Joaquín M. M. Vaquero

Qualitative Differences Between Implicit and Explicit Sequence Learning

Four experiments investigate the differences between implicit and explicit sequence learning concerning their resilience to structural and superficial task changes. A superficial change that embedded the SRT task in the context of a selection task, while maintaining the sequence, did selectively hinder the expression of implicit learning. In contrast, a manipulation that maintained the task surface, but decreased the sequence validity, affected the expression of learning specifically when it was explicit. These results are discussed in the context of a dynamic framework (Cleeremans & Jiménez, 2002), which assumes that implicit knowledge is specially affected by contextual factors and that, as knowledge becomes explicit, it allows for the development of relevant metaknowledge that modulates the expression of explicit knowledge.

Dyslexic children show deficits in implicit sequence learning, but not in explicit sequence learning or contextual cueing

Dyslexia is a specific learning disability characterized by difficulties with accurate and/or fluent word recognition and by poor spelling abilities. The absence of other high level cognitive deficits in the dyslexic population has led some authors to propose that non-strategical processes like implicit learning could be impaired in this population. Most studies have addressed this issue by using sequence learning tasks, but so far the results have not been conclusive. We test this hypothesis by comparing the performance of dyslexic children and good readers in both implicit and explicit versions of the sequence learning task, as well as in another implicit learning task not involving sequential information. The results showed that dyslexic children failed to learn the sequence when they were not informed about its presence (implicit condition). In contrast, they learned without significant differences in relation to the good readers group when they were encouraged to discover the sequence and to use it in order to improve their performance (explicit condition). Moreover, we observed that this implicit learning deficit was not extended to other forms of non-sequential, implicit learning such as contextual cueing. In this case, both groups showed similar implicit learning about the information provided by the visual context. These results help to clarify previous contradictory data, and they are discussed in relation to how the implicit sequence learning deficit could contribute to the understanding of dyslexia.

Sequential congruency effects in implicit sequence learning

We deal with situations incongruent with our automatic response tendencies much better right after having done so on a previous trial than after having reacted to a congruent trial. The nature of the mechanisms responsible for these sequential congruency effects is currently a hot topic of debate. According to the conflict monitoring model these effects depend on the adjustment of control triggered by the detection of conflict on the preceding situation. We tested whether these conflict monitoring processes can operate implicitly in an implicit learning procedure, modulating the expression of knowledge of which participants are not aware. We reanalyze recently published data, and present an experiment with a probabilistic sequence learning procedure, both showing consistent effects of implicit sequence learning. Despite being implicit, the expression of learning was reduced or completely eliminated right after trials incongruent with the learned sequence, thus showing that sequential congruency effects can be obtained even when the source of congruency itself remains implicit.

The perirhinal cortex of the rat is necessary for spatial memory retention long after but not soon after learning

Many observations in humans and experimental animals support the view that the hippocampus is critical immediately after learning in order for long-term memory formation to take place. However, exactly when the medial temporal cortices adjacent to the hippocampus are necessary for this process to occur normally is not yet well known. Using a spatial task, we studied whether the perirhinal cortex of rats is necessary to establish representations in long-term memory. Results showed that, in a spatial task sensitive to hippocampal lesions, control and perirhinal lesioned rats can both learn at the same rate (Experiment 1). Interestingly, a differential involvement of the perirhinal cortex in memory retention was observed as time passes after learning. Thus, 24 days following the end of learning, lesioned and control rats remembered the task perfectly as measured by a retraining test. In contrast, 74 days after the learning the perirhinal animals showed a profound impairment in the retention of the spatial information (Experiment 2). Taken together, these results suggest that the perirhinal region is critical for the formation of long-term spatial memory. However, its contribution to memory formation and retention is time-dependent, it being necessary only long after learning takes place and not during the phase immediately following acquisition.

The hippocampus and flexible spatial knowledge in rats.

Lesions to the hippocampal system in rats result in a profound impairment of place or locale spatial learning although other learning strategies remain unaltered. The main objective of the present study was to investigate whether the spatial knowledge preserved in the hippocampal animals can be expressed flexibly under conditions different from those of the acquisition period. Rats with neurotoxic lesions to the dorsal hippocampus and sham-operated subjects were trained to reach the goal arm in a four-arm plus-shaped maze using a constant starting arm. During the training a transparent plexiglas barrier divided the maze in two equal halves in such a way that the animals could only travel from the starting arm to the goal arm, not having access to the remaining 50% of the maze. After seven days of training, a transfer test was used in which the starting arms were the two arms from which the animals had not started during the training phase. Results indicated that the lesioned rats made significantly more errors than the control subjects. But the most interesting results revealed that the kind of error made by the lesioned animals was congruent with the turn that they had to make during the acquisition phase in order to access the goal arm (reinforced). These results suggest that when the hippocampus is damaged a preserved highly inflexible egocentric strategy is employed to solve the spatial problem.ResumenRatas con lesiones en el sistema hipocampal presentan un profundo deterioro en la adquisición de una tarea espacial cuando usan una estrategia de tipo cartográfico, pero no cuando emplean estrategias alternativas. En este estudio se investiga si el conocimiento espacial preservado en animales con daño hipocampal puede ser expresado flexiblemente bajo condiciones diferentes a las de adquisición. Ratas con lesiones neurotóxicas del hipocampo dorsal y animales controles se entrenan para alcanzar el brazo meta de un laberinto radial en forma de signo más. Durante el periodo de entrenamiento, una barrera de plexiglas transparente divide el laberinto en dos mitades iguales, de modo que los sujetos sólo pueden desplazarse desde el brazo de salida hasta el brazo meta. Después de siete días de entrenamiento, se realiza una prueba de transferencia en la que los brazos de salida son los dos brazos nunca visitados durante el periodo de entrenamiento. Los resultados indican que las ratas lesionadas cometen más errores que los controles y que el tipo de error cometido por los animales lesionados es congruente con el giro que los sujetos deben hacer durante la adquisición para acceder al brazo meta (oeste). Estos resultados sugieren que cuando el hipocampo está lesionado, los animales tienden a emplear una estrategia egocéntrica, altamente inflexible, para resolver problemas espaciales que normalmente los animales controles los resuelven de modo cartográfico o flexible.

Recollection and familiarity for words and faces: a study comparing Remember-Know judgements and the Process Dissociation Procedure.

ABSTRACT Measures of recollection and familiarity often differ depending on the paradigm utilised. Remember–Know (R–K) and Process Dissociation Procedure (PDP) methods have been commonly used but rarely compared within a single study. In the current experiments, R–K and PDP were compared by examining the effect of attention at study and time to respond at test on recollection and familiarity using the same experimental procedures for each paradigm. We also included faces in addition to words to test the generality of the findings often obtained using words. The results from the R–K paradigm revealed that recollection and familiarity were similarly affected by attention at study and time to respond at test. However, in the case of PDP, the measures of recollection and familiarity showed a different pattern of results. The effects observed for recollection were similar to those obtained with the R–K method, whereas familiarity was affected by time to respond but not by attention at study. These results are discussed in relation to the controlled-automatic processing distinction and the contribution of each paradigm to research on recognition memory.