Aspects of sensory guidance in sequence learning

Online measurement of learning temporal statistical structure in categorization tasks

The ability to grasp relevant patterns from a continuous stream of environmental information is called statistical learning. Although the representations that emerge during visual statistical learning (VSL) are well characterized, little is known about how they are formed. We developed a sensitive behavioral design to characterize the VSL trajectory during ongoing task performance. In sequential categorization tasks, we assessed two previously identified VSL markers: priming of the second predictable image in a pair manifested by a reduced reaction time (RT) and greater accuracy, and the anticipatory effect on the first image revealed by a longer RT. First, in Experiment 1A, we used an adapted paradigm and replicated these VSL markers; however, they appeared to be confounded by motor learning. Next, in Experiment 1B, we confirmed the confounding influence of motor learning. To assess VSL without motor learning, in Experiment 2 we (1) simplified the categorization task, (2) raised the number of subjects and image repetitions, and (3) increased the number of single unpaired images. Using linear mixed-effect modeling and estimated marginal means of linear trends, we found that the RT curves differed significantly between predictable paired and control single images. Further, the VSL curve fitted a logarithmic model, suggesting a rapid learning process. These results suggest that our paradigm in Experiment 2 seems to be a viable online tool to monitor the behavioral correlates of unsupervised implicit VSL.

Differences in implicit motor learning between adults who do and do not stutter

Implicit learning allows us to acquire complex motor skills through repeated exposure to sensory cues and repetition of motor behaviours, without awareness or effort. Implicit learning is also critical to the incremental fine-tuning of the perceptual-motor system. To understand how implicit learning and associated domain-general learning processes may contribute to motor learning differences in people who stutter, we investigated implicit finger-sequencing skills in adults who do (AWS) and do not stutter (ANS) on an Alternating Serial Reaction Time task. Our results demonstrated that, while all participants showed evidence of significant sequence-specific learning in their speed of performance, male AWS were slower and made fewer sequence-specific learning gains than their ANS counterparts. Although there were no learning gains evident in accuracy of performance, AWS performed the implicit learning task more accurately than ANS, overall. These findings may have implications for sex-based differences in the experience of developmental stuttering, for the successful acquisition of complex motor skills during development by individuals who stutter, and for the updating and automatization of speech motor plans during the therapeutic process.

Regular rhythmic and audio-visual stimulations enhance procedural learning of a perceptual-motor sequence in healthy adults: A pilot study

Procedural learning is essential for the effortless execution of many everyday life activities. However, little is known about the conditions influencing the acquisition of procedural skills. The literature suggests that sensory environment may influence the acquisition of perceptual-motor sequences, as tested by a Serial Reaction Time Task. In the current study, we investigated the effects of auditory stimulations on procedural learning of a visuo-motor sequence. Given that the literature shows that regular rhythmic auditory rhythm and multisensory stimulations improve motor speed, we expected to improve procedural learning (reaction times and errors) with repeated practice with auditory stimulations presented either simultaneously with visual stimulations or with a regular tempo, compared to control conditions (e.g., with irregular tempo). Our results suggest that both congruent audio-visual stimulations and regular rhythmic auditory stimulations promote procedural perceptual-motor learning. On the contrary, auditory stimulations with irregular or very quick tempo alter learning. We discuss how regular rhythmic multisensory stimulations may improve procedural learning with respect of a multisensory rhythmic integration process.

Occipital sleep spindles predict sequence learning in a visuo-motor task

STUDY OBJECTIVES

The brain appears to use internal models to successfully interact with its environment via active predictions of future events. Both internal models and the predictions derived from them are based on previous experience. However, it remains unclear how previously encoded information is maintained to support this function, especially in the visual domain. In the present study, we hypothesized that sleep consolidates newly encoded spatio-temporal regularities to improve predictions afterwards.

METHODS

We tested this hypothesis using a novel sequence-learning paradigm that aimed to dissociate perceptual from motor learning. We recorded behavioral performance and high-density electroencephalography (EEG) in male human participants during initial training and during testing two days later, following an experimental night of sleep (n = 16, including high-density EEG recordings) or wakefulness (n = 17).

RESULTS

Our results show sleep-dependent behavioral improvements correlated with sleep-spindle activity specifically over occipital cortices. Moreover, event-related potential (ERP) responses indicate a shift of attention away from predictable to unpredictable sequences after sleep, consistent with enhanced automaticity in the processing of predictable sequences.

CONCLUSIONS

These findings suggest a sleep-dependent improvement in the prediction of visual sequences, likely related to visual cortex reactivation during sleep spindles. Considering that controls in our experiments did not fully exclude oculomotor contributions, future studies will need to address the extent to which these effects depend on purely perceptual versus oculomotor sequence learning.

Order, please! Explicit sequence learning in hybrid search in younger and older age

Sequence learning effects in simple perceptual and motor tasks are largely unaffected by normal aging. However, less is known about sequence learning in more complex cognitive tasks that involve attention and memory processes and how this changes with age. In this study, we examined whether incidental and intentional sequence learning would facilitate hybrid visual and memory search in younger and older adults. Observers performed a hybrid search task, in which they memorized four or 16 target objects and searched for any of those target objects in displays with four or 16 objects. The memorized targets appeared either in a repeating sequential order or in random order. In the first experiment, observers were not told about the sequence before the experiment. Only a subset of younger adults and none of the older adults incidentally learned the sequence. The "learners" acquired explicit knowledge about the sequence and searched faster in the sequence compared to random condition. In the second experiment, observers were told about the sequence before the search task. Both younger and older adults searched faster in sequence blocks than random blocks. Older adults, however, showed this sequence-learning effect only in blocks with smaller target sets. Our findings indicate that explicit sequence knowledge can facilitate hybrid search, as it allows observers to predict the next target and restrict their visual and memory search. In older age, the sequence-learning effect is constrained by load, presumably due to age-related decline in executive functions.

Effects of an Additional Sequence of Color Stimuli on Visuomotor Sequence Learning

Through practice, people are able to integrate a secondary sequence (e.g., a stimulus-based sequence) into a primary sequence (e.g., a response-based sequence), but it is still controversial whether the integrated sequences lead to better learning than only the primary sequence. In the present study, we aimed to investigate the effects of a sequence that integrated space and color sequences on early and late learning phases (corresponding to effector-independent and effector-dependent learning, respectively) and how the effects differed in the integrated and primary sequences in each learning phase. In the task, the participants were required to learn a sequence of button presses using trial-and-error and to perform the sequence successfully for 20 trials (m × n task). First, in the baseline task, all participants learned a non-colored sequence, in which the response button always turned red. Then, in the learning task, the participants were assigned to two groups: a colored sequence group (i.e., space and color) or a non-colored sequence group (i.e., space). In the colored sequence, the response button turned a pre-determined color and the participants were instructed to attend to the sequences of both location and color as much as they could. The results showed that the participants who performed the colored sequence acquired the correct button presses of the sequence earlier, but showed a slower mean performance time than those who performed the non-colored sequence. Moreover, the slower performance time in the colored sequence group remained in a subsequent transfer task in which the spatial configurations of the buttons were vertically mirrored from the learning task. These results indicated that if participants explicitly attended to both the spatial response sequence and color stimulus sequence at the same time, they could develop their spatial representations of the sequence earlier (i.e., early development of the effector-independent learning), but might not be able to enhance their motor representations of the sequence (i.e., late development of the effector-dependent learning). Thus, the undeveloped effector-dependent representations in the colored sequence group directly led to a long performance time in the transfer sequence.

The impact of concurrent visual feedback on coding of on-line and pre-planned movement sequences

The purpose of this study was to determine the extent to which participants could effectively switch from on-line (OL) to pre-planned (PP) control (or vice versa) depending on previous practice conditions and whether concurrent visual feedback was available during transfer testing. The task was to reproduce a 2000 ms spatial-temporal pattern of a sequence of elbow flexions and extensions. Participants were randomly assigned to one of two practice conditions termed OL or PP. In the OL condition the criterion waveform and the cursor were provided during movement production while this information was withheld during movement production for the PP condition. A retention test and two effector transfer tests were administered to half of the participants in each acquisition conditions under OL conditions and the other half under PP conditions. The mirror effector transfer test required the same pattern of muscle activation and limb joint angles as required during acquisition. The non-mirror transfer test required movements to the same visual-spatial locations as experienced during acquisition. The results indicated that when visual information was available during the transfer tests performers could switch from PP to OL. When visual information was withdrawn, they shifted from the OL to the PP-control mode. This finding suggests that performers adopt a mode of control consistent with the feedback conditions provided during testing.

Developmental differences in effects of task pacing on implicit sequence learning

Although there is now substantial evidence that developmental change occurs in implicit learning abilities over the lifespan, disparate results exist regarding the specific developmental trajectory of implicit learning skills. One possible reason for discrepancies across implicit learning studies may be that younger children show an increased sensitivity to variations in implicit learning task procedures and demands relative to adults. Studies using serial-reaction time (SRT) tasks have suggested that in adults, measurements of implicit learning are robust across variations in task procedures. Most classic SRT tasks have used response-contingent pacing in which the participant's own reaction time determines the duration of each trial. However, recent paradigms with adults and children have used fixed trial pacing, which leads to alterations in both response and attention demands, accuracy feedback, perceived agency, and task motivation for participants. In the current study, we compared learning on fixed-paced and self-paced versions of a spatial sequence learning paradigm in 4-year-old children and adults. Results indicated that preschool-aged children showed reduced evidence of implicit sequence learning in comparison to adults, regardless of the SRT paradigm used. In addition, we found the preschoolers showed significantly greater learning when stimulus presentation was self-paced. These data provide evidence for developmental differences in implicit sequence learning that are dependent on specific task demands such as stimulus pacing, which may be related to developmental changes in the impact of broader constructs such as attention and task motivation on implicit learning.

Modality-specific organization in the representation of sensorimotor sequences

Sensorimotor representations of movement sequences are hierarchically organized. Here we test the effects of different stimulus modalities on such organizations. In the visual group, participants responded to a repeated sequence of visually presented stimuli by depressing spatially compatible keys on a response pad. In the auditory group, learners were required to respond to auditorily presented stimuli, which had no direct spatial correspondence with the response keys: the lowest pitch corresponded to the leftmost key and the highest pitch to the rightmost key. We demonstrate that hierarchically and auto-organized sensorimotor representations are developed through practice, which are specific both to individuals and stimulus modalities. These findings highlight the dynamic and sensory-specific modulation of chunk processing during sensorimotor learning - sensorimotor chunking - and provide evidence that modality-specific mechanisms underlie the hierarchical organization of sequence representations.

Learning what from where: Effects of spatial regularity on nonspatial sequence learning and updating

The current study examined the influence of redundant stimulus features on our ability to build and update representations of our environment. We hypothesized that our ability to process redundant spatial features would speed our ability to adapt to changing nonspatial regularities. Using a computerized version of the children's game "rock-paper-scissors", undergraduates were instructed to win as often as possible against a computer opponent. The computer's plays were repeating sequences of five choices that were presented either with spatial regularity (i.e., "rock" would always appear on the left, "paper" in the middle, and "scissors" on the right) or without spatial regularity (i.e., the items were equally likely to appear in any of the three locations). Once participants learned a sequence, the computer switched to a different sequence without participants being informed that a switch had occurred. Redundant spatial regularity improved a participant's ability both to learn sequences of plays and to update their plays to reflect new computer sequences. Our results suggest that our perceptual system is sensitive to redundant spatial stimulus features and that this information can improve learning and updating.

Perceptual sequence learning is more severely impaired than motor sequence learning in patients with chronic cerebellar stroke

Patients with cerebellar stroke are impaired in procedural learning. Several different learning mechanisms contribute to procedural learning in healthy individuals. The aim was to compare the relative share of different learning mechanisms in patients and healthy controls. Ten patients with cerebellar stroke and 12 healthy controls practiced a visuomotor serial reaction time task. Learning blocks with high stimulus-response compatibility were exercised repeatedly; in between these, participants performed test blocks with the same or a different (mirror-inverted or unrelated) stimulus sequence and/or the same or a different (mirror-inverted) stimulus-response allocation. This design allowed to measure the impact of motor learning and perceptual learning independently and to separate both mechanisms from the learning of stimulus-response pairs. Analysis of the learning blocks showed that, as expected, both patients and controls improved their performance over time, although patients remained significantly slower. Analysis of the test blocks revealed that controls showed significant motor learning as well as significant visual perceptual learning, whereas cerebellar patients showed only significant motor learning. Healthy participants were able to use perceptual information for procedural learning even when the rule linking stimuli and responses had been changed, whereas patients with cerebellar lesions could not recruit this perception-based mechanism. Therefore, the cerebellum appears involved in the accurate processing of perceptual information independent from prelearned stimulus-response mappings.

Redundant sensory information does not enhance sequence learning in the serial reaction time task

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.

A distraction can impair or enhance motor performance

Humans have a prodigious capacity to perform multiple tasks simultaneously. Being distracted while, for example, performing a complex motor skill adds complexity to a task and thus leads to a performance impairment. Yet, it may not be just the presence or absence of a distraction that affects motor performance. Instead, the characteristics of the distraction may play a critical role in affecting human motor performance. Here, we show that performance of a motor sequence can be substantially enhanced by simultaneously learning an independent color sequence. In contrast, performance of the same motor sequence was impaired by concurrently counting the number of red cues that were in the color sequence. The color and motor sequences had different lengths (10 vs 12 items), different numbers of elements (five vs four elements), and different temporal patterns (randomly intermittent vs continuous) and thus were independent of one another. These observations show that distracting information does not always impair motor performance, and so is not a sufficient explanation for the impaired performance. Instead, the influence that a distraction exerts upon performance is mediated by the type of processes engaged: when similar core processes are engaged, motor performance is enhanced, whereas when very different processes are engaged (i.e., counting and sequence performance), performance is impaired. Thus, these observations deepen our understanding of how a distraction, depending on its characteristics, can either impair or enhance performance and may offer novel approaches to optimizing human cognition.

Implicit learning in aging: extant patterns and new directions

Research suggests that the striatum plays an important role in implicit learning (IL). The striatum exhibits marked age-related morphological and neurochemical losses. Yet, behavioral studies suggest that IL is generally well preserved in old age, and that age-related differences emerge only when highly complex IL tasks are used. In this review, we integrate behavioral and neuroimaging evidence on IL in aging. We suggest that relative stability of IL in old age may reflect neural reorganization that compensates for age-related losses in striatal functions. Specifically, there may be an age-related increase in reliance on extrastriatal regions (e.g., medial-temporal, frontal) during IL. This reorganization of function may be beneficial under less taxing performance conditions, but not when task demands become more challenging.

Sensory information in perceptual-motor sequence learning: visual and/or tactile stimuli

Sequence learning in serial reaction time (SRT) tasks has been investigated mostly with unimodal stimulus presentation. This approach disregards the possibility that sequence acquisition may be guided by multiple sources of sensory information simultaneously. In the current study we trained participants in a SRT task with visual only, tactile only, or bimodal (visual and tactile) stimulus presentation. Sequence performance for the bimodal and visual only training groups was similar, while both performed better than the tactile only training group. In a subsequent transfer phase, participants from all three training groups were tested in conditions with visual, tactile, and bimodal stimulus presentation. Sequence performance between the visual only and bimodal training groups again was highly similar across these identical stimulus conditions, indicating that the addition of tactile stimuli did not benefit the bimodal training group. Additionally, comparing across identical stimulus conditions in the transfer phase showed that the lesser sequence performance from the tactile only group during training probably did not reflect a difference in sequence learning but rather just a difference in expression of the sequence knowledge.

Perceptual sequence learning in a 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 sequence learning without motor sequencing in young and old adults

The ability to detect patterns and organize individual events into complex sequences is a fundamental cognitive skill that is often learned implicitly. The serial response time (SRT) task has been widely used to investigate implicit sequence learning, but it remains unclear whether people learn a perceptual or motor sequence in this task. This study reports three experiments that build on previous research by Goschke and colleagues using an auditory SRT task in which the stimulus-to-response mapping changes on every trial to eliminate spatio-motor sequencing. The current study extends earlier work in three ways. First, healthy young and older adults were tested rather than the neuropsychological patients used in previous research. Second, sequences of different structural complexity were investigated including first- and second-order repeating sequences as well as higher-order probabilistic sequences. Third, the potential role of explicit knowledge was examined using three separate tests of declarative knowledge. Results indicate that young and old adults are able to learn purely perceptual auditory sequences, but that explicit knowledge contributes to learning of repeating sequences by young adults.

Implicit motor learning deficits in dyslexic adults

Children with developmental dyslexia fail to develop age-appropriate reading skills despite adequate intelligence and education. It has been suggested that dyslexics' various literacy, sensory and motor difficulties may be related to impaired cerebellar function. As the cerebellum is involved in motor learning, we measured serial reaction time performance in 40 adults (21 controls, 19 dyslexics). Dyslexic subjects performed comparably to controls during the randomly-ordered reaction time blocks, indicating that the dyslexics were as able as controls to make appropriate stimulus-response associations. However, the dyslexics failed to show the reaction time reduction that the control group showed during the repeated sequences (p = 0.018) and there was a significant group by condition effect when comparing the last two blocks of the sequence condition with the first two blocks of the final random condition (p = 0.008). Furthermore, there was a significant difference between good and poor readers on the degree of learning during the task (p = 0.015). This suggests that some dyslexics may suffer from an implicit motor learning deficit, which could generalize to non-motor learning.

The implicit sequence learning deficit in patients with Parkinson's disease: a matter of impaired sequence integration?

Despite the wealth of research investigating the serial reaction time (SRT) learning abilities of people with Parkinson's disease (PD), the role of the basal ganglia in implicit sequence learning remains largely unclear. The present research sought to examine the ability of people with PD to implicitly learn simultaneously operating sequences and integrate patterned information from each sequence dimension. Using a version of the SRT which reduced motor demands, the present experiment investigated the implicit learning of a spatial sequence, a stimulus-response sequence, and an integrated spatial/stimulus-response sequence, all of which are usually confounded in the standard SRT task. Whereas both PD and control groups demonstrated robust learning for the individual spatial and response sequences, only control participants evidenced learning for the integrated sequence. Further, unlike implicit learning for the spatial and object sequences, impaired integrated sequence acquisition was specifically related to the severity of patients' PD symptomatology. The implicit learning deficits of PD patients are discussed with regard to the role played by the basal ganglia in integrative sequence learning in the SRT.

Transcranial magnetic stimulation and the human brain: an ethical evaluation

Transcranial magnetic stimulation (TMS) is a neuroscientific technique that induces an electric current in the brain via application of a localized magnetic field pulse. The pulse penetrates the scalp and skull non-invasively and, depending on the parameters of stimulation, facilitates or depresses the local neuronal response with effects that can be transient or long lasting. While the mechanisms by which TMS acts remain largely unknown, the behavioral effects of the stimulation are reproducible and, in some cases, are highly beneficial. This chapter reviews the technique in detail and discusses safety as the paramount ethics issue for TMS. It further examines the ethical arguments for and against neuroenhancement with TMS and how the framework for acceptable practice must differ for patient and non-patient populations.

Surgery of tumors of the cerebellum and prefrontal cortex, and sensory memory and motor planning disturbances in children

OBJECT

This study addressed the integration of sensory short-term memory (SSTM) and motor planning (MP) in the lateral cerebellar region, where the dentate nucleus is localized, and in the prefrontal cortex (PF).

METHODS

Boucher and Lewis's test of SSTM and MP was administered pre- and postsurgically to 8 patients of either sex, between 5 and 19 years of age, with tumors of the cerebellum, PF (area 9 medial) or the parieto-occipital region, and on one occasion to 8 corresponding controls.

RESULTS

Whereas lesions of the midline portions of the cerebellum and of the parietal-occipital region did not appear to cause any cognitive defects, patients with lesions affecting either the lateral cerebellar region or PF exhibited statistically significant deficits of SSTM and MP.

CONCLUSIONS

The lateral cerebellum seems to act in concert with PF to integrate different cognitive activities related to holding objects in SSTM and planning motor strategies in reference to them.