Is implicit learning spared in amnesia? Rule abstraction and item familiarity in artificial grammar learning

Altered learning and transfer abilities in Korsakoff's syndrome depending on task complexity

Korsakoff's syndrome (KS) is characterized by episodic memory impairment due to damage to the medial diencephalic structures. Although commonly associated with chronic alcoholism, starvation due to the hunger strike is one of its nonalcoholic causes. Learning the stimulus-response associations and transferring the just-learned associations to novel combinations were previously tested by specific tasks in memory-impaired patients with hippocampal, basal forebrain, and basal ganglia damage. To add to this previous research, we aimed to use the same tasks in a group of patients with hunger strike-related KS presenting a stable isolated amnestic profile. Twelve patients with hunger strike-related KS and matched healthy controls were tested in two tasks varying in task complexity. Each task included two phases: the initial phase is feedback-based learning of (simple vs. complex) stimulus-response associations, and the following phase is transfer generalization (in the presence vs. absence of feedback). On a task involving simple associations, five patients with KS failed to learn the associations, while the other seven patients showed intact learning and transfer. On the other task involving more complex associations, seven patients showed slower learning and failed at transfer generalization, whereas the other five patients failed even at the acquisition phase. These findings of a task-complexity-related impairment on associative learning and transfer represent a distinct pattern from the spared learning but impaired transfer previously observed on these tasks in patients with medial temporal lobe amnesia.

Implicit sequence learning of chunking and abstract structures

The current study investigated whether people can simultaneously acquire knowledge about concrete chunks and abstract structures in implicit sequence learning; and whether the degree of abstraction determines the conscious status of the acquired knowledge. We adopted three types of stimuli in a serial reaction time task in three experiments. The RT results indicated that people could simultaneously acquire knowledge about concrete chunks and abstract structures of the temporal sequence. Generation performance revealed that ability to control was mainly based on abstract structures rather than concrete chunks. Moreover, ability to control was not generally accompanied with awareness of knowing or knowledge, as measured by confidence ratings and attribution tests, confirming that people could control the use of unconscious knowledge of abstract structures. The results present a challenge to computational models and theories of implicit learning.

Repeated exposure to exemplars does not enhance implicit learning: A puzzle for models of learning and memory

We learn regularities in the world around us, frequently without conscious effort, a phenomenon known as implicit learning. These regularities are often impossible to verbalise. One example of implicit learning is the structural effect, in which participants learn a rule set combining two factors, such as lexical frequency and concreteness. Theories of implicit learning predict that repetition of exemplar words would result in improved learning of the rule set, increasing the magnitude of the structural effect. Over four experiments, we demonstrate that this is, in fact, not the case. In Experiments 1 and 2, three repetitions of exemplar words result in superior item memory, but no change in the magnitude of the structural effect, compared with individually presented words. In Experiments 3 and 4, the structural effect is shown to be invariant to five repetitions of exemplar words and at high and low numbers of exemplars. In all four experiments, participants were unable to describe the rule set underlying the structural effect. However, confidence ratings demonstrated sensitivity to the structure and this sensitivity, unlike endorsements, increased with strength. The results are discussed in reference to differentiation, structural versus judgement knowledge, and flexible learning systems.

The Necessity of the Hippocampus for Statistical Learning

Converging evidence points to a role for the hippocampus in statistical learning, but open questions about its necessity remain. Evidence for necessity comes from Schapiro and colleagues who report that a single patient with damage to hippocampus and broader medial temporal lobe cortex was unable to discriminate new from old sequences in several statistical learning tasks. The aim of the current study was to replicate these methods in a larger group of patients who have either damage localized to hippocampus or broader medial temporal lobe damage, to ascertain the necessity of the hippocampus in statistical learning. Patients with hippocampal damage consistently showed less learning overall compared with healthy comparison participants, consistent with an emerging consensus for hippocampal contributions to statistical learning. Interestingly, lesion size did not reliably predict performance. However, patients with hippocampal damage were not uniformly at chance and demonstrated above-chance performance in some task variants. These results suggest that hippocampus is necessary for statistical learning levels achieved by most healthy comparison participants but significant hippocampal pathology alone does not abolish such learning.

Performance of children with developmental dyslexia on high and low topological entropy artificial grammar learning task

Graph complexity as measured by topological entropy has been previously shown to affect performance on artificial grammar learning tasks among typically developing children. The aim of this study was to examine the effect of graph complexity on implicit sequential learning among children with developmental dyslexia. Our goal was to determine whether children's performance depends on the complexity level of the grammar system learned. We conducted two artificial grammar learning experiments that compared performance of children with developmental dyslexia with that of age- and reading level-matched controls. Experiment 1 was a high topological entropy artificial grammar learning task that aimed to establish implicit learning phenomena in children with developmental dyslexia using previously published experimental conditions. Experiment 2 is a lower topological entropy variant of that task. Results indicated that given a high topological entropy grammar system, children with developmental dyslexia who were similar to the reading age-matched control group had substantial difficulty in performing the task as compared to typically developing children, who exhibited intact implicit learning of the grammar. On the other hand, when tested on a lower topological entropy grammar system, all groups performed above chance level, indicating that children with developmental dyslexia were able to identify rules from a given grammar system. The results reinforced the significance of graph complexity when experimenting with artificial grammar learning tasks, particularly with dyslexic participants.

New learning of music after bilateral medial temporal lobe damage: evidence from an amnesic patient

Damage to the hippocampus impairs the ability to acquire new declarative memories, but not the ability to learn simple motor tasks. An unresolved question is whether hippocampal damage affects learning for music performance, which requires motor processes, but in a cognitively complex context. We studied learning of novel musical pieces by sight-reading in a newly identified amnesic, LSJ, who was a skilled amateur violist prior to contracting herpes simplex encephalitis. LSJ has suffered virtually complete destruction of the hippocampus bilaterally, as well as extensive damage to other medial temporal lobe structures and the left anterior temporal lobe. Because of LSJ's rare combination of musical training and near-complete hippocampal destruction, her case provides a unique opportunity to investigate the role of the hippocampus for complex motor learning processes specifically related to music performance. Three novel pieces of viola music were composed and closely matched for factors contributing to a piece's musical complexity. LSJ practiced playing two of the pieces, one in each of the two sessions during the same day. Relative to a third unpracticed control piece, LSJ showed significant pre- to post-training improvement for the two practiced pieces. Learning effects were observed both with detailed analyses of correctly played notes, and with subjective whole-piece performance evaluations by string instrument players. The learning effects were evident immediately after practice and 14 days later. The observed learning stands in sharp contrast to LSJ's complete lack of awareness that the same pieces were being presented repeatedly, and to the profound impairments she exhibits in other learning tasks. Although learning in simple motor tasks has been previously observed in amnesic patients, our results demonstrate that non-hippocampal structures can support complex learning of novel musical sequences for music performance.

The necessity of the medial temporal lobe for statistical learning

The sensory input that we experience is highly patterned, and we are experts at detecting these regularities. Although the extraction of such regularities, or statistical learning (SL), is typically viewed as a cortical process, recent studies have implicated the medial temporal lobe (MTL), including the hippocampus. These studies have employed fMRI, leaving open the possibility that the MTL is involved but not necessary for SL. Here, we examined this issue in a case study of LSJ, a patient with complete bilateral hippocampal loss and broader MTL damage. In Experiments 1 and 2, LSJ and matched control participants were passively exposed to a continuous sequence of shapes, syllables, scenes, or tones containing temporal regularities in the co-occurrence of items. In a subsequent test phase, the control groups exhibited reliable SL in all conditions, successfully discriminating regularities from recombinations of the same items into novel foil sequences. LSJ, however, exhibited no SL, failing to discriminate regularities from foils. Experiment 3 ruled out more general explanations for this failure, such as inattention during exposure or difficulty following test instructions, by showing that LSJ could discriminate which individual items had been exposed. These findings provide converging support for the importance of the MTL in extracting temporal regularities.

Implizites Lernen und LRS: Spielen Defizite im impliziten Lernen eine Rolle bei der Entstehung von Schwierigkeiten im Lesen und Rechtschreiben?

Zusammenfassung:Zirka fünf Prozent aller Kinder und Jugendlichen in Deutschland leiden an einer Lese-Rechtschreibstörung (LRS). Bisher ist kaum bekannt, auf welche Art und Weise das Lesen- und Schreibenlernen bei Kindern mit einer LRS beeinträchtigt ist. Studien zeigen, dass der Erwerb der Schriftsprache nicht nur explizit durch Unterrichtung stattfindet, sondern auch implizit (unbewusst) durch häufigen Kontakt mit geschriebenen Wörtern. D. h. Kinder lernen implizit, welche Buchstabenkombinationen häufig vorkommen und wie oft und unter welchen Bedingungen Laute und Buchstaben miteinander assoziiert sind. Möglicherweise können Schwierigkeiten im Lesen und Rechtschreiben dadurch erklärt werden, dass diese impliziten Lernprozesse beeinträchtigt sind. In aktuellen Studien wurden daher anhand von Serial Reaction Time (SRT) und Artificial Grammar Learning (AGL) Aufgaben implizite Lernprozesse bei Kindern und Erwachsenen mit einer LRS untersucht. In der vorliegenden Arbeit werden die Ergebnisse dieser Studien systematisch zusammengefasst und kritisch diskutiert. Die Mehrzahl der Studien weist darauf hin, dass Kinder mit einer LRS sowohl im impliziten Lernen von Reihenfolgen (gemessen mit SRT-Aufgaben) als auch im impliziten Lernen von Regeln und Fragmenthäufigkeiten (gemessen mit AGL-Aufgaben) beeinträchtigt sind. Implikationen für die Praxis werden vorgestellt.

Levels of processing and amnesia affect perceptual priming in fragmented picture naming

In this paper we examine the impact of amnesia and of levels of processing on implicit memory by using a well-established fragmented picture-naming test with proven adequate reliability. A group of patients with amnesia of non-Korsakoff etiology was compared to a control group. While amnesic patients showed a deficit in perceptual priming, both groups showed a comparable level of processing effect. Our results confirm that when a reliable implicit memory test is used amnesia and levels of processing can both be shown to affect implicit memory performance. Thus, functional dissociations between explicit and implicit memory tests may be the consequence of a methodological artifact, that is, a difference in the reliability of the tests.

Prior familiarity with components enhances unconscious learning of relations

The influence of prior familiarity with components on the implicit learning of relations was examined using artificial grammar learning. Prior to training on grammar strings, participants were familiarized with either the novel symbols used to construct the strings or with irrelevant geometric shapes. Participants familiarized with the relevant symbols showed greater accuracy when judging the correctness of new grammar strings. Familiarity with elemental components did not increase conscious awareness of the basis for discriminations (structural knowledge) but increased accuracy even in its absence. The subjective familiarity of test strings predicted grammaticality judgments. However, prior exposure to relevant symbols did not increase overall test string familiarity or reliance on familiarity when making grammaticality judgments. Familiarity with the symbols increased the learning of relations between them (bigrams and trigrams) thus resulting in greater familiarity for grammatical versus ungrammatical strings. The results have important implications for models of implicit learning.

Strengthening the case for stimulus-specificity in artificial grammar learning: no evidence for abstract representations with extended exposure

Different theories have been proposed regarding the nature of the mental representations formed as a result of implicit learning of sequential regularities. Some theories postulate abstract surface-independent representations, while other theories postulate stimulus-specific representations. This article reports three experiments investigating the development of abstract representations in artificial grammar learning (AGL), using a methodological approach developed by Conway and Christiansen (2006). In all the experiments, the number of blocks during the exposure phase was manipulated (6 blocks vs. 18 blocks of exposure to sequences). Experiments 1 and 2 investigated both visual and auditory learning where sequences were presented element-by-element. Experiment 3 investigated visual learning using a sequence-by-sequence presentation technique more commonly used in visual AGL studies. Extending previous research (Conway & Christiansen, 2006) and in support of stimulus-specific accounts, the results of the experiments showed that extended observational learning results in increased stimulus-specific knowledge rather than abstraction towards surface-independent representations.

Harmonic priming in an amusic patient: the power of implicit tasks

Our study investigated with an implicit method (i.e., priming paradigm) whether I.R. - a brain-damaged patient exhibiting severe amusia - processes implicitly musical structures. The task consisted in identifying one of two phonemes (Experiment 1) or timbres (Experiment 2) on the last chord of eight-chord sequences (i.e., target). The targets were harmonically related or less related to the prior chords. I.R. displayed harmonic priming effects: Phoneme and timbre identification was faster for related than for less related targets (Experiments 1 and 2). However, I.R.'s explicit judgements of completion for the same sequences did not differ between related and less related contexts (Experiment 3). Her impaired performance in explicit judgements was not due to general difficulties with task demands since she performed like controls for completion judgements on spoken sentences (Experiment 4). The findings indicate that implicit knowledge of musical structures might remain intact and accessible, even when explicit judgements and overt recognition have been lost.

Subjective measures of unconscious knowledge

The chapter gives an overview of the use of subjective measures of unconscious knowledge. Unconscious knowledge is knowledge we have, and could very well be using, but we are not aware of. Hence appropriate methods for indicating unconscious knowledge must show that the person (a) has knowledge but (b) does not know that she has it. One way of determining awareness of knowing is by taking confidence ratings after making judgments. If the judgments are above baseline but the person believes they are guessing (guessing criterion) or confidence does not relate to accuracy (zero-correlation criterion) there is evidence of unconscious knowledge. The way these methods can deal with the problem of bias is discussed, as is the use of different types of confidence scales. The guessing and zero-correlation criteria show whether or not the person is aware of knowing the content of the judgment, but not whether the person is aware of what any knowledge was that enabled the judgment. Thus, a distinction is made between judgment and structural knowledge, and it is shown how the conscious status of the latter can also be assessed. Finally, the use of control over the use of knowledge as a subjective measure of judgment knowledge is illustrated. Experiments using artificial grammar learning and a serial reaction time task explore these issues.

Transfer in artificial grammar learning: The role of repetition information

In this article, the authors report 2 experiments that investigated the sources of information used in transfer and nontransfer tasks in artificial grammar learning. Multiple regression analyses indicated that 2 types of information about repeating elements were crucial for performance in both tasks: information about the repetition of adjacent elements and information about repetition of elements in the whole item. Similarity of test items to specific training items and chunk information influenced participants' judgments only in nontransfer tasks.

Is categorization performance really intact in amnesia? A meta-analysis

Most published studies of category learning in amnesia have reported intact categorization performance. These results have been used to challenge single-system accounts of categorization and recognition, in which a single representational system mediates performance in these two tasks. Many of the published studies, however, have shown a numerical advantage for controls over amnesics and often have had low statistical power. A meta-analysis was conducted to assess whether this numerical advantage is significant when the data are pooled across studies. This analysis indicates that amnesic subjects do, in fact, show deficits in categorization tasks, which is consistent with single-system exemplar model predictions.

Measuring unconscious knowledge: distinguishing structural knowledge and judgment knowledge

This paper investigates the dissociation between conscious and unconscious knowledge in an implicit learning paradigm. Two experiments employing the artificial grammar learning task explored the acquisition of unconscious and conscious knowledge of structure (structural knowledge). Structural knowledge was contrasted to knowledge of whether an item has that structure (judgment knowledge). For both structural and judgment knowledge, conscious awareness was assessed using subjective measures. It was found that unconscious structural knowledge could lead to both conscious and unconscious judgment knowledge. When structural knowledge was unconscious, there was no tendency for judgment knowledge to become more conscious over time. Furthermore, conscious rather than unconscious structural knowledge produced more consistent errors in judgments, was facilitated by instructions to search for rules, and after such instructions was harmed by a secondary task. The dissociations validate the use of these subjective measures of conscious awareness.

The cognitive neuroscience of category learning

Recently, a multidisciplinary approach has provided new insights into the mechanisms of category learning. In this article, results from theoretical modeling, experimental psychology, clinical neuropsychology, functional neuroimaging, and single-cell studies are reviewed. Although the results are not conclusive, some general principles have emerged. Areas localized in the sensory neocortex are responsible for the perceptual representation of category exemplars, whereas lateral and anterior prefrontal structures are necessary for the encoding of category boundaries and abstract rules. The prefrontal cortex may influence categorical representation in the sensory neocortex via top-down control. The neostriatum is important in stimulus-response mapping, and the orbitofrontal cortex/ventral striatum are related to stimulus-reward associations accompanying category learning. Many category learning tasks can be performed implicitly. In conclusion, category learning paradigms provide a unique opportunity to investigate cognitive processes such as perception, memory, and attention in a systematic and interactive manner. Category learning tasks are suitable for mapping damaged brain systems in clinical populations.

Neuropsychological dissociations between priming and recognition: a single-system connectionist account

A key claim of current theoretical analyses of the memory impairments associated with amnesia is that certain distinct forms of learning and memory are spared. A compelling example is that amnesic patients and controls are indistinguishable in repetition priming but amnesic patients are impaired at recognizing the study items. The authors show that this pattern of results is predicted by a single-system connectionist model of learning in which amnesia is simulated by a reduced learning rate. They also demonstrate that the model can reproduce the converse pattern in which priming but not recognition is impaired if the input is assumed to be additionally degraded in a priming test. The authors conclude that dissociations between priming and recognition do not require functionally or neurally distinct memory systems.

Subjective measures of awareness and implicit cognition

In this article, we examine whether artificial grammar learning is implicit according to a subjective criterion of awareness based on confidence ratings. In four experiments, participants discriminated between grammatical and ungrammatical sequences in both the same (Experiment 1) and a novel (Experiments 2-4) vocabulary and indicated their confidence in each decision. Replicating earlier studies, confidence judgments reported on a continuous scale (50%-100%) were only weakly related to accuracy, suggesting that learning was implicit. In contrast, confidence judgments reported on a binary scale (high vs. low) revealed that confidence was related to accuracy. We show that participants are better able to place their phenomenal states on a binary scale, as compared with a continuous scale.