effects of lorazepam and diazepam on perceptual integration.
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ABSTRACT: Recent research has established the detrimental effect of lorazepam, a benzodiazepine, on both implicit and explicit memory. Furthermore, lorazepam is known to affect perceptual integration. Diazepam, on the other hand, though being a benzodiazepine too, only impairs explicit memory, leaving implicit memory fairly intact. Little is known about the effect of diazepam on perceptual integration. The present study aimed at filling in this gap, by comparing the effects of lorazepam and diazepam on the detection of discontinuities in random-shaped outlines. In line with previous findings, the results in a lorazepam-treated group were quite different from the results in a placebo-treated group. The results in a diazepam-treated group were analogous to the results in the placebo-treated group and different from the results in the lorazepam-treated group. This shows that lorazepam and diazepam differ, not only with respect to their effect on implicit memory, but also with respect to their effect on perceptual integration. It is argued that this bears important consequences for memory research that makes use of a pharmacological dissociation rationale.Vision Research 09/2001; 41(17):2297-303. · 2.41 Impact Factor -
Article: Effects of lorazepam on vision and oculomotor balance.
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ABSTRACT: Previous studies have shown an effect of the tranquilizer lorazepam on visual perception. We explored the effects of the drug on binocular vision, visual acuity and accommodation. Twenty-four paid healthy volunteers (13 women, 11 men) were recruited from the University of Strasbourg (mean age: 23.6 years, mean weight: 66.8 Kg). They were randomly assigned to one of two parallel groups of 12 subjects each (a placebo group and a lorazepam 0.038 mg/kg group). Visual acuity was measured for each eye separately (Snellen chart and Parinaud scale). Binocular vision was studied using the cover tests, measurement of the fusional amplitudes (with Berens prisms), and the Duane Scale Test (near point rule) measuring convergence and/or accommodation in centimeters or diopters as a function of age. Regarding vision, there was no lorazepam effect, at either 33 cm or 5 m. An esophoria was observed after the intake of lorazepam (0Delta before intake and 2.8Delta after intake, p=0.001). Both fusional convergence and fusional divergence amplitudes decreased by lorazepam, (p=0.008, and p=0.002). Lorazepam also impaired the near point of convergence but did not affect accommodation. A single dose of lorazepam induces an esophoric oculomotor imbalance and impaired fusional convergence and divergence amplitudes without impairing visual acuity or accommodation.Binocular vision & strabismus quarterly 02/2001; 16(2):99-104.
