Associative-memory deficit as a function of age and stimuli serial position.

Studies have shown associative-memory decline in aging. While the literature is inconclusive regarding the source of the deficit, some researchers argue that it is caused by impaired encoding and maintenance processes in working-memory (WM). Successful retrieval of a stimulus depends on its sequential presentation in the learning list: stimuli at the beginning or the end of the learning list benefit from higher retrieval probability. These effects are known as "primacy" and "recency" effects, respectively. In the case of the primacy-effect, stimuli at early list positions benefit from extensive rehearsal that results in enhanced consolidation and trace in long-term memory (LTM). In the case of the recency-effect, target stimuli at later serial positions are still maintained in WM and can therefore be effortlessly retrieved. Considering these effects could shed light on the involvement of WM in associative-binding. Both behavioral and neuroimaging researchers have studied associative-decline in aging. However, no work has explicitly tested age differences in memory for items versus associations as a function of stimuli serial position (SSP). In the current study, 22 younger and 22 older adults were recruited to participate in a study aimed to test the separate and joint effects of both SSP and aging on memory-recognition of items and associations. In the task used, retrieval was manipulated for SSP (beginning/middle/end of the list) and item/associations recognition modes. We hypothesized that greater associative-decline will be observed in older adults, specifically for recently presented material. The results showed that both groups presented a significant associative-deficit at the recency positions; this decrease was additive and did not correspond to the expected interaction effect. Further analysis showed that the source of associative-memory decline for stimuli at recency position in older adults resulted from an increase in false-alarm (FA) rates. These results support the involvement of WM-binding impairment in aging.

Intact capacity for implicit learning in obsessive-compulsive disorder.

BACKGROUND AND OBJECTIVES: Individuals with OCD tend to rely on explicit processing when performing implicit learning tasks. However, it is unclear whether this tendency reflects impaired capacity for implicit processing or a preference toward explicit processing. We sought to use a psychometrically valid task to examine the hypothesis that individuals with OCD have intact capacity for implicit learning. METHODS: Twenty-four participants with OCD and 24 non-psychiatric controls completed a modified artificial grammar learning task where acquisition and retrieval of the underlying grammatical rules are considered strictly implicit. In an exploratory condition designed to examine the effect of nudging participants toward controlled processing, 12 participants in each group were told that the stimuli presented at acquisition were composed according to grammatical rules and were encouraged to identify these rules. RESULTS: As predicted, participants with OCD acquired and expressed knowledge of the grammatical rule, demonstrating intact capacity for implicit learning, with no differences found between the OCD and controls on the extent of implicit learning. The exploratory intentional learning instructions had no effect, as participants in this condition were unable to adhere to the instructions, supporting the robust implicit nature of the artificial grammar learning task. LIMITATIONS: The relatively small sample size did not allow comparisons between OCD symptom subtypes. CONCLUSIONS: Our results provide evidence for intact implicit learning in OCD, and challenge previous studies suggesting a general deficiency in implicit learning in OCD.

Modes of knowledge acquisition and retrieval in artificial grammar learning.

The aim of this study was to conceptualize artificial grammar learning (AGL) in terms of two orthogonal dimensions--the mode of knowledge acquisition and the mode of knowledge retrieval--as was done by Perlman and Tzelgov (2006) for sequence learning. Experiment 1 was carried out to validate our experimental task; Experiments 2-4 tested, respectively, performance in the intentional, incidental, and automatic retrieval modes, for each of the three modes of acquisition. Furthermore, signal detection theory (SDT) was used as an analytic tool, consistent with our assumption that the processing of legality-relevant information involves decisions along a continuous dimension of fluency. The results presented support the analysis of AGL in terms of the proposed dimensions. They also indicate that knowledge acquired during training may include many aspects of the presented stimuli (whole strings, relations among elements, etc.). The contribution of the various components to performance depends on both the specific instruction in the acquisition phase and the requirements of the retrieval task.