A Comparison of Implicit Memory Tests in Schizophrenic Patients and Normal Controls

Abstract

The objective of the current study was to compare the performance of schizophrenic patients and normal controls on implicit memory tests. Two neuropsychological tasks were administered to 29 patients and normal participant samples. The implicit tests were: Word fragment completion and Word production from semantic categories. The priming score was the variable of interest. Priming effects are obtained in normal subjects and schizophrenia patients, regardless of the implicit test used. However, a dissociation in priming between normal and patient groups was observed, depending on the test used. For word fragment test, priming was identical between the two groups. However, for word production, priming obtained in schizophrenics was lower than priming in normal controls. Results confirm a dissociation effect in implicit memory tests. These results could be explained in the context of the Roediger and Blaxton (1987) distinction between data-driven and conceptually-driven processing. This evidence suggests that a complete neuropsychological assessment of memory in schizophrenia should include different kinds of implicit memory tests (procedural, perceptual, and conceptual tasks). Keywords: priming, implicit memory, schizophrenia, memory impairmentEl objetivo de este estudio fue comparar la ejecución de pacientes esquizofrénicos y controles no clínicos en tests de memoria implícita. Se administraron dos pruebas neuropsicológicas a una muestra de 29 pacientes y a dos muestras de participantes no clínicos. Los tests implícitos fueron: Completar fragmentos de palabras y Generación de ejemplares de categorías semánticas. La variable de interés fue la facilitación. Los efectos de facilitación se obtienen en sujetos no clínicos y en pacientes esquizofrénicos, independientemente del test implícito que se utilice. Sin embargo, se ha observado una disociación en la facilitación entre grupos de controles y pacientes, dependiendo del test utilizado. En tests de fragmentos de palabras la facilitación es idéntica en los dos grupos. Sin embargo, en producción de palabras, la facilitación obtenida en esquizofrénicos es menor que la facilitación en controles. Los resultados confirman la existencia de un efecto disociativo en tests de memoria implícita. Estos resultados podrían explicarse en el contexto de la distinción de Roediger y Blaxton (1987) entre procesamiento guiado por los datos y procesamiento guiado conceptualmente. Esta evidencia sugiere que la evaluación neuropsicológica de la memoria en la esquizofrenia debería incluir distintos tipos de pruebas de memoria implícita (procedimentales, perceptuales, y conceptuales). Palabras clave: facilitación, memoria implícita, esquizofrenia, daños en memoria

Is conceptual implicit memory impaired in schizophrenia? Evidence from lexical decision and category verification

“…In summary, Experiment 2 extended to a semantic identification task previous findings indicating that conceptually driven implicit memory is significantly impaired in schizophrenia Soler et al, 2007). On the other hand, we did not replicate the finding that schizophrenic patients are less accurate than controls in making semantic decisions to category exemplar pairs (Rossell & David, 2006).…”

“…In summary, Experiment 1 showed that, in a lexical decision task, schizophrenic patients benefited from repetition priming to the same extent as healthy controls. Such a finding replicates the results reported by Sponheim et al (2004) and, more generally, is in line with the hypothesis that perceptual implicit memory is intact in schizophrenia Soler et al, 2007).…”

“…As mentioned in the Introduction, Ruiz et al (2007) and Soler et al (2007) found that repetition priming in schizophrenic patients was comparable to that of healthy controls in the word-fragment completion task, but significantly reduced in the category exemplar generation task. These findings suggest that schizophrenia may be associated with a specific deficit in conceptually driven implicit memory.…”

“…However, besides the perceptual/ conceptual distinction, the aforementioned tasks also differ in the involvement of identification/production processes. Word-fragment completion is primarily based on identification processes because in most studies (including those by Ruiz et al, 2007, andSoler et al, 2007), the to-be-solved fragments have unique solutions, implying small or no competition during the retrieval phase (Spataro et al, 2010). In contrast, the category generation task is heavily based on production processes (Gabrieli et al, 1999;Vaidya et al, 1997) because participants are instructed to produce the first instances that come to mind in response to a category label: in these conditions, the encoded exemplars must be selected among multiple competing responses.…”

“…As briefly reviewed earlier, evidence in support of a deficit in conceptual implicit memory in schizophrenia primarily comes from reduced repetition priming in category exemplar generation Soler et al, 2007), a task which is heavily based on production processes (Gabrieli et al, 1999). This suggests the alternative possibility that the impairment in schizophrenic patients might not be caused by the conceptual nature of the category exemplar generation task, but rather by the necessity to select the encoded items among multiple competitors at the time of retrieval (i.e., by the production nature of the task).…”