The role of stimulus-based and response-based spatial information in sequence learning

C-SMB 2.0: Integrating over 25 years of motor sequencing research with the Discrete Sequence Production task

An exhaustive review is reported of over 25 years of research with the Discrete Sequence Production (DSP) task as reported in well over 100 articles. In line with the increasing call for theory development, this culminates into proposing the second version of the Cognitive framework of Sequential Motor Behavior (C-SMB 2.0), which brings together known models from cognitive psychology, cognitive neuroscience, and motor learning. This processing framework accounts for the many different behavioral results obtained with the DSP task and unveils important properties of the cognitive system. C-SMB 2.0 assumes that a versatile central processor (CP) develops multimodal, central-symbolic representations of short motor segments by repeatedly storing the elements of these segments in short-term memory (STM). Independently, the repeated processing by modality-specific perceptual and motor processors (PPs and MPs) and by the CP when executing sequences gradually associates successively used representations at each processing level. The high dependency of these representations on active context information allows for the rapid serial activation of the sequence elements as well as for the executive control of tasks as a whole. Speculations are eventually offered as to how the various cognitive processes could plausibly find their neural underpinnings within the intricate networks of the brain.

Differential effects of bilateral hippocampal CA3 damage on the implicit learning and recognition of complex event sequences

Learning regularities in the environment is a fundament of human cognition, which is supported by a network of brain regions that include the hippocampus. In two experiments, we assessed the effects of selective bilateral damage to human hippocampal subregion CA3, which was associated with autobiographical episodic amnesia extending ~50 years prior to the damage, on the ability to recognize complex, deterministic event sequences presented either in a spatial or a non-spatial configuration. In contrast to findings from related paradigms, modalities, and homologue species, hippocampal damage did not preclude recognition memory for an event sequence studied and tested at four spatial locations, whereas recognition memory for an event sequence presented at a single location was at chance. In two additional experiments, recognition memory for novel single-items was intact, whereas the ability to recognize novel single-items in a different location from that presented at study was at chance. The results are at variance with a general role of the hippocampus in the learning and recognition of complex event sequences based on non-adjacent spatial and temporal dependencies. We discuss the impact of the results on established theoretical accounts of the hippocampal contributions to implicit sequence learning and episodic memory.

The role of environmental contextual cues in sequence learning: evidence from a virtual maze context

Studies on sequence learning usually focus on single, isolated stimuli that are presented sequentially. For example, in the serial reaction time (RT) task, stimuli are either presented in a predictable sequence or in a random sequence, and better performance with the predictable sequence is taken as evidence for sequence-specific learning. Yet, little is known about the role of environmental context cues in sequence learning. If the target stimuli are embedded in a meaningful context, would this facilitate learning by providing helpful contextual associations or would it hinder learning by adding distracting stimuli? This question was examined in two studies. A pilot study compared sequence learning in a virtual maze with a horizontal vs. vertical maze context, in which arrow stimuli guide spatial lever movement responses that resulted in a corresponding virtual transport on the screen. The results showed only overall somewhat better performance with the vertical maze compared to the horizontal maze, but general practice effects and sequence-specific learning effects were the same for both contexts. The main study compared sequence learning with a maze context to sequence learning of arrows without a maze context. The results showed significantly better learning with maze context than without context. These data suggest that the maze context facilitated sequence learning by inducing a meaningful spatial representation ("mental map") similar to that formed in wayfinding.

Learning a covert sequence of effector movements: limits to its acquisition

Sequence learning in serial reaction time (SRT) tasks is an established, lab-based experimental paradigm to study acquisition and transfer of skills based on the detection of predictable regularities in stimulus and motor response sequences. Participants learn a sequence of targets and responses to these targets by associating the responses with subsequently presented targets. In the traditional paradigm, however, actions and response targets are directly related. In contrast, the present study asked whether participants would demonstrate acquisition of a sequence of effector movements of the left vs. right hand (e.g., hand sequence learning), whilst the actual targets and associated finger responses are unpredictable. Twenty-seven young adults performed a SRT task to visually presented characters with the index or middle fingers of both hands. While the specific fingers to respond with were randomly selected for each target presentation, both hands followed a covert sequence. We asked whether participants would learn the underlying hand sequence as demonstrated by shortened response latencies and increased accuracy compared to a fully randomized hand sequence. The results show sequence-specific learning effects. However, categorization of hand responses depending on the previous response suggested that learning occurred predominantly for subsequent finger responses of the same hand, which added to general hand-based priming. Nevertheless, a marginally significant effect was observed even for predictable shifts between hands when homologous fingers were involved. Our results thus suggest that humans are able to benefit from predictable within-hand finger shifts but less so for predicted shifts between hands.

Imagine to automatize: automatization of stimulus-response coupling after action imagery practice in implicit sequence learning

Action imagery practice (AIP) describes the repetitive imagination of an action to improve subsequent action execution. Because AIP and action execution practice (AEP) draw on partly similar motor mechanisms, it was assumed that AIP may lead to motor automatization, which is observable in a reduction of dual-task costs after AEP. To investigate automatization in AIP, we compared dual-task and single-task performance in practice and random sequences in pretests and posttests. All participants practiced serial reactions to visual stimuli in ten single-task practice sessions. An AIP group imagined the reactions. An AEP group and a control practice group executed the reactions. Practice followed a sequential sequence in AIP and AEP but was random in control practice. In dual-task test conditions, tones were counted that appeared in addition to the visual stimuli. RTs decreased from pretest to posttest in both practice and random sequences in all groups indicating general sequence-unspecific learning. Further, RTs decreased to a greater extent in the practice sequence than in the random sequence after AIP and AEP, indicating sequence-specific learning. Dual-task costs-the difference between RTs after tone and no tone events-were reduced independent from the performed sequence in all groups indicating sequence-unspecific automatization. It is concluded that the stimulus-response coupling can be automatized by both, AEP and AIP.

Concurrent visual sequence learning

Many researchers in the field of implicit statistical learning agree that there does not exist one general implicit learning mechanism, but rather, that implicit learning takes place in highly specialized encapsulated modules. However, the exact representational content of these modules is still under debate. While there is ample evidence for a distinction between modalities (e.g., visual, auditory perception), the representational content of the modules might even be distinguished by features within the same modalities (e.g., location, color, and shape within the visual modality). In implicit sequence learning, there is evidence for the latter hypothesis, as a stimulus-color sequence can be learned concurrently with a stimulus-location sequence. Our aim was to test whether this also holds true for non-spatial features within the visual modality. This has been shown in artificial grammar learning, but not yet in implicit sequence learning. Hence, in Experiment 1, we replicated an artificial grammar learning experiment of Conway and Christiansen (2006) in which participants were supposed to learn color and shape grammars concurrently. In Experiment 2, we investigated concurrent learning of sequences with an implicit sequence learning paradigm: the serial reaction time task. Here, we found evidence for concurrent learning of two sequences, a color and shape sequence. Overall, the findings converge to the assumption that implicit learning might be based on features.

Keeping in step with the young: Chronometric and kinematic data show intact procedural locomotor sequence learning in older adults

Sequence learning in serial reaction time tasks (SRTT) is an established, lab-based experimental paradigm to study acquisition and transfer of skill based on the detection of predictable stimulus and motor response sequences. Sequence learning has been mainly studied in key presses using visual target stimuli and is demonstrated by better performance in predictable sequences than in random sequences. In this study, we investigated sequence learning in the context of more complex locomotor responses. To this end, we developed a novel goal-directed stepping SRTT with auditory target stimuli in order to subsequently assess the effect of aging on sequence learning in this task, expecting that age-related performance reductions in postural control might disturb the acquisition of the sequence. We used pressure-sensitive floor mats to characterise performance across ten blocks of trials. In Experiment 1, 22 young adults demonstrated successful acquisition of the sequence in terms of the time to step on the target mat and percent error and thus validated our new paradigm. In Experiment 2, in order to contrast performance improvements in the stepping SRTT between 27 young and 22 old adults, motion capture of the feet was combined with the floor mat system to delineate individual movement phases during stepping onto a target mat. The latencies of several postural events as well as other movement parameters of a step were assessed. We observed significant learning effects in the latency of step initiation, the time to step on the target mat, and motion parameters such as stepping amplitude and peak stepping velocity, as well as in percent error. The data showed general age-related slowing but no significant performance differences in procedural locomotor sequence learning between young and old adults. The older adults also had comparable conscious representations of the sequence of stimuli as the young adults. We conclude that sequence learning occurred in this locomotor learning task that is much more complex than typical finger-tapping sequence learning tasks, and that healthy older adults showed similar learning effects compared to young adults, suggesting intact locomotor sequence learning capabilities despite general slowing and normal age-related decline in sensorimotor function.

Inhibition of Eye Movements Disrupts Spatial Sequence Learning

Implicit sequence learning is an integral part of human experience, yet the nature of the mechanisms underlying this type of learning remains a matter of debate. In the current study, we provide a test for two accounts of implicit sequence learning, that is, one that highlights sequence learning in the absence of any motor responses (with suppressed eye movements) and one that highlights the relative contribution of the motor processes (i.e., eye movements) to learning. To adjudicate between these accounts and determine whether a motor response is a requisite process in sequence learning, we used anticipation measures to compare performance on the standard oculomotor serial reaction time (SRT) task and on a version of the SRT task where the eye movements were restricted during the learning phase. our results demonstrated an increased proportion of correct anticipations in the standard SRT task compared to the restricted-movement task.

Lack of Automatic Vocal Response Learning While Reading Aloud

Research on implicit sequence learning with the Serial Reaction Task (SRT) has demonstrated that people automatically acquire knowledge about fixed repeating sequences of responses and can transfer response sequence knowledge to novel stimuli. Such demonstrations are, however, mostly limited to setups with visual stimuli and manual responses. Here we systematically follow up on scarce attempts to demonstrate implicit sequence learning in word reading. While the literature on implicit sequence learning can be taken to suggest that sequence knowledge is acquired and affecting performance in word reading, we show that neither is the case in a series of four experiments. Sequence knowledge was acquired and affecting performance in color naming but not in word reading. On the one hand, we observed slowing of voice-onset times in off-sequence as compared to regularly sequenced trials when people named the color of a centrally presented disk. Yet, hardly any effect was observed when the very same sequence of words was verbalized in word reading instead. Transfer of sequence knowledge to and from color naming was not observed, either. This contrasts with sequence learning studies with manual responses, which have been taken to suggest that a fixed and repeating sequence of responses is sufficient for learning to occur even in fast choice reaction tasks and to transfer across stimuli as long as the sequence of responses remains intact. Rather, in line with dimensional action accounts of task performance, the results underline the role of translation between processing streams for implicit sequence learning.

How movement direction shapes the spatial representation of its effects: About the consequence of the ideomotor bidirectional association

Ideomotor theories assume that action and perception share a common representational system in which a movement and its effect are equally represented and integrated by a bidirectional association. However, there is no mention of how this association leads to influence the representational content of each part. In this article, we investigated the influence of movement properties on the spatial representation of auditory effects. In line with the Action Constrains Theory of space perception, we suggest that changes in the movement direction leads to correlative changes in the spatial representation of the effect. In a pre-experiment, we replicated traditional ideomotor results with a response-effect (R-E) compatibility procedure. In two experiments, we used one condition of this procedure (i.e., the corresponding R-E mapping) to manipulate the movement properties associated to a non-spatialised effect. In the first experiment, the effect was associated with horizontal outward movements or with forward-backward movements. In the second experiment, we tested some alternative explanations for the results obtained in the first experiment. Globally, we showed that rightward movements led to localised auditory effect more on the right space than leftward movements and that backward movements led to localisation of the effect closer from the subjects than forward movements. In accordance with the Action Constrains Theory of space perception, these data suggest that movement shapes the spatial organisation of the effect representation.

Motor sequence awareness is impaired in dystonia despite normal performance

OBJECTIVE

Dystonia is a movement disorder that has been associated with impaired motor learning and sequence recognition. However, despite evidence that patients with dystonia have a reduced sense of agency, it is unclear whether dystonia is specifically associated with impaired recognition of a movement sequence. We have shown previously that performance consistency in the temporal and kinematic domains predicts awareness of underlying motor patterns in a finger-tapping task. Since movements in dystonia are characterized by high variability, we predicted that subjects with dystonia would have decreased motor sequence awareness.

METHODS

Subjects with dystonia (n = 20) and healthy control adults (n = 30) performed finger-tapping sequences with a common motor pattern and changing stimulus-to-response mappings. Subjects were said to be "aware" of the motor pattern if they recognized that their fingers moved in the same order during each stimulus-to-response remapping.

RESULTS

Subjects with dystonia had decreased motor pattern awareness, but those differences were not due to greater performance variability. Subjects with dystonia tapped sequences as series of discrete movements, rather than as a combined series.

INTERPRETATION

Dystonia is associated with impaired recognition of a repeating movement pattern. This difference may result from a strategy of separating sequential elements and attending to them individually. Ann Neurol 2018;83:52-60.

Action-effects enhance explicit sequential learning

Different studies have shown that action-effect associations seem to enhance implicit learning of motor sequences. In a recent study (Haider et al., Conscious Cognit 26:145-161, 2014), we found indications that action-effect learning might play a special role in acquiring explicit knowledge within an implicit learning situation. The current study aims at directly manipulating the action-effect contingencies in a Serial Reaction Time Task and examining its impact on explicit sequence knowledge. For this purpose, we created a situation in which the participants' responses led to a melodic tone sequence. For one group, these effect tones were contingently bound to the sequential responses and immediately followed the key press; for the second group, the tones were delayed by 400 ms. For a third group, the tones also followed the response immediately and resulted in the same melody but were not contingently bound to the responses. A fourth control group received no effect tones at all. Only the group that experienced contingent effect tones that directly followed the response showed an increase in explicit sequence knowledge. The results are discussed in terms of the multi-modal structure of action-effect associations and the ideomotor principle of action control.

Temporal and kinematic consistency predict sequence awareness

Many human motor skills can be represented as a hierarchical series of movement patterns. Awareness of underlying patterns can improve performance and decrease cognitive load. Subjects (n = 30) tapped a finger sequence with changing stimulus-to-response mapping and a common movement sequence. Thirteen subjects (43 %) became aware that they were tapping a familiar movement sequence during the experiment. Subjects who became aware of the underlying motor pattern tapped with greater kinematic and temporal consistency from task onset, but consistency was not sufficient for awareness. We found no effect of age, musical experience, tapping evenness, or inter-key-interval on awareness of the pattern in the motor response. We propose that temporal or kinematic consistency reinforces a pattern representation, but cognitive engagement with the contents of the sequence is necessary to bring the pattern to conscious awareness. These findings predict benefit for movement strategies that limit temporal and kinematic variability during motor learning.

Transfer in Motor Sequence Learning: Effects of Practice Schedule and Sequence Context

Transfer (i.e., the application of a learned skill in a novel context) is an important and desirable outcome of motor skill learning. While much research has been devoted to understanding transfer of explicit skills the mechanisms of skill transfer after incidental learning remain poorly understood. The aim of this study was to (1) examine the effect of practice schedule on transfer and (2) investigate whether sequence-specific knowledge can transfer to an unfamiliar sequence context. We trained two groups of participants on an implicit serial response time task under a Constant (one sequence for 10 blocks) or Variable (alternating between two sequences for a total of 10 blocks) practice schedule. We evaluated response times for three types of transfer: task-general transfer to a structurally non-overlapping sequence, inter-manual transfer to a perceptually identical sequence, and sequence-specific transfer to a partially overlapping (three shared triplets) sequence. Results showed partial skill transfer to all three sequences and an advantage of Variable practice only for task-general transfer. Further, we found expression of sequence-specific knowledge for familiar sub-sequences in the overlapping sequence. These findings suggest that (1) constant practice may create interference for task-general transfer and (2) sequence-specific knowledge can transfer to a new sequential context.

Generalisation of new sequence knowledge depends on response modality

New visuomotor skills can guide behaviour in novel situations. Prior studies indicate that learning a visuospatial sequence via responses based on manual key presses leads to effector- and response-independent knowledge. Little is known, however, about the extent to which new sequence knowledge can generalise, and, thereby guide behaviour, outside of the manual response modality. Here, we examined whether learning a visuospatial sequence either via manual (key presses, without eye movements), oculomotor (obligatory eye movements), or perceptual (covert reorienting of visuospatial attention) responses supported generalisation to direct and indirect tests administered either in the same (baseline conditions) or a novel response modality (transfer conditions) with respect to initial study. Direct tests measured the use of conscious knowledge about the studied sequence, whereas the indirect tests did not ostensibly draw on the study phase and measured response priming. Oculomotor learning supported the use of conscious knowledge on the manual direct tests, whereas manual learning supported generalisation to the oculomotor direct tests but did not support the conscious use of knowledge. Sequence knowledge acquired via perceptual responses did not generalise onto any of the manual tests. Manual, oculomotor, and perceptual sequence learning all supported generalisation in the baseline conditions. Notably, the manual baseline condition and the manual to oculomotor transfer condition differed in the magnitude of general skill acquired during the study phase; however, general skill did not predict performance on the post-study tests. The results demonstrated that generalisation was only affected by the responses used to initially code the visuospatial sequence when new knowledge was applied to a novel response modality. We interpret these results in terms of response-effect distinctiveness, the availability of integrated effector- and motor-plan based information, and discuss their implications for neurocognitive accounts of sequence learning.

Symbolic representations in motor sequence learning

It has been shown that varying the spatial versus symbolic nature of stimulus presentation and response production, which affects stimulus-response (S-R) mapping requirements, influences the magnitude of implicit sequence learning (Koch and Hoffman, 2000). Here, we evaluated how spatial and symbolic stimuli and responses affect the neural bases of sequence learning. We selectively eliminated the spatial component of stimulus presentation (spatial vs. symbolic), response execution (manual vs. vocal), or both. Fourteen participants performed the alternating serial reaction time task under these conditions in an MRI scanner, with interleaved acquisition to allow for recording of vocal response reaction times. Nine regions of interest (ROIs) were selected to test the hypothesis that the dorsolateral prefrontal cortex (DLPFC) was preferentially engaged for spatially cued conditions and cerebellum lobule HVI, crus I and II were associated with symbolically cued learning. We found that the left cerebellum lobule HVI was selectively recruited for symbolic learning and the percent signal change in this region was correlated with learning magnitude under the symbolic conditions. In contrast, the DLPFC did not exhibit selective activation for learning under spatial conditions. The inferior parietal lobule exhibited increased activation during learning regardless of the condition, supporting its role in forming an abstract representation of learned sequences. These findings reveal different brain networks that are flexibly engaged depending on the conditions of sequence learning.

Response-dependent contributions of human primary motor cortex and angular gyrus to manual and perceptual sequence learning

Motor sequence learning on the serial reaction time task involves the integration of response-, stimulus-, and effector-based information. Human primary motor cortex (M1) and the inferior parietal lobule (IPL) have been identified with supporting the learning of effector-dependent and -independent information, respectively. Current neurocognitive data are, however, exclusively based on learning complex sequence information via perceptual-motor responses. Here, we investigated the effects of continuous theta-burst transcranial magnetic stimulation (cTBS)-induced disruption of M1 and the angular gyrus (AG) of the IPL on learning a probabilistic sequence via sequential perceptual-motor responses (experiment 1) or covert orienting of visuospatial attention (experiment 2). Functional effects on manual sequence learning were evident during 75% of training trials in the cTBS M1 condition, whereas cTBS over the AG resulted in interference confined to a midpoint during the training phase. Posttraining direct (declarative) tests of sequence knowledge revealed that cTBS over M1 modulated the availability of newly acquired sequence knowledge, whereby sequence knowledge was implicit in the cTBS M1 condition but was available to conscious awareness in the cTBS AG and control conditions. In contrast, perceptual sequence learning was abolished in the perceptual cTBS AG condition, whereas learning was intact and available to conscious awareness in the cTBS M1 and control conditions. These results show that the right AG had a critical role in perceptual sequence learning, whereas M1 had a causal role in developing experience-dependent functional attributes relevant to conscious knowledge on manual but not perceptual sequence learning.

Multidimensional motor sequence learning is impaired in older but not younger or middle-aged adults

BACKGROUND AND PURPOSE

The purpose of this study was to identify which characteristics of a multidimensional sequence containing motor, spatial, and temporal elements would be most salient for motor sequence learning and whether age might differentially affect this learning.

SUBJECTS

Younger (n=11, mean age=26.0 years), middle-aged (n=13, mean age=50.7 years), and older (n=11, mean age=77.5 years) adults who were neurologically intact participated in the study.

METHODS

Participants practiced a sequencing task with repeated motor, spatial, and temporal dimensions for 2 days; on a separate third day, participants completed retention and interference tests designed to assess sequence learning and which elements of the sequence were learned. The mean median response time for each block of responses was used to assess motor sequence learning.

RESULTS

Younger and middle-aged adults demonstrated sequence-specific motor learning at retention testing via faster response times for repeated sequences than random sequences; both of these groups showed interference for the motor dimension. In contrast, older adults demonstrated nonspecific learning (ie, similar improvements in response time for both random and repeated sequences). These findings were shown by a lack of difference between random and repeated sequence performance in the older adult group both at retention testing and during interference tests.

CONCLUSION AND DISCUSSION

Our data suggest that, when younger and middle-aged adults practice sequences containing multiple dimensions of movement, the motor element is most important for motor learning. The absence of sequence-specific change demonstrated by an older adult group that was healthy suggests an age-related impairment in motor learning that may have profound implications for rehabilitation.

Short Article: Sequence Learning at Optimal Stimulus–Response Mapping: Evidence from a Serial Reaction Time Task

We propose a new version of the serial reaction time (SRT) task in which participants merely looked at the target instead of responding manually. As response locations were identical to target locations, stimulus–response compatibility was maximal in this task. We demonstrated that saccadic response times decreased during training and increased again when a new sequence was presented. It is unlikely that this effect was caused by stimulus–response (S–R) learning because bonds between (visual) stimuli and (oculomotor) responses were already well established before the experiment started. Thus, the finding shows that the building of S–R bonds is not essential for learning in the SRT task.

The representation of explicit motor sequence knowledge

Much research has investigated the representation of implicitly learned motor sequences: Do subjects learn sequences of stimuli, responses, response locations, or some combination? Most of the work on this subject indicates that when sequences are learned implicitly, it is in terms of response locations. The present work investigated the representation of explicitly learned motor sequences. In four experiments, we found consistent evidence that explicitly learned sequences are represented in terms of stimulus locations. This conclusion held true for both self-report measures (subjects said that they learned stimuli) and performance measures, but when stimuli changed, performance degraded. We interpret these data in a multiple-memory-systems framework.

Learning hierarchically structured action sequences is unaffected by prefrontal-cortex lesion

This study tested the impact of prefrontal-cortex lesion on learning hierarchically structured action sequences. Using a visual-manual serial reaction time task, we had subjects first perform five blocks of trials with a hierarchically structured 14-element action sequence and then tested for sequence-specific learning by introducing a pseudo-random transfer sequence. Relative to control subjects (N = 39), we found that both lateral frontal (N = 16) and medial frontal (N = 18) patients showed reduced overall performance benefits across the training phase. In contrast, the negative transfer test showed significantly increased reaction times in all patient groups, indicating robust sequence-specific learning. This learning was not significantly different from that of the control group. Taken together, the data suggest that learning hierarchically structured action sequences is unimpaired in patients with prefrontal-cortex lesion.

The role of response selection in sequence learning

We investigated the role of response selection in sequence learning in the serial reaction time (SRT) task, by manipulating stimulus-response compatibility. Under conditions in which other types of learning, like perceptual, response-based, and response-effect learning, were unaffected, sequence learning was better with an incompatible than with a compatible stimulus-response mapping. Stimulus discriminability, on the other hand, had no influence on the amount of sequence learning. This indicates that the compatibility effects cannot be accounted for by a different level of task difficulty. Relating our results to the dimensional overlap model (Kornblum, Hasbroucq, & Osman, 1990), which assumes that incompatible stimulus-response mappings require more controlled response selection than do compatible stimulus-response mapping, we suggest that sequence learning in the SRT task is particularly effective when response selection occurs in a controlled way.

Effects of explicit knowledge of workspace rotation in visuomotor sequence learning

Previous experimental and theoretical studies have suggested that two separate neural networks contribute to visuomotor learning of spatial sequences, one to the accuracy of performance and the other to the speed of performance (Nakahara et al. in J Cogn Neurosci 13:626-647, 2001). This study examined the influence of explicit knowledge of stimulus configuration (workspace) in visuomotor sequence learning. Twenty-eight right-handed subjects learned the sequences of button presses by trial and error (Hikosaka et al. in J Neurophysiol 76:617-621, 1996) in the course of two sessions. In the first session, both the number of completion failures (accuracy measure) and the performance time to complete a sequence (speed measure) decreased. In the second session, the workspace was rotated without notifying the subjects. About half the subjects remained unaware of the workspace rotation, and no transfer of learning occurred (i.e., neither accuracy nor speed of performance was preserved in the second session). The remaining subjects spontaneously noticed the rotation and they were able to use this knowledge to perform the task with less completion failures in the second session. However, the knowledge of workspace rotation did not decrease the performance time in the second session. The lack of influence of explicit knowledge on the speed of performance is consistent with the two-loop model of visuomotor sequence learning (Nakahara et al. in J Cogn Neurosci 13:626-647, 2001).

The effect of old age on the learning of supraspan sequences

Two experiments examined age-related differences in sequence learning using computerized versions of the D. O. Hebb (1961) paradigm. In this learning task, the participant executes immediate serial recall of 24 supraspan sequences. Without the participants' knowledge, 1 sequence is presented several times. Repetition leads to improved recall of this repeated sequence relative to random sequences. Results showed a dissociation in age-related learning deficits depending on the nature of the to-be-remembered material. The effect of repetition is similar for younger and older adults with familiar and unfamiliar verbal material (words and pseudowords) but is significantly reduced in older adults when learning is assessed with a visuospatial version of Hebb's supraspan learning task (P. M. Corsi, 1972).

Incidental task sequence learning: perceptual rather than conceptual?

In four experiments we investigated whether incidental task sequence learning occurs when no instructional task cues are available (i.e. with univalent stimuli). We manipulated task sequence by presenting three simple binary-choice tasks (colour, form or letter case decisions) in regular repeated or random order. Participants were required to use the same two response keys for each of the tasks. We manipulated response sequence by ordering the stimuli so as to produce either a regular or a random order of left versus right-hand key presses. When sequencing in both, or either, separate stream (i.e. task sequence and/or response sequence) was changed to random, only those participants who had processed both sequences together showed evidence of sequence learning in terms of significant response time disruption (Experiments 1-3). This effect disappeared when the sequences were uncorrelated (Experiment 4). The results indicate that only the correlated integration of task sequence and response sequence produced a reliable incidental learning effect. As this effect depends on the predictable ordering of stimulus categories, it suggests that task sequence learning is perceptual rather than conceptual in nature.

Probability detection mechanisms and motor learning

The automatic detection of patterns or regularities in the environment is central to certain forms of motor learning, which are largely procedural and implicit. The rules underlying the detection and use of probabilistic information in the perceptual-motor domain are largely unknown. We conducted two experiments involving a motor learning task with direct and crossed mapping of motor responses in which probabilities were present at the stimulus set level, the response set level, and at the level of stimulus-response (S-R) mapping. We manipulated only one level at a time, while controlling for the other two. The results show that probabilities were detected only when present at the S-R mapping and motor levels, but not at the perceptual one (experiment 1), unless the perceptual features have a dimensional overlap with the S-R mapping rule (experiment 2). The effects of probability detection were mostly facilitatory at the S-R mapping, both facilitatory and inhibitory at the perceptual level, and predominantly inhibitory at the response-set level. The facilitatory effects were based on learning the absolute frequencies first and transitional probabilities later (for the S-R mapping rule) or both types of information at the same time (for perceptual level), whereas the inhibitory effects were based on learning first the transitional probabilities. Our data suggest that both absolute frequencies and transitional probabilities are used in motor learning, but in different temporal orders, according to the probabilistic properties of the environment. The results support the idea that separate neural circuits may be involved in detecting absolute frequencies as compared to transitional probabilities.

Effector dependent sequence learning in the serial RT task

At least five earlier studies could not find effector-dependent learning in the keying version of the serial reaction time (RT) task. Experiment 1 examined whether effector-dependent learning occurs when participants practice the serial RT task with three fingers of one hand for about 1,300 sequence repetitions instead of the more common 50-100 repetitions. The results confirm that, following extended practice, sequence learning produces an effector-dependent component. Specifically, an unpracticed hand executed a practiced sequence slower than a practiced hand. However, Experiment 2 showed that effector-dependent sequence learning develops only when fingers of one hand are used, suggesting that effector-dependent sequence learning involves adjustment to the mechanical interactions between the fingers of one hand. In addition, when sequences had been practiced with one hand, mirror versions of the practiced sequences in both experiments showed moderate transfer. But when practiced with two hands no transfer to a mirrored version of the sequence was observed. This suggests that only practice with one hand produces a representation that facilitates the execution of mirror sequences. Generally, the same results were found in more or less aware participants, congruent with the idea that the effector-dependent representation and the representation allowing transfer to mirror sequences are implicit.

Neural substrates of response-based sequence learning using fMRI

Representation of sequential structure can occur with respect to the order of perceptual events or the order in which actions are linked. Neural correlates of sequence retrieval associated with the order of motor responses were identified in a variant of the serial reaction time task in which training occurred with a spatially incompatible mapping between stimuli and finger responses. After transfer to a spatially compatible version of the task, performance enhancements indicative of learning were only present in subjects required to make finger movements in the same order used during training. In contrast, a second group of subjects performed the compatible task using an identical sequence of stimuli (and different order of finger movements) as in training. They demonstrated no performance benefit, indicating that learning was response based. Analysis was restricted to subjects demonstrating low recall of the sequence structure to rule out effects of explicit awareness. The interaction of group (motor vs. perceptual transfer) with sequence retrieval (sequencing vs. rest) revealed significantly greater activation in the bilateral supplementary motor area, cingulate motor area, ventral premotor cortex, left caudate, and inferior parietal lobule for subjects in the motor group (illustrating successful sequence retrieval at the response level). Retrieval of sequential responses occurs within mesial motor areas and related motor planning areas.

The impact of response mode on implicit and explicit sequence learning

Evidence regarding the influence of response mode on sequence learning in serial reaction time (SRT) tasks has been mixed so far. In the present study, sequence learning was investigated under two different response conditions: manual (button presses) versus verbal (pronunciation of digits). Additionally, participants were divided post hoc into subgroups differing in their degree of explicit knowledge about the sequence. Results showed an interaction between response mode and type of learning (implicit vs. explicit), with explicit learning functioning more effectively under verbal than under manual conditions, whereas implicit learning was unaffected by the variation of the response mode. Implications concerning different underlying learning mechanisms (R-R learning vs. R-S learning) are discussed. Specifically, we suggest that the high response-effect distinctiveness of the verbal responses facilitated R-R learning.

Authorship effects in the prediction of handwriting strokes: evidence for action simulation during action perception

Does the action system contribute to action perception? Recent evidence suggests that actions are simulated while being observed. Given that the planning and simulating system are the same only when one observes one's own actions, it might be easier to predict the future outcomes of actions when one has carried them out oneself earlier on. In order to test this hypothesis, three experiments were conducted in which participants observed parts of earlier self- and other-produced trajectories and judged whether another stroke would follow or not. When the trajectories were produced without constraints, participants accomplished this task only for self-produced trajectories. When the trajectories were produced under narrow constraints, the predictions were equally accurate for self- and for other-generated trajectories. These results support the action simulation assumption. The more the actions that one observes resemble the way one would carry them out oneself, the more accurate the simulation.

Statistical learning of higher-order temporal structure from visual shape sequences

In 3 experiments, the authors investigated the ability of observers to extract the probabilities of successive shape co-occurrences during passive viewing. Participants became sensitive to several temporal-order statistics, both rapidly and with no overt task or explicit instructions. Sequences of shapes presented during familiarization were distinguished from novel sequences of familiar shapes, as well as from shape sequences that were seen during familiarization but less frequently than other shape sequences, demonstrating at least the extraction of joint probabilities of 2 consecutive shapes. When joint probabilities did not differ, another higher-order statistic (conditional probability) was automatically computed, thereby allowing participants to predict the temporal order of shapes. Results of a single-shape test documented that lower-order statistics were retained during the extraction of higher-order statistics. These results suggest that observers automatically extract multiple statistics of temporal events that are suitable for efficient associative learning of new temporal features.

Automatic and intentional activation of task sets

Four experiments examined automatic and intentional activation of task sets in a switching paradigm. Experiment 1 demonstrated incidental task sequence learning that was not accompanied by verbalizable task sequence knowledge. This learning did not affect task shift cost and may be attributed to automatic task-set activation. In Experiment 2, both shift cost and learning effect increased when the response-cue interval was short, indicating the influence of residual, persisting activation of the preceding task set. In Experiment 3, learning disappeared with a long cue-stimulus interval (CSI), which resulted in a strong preparation effect. This preparation, however, reduced reaction time level but was not specific to task shifts. Finally, Experiment 4 showed that a within-subject C