Biomedical subjects

T Meulemans

Publications and source records attributed to T Meulemans.

8 recordsLinked to original sources

PubMed2001

Acquisition of a novel vocabulary in an amnesic patient.

This study explored the ability of a severe amnesic patient (AC) to acquire new vocabulary words. We compared AC's knowledge of words entered into the French lexicon during three different periods: before 1920, between 1965 and 1985, and after 1986 (i.e. after the onset of his amnesia). AC's knowledge was assessed by asking him to give, for each word, its definition (word-definition task), the general domain to which the word belonged ("domain" task), and to generate a sentence containing the word (sentence-generation task). Finally, we administered a recognition task in which AC had to select, for each word, its correct definition amongst four definitions. For all of these tasks, the results showed that AC's performance was similar to that of four control subjects matched for age, education, and profession. In particular, there was no difference with regard to AC's knowledge of words entered into the language after the onset of his amnesia. Therefore, these results indicate that, despite his profound amnesia, AC was able to learn normally new vocabulary words. More generally, they confirm that, at least is some cases, semantic learning can be spared in amnesia.

Adult↗

PubMed2001

Intact implicit learning in schizophrenia.

OBJECTIVE: Schizophrenia impairs performance on explicit, but not implicit, memory tasks, indicating that conscious awareness at retrieval is a critical determinant of impaired memory. The authors investigated implicit learning, i.e., knowledge acquisition in the absence of conscious awareness, in patients with schizophrenia. METHOD: An artificial grammar learning task was used to assess implicit learning in 48 patients with schizophrenia and 24 healthy comparison subjects. The subjects were first presented with letter strings that were generated according to the rules of a finite-state grammar paradigm. They were then required to indicate whether new letter strings were "grammatical," depending on whether or not the strings corresponded to the rules. IQ, working memory, explicit memory, verbal fluency, and speed of processing were also assessed. RESULTS: Patients performed significantly worse than the comparison subjects on cognitive tasks that assessed episodic memory, verbal fluency, working memory, and speed of processing. In contrast, patients classified as being correct more grammatical than nongrammatical letter strings, and the magnitude of the difference was similar to that observed in healthy comparison subjects. CONCLUSIONS: Implicit learning, as assessed with an artificial grammar learning task, is intact in patients with schizophrenia. Conscious awareness might be a critical determinant of memory impairment both at encoding and at retrieval.

Adult↗

PubMed2000

Striatum forever, despite sequence learning variability: a random effect analysis of PET data.

This PET study is concerned with the what, where, and how of implicit sequence learning. In contrast with previous studies imaging the serial reaction time (SRT) task, the sequence of successive locations was determined by a probabilistic finite-state grammar. The implicit acquisition of statistical relationships between serially ordered elements (i.e., what) was studied scan by scan, aiming to evidence the brain areas (i.e., where) specifically involved in the implicit processing of this core component of sequential higher-order knowledge. As behavioural results demonstrate between- and within-subjects variability in the implicit acquisition of sequential knowledge through practice, functional PET data were modelled using a random-effect model analysis (i.e., how) to account for both sources of behavioural variability. First, two mean condition images were created per subject depending on the presence or not of implicit sequential knowledge at the time of each of the 12 scans. Next, direct comparison of these mean condition images provided the brain areas involved in sequential knowledge processing. Using this approach, we have shown that the striatum is involved in more than simple pairwise associations and that it has the capacity to process higher-order knowledge. We suggest that the striatum is not only involved in the implicit automatization of serial information through prefrontal cortex-caudate nucleus networks, but also that it plays a significant role for the selection of the most appropriate responses in the context created by both the current and previous stimuli, thus contributing to better efficiency and faster response preparation in the SRT task.

Adult↗

PubMed2000

Experience-dependent changes in cerebral activation during human REM sleep.

The function of rapid-eye-movement (REM) sleep is still unknown. One prevailing hypothesis suggests that REM sleep is important in processing memory traces. Here, using positron emission tomography (PET) and regional cerebral blood flow measurements, we show that waking experience influences regional brain activity during subsequent sleep. Several brain areas activated during the execution of a serial reaction time task during wakefulness were significantly more active during REM sleep in subjects previously trained on the task than in non-trained subjects. These results support the hypothesis that memory traces are processed during REM sleep in humans.

Adult↗

PubMed1999

Exploration of implicit artificial grammar learning in Parkinson's disease.

Parkinson's disease (PD) patients and matched control subjects were compared in an artificial grammar learning task, one of the main paradigms of implicit learning. The evaluation material was constructed in such a way that grammaticality judgements (classification task) made on the test strings could not be based on some superficial features of the learning strings: the grammatical and nongrammatical test strings did not differ according to different measures of chunk strength (based on the frequency with which their bigram and trigram components appear in the learning strings). Unknown to participants, two successive presentations of the set of test strings were allowed during the classification task. Results show that PD patients and controls performed at the same level during the first presentation of the test strings series, which suggests that the striatum is not (crucially) implicated in the ability to learn implicitly the complex conditional associations between elements present in a set of examples generated by a finite-state grammar. However, and contrary to control subjects, the classification performance of PD patients was at chance during the second presentation of the test strings. We argue that this latter result could be the consequence of the attentional deficit of PD patients.

Association Learning↗

PubMed1998

Implicit sequence learning in children.

The main purpose of the present study was to examine whether implicit learning abilities, assessed by means of a serial reaction time task, are present to the same extent in 6- and 10-year-old children as in adults. We also wondered whether the knowledge acquired after one learning session is retained after a 1-week delay. And finally, we studied the explicit knowledge developed by the children in this task. Our results show no age-related difference in the serial reaction time performance, which is consistent with the idea that implicit learning abilities may be efficient early in development.

Adolescent↗

PubMed1996

Anterior cingulate dysfunction in presenile dementia due to progressive supranuclear palsy.

We report neuropsychological and neuroimaging investigations performed in a patient suffering from presenile onset degenerative dementia and subsequent mild extrapyramidal and pyramidal signs. Early neuropsychological testing revealed frontal lobe dysfunction. Neuroanatomical pictures were not contributive. After four years of evolution, the clinical pattern was consistent with progressive supranuclear palsy. Statistical parametric mapping analysis of functional imaging revealed a highly significant metabolic impairment in the anterior cingulate gyrus, that might be a key feature of subcortico-frontal dementia in progressive supranuclear palsy.

Brain↗

PubMed1994

Acquisition of new concepts by two amnesic patients.

Two Korsakoff amnesics (A.G. and G.S.) and two control subjects were taught six new concepts. Each concept was composed of three parts: the name of the concept, the context in which the concept originated and its definition. The learning procedure consisted of two phases: (1) learning the concept names and definitions by means of the vanishing-cues method; (2) practice on examples of the concepts through a classification task: examples were either set in the same context as that given in the original definition or in mixed contexts (same and new contexts). Subjects were then tested after 24 hours, a week and a month on their ability to identify new examples as belonging to one of the conceptual rules studied (transfer tests). Both patients showed substantial learning. Patient A.G. was slow and dependent of the first letter cues in the vanishing-cues learning phase but nevertheless, she acquired a large and flexible conceptual knowledge and this was especially true for concepts that were practised by means of mixed-context examples. Patient G.S. easily learned to associate the definitions with the concept names but her conceptual knowledge remained more limited. These results confirm the existence of a semantic learning ability in amnesic patients. They also suggest that under appropriate learning conditions, amnesics may eventually acquire a new flexible conceptual knowledge.

Alcohol Amnestic Disorder↗