During sentence processing we decode the sequential combination of words, phrases or sentences according to previously learned rules. The computational mechanisms and neural correlates of these rules are still much debated. Other key issue is whether sentence processing solely relies on language-specific mechanisms or is it also governed by domain-general principles.
In the present study, we investigated the relationship between sentence processing and implicit sequence learning in a dual-task paradigm in which the primary task was a non-linguistic task (Alternating Serial Reaction Time Task for measuring probabilistic implicit sequence learning), while the secondary task were a sentence comprehension task relying on syntactic processing. We used two control conditions: a non-linguistic one (math condition) and a linguistic task (word processing task). Here we show that the sentence processing interfered with the probabilistic implicit sequence learning task, while the other two tasks did not produce a similar effect.
Our findings suggest that operations during sentence processing utilize resources underlying non-domain-specific probabilistic procedural learning. Furthermore, it provides a bridge between two competitive frameworks of language processing. It appears that procedural and statistical models of language are not mutually exclusive, particularly for sentence processing. These results show that the implicit procedural system is engaged in sentence processing, but on a mechanism level, language might still be based on statistical computations.
Patients with amnesia have deficits in declarative memory but intact memory for motor and perceptual skills, which suggests that explicit memory and implicit memory are distinct. However, the evidence that implicit motor learning is intact in amnesic patients is contradictory. This study investigated implicit sequence learning in amnesic patients with Korsakoff’s syndrome (N = 20) and matched controls (N = 14), using the classical Serial Reaction Time Task and a newly developed Pattern Learning Task in which the planning and execution of the responses are more spatially demanding. Results showed that implicit motor learning occurred in both groups of participants; however, on the Pattern Learning Task, the percentage of errors did not increase in the Korsakoff group in the random test phase, which is indicative of less implicit learning. Thus, our findings show that the performance of patients with Korsakoff’s syndrome is compromised on an implicit learning task with a strong spatial response component.
Korsakoff’s syndrome; Amnesia; Implicit learning; Motor learning; Sequence learning; Memory
In the special issue “Signaling Molecules and Signal Transduction in Cells” authors were invited to submit papers regarding important and novel aspects of extra- and intracellular signaling which have implications on physiological and pathophysiological processes. These aspects included compounds which are involved in these processes, elucidation of signaling pathways, as well as novel techniques for the analysis of signaling pathways. In response, various novel and important topics are elucidated in this special issue.
signaling; signaling molecules; receptors; second messenger; kinases; phosphatases; posttranslational modifications; intercellular signaling
The special issue “Antimicrobial Polymers” includes research and review papers concerning the recent advances on preparation of antimicrobial polymers and their relevance to industrial settings and biomedical field. Antimicrobial polymers have recently emerged as promising candidates to fight microbial contamination onto surfaces thanks to their interesting properties. In this special issue, the main strategies pursued for developing antimicrobial polymers, including polymer impregnation with antimicrobial agents or synthesis of polymers bearing antimicrobial moieties, were discussed. The future application of these polymers either in industrial or healthcare settings could result in an extremely positive impact not only at the economic level but also for the improvement of quality of life.
antimicrobial polymers; antifouling polymers; antimicrobial agent delivery systems; cationic polymers; microbial biofilms; titania; silver; magnetic nanoparticles; nanocomposites; chitosan; usnic acid
The present fMRI study investigated the neural areas involved in implicit perceptual sequence learning. To obtain more insight in the functional contributions of the brain areas, we tracked both the behavioral and neural time course of the learning process, using a perceptual serial color matching task. Next, to investigate whether the neural time course was specific for perceptual information, imaging results were compared to the results of implicit motor sequence learning, previously investigated using an identical serial color matching task (Gheysen et al., 2010). Results indicated that implicit sequences can be acquired by at least two neural systems: the caudate nucleus and the hippocampus, having different operating principles. The caudate nucleus contributed to the implicit sequence learning process for perceptual as well as motor information in a similar and gradual way. The hippocampus, on the other hand, was engaged in a much faster learning process which was more pronounced for the motor compared to the perceptual task. Interestingly, the perceptual and motor learning process occurred on a comparable implicit level, suggesting that consciousness is not the main determinant factor dissociating the hippocampal from the caudate learning system. This study is not only the first to successfully and unambiguously compare brain activation between perceptual and motor levels of implicit sequence learning, it also provides new insights into the specific hippocampal and caudate learning function.
implicit sequence learning; perceptual sequence learning; motor sequence learning; fMRI; caudate nucleus; hippocampus
Ethanol interactions with gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the brain, play key roles in acute intoxication. However, the exact mechanisms of these ethanol interactions have been the subject of considerable confusion and controversy. Many studies suggest that ethanol potentiates the function of the type A GABA receptor (GABAA-R). However, these findings have not been consistently replicated in experiments that directly examined ethanol effects on GABAA-R-mediated ion current. Differences in ethanol sensitivity of different GABAA-R subtypes have been invoked as a potential explanation for the inconsistent findings, and recent work suggests that GABAA-Rs that contain the delta subunit and/or mediate tonic extrasynaptic GABA responses may be especially ethanol-sensitive. However, considerable disagreement has arisen over these findings. This special issue of Alcohol contains articles from eight research groups who are examining this issue. The authors present their work, their views on the present state of this area of alcohol research, and their ideas about how to proceed with future studies that may help to address the present confusion and controversy. This editorial provides an introduction to this line of research and the current findings and controversies.
Ethanol; Synaptic Inhibition; Intoxication; RO15-4513
An electroencephalogram (EEG) signal is extremely nonstationary, highly composite and very complex, all of which reflects the underlying integral neurodynamics. Understanding the EEG “grammar”, its internal structural organization would place a “Rozetta stone” in researchers’ hands, allowing them to more adequately describe the information processes of the brain in terms of EEG phenomenology. This Special Issue presents a framework where short-term EEG spectral pattern (SP) of a particular type is viewed as an information-rich event in EEG phenomenology. It is suggested that transition from one type of SP to another is accompanied by a “switch” between brain microstates in specific neuronal networks, or in cortex areas; and these microstates are reflected in EEG as piecewise stationary segments. In this context multiple faces of a short-term EEG SP reflect the poly-operational structure of brain activity.
Electroencephalogram (EEG) phenomenology; short-term spectral patterns; neuronal assemblies; EEG oscillatory states; brain oscillations; EEG frequencies.
This special section of Genes and Nutrition presents a baseline analysis of ethical and legal issues undertaken within the EU FP7 research project Food4Me, which investigates the feasibility today of the vision for delivering personalized nutrition. Four major topics are addressed: Do we know enough for offering personalized nutritional advice? How can personal, cultural, and scientific perspectives on food and health be integrated? How does personalized nutrition affect individual autonomy? Which urgent ethical and legal matters stand out when personalized nutrition is commercialized?
Personalized nutrition; Ethics; Values; Dilemmas; Legal issues; Food4Me
Tight regulation of calcium (Ca2+) dynamics is critical for all neurons. Ca2+ is a major mediator of cellular excitability, synaptic plasticity, regulation of transcription, amongst others. Recent years have seen major developments in terms of understanding the roles of Ca2+ signals in the cerebellar circuitry, especially for Purkinje neurons and granule cells. The unique morphology of Purkinje neurons serves as a platform to unravel the secrets of Ca2+ homeostasis in cerebellar microcircuits. This special issue covers recent advances in Ca2+ signaling and imaging, and highlights the importance of spatio-temporal compartmentalization underlying Ca2+ dynamics. Sorting out the pieces of the puzzle of homeostatic regulation of Ca2+ remains an instrumental step to start rational therapies of Ca2+ deregulation.
Calcium; Purkinje neuron; signalling; circuits; imaging
When Human Immunology retracted an article from a special issue, it blamed the guest editor, who was also one of the authors. But journals should not hand responsibility to someone unfamiliar with that journal's editorial procedures without written guidance or oversight
In daily life we encounter multiple sources of sensory information at any given
moment. Unknown is whether such sensory redundancy in some way affects implicit
learning of a sequence of events. In the current paper we explored this issue in
a serial reaction time task. Our results indicate that redundant sensory
information does not enhance sequence learning when all sensory information is
presented at the same location (responding to the position and/or color of the
stimuli; Experiment 1), even when the distinct sensory sources provide more or
less similar baseline response latencies (responding to the shape and/or color
of the stimuli; Experiment 2). These findings support the claim that sequence
learning does not (necessarily) benefit from sensory redundancy. Moreover,
transfer was observed between various sets of stimuli, indicating that learning
was predominantly response-based.
sequence learning; implicit learning; sensory redundancy; serial reaction time task
Objective: The purpose of this study was to investigate the effects of specific types of tasks on the efficiency of implicit procedural learning in the presence of developmental dyslexia (DD).
Methods: Sixteen children with DD (mean (SD) age 11.6 (1.4) years) and 16 matched normal reader controls (mean age 11.4 (1.9) years) were administered two tests (the Serial Reaction Time test and the Mirror Drawing test) in which implicit knowledge was gradually acquired across multiple trials. Although both tests analyse implicit learning abilities, they tap different competencies. The Serial Reaction Time test requires the development of sequential learning and little (if any) procedural learning, whereas the Mirror Drawing test involves fast and repetitive processing of visuospatial stimuli but no acquisition of sequences.
Results: The children with DD were impaired on both implicit learning tasks, suggesting that the learning deficit observed in dyslexia does not depend on the material to be learned (with or without motor sequence of response action) but on the implicit nature of the learning that characterises the tasks.
Conclusion: Individuals with DD have impaired implicit procedural learning.
Much research has been conducted aimed at the representations and mechanisms that
enable learning of sequential structures. A central debate concerns the question
whether item-item associations (i.e., in the sequence A-B-C-D,
B comes after A) or associations of item
and serial list position (i.e., B is the second item in the
list) are used to represent serial order. Previously, we showed that in a
variant of the implicit serial reaction time task, the sequence representation
contains associations between serial position and item information (Schuck, Gaschler, Keisler, & Frensch,
2011). Here, we applied models and research methods from working
memory research to implicit serial learning to replicate and extend our
findings. The experiment involved three sessions of sequence learning. Results
support the view that participants acquire knowledge about order structure
(item-item associations) and about ordinal structure (serial position-item
associations). Analyses suggest that only the simultaneous use of the two types
of knowledge acquisition can explain learning-related performance increases.
Additionally, our results indicate that serial list position information plays a
role very early in learning and that inter-item associations increasingly
control behavior in later stages.
implicit sequence learning; serial order; SRT; chaining; race model
Although autistic people have shown impairments in various learning and memory tasks, recent studies have reported mixed findings concerning implicit learning in ASD. Implicit skill learning, with its unconscious and statistical properties, underlies not only motor but also cognitive and social skills, and it therefore plays an important role from infancy to old age.
We investigated probabilistic implicit sequence learning and its consolidation in Autism Spectrum Disorder (ASD). Three groups of children participated: thirteen with high-functioning ASD, 14 age-matched controls, and 13 IQ-matched controls. All were tested on the Alternating Serial Reaction Time Task (ASRT), making it possible to separate general skill learning from sequence-specific learning. The ASRT task was repeated after 16 hours. We found that control and ASD children showed similar sequence-specific and general skill learning in the learning phase. Consolidation of skill learning and sequence-specific learning were also intact in the ASD compared to the control groups.
These results suggest that autistic children can use the effects/results of implicit learning not only for a short period, but also for a longer stretch of time. Using these findings, therapists can design more effective educational and rehabilitation programs.
Brain-derived neurotrophic factor (BDNF) has been suggested to play a major role in plasticity, neurogenesis and learning in the adult brain. The BDNF gene contains a common val66met polymorphism associated with decreased activity-dependent excretion of BDNF and a potential influence on behaviour, more specifically, on motor learning. The objective of this study was to determine the influence of the BDNF val66met polymorphism on short-term implicit associative learning and whether its influence is cognitive domain-specific (motor vs. language). A sample of 38 young healthy participants was genotyped, screened for background and neuropsychological differences, and tested with two associative implicit learning paradigms in two different cognitive domains, i.e., motor and vocabulary learning. Subjects performed the serial reaction time task (SRTT) to determine implicit motor learning and a recently established associative vocabulary learning task (AVL) for implicit learning of action and object words. To determine the influence of the BDNF polymorphism on domain-specific implicit learning, behavioural improvements in the two tasks were compared between val/val (n = 22) and met carriers (val/met: n = 15 and met/met: n = 1). There was no evidence for an impact of the BDNF val66met polymorphism on the behavioural outcome in implicit short-term learning paradigms in young healthy subjects. Whether this polymorphism plays a relevant role in long-term training paradigms or in subjects with impaired neuronal plasticity or reduced learning capacity, such as aged individuals, demented patients or patients with brain lesions, has to be determined in future studies.
The basal ganglia are thought to participate in implicit sequence learning. However, the exact nature of this role has been difficult to determine in light of the conflicting evidence on implicit learning in subjects with Parkinson’s disease (PD). We examined the performance of PD subjects using a modified form of the serial reaction time task, which ensured that learning remained implicit. Subjects with predominantly right-sided symptoms were trained on a 12-element sequence using the right hand. Although there was no evidence of sequence learning on the basis of response time savings, the subjects showed knowledge of the sequence when performance was assessed in terms of the number of errors made. This effect transferred to the left (untrained) hand as well. Thus, these data demonstrate that PD patients are not impaired at implicitly learning sequential order, but rather at the translation of sequence knowledge into rapid motor performance. Furthermore, the results suggest that the basal ganglia are not essential for implicit sequence learning in PD.
sequence learning; parkinson’s disease; implicit; serial reaction time
It is well documented that positive rather than negative moods encourage integrative processing of conscious information. However, the extent to which implicit or unconscious learning can be influenced by affective states remains unclear.
A Serial Reaction Time (SRT) task with sequence structures requiring integration over past trials was adopted to examine the effect of affective states on implicit learning. Music was used to induce and maintain positive and negative affective states. The present study showed that participants in negative rather than positive states learned less of the regularity. Moreover, the knowledge was shown by a Bayesian analysis to be largely unconscious as participants were poor at recognizing the regularity.
The results demonstrated that negative rather than positive affect inhibited implicit learning of complex structures. Our findings help to understand the effects of affective states on unconscious or implicit processing.
It is well documented that East Asians differ from Westerners in conscious perception and attention. However, few studies have explored cultural differences in unconscious processes such as implicit learning.
The global-local Navon letters were adopted in the serial reaction time (SRT) task, during which Chinese and British participants were instructed to respond to global or local letters, to investigate whether culture influences what people acquire in implicit sequence learning. Our results showed that from the beginning British expressed a greater local bias in perception than Chinese, confirming a cultural difference in perception. Further, over extended exposure, the Chinese learned the target regularity better than the British when the targets were global, indicating a global advantage for Chinese in implicit learning. Moreover, Chinese participants acquired greater unconscious knowledge of an irrelevant regularity than British participants, indicating that the Chinese were more sensitive to contextual regularities than the British.
The results suggest that cultural biases can profoundly influence both what people consciously perceive and unconsciously learn.
Learning as measured by eyeblink classical conditioning is preserved in patients with idiopathic Parkinson's disease, but severely affected in patients with progressive supranuclear palsy. We here sought to clarify whether procedural learning is impaired in multiple system atrophy (MSA), and whether it may be helpful for the differentiation of parkinsonian syndromes.
We investigated learning using (1) eyeblink classical conditioning with a delay (interstimulus interval 0 ms) and a trace (600 ms) paradigm and (2) a serial reaction time task.
Participants were recruited from academic research centres.
11 patients with MSA and 11 healthy controls.
Implicit learning in eyeblink classical conditioning (acquisition of conditioned responses) as well as the serial reaction time task measures of implicit learning (reaction time change) are impaired in patients with MSA as compared with controls, whereas explicit learning as measured by the sequence recall of the serial reaction time task is relatively preserved.
We hypothesise that the learning deficits of patients with MSA are due to lesions of cerebellar and connected brainstem areas.
A retrospective synopsis of these novel data on patients with MSA and groups of patients with idiopathic Parkinson's disease and progressive supranuclear palsy studied earlier suggest that eyeblink classical conditioning may contribute to the early differentiation of atypical Parkinson syndromes from idiopathic Parkinson's disease. This hypothesis should be tested in a prospective trial.
Parkinsons disease; Learning
Over the last 20 years researchers have used the serial reaction time (SRT) task
to investigate the nature of spatial sequence learning. They have used the task
to identify the locus of spatial sequence learning, identify situations that
enhance and those that impair learning, and identify the important cognitive
processes that facilitate this type of learning. Although controversies remain,
the SRT task has been integral in enhancing our understanding of implicit
sequence learning. It is important, however, to ask what, if anything, the
discoveries made using the SRT task tell us about implicit learning more
generally. This review analyzes the state of the current spatial SRT sequence
learning literature highlighting the stimulus-response rule hypothesis of
sequence learning which we believe provides a unifying account of discrepant SRT
data. It also challenges researchers to use the vast body of knowledge acquired
with the SRT task to understand other implicit learning literatures too often
ignored in the context of this particular task. This broad perspective will make
it possible to identify congruences among data acquired using various different
tasks that will allow us to generalize about the nature of implicit
sequence learning; implicit learning; serial reaction time task
In the serial reaction time task (SRTT), a sequence of visuo-spatial cues instructs subjects to perform a sequence of movements which follow a repeating pattern. Though motor responses are known to support implicit sequence learning in this task, the goal of the present experiments is to determine whether observation of the sequence of cues alone can also yield evidence of implicit sequence learning. This question has been difficult to answer because in previous research, performance improvements which appeared to be due to implicit perceptual sequence learning could also be due to spontaneous increases in explicit knowledge of the sequence. The present experiments use probabilistic sequences to prevent the spontaneous development of explicit awareness. They include a training phase, during which half of the subjects observe and the other half respond, followed by a transfer phase in which everyone responds. Results show that observation alone can support sequence learning, which translates at transfer into equivalent performance as that of a group who made motor responses during training. However, perceptual learning or its expression is sensitive to changes in target colors, and its expression is impaired by concurrent explicit search. Motor-response based learning is not affected by these manipulations. Thus, observation alone can support implicit sequence learning, even of higher order probabilistic sequences. However, perceptual learning can be prevented or concealed by variations of stimuli or task demands.
Implicit; Explicit; Perceptual Learning; Sequence Learning; Motor Learning
Implicit learning of sequential structures has been investigated mostly for visual, spatial, or motor learning, but rarely for temporal structure learning. The few experiments investigating temporal structure learning have concluded that temporal structures can be learned only when coupled with another structural dimension, such as musical pitch or spatial location. In these studies, the temporal structures were without metrical organization and were dependent upon participants’ response times (Response-to-Stimulus Intervals). In our study, two experiments investigated temporal structure learning based on Inter-Onset-Intervals in the presence of an uncorrelated second dimension (ordinal structure) with metrically organized temporal structures. Our task was an adaptation of the classical Serial Reaction Time paradigm, using an implicit task in the auditory domain (syllable identification). Reaction times (RT) revealed that participants learned the temporal structures over the exposure blocks (decrease in RT) without a correlated ordinal dimension. The introduction of a test block with a novel temporal structure slowed RT and exemplified the typical implicit learning profile. Post-test results suggested that participants did not have explicit knowledge of the metrical temporal structures. These findings provide the first evidence of the learning of temporal structure with an uncorrelated ordinal structure, and set a foundation for further investigation of temporal cognition.
temporal cognition; metrical organization; serial reaction time task; implicit learning; incidental learning; auditory modality
Recent studies have reported abnormal implicit learning of sequential patterns in patients with schizophrenia. Because these studies were based on visuospatial cues, the question remained whether patients were impaired simply due to the demands of spatial processing. This study examined implicit sequence learning in 24 patients with schizophrenia and 24 healthy controls using a non-spatial variation of the serial reaction time test (SRT) in which pattern stimuli alternated with random stimuli on every other trial. Both groups showed learning by responding faster and more accurately to pattern trials than to random trials. Patients, however, showed a smaller magnitude of sequence learning. Both groups were unable to demonstrate explicit knowledge of the nature of the pattern, confirming that learning occurred without awareness. Clinical variables were not correlated with the patients' learning deficits. Patients with schizophrenia have a decreased ability to develop sensitivity to regularly occurring sequences of events within their environment. This type of deficit may affect an array of cognitive and motor functions that rely on the perception of event regularity.
Serial learning; Motor skills; Cognition; Psychiatry; Memory; Behavior
Three experiments investigated the aging of implicit spatial and spatiotemporal context learning in 2 tasks. In contextual cuing, people learn to use repeated spatial configurations to facilitate search for a target, whereas in higher order serial learning, they learn to use subtle sequence regularities to respond more quickly and accurately to a series of events. Results reveal a dissociation; overall contextual cuing is spared in healthy aging, whereas higher order sequence learning is impaired in the same individuals. This finding suggests that these 2 forms of implicit learning rely on different neural substrates that age differently; the results are also consistent with recent evidence that fronto–striatal circuits are particularly susceptible to decline in health aging.
Attention Deficit Hyperactivity Disorder (ADHD) is characterized by inattention, impulsivity and hyperactivity mediated by frontal-striatal-cerebellar dysfunction. These circuits support implicit learning of perceptual-motor sequences but not visual-spatial context. ADHD and control children performed the Alternating Serial Reaction Time (ASRT) task, a measure of sequence learning, and the Contextual Cueing (CC) task, a measure of spatial contextual learning. Relative to controls, children with ADHD showed inconsistent ASRT learning but did not differ on CC learning. Thus, implicit sequence learning, a cognitive process mediated by frontal-striatal-cerebellar circuitry that is not under executive control, was atypical in ADHD.