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Stephan Ludewig

Publications and source records attributed to Stephan Ludewig.

5 recordsLinked to original sources
PubMed2005

Rapid visual information processing in schizophrenic patients: the impact of cognitive load and duration of stimulus presentation. A pilot study.

The inability to sustain attention has been proposed as a core deficit in schizophrenia. The Continuous Performance Task (AX-CPT) and the Rapid Visual Information Processing Task (RVP) are widely used neuropsychological tasks to measure sustained attention. The RVP displays numbers as stimuli, whereas the AX-CPT uses letters. Ten patients with chronic schizophrenia and 18 healthy control subjects were studied using four different versions of the RVP. The versions differed with regard to stimulus presentation time (600 vs. 1,200 ms) and the number of target sequences to be memorized: either one sequence (low cognitive load) or two sequences (high cognitive load). Schizophrenic patients showed a reduced number of hits only on the task version with 600 ms stimulus duration coupled with high cognitive load. The combination of high cognitive load and short stimulus duration created a critical performance breaking point for schizophrenic patients. This finding supports the hypothesis that patients have an impaired ability to coactivate different cognitive performances; thus the results favor the theory of impaired functional connectivity in schizophrenia.

Adult↗
PubMed2005

Information-processing deficits and cognitive dysfunction in panic disorder.

OBJECTIVE: The plasticity of the startle reflex, including prepulse inhibition (PPI) and habituation, provides operational measures of information processing that are abnormal in several neuropsychiatric disorders characterized by deficits in suppression or inhibition of intrusive or irrelevant stimuli. Clinically, patients with panic disorder (PD) have been described as having difficulties in the inhibition of their response to sensory and cognitive events. Because such difficulties may be the result of failures in early stages of information processing, we hypothesized that startle reactivity, PPI and habituation are deficient in unmedicated patients with PD. Moreover, we tested whether there was a relation between startle reflex measures and dysfunctional cognition. METHODS: Fourteen unmedicated patients with PD (7 men, 7 women) and 28 healthy comparison subjects (14 men, 14 women) were recruited. Acoustic startle reactivity, habituation and PPI (30-ms, 60-ms, 120-ms, 240-ms and 2000-ms interstimulus intervals) were assessed in the patients with PD and the age-matched and sex-matched healthy controls. These data for unmedicated patients with PD were compared with those for 24 medicated patients with PD. Moreover, dysfunctional cognition in patients with PD was measured using the Body Sensations Questionnaire. RESULTS: Unmedicated patients with PD exhibited increased startle reactivity, reduced habituation and significantly reduced PPI in the 30-ms, 60-ms, 120-ms and 240-ms prepulse conditions. Furthermore, in unmedicated patients with PD, increased startle response and decreased habituation were correlated significantly with higher cognitive dysfunction scores, but this was not the case for PPI. CONCLUSIONS: These data indicate that the early stages of sensory information processing are abnormal in patients with PD in the absence of medication. The observed deficits in PPI and habituation could reflect a more generalized difficulty in suppressing or gating information in PD. The correlation between cognitive symptoms and higher startle response and deficient habituation supports the hypothesis that subjects with PD have abnormalities in the early stages of information processing that lead to a cascade of downstream effects on cognition.

Adult↗
PubMed2003

Decision-making strategies by panic disorder subjects are more sensitive to errors.

BACKGROUND: Decision-making is a complex process, which can be assessed experimentally by the two-choice prediction task. Error-rate, i.e. the frequency of incorrect predictions during this task, is an important factor for the response selection during decision-making. This investigation examined whether the frequency of incorrect predictions has an augmented effect on the number of different strategies underlying decision-making in patients with panic disorder. METHODS: Patients with a DSM-IV diagnosis of panic disorder (PD; N=18), unipolar major depressive disorder (MDD; N=18) and normal comparison subjects (C; N=35) were tested with the two-choice prediction task using three error-rate conditions (20, 50, or 80%). The dynamical entropy of the response sequences was used to quantify the number of different strategies generated during the different error-rates. RESULTS: At 20% error-rates, panic disorder subjects when compared to MDD and C subjects generated more strategies and switched more frequently between strategies as measured by the dynamical entropy and the range of local dynamical entropies. Response bias measures during the two-choice prediction task and post-test self-assessment did not differ between panic disorder subjects and MDD or C subjects. LIMITATIONS: First, panic disorder subjects were medicated. Second, the frequency and intensity of panic attacks and the degree of avoidance behaviors, was not assessed. Third, subjects were tested once only. CONCLUSIONS: Panic disorder subjects show uniformly high response sequence unpredictability in the presence of low error-rates, which is consistent with continued search for an optimal response strategy even when the error-rate is low.

Adult↗
PubMed2003

The acoustic startle reflex and its modulation: effects of age and gender in humans.

The acoustic startle reflex and its modulation by prepulse inhibition (PPI) and habituation are used in many studies in different fields of neuropsychiatric research. The aim of this study was to examine the effects of age and gender on PPI, startle magnitude, and habituation in healthy human volunteers. Twenty-seven male and 28 female participants of four different age groups (range: 20-60 years) were investigated in an acoustic startle paradigm using a startle stimulus of 115 dB and a prepulse of 86 dB (16 dB over the white noise background) with five different lead intervals (30, 60, 120, 240, and 2000 ms). Seventeen males and 16 female participants were tested three times at monthly intervals. Aged participants showed significantly lower startle magnitude and significantly more habituation than younger participants, but there was no effect of age on PPI or prepulse facilitation. Moreover, there were no effects of gender on startle magnitude, PPI, prepulse facilitation, or habituation measures. Healthy males and females exhibited stable startle magnitudes and PPI across sessions. The results demonstrated that PPI and startle are reliable measures of sensory information processing in both genders and that startle magnitude and habituation are age-dependent measures.

Acoustic Stimulation↗