Dissociation between priming and recognition in the expression of sequential knowledge

Conscious and unconscious memory and eye movements in context-guided visual search: A computational and experimental reassessment of Ramey, Yonelinas, and Henderson (2019)

Are eye movements unconsciously guided towards target locations in familiar scenes? In a recent eyetracking study, Ramey, Yonelinas, and Henderson (2019) measured eye-movement efficiency (scanpath ratio) and memory judgments when participants searched for targets in repeated and novel scenes. When trials judged new with high confidence were selected, scanpath ratio was lower for old scenes (misses) than for new scenes (correct rejections). In addition, familiarity as measured by recognition confidence did not significantly predict scanpath ratio. Ramey et al. attributed these results to unconscious learning guiding eye movements. In a re-assessment of Ramey et al.'s data, we show that their findings can be accounted for by a single-system computational model in which eye movements and memory judgments are driven by a common latent memory representation. In particular, (a) the scanpath ratio difference between high-confidence misses and correct rejections is a consequence of regression to the mean, while (b) the null correlation between familiarity and scanpath ratio, partly a natural consequence of the low reliability of the scanpath ratio measure, is also reproduced by the model. Two pre-registered experiments confirm a novel prediction of the alternative single-system model. This work offers a parsimonious account of Ramey et al.'s findings without recourse to unconscious guidance of eye movements.

EXPRESS: Are animates special? Exploring the effects of selective attention and animacy on visual statistical learning

Our visual system is built to extract regularities in how objects within our visual environment appear in relation to each other across time and space ('visual statistical learning'). Existing research indicates that visual statistical learning is modulated by selective attention. Our attentional system prioritises information that enables behaviour; for example, animates are prioritised over inanimates (the 'animacy advantage'). The present study examined the effects of selective attention and animacy on visual statistical learning in young adults (N = 284). We tested visual statistical learning of attended and unattended information across four animacy conditions: (i) living things that can self-initiate movement (animals); (ii) living things that cannot self-initiate movement (fruits and vegetables); (iii) non-living things that can generate movement (vehicles); and (iv) non-living things that cannot generate movement (tools and kitchen utensils). We implemented a four-point confidence-rating scale as an assessment of participants' awareness of the regularities in the visual statistical learning task. There were four key findings. First, selective attention plays a critical role by modulating visual statistical learning. Second, animacy does not play a special role in visual statistical learning. Third, visual statistical learning of attended information cannot be exclusively accounted for by unconscious knowledge. Fourth, performance on the visual statistical learning task is associated with the proportion of stimuli that were named or labelled. Our findings support the notion that visual statistical learning is a powerful mechanism by which our visual system resolves an abundance of sensory input over time.

Sequence Learning in an Online Serial Reaction Time Task: The Effect of Task Instructions

The serial reaction time task (SRTT) is commonly used to study motor learning and memory. The task is traditionally administered in a lab setting with participants responding via button box or keyboard to targets on a screen. By comparing response times of sequential versus random trials and accuracy across sequential trials, different forms of learning can be studied. The present study utilized an online version of the SRTT to study the effects of instructions on learning. Participants were randomly assigned to an explicit learning condition (with instructions to learn the visual sequence and associated tone) or an implicit learning condition (without instructions). Stimuli in both learning conditions were presented in two phases: auditory and visual (training phase), followed by auditory only (testing phase). Results indicated that learning occurred in both training and testing phases, as shown by a significant decrease in response times. There was no significant main effect of learning condition (explicit or implicit) on sequence learning. This suggests that providing explicit instructions does not seem to influence sequence learning in the SRTT learning paradigm. Future online studies utilizing the SRTT should explore varying task instructions in a parametric manner to better understand cognitive processes that underlie sequence learning.

From incidental learning to explicit memory: The role of sleep after exposure to a serial reaction time task

This laboratory study explores whether sleep has different effects on explicit (recognition-based) and implicit (priming-based) memory. Eighty-nine healthy participants were randomly assigned to one of two experimental conditions: sleep or wake. All participants were previously exposed to an incidental learning session involving a 12-element deterministic second-order conditional sequence embedded in a serial reaction time task. The participants' explicit and implicit knowledge was assessed both immediately after the learning session (pretest) and after 12 h (posttest). For the sleep group, participants had a night of normal sleep between pretest and posttest, whereas the wake group spent 12 h awake during the day. The measures involved an explicit recognition test and an implicit priming reaction-time test with old fragments from a previously learned sequence and new fragments of a different control sequence. The sleep group showed statistically significant improvement between the pretest and the posttest in the explicit memory measure, whereas the wake group did not. In the implicit task, both groups improved similarly after a 12-h retention interval. These results suggest that throughout sleep, implicitly acquired information is processed offline to yield an explicit representation of knowledge incidentally acquired the night before.

Tracking statistical learning online: Word segmentation in a target detection task

Despite the essential role of statistical learning in shaping human behavior, there are still controversies concerning its measurement. In this paper, we present a novel online target-detection task in an acoustic word segmentation paradigm, which is able to track the process of learning and does not build on deliberation and decision making. Beside testing the novel online task, we also examined its relationship with two offline measures: the traditional two-alternative forced choice (2AFC) task, and the statistically-induced chunking recall (SICR) task (Isbilen et al., 2017). Participants showed a significant learning effect on the online task, reflected in the decrease of reaction times during training and in the differences between reaction times to predictable versus unpredictable targets. Online learning scores correlated with the 2AFC scores, but this association was only present when participants did not have explicit knowledge about stimuli. SICR scores were not associated with any of the other measures. The internal consistency was higher for online learning measures than for the other two tasks. These findings show that the online target detection task is a good tool for assessing statistical learning, and invite further research on its psychometric properties.

Event-related brain potentials related to the identification of different types of signs

The present study examined the electrophysiological activity during the processing in the identification of signs. Participants performed a sign identification task, in which real, pseudo, and fake signs were adopted as stimuli. Common mathematical operation signs (e.g. +, -, ×, and ÷), which were known to the participants were adopted as the real signs. The pseudo signs had a similar appearance to the real signs (e.g. (Equation is included in full-text article.), (Equation is included in full-text article.), ×, and ÷). The fake signs were also unknown, but had an entirely different shape from the real signs (e.g. (Equation is included in full-text article.), (Equation is included in full-text article.), (Equation is included in full-text article.), and (Equation is included in full-text article.)). The behavioral results showed inferior recognition performance for pseudo signs relative to real or fake signs. Event-related potential results showed that (a) pseudo signs evoked a more positive P200 component than did real or fake signs, suggesting that more attentional resources might be allocated to the pseudo signs relative to the real or fake signs and (b) fake signs evoked a more negative N300 component than real or pseudo signs, suggesting that more cognitive resources might be recruited in processing the visual aspects for fake signs relative to real or pseudo signs. These results suggested that the P200 component, which is associated with attentional resource allocation, and the N300, which is sensitive to visual aspects, were evoked in processing the signs.

Forgetting cues are ineffective in promoting forgetting in the item-method directed forgetting paradigm

This study aims to investigate the effectiveness of forgetting cues in an item-method directed forgetting (DF) paradigm. A modified no-cue (NC) condition, in which participants could not adopt intentional forgetting strategy, was added to an item-method DF paradigm. Memory retention was compared between NC condition and to-be-forgotten (TBF) condition. The results revealed that the recognition reaction times (RTs) were shorter for the remembered TBF (TBF-R) words than for the remembered NC (NC-R) words, and were longer for the forgotten TBF words relative to the forgotten NC words, indicating that participants might be more familiar with the TBF words than the NC words. Event-related potential results showed that both LPC activity and frontal old/new effect were enhanced for TBF-R words relative to the NC-R words. These results might indicate that participants were more familiar with TBF words than NC words. This study further supports the view that forgetting cues may not in fact promote forgetting in the item-method DF paradigm.

Elaborately rehearsed information can be forgotten: A new paradigm to investigate directed forgetting

In previous item-method directed forgetting (DF) studies, forgetting may have occurred when the maintenance rehearsal of memory items was performed. In this study, a modified item-method DF paradigm was adopted to investigate whether forgetting instruction could produce a positive effect on forgetting the items that were elaborately rehearsed. During the study phase, a to-be-forgotten (TBF) word was followed by a forgetting cue. If no cue followed, the word was a to-be-remembered (TBR) item. Participants were required to intentionally memorize the word when it appeared. During the test phase, a yes/no recognition (Experiment 1) or a remember/know procedure (Experiment 2) was adopted. The behavioural results revealed that both the hit rate (Experiment 1) and remembering rate (Experiment 2) were higher for TBR relative to TBF words. For correctly identified old words, reaction times were consistently shorter for TBR compared to TBF words. These results revealed superior memory retention for TBR than for TBF words. The event-related potential (ERP) results revealed that, during both FN400 and late-positive complex (LPC) time windows, the remembered TBR words evoked more positive ERPs than the remembered TBF words and correctly rejected (CR) words (i.e., FN400 and LPC old/new effects). However, more negative ERPs were evoked for both remembered and forgotten TBF words than for CR words during the LPC time window (i.e., reversed LPC old/new effect). These results demonstrated that TBF words were associated with lower level of familiarity and recollection process than TBR words. The memory representation of TBF information might be inhibited.

Testing enhances motor practice

We investigated how retrieval of a set of newly learned motor sequences influences subsequent learning of another set of motor sequences. In four experiments, retrieval reduced an acceleration of movement execution over subsequent study trials. This relative slowing-down was associated with better recall performance in a final memory test. Explicit retrievability of motor sequences benefited from longer study-trial response times (RTs), suggesting that retrieval caused more attentive encoding. The use of motor sequences requiring overt action during encoding allowed for this demonstration of a twofold forward effect of testing on encoding quality and on recall. Experiment 1 adopted a paradigm used in previous studies with verbal materials. Experiment 2 changed the test format to be less susceptible to interference. Experiments 3 and 4 additionally switched from a between-participants design to a within-participants design. These modifications did not affect the occurrence of the twofold forward effect of testing but enabled detecting a correlation between recall and study-trial performance that had been precluded by the strongly interference-dependent test format of the original paradigm. Our findings demonstrate an immediate learning benefit of testing. It enhances encoding in subsequent study trials.

Skill in discrete keying sequences is execution rate specific

The present study tested the hypothesis that in motor sequences, the interval between successive movements is critical for the type of representation that develops. Participants practiced two 7-key sequences in the context of a discrete sequence production (DSP) task. The 0-RSI group practiced these sequences with response stimulus intervals (RSIs) of 0, which is typical for the DSP task, while the long-RSI group practiced the same sequences with unpredictable RSIs between 500 and 2000 ms. The ensuing test phase examined performance of these familiar and of unfamiliar sequences for both groups under both RSI regimes. The results support our hypothesis that the motor chunks that 0-RSI participants developed could not be used with long RSIs, whereas the long-RSI participants developed sequence representations that cannot be used with 0 RSIs. A new, computerized, sequence awareness task showed that long-RSI participants had limited sequence knowledge. The sequencing skill developed by long-RSI participants can, therefore, not have been based on explicit knowledge.

Computational and empirical simulations of selective memory impairments: Converging evidence for a single-system account of memory dissociations

Current theory has divided memory into multiple systems, resulting in a fractionated account of human behaviour. By an alternative perspective, memory is a single system. However, debate over the details of different single-system theories has overshadowed the converging agreement among them, slowing the reunification of memory. Evidence in favour of dividing memory often takes the form of dissociations observed in amnesia, where amnesic patients are impaired on some memory tasks but not others. The dissociations are taken as evidence for separate explicit and implicit memory systems. We argue against this perspective. We simulate two key dissociations between classification and recognition in a computational model of memory, A Theory of Nonanalytic Association. We assume that amnesia reflects a quantitative difference in the quality of encoding. We also present empirical evidence that replicates the dissociations in healthy participants, simulating amnesic behaviour by reducing study time. In both analyses, we successfully reproduce the dissociations. We integrate our computational and empirical successes with the success of alternative models and manipulations and argue that our demonstrations, taken in concert with similar demonstrations with similar models, provide converging evidence for a more general set of single-system analyses that support the conclusion that a wide variety of memory phenomena can be explained by a unified and coherent set of principles.

Regressive research: The pitfalls of post hoc data selection in the study of unconscious mental processes

Many studies of unconscious processing involve comparing a performance measure (e.g., some assessment of perception or memory) with an awareness measure (such as a verbal report or a forced-choice response) taken either concurrently or separately. Unconscious processing is inferred when above-chance performance is combined with null awareness. Often, however, aggregate awareness is better than chance, and data analysis therefore employs a form of extreme group analysis focusing post hoc on participants, trials, or items where awareness is absent or at chance. The pitfalls of this analytic approach are described with particular reference to recent research on implicit learning and subliminal perception. Because of regression to the mean, the approach can mislead researchers into erroneous conclusions concerning unconscious influences on behavior. Recommendations are made about future use of post hoc selection in research on unconscious cognition.

Parameter recovery, bias and standard errors in the linear ballistic accumulator model

The linear ballistic accumulator (LBA) model (Brown & Heathcote, , Cogn. Psychol., 57, 153) is increasingly popular in modelling response times from experimental data. An R package, glba, has been developed to fit the LBA model using maximum likelihood estimation which is validated by means of a parameter recovery study. At sufficient sample sizes parameter recovery is good, whereas at smaller sample sizes there can be large bias in parameters. In a second simulation study, two methods for computing parameter standard errors are compared. The Hessian-based method is found to be adequate and is (much) faster than the alternative bootstrap method. The use of parameter standard errors in model selection and inference is illustrated in an example using data from an implicit learning experiment (Visser et al., , Mem. Cogn., 35, 1502). It is shown that typical implicit learning effects are captured by different parameters of the LBA model.

The Emergence of Explicit Knowledge in a Serial Reaction Time Task: The Role of Experienced Fluency and Strength of Representation

The Serial Reaction Time Task (SRTT) is an important paradigm to study the properties of unconscious learning processes. One specifically interesting and still controversially discussed topic are the conditions under which unconsciously acquired knowledge becomes conscious knowledge. The different assumptions about the underlying mechanisms can contrastively be separated into two accounts: single system views in which the strengthening of associative weights throughout training gradually turns implicit knowledge into explicit knowledge, and dual system views in which implicit knowledge itself does not become conscious. Rather, it requires a second process which detects changes in performance and is able to acquire conscious knowledge. In a series of three experiments, we manipulated the arrangement of sequential and deviant trials. In an SRTT training, participants either received mini-blocks of sequential trials followed by mini-blocks of deviant trials (22 trials each) or they received sequential and deviant trials mixed randomly. Importantly the number of correct and deviant transitions was the same for both conditions. Experiment 1 showed that both conditions acquired a comparable amount of implicit knowledge, expressed in different test tasks. Experiment 2 further demonstrated that both conditions differed in their subjectively experienced fluency of the task, with more fluency experienced when trained with mini-blocks. Lastly, Experiment 3 revealed that the participants trained with longer mini-blocks of sequential and deviant material developed more explicit knowledge. Results are discussed regarding their compatibility with different assumptions about the emergence of explicit knowledge in an implicit learning situation, especially with respect to the role of metacognitive judgements and more specifically the Unexpected-Event Hypothesis.

The effects of ordinal load on incidental temporal learning

How can we grasp the temporal structure of events? A few studies have indicated that representations of temporal structure are acquired when there is an intention to learn, but not when learning is incidental. Response-to-stimulus intervals, uncorrelated temporal structures, unpredictable ordinal information, and lack of metrical organization have been pointed out as key obstacles to incidental temporal learning, but the literature includes piecemeal demonstrations of learning under all these circumstances. We suggest that the unacknowledged effects of ordinal load may help reconcile these conflicting findings, ordinal load referring to the cost of identifying the sequence of events (e.g., tones, locations) where a temporal pattern is embedded. In a first experiment, we manipulated ordinal load into simple and complex levels. Participants learned ordinal-simple sequences, despite their uncorrelated temporal structure and lack of metrical organization. They did not learn ordinal-complex sequences, even though there were no response-to-stimulus intervals nor unpredictable ordinal information. In a second experiment, we probed learning of ordinal-complex sequences with strong metrical organization, and again there was no learning. We conclude that ordinal load is a key obstacle to incidental temporal learning. Further analyses showed that the effect of ordinal load is to mask the expression of temporal knowledge, rather than to prevent learning.

The Things You Do: Internal Models of Others' Expected Behaviour Guide Action Observation

Predictions allow humans to manage uncertainties within social interactions. Here, we investigate how explicit and implicit person models-how different people behave in different situations-shape these predictions. In a novel action identification task, participants judged whether actors interacted with or withdrew from objects. In two experiments, we manipulated, unbeknownst to participants, the two actors action likelihoods across situations, such that one actor typically interacted with one object and withdrew from the other, while the other actor showed the opposite behaviour. In Experiment 2, participants additionally received explicit information about the two individuals that either matched or mismatched their actual behaviours. The data revealed direct but dissociable effects of both kinds of person information on action identification. Implicit action likelihoods affected response times, speeding up the identification of typical relative to atypical actions, irrespective of the explicit knowledge about the individual's behaviour. Explicit person knowledge, in contrast, affected error rates, causing participants to respond according to expectations instead of observed behaviour, even when they were aware that the explicit information might not be valid. Together, the data show that internal models of others' behaviour are routinely re-activated during action observation. They provide first evidence of a person-specific social anticipation system, which predicts forthcoming actions from both explicit information and an individuals' prior behaviour in a situation. These data link action observation to recent models of predictive coding in the non-social domain where similar dissociations between implicit effects on stimulus identification and explicit behavioural wagers have been reported.

Intending to forget is not easy: Behavioral and electrophysiological evidence

Previous researches have shown that recognition accuracy is lower for items cued to-be-forgotten (TBF) than to-be-remembered (TBR). Does directed forgetting help people forget more items than non-directed forgetting? Here, we modified the directed forgetting paradigm by adding a non-cue condition (NC). Consequently, non-directed forgetting would occur in NC. Behavioral results showed higher recognition accuracy for TBF than NC items, indicating that directed forgetting is less effective than non-directed forgetting. Electrophysiological results indicated that: (1) Remembered TBF items evoke an increased late positive component (LPC) than remembered NC items; (2) compared with remembered NC items, remembered TBF items showed a pronounced left-lateralized old/new effect and a reduced right-lateralized reversed old/new effect; (3) a right-lateralized reversed old/new effect was observed for forgotten TBF, but it was absent for forgotten NC items. These results demonstrate that the TBF items have a greater memory trace than the NC items. Forgetting cue has little effect of forgetting item from memory, and it might prompt subject to process or at least focus attention on the TBF items.

Rapid Serial Auditory Presentation

Abstract. The Rapid Serial Visual Presentation procedure is a method widely used in visual perception research. In this paper we propose an adaptation of this method which can be used with auditory material and enables assessment of statistical learning in speech segmentation. Adult participants were exposed to an artificial speech stream composed of statistically defined trisyllabic nonsense words. They were subsequently instructed to perform a detection task in a Rapid Serial Auditory Presentation (RSAP) stream in which they had to detect a syllable in a short speech stream. Results showed that reaction times varied as a function of the statistical predictability of the syllable: second and third syllables of each word were responded to faster than first syllables. This result suggests that the RSAP procedure provides a reliable and sensitive indirect measure of auditory statistical learning.

Implicit and explicit contributions to statistical learning

Statistical learning allows learners to detect regularities in the environment and appears to emerge automatically as a consequence of experience. Statistical learning paradigms bear many similarities to those of artificial grammar learning and other types of implicit learning. However, whether learning effects in statistical learning tasks are driven by implicit knowledge has not been thoroughly examined. The present study addressed this gap by examining the role of implicit and explicit knowledge within the context of a typical auditory statistical learning paradigm. Learners were exposed to a continuous stream of repeating nonsense words. Learning was tested (a) directly via a forced-choice recognition test combined with a remember/know procedure and (b) indirectly through a novel reaction time (RT) test. Behavior and brain potentials revealed statistical learning effects with both tests. On the recognition test, accurate responses were associated with subjective feelings of stronger recollection, and learned nonsense words relative to nonword foils elicited an enhanced late positive potential indicative of explicit knowledge. On the RT test, both RTs and P300 amplitudes differed as a function of syllable position, reflecting facilitation attributable to statistical learning. Explicit stimulus recognition did not correlate with RT or P300 effects on the RT test. These results provide evidence that explicit knowledge is accrued during statistical learning, while bringing out the possibility that dissociable implicit representations are acquired in parallel. The commonly used recognition measure primarily reflects explicit knowledge, and thus may underestimate the total amount of knowledge produced by statistical learning. Indirect measures may be more sensitive indices of learning, capturing knowledge above and beyond what is reflected by recognition accuracy.

Visual statistical learning in children and young adults: how implicit?

Visual statistical learning (VSL) is the ability to extract the joint and conditional probabilities of shapes co-occurring during passive viewing of complex visual configurations. Evidence indicates that even infants are sensitive to these regularities (e.g., Kirkham et al., 2002). However, there is continuing debate as to whether VSL is accompanied by conscious awareness of the statistical regularities between sequence elements. Bertels et al. (2012) addressed this question in young adults. Here, we adapted their paradigm to investigate VSL and conscious awareness in children. Using the same version of the paradigm, we also tested young adults so as to directly compare results from both age groups. Fifth graders and undergraduates were exposed to a stream of visual shapes arranged in triplets. Learning of these sequences was then assessed using both direct and indirect measures. In order to assess the extent to which learning occurred explicitly, we also measured confidence through subjective measures in the direct task (i.e., binary confidence judgments). Results revealed that both children and young adults learned the statistical regularities between shapes. In both age groups, participants who performed above chance in the completion task had conscious access to their knowledge. Nevertheless, although adults performed above chance even when they claimed to guess, there was no evidence of implicit knowledge in children. These results suggest that the role of implicit and explicit influences in VSL may follow a developmental trajectory.

Integrated Implicit-Explicit Learning Approach to Voice Therapy

This article is intended to define, compare, and provide outcomes for an integrated implicit-explicit learning approach to voice therapy related to current motor learning theories.

Clients from the Misericordia University voice clinic have undergone therapy using this integrated approach. The article will review previous literature on motor learning theories related to voice, define the protocol used in the integrated approach, and highlight the diagnostic, clinical outcomes exhibited by these clients. Steps for the therapy protocol will be highlighted. Results indicate that individuals participating in an integrated implicit-explicit learning approach to voice therapy report that initial instruction and target production take increased effort to learn; however once acquired, targets are easily generalized to more complex speaking (e.g., conversation) tasks. Implicit-only voice therapy approaches are effective in treating voice disorders. Limited published data, however, has compared traditional, implicit-only therapy to other methods of voice therapy. Another approach may be one that employs more explicit teaching of the mechanics of voice production. The integrated implicit-explicit learning approach discussed in this article combines explicit instruction with implicit facilitators, and initiates simple and complex tasks from the start of therapy.

Neurocognitive mechanisms of statistical-sequential learning: what do event-related potentials tell us?

Statistical-sequential learning (SL) is the ability to process patterns of environmental stimuli, such as spoken language, music, or one's motor actions, that unfold in time. The underlying neurocognitive mechanisms of SL and the associated cognitive representations are still not well understood as reflected by the heterogeneity of the reviewed cognitive models. The purpose of this review is: (1) to provide a general overview of the primary models and theories of SL, (2) to describe the empirical research - with a focus on the event-related potential (ERP) literature - in support of these models while also highlighting the current limitations of this research, and (3) to present a set of new lines of ERP research to overcome these limitations. The review is articulated around three descriptive dimensions in relation to SL: the level of abstractness of the representations learned through SL, the effect of the level of attention and consciousness on SL, and the developmental trajectory of SL across the life-span. We conclude with a new tentative model that takes into account these three dimensions and also point to several promising new lines of SL research.

Age effects on explicit and implicit memory

It is well-documented that explicit memory (e.g., recognition) declines with age. In contrast, many argue that implicit memory (e.g., priming) is preserved in healthy aging. For example, priming on tasks such as perceptual identification is often not statistically different in groups of young and older adults. Such observations are commonly taken as evidence for distinct explicit and implicit learning/memory systems. In this article we discuss several lines of evidence that challenge this view. We describe how patterns of differential age-related decline may arise from differences in the ways in which the two forms of memory are commonly measured, and review recent research suggesting that under improved measurement methods, implicit memory is not age-invariant. Formal computational models are of considerable utility in revealing the nature of underlying systems. We report the results of applying single and multiple-systems models to data on age effects in implicit and explicit memory. Model comparison clearly favors the single-system view. Implications for the memory systems debate are discussed.

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.

Explicit pre-training instruction does not improve implicit perceptual-motor sequence learning

Memory systems theory argues for separate neural systems supporting implicit and explicit memory in the human brain. Neuropsychological studies support this dissociation, but empirical studies of cognitively healthy participants generally observe that both kinds of memory are acquired to at least some extent, even in implicit learning tasks. A key question is whether this observation reflects parallel intact memory systems or an integrated representation of memory in healthy participants. Learning of complex tasks in which both explicit instruction and practice is used depends on both kinds of memory, and how these systems interact will be an important component of the learning process. Theories that posit an integrated, or single, memory system for both types of memory predict that explicit instruction should contribute directly to strengthening task knowledge. In contrast, if the two types of memory are independent and acquired in parallel, explicit knowledge should have no direct impact and may serve in a "scaffolding" role in complex learning. Using an implicit perceptual-motor sequence learning task, the effect of explicit pre-training instruction on skill learning and performance was assessed. Explicit pre-training instruction led to robust explicit knowledge, but sequence learning did not benefit from the contribution of pre-training sequence memorization. The lack of an instruction benefit suggests that during skill learning, implicit and explicit memory operate independently. While healthy participants will generally accrue parallel implicit and explicit knowledge in complex tasks, these types of information appear to be separately represented in the human brain consistent with multiple memory systems theory.

Are there multiple memory systems? Tests of models of implicit and explicit memory

[Formula: see text]

This article reviews recent work aimed at developing a new framework, based on signal detection theory, for understanding the relationship between explicit (e.g., recognition) and implicit (e.g., priming) memory. Within this framework, different assumptions about sources of memorial evidence can be framed. Application to experimental results provides robust evidence for a single-system model in preference to multiple-systems models. This evidence comes from several sources including studies of the effects of amnesia and ageing on explicit and implicit memory. The framework allows a range of concepts in current memory research, such as familiarity, recollection, fluency, and source memory, to be linked to implicit memory. More generally, this work emphasizes the value of modern computational modelling techniques in the study of learning and memory.

Sequence learning by action, observation and action observation

The serial reaction time (SRT) task was used to compare learning of a complex sequence by action (participants responded to sequential stimuli), by observation (participants watched but did not respond to sequential stimuli), and by action-observation (participants watched an expert model responding to sequential stimuli). Each of these groups was compared with an untrained control group. Experiment 1 indicated that both observation and action-observation were sufficient to support learning of a 12-item second-order conditional (SOC) sequence. Experiment 2 confirmed these findings, and showed that, as indexed by reaction time (RT), the extent of learning by observation and by action-observation was comparable to that of action-based learning. Using a recognition test, Experiment 2 and 3 also provided evidence that, whereas learning by stimulus observation was explicit, learning by action-observation was implicit. These findings are consistent with a connection between motor systems and implicit learning, but do not support the hypothesis that overt action is necessary for implicit learning.

Visuospatial sequence learning without seeing

BACKGROUND

The ability to detect and integrate associations between unrelated items that are close in space and time is a key feature of human learning and memory. Learning sequential associations between non-adjacent visual stimuli (higher-order visuospatial dependencies) can occur either with or without awareness (explicit vs. implicit learning) of the products of learning. Existing behavioural and neurocognitive studies of explicit and implicit sequence learning, however, are based on conscious access to the sequence of target locations and, typically, on conditions where the locations for orienting, or motor, responses coincide with the locations of the target sequence.

METHODOLOGY/PRINCIPAL FINDINGS

Dichoptic stimuli were presented on a novel sequence learning task using a mirror stereoscope to mask the eye-of-origin of visual input from conscious awareness. We demonstrate that conscious access to the sequence of target locations and responses that coincide with structure of the target sequence are dispensable features when learning higher-order visuospatial associations. Sequence knowledge was expressed in the ability of participants to identify the trained higher-order visuospatial sequence on a recognition test, even though the trained and untrained recognition sequences were identical when viewed at a conscious binocular level, and differed only at the level of the masked sequential associations.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate that unconscious processing can support perceptual learning of higher-order sequential associations through interocular integration of retinotopic-based codes stemming from monocular eye-of-origin information. Furthermore, unlike other forms of perceptual associative learning, visuospatial attention did not need to be directed to the locations of the target sequence. More generally, the results pose a challenge to neural models of learning to account for a previously unknown capacity of the human visual system to support the detection, learning and recognition of higher-order sequential associations under conditions where observers are unable to see the target sequence or perform responses that coincide with structure of the target sequence.

Learning: from association to cognition

Since the very earliest experimental investigations of learning, tension has existed between association-based and cognitive theories. Associationism accounts for the phenomena of both conditioning and "higher" forms of learning via concepts such as excitation, inhibition, and reinforcement, whereas cognitive theories assume that learning depends on hypothesis testing, cognitive models, and propositional reasoning. Cognitive theories have received considerable impetus in regard to both human and animal learning from recent research suggesting that the key illustration of cue selection in learning, blocking, often arises from inferential reasoning. At the same time, a dichotomous view that separates noncognitive, unconscious (implicit) learning from cognitive, conscious (explicit) learning has gained favor. This review selectively describes key findings from this research, evaluates evidence for and against associative and cognitive explanatory constructs, and critically examines both the dichotomous view of learning as well as the claim that learning can occur unconsciously.

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.

Characterizing sequence knowledge using online measures and hidden Markov models

What knowledge do subjects acquire in sequence-learning experiments? How can they express that knowledge? In two sequence-learning experiments, we studied the acquisition of knowledge of complex probabilistic sequences. Using a novel experimental paradigm, we were able to compare reaction time and generation measures of sequence knowledge online. Hidden Markov models were introduced as a novel way of analyzing generation data that allowed for a characterization of sequence knowledge in terms of the grammar that was used to generate the stimulus material. The results indicated a strong correlation between the decrease in reaction times and an increase in generation performance. This pattern of results is consistent with a common knowledge base for improvement on both measures. On a more detailed level, the results indicate that at the start of training, generation performance and reaction times are uncorrelated and that this correlation increases with training.

Interference produces different forgetting rates for implicit and explicit knowledge

Exposure to a repeating set of target strings generated by an artificial grammar in a speeded matching task generates both explicit and implicit knowledge. Previous research has shown that implicit knowledge (assessed via a priming measure) is preserved after a retention interval of one week but explicit knowledge (assessed via recognition) is significantly reduced. In two experiments, we replicated and extended Tunney's findings. Experiment 1 was a partial replication of the experiment conducted by Tunney, and demonstrated that the decline in recognition shown by Tunney was not due to a repetition of test items at the pre and post times of assessment. In addition, Experiment 1 lends credibility to Tunney's assumption that recognition scores assess explicit rather than implicit knowledge. Experiment 2 extended Tunney's findings theoretically by demonstrating that interference can produce the pattern of findings demonstrated in the present Experiment 1 as well as in Tunney.

Effects of retention intervals on receiver operating characteristics in artificial grammar learning

Current theories of memory suggest that recognition is composed of separate processes of familiarity and recollection (e.g. [Yonelinas, A. P. (2002). The nature of recollection and familiarity: a review of 30 years of research. Journal of Memory and Language, 46, 441-517]). A key feature of these two processes is that they decay, or are forgotten at different rates. The dual-process model has also been useful in understanding artificial grammar learning. We obtained evidence for recollection and familiarity in artificial grammar learning by analyses of receiver operating characteristics (ROC). Furthermore we found that these were dissociated by retention intervals of 14 days. The slope of the zROC curves deviated reliably from 1 immediately after study and increased towards 1 suggesting that recollection contributed to recognition decisions but declined over the 14-day period leaving familiarity as the only basis for recognition. These data show similar patterns to those observed in word-recognition [Gardiner, J. M., & Java, R. I. (1991). Forgetting in recognition memory with and without recollective experience. Memory &Cognition, 19, 617-623; Tunney, R. J. (submitted for publication). Changes in the subjective experience of recognition over time suggest independent processes] and confirm the view that recollection and familiarity are implicated in artificial grammar learning. Moreover, the data confirm the finding that recollection and familiarity-based memory show different patterns of forgetting.

The striatum and probabilistic implicit sequence learning

The distinction between implicit (unconscious) and explicit (conscious) learning is controversial. Some argue that explicit learning is dependent on the medial temporal lobes, whereas implicit learning is mediated by the basal ganglia and others propose that all learning is explicit. The purpose of the present study was to investigate the involvement of the basal ganglia in implicit learning by examining learning of a probabilistic sequence of targets, in patients with Parkinson's disease (PD) and controls. Following learning, we assessed participants' awareness of the sequence structure by asking them to generate or withhold sequence consistent responses (process dissociation procedure) and to perform a recognition test in which measures of priming and recognition were obtained concurrently. Although the PD group demonstrated evidence of probabilistic sequence learning in this study, learning was significantly attenuated compared to controls. Residual learning in the PD group was genuinely implicit in nature because (a) PD patients were not able to control the expression of their acquired knowledge, and (b) their knowledge supported subsequent priming of sequence-consistent responses but recognition ratings were at chance. In contrast, following learning controls were capable of above chance recognition indicating that their sequential knowledge was acquired in a more explicit way. The results support the view that (i) the basal ganglia contribute to probabilistic implicit sequence learning (ii) that such learning can occur implicitly without explicit knowledge in PD patients.

Qualitative differences between implicit and explicit sequence learning

Four experiments investigate the differences between implicit and explicit sequence learning concerning their resilience to structural and superficial task changes. A superficial change that embedded the SRT task in the context of a selection task, while maintaining the sequence, did selectively hinder the expression of implicit learning. In contrast, a manipulation that maintained the task surface, but decreased the sequence validity, affected the expression of learning specifically when it was explicit. These results are discussed in the context of a dynamic framework (Cleeremans & Jiménez, 2002), which assumes that implicit knowledge is specially affected by contextual factors and that, as knowledge becomes explicit, it allows for the development of relevant metaknowledge that modulates the expression of explicit knowledge.

Implicit learning of a repeated segment in continuous tracking: a reappraisal

Several prior studies (e.g., Shea, Wulf, Whitacre, & Park, 2001; Wulf & Schmidt, 1997) have apparently demonstrated implicit learning of a repeated segment in continuous-tracking tasks. In two conceptual replications of these studies, we failed to reproduce the original findings. However, these findings were reproduced in a third experiment, in which we used the same repeated segment as that used in the Wulf et al. studies. Analyses of the velocity and the acceleration of the target suggests that this repeated segment could be easier to track than the random segments serving as control, accounting for the results of Wulf and collaborators. Overall these experiments suggest that learning a repeated segment in continuous-tracking tasks may be much more difficult than learning from a repeated sequence in conventional serial reaction time tasks. A possible explanation for this difference is outlined.

Disruption of sequential priming in organic and pharmacological amnesia: a role for the medial temporal lobes in implicit contextual learning

We examined learning and expression of contextual implicit learning of a sequence of targets in a speeded target-detection task in amnesic and control participants. Amnesia was of organic origin in one participant group and induced psychopharmacologically (diazepam 7.5 or 15 mg) in another. Although the amnesic groups were able to learn the target sequence normally, their expression of sequence knowledge (priming) was attenuated when contextual support was limited. This was evaluated by studying response latencies for targets primed by between 0 and 5 preceding context locations. Whereas control participants showed priming when the current target location was primed by only two previous locations, priming was eliminated with two (but not four) previous locations by a low dose of diazepam and was eliminated even with four elements of context under a high dose of diazepam and in amnesia of organic origin. The results suggest that a function of the hippocampal memory system is to support contextual learning and performance, even when that learning is nondeclarative.

Sequence learning under dual-task conditions: alternatives to a resource-based account

In two experiments with the serial reaction-time task, participants were presented with deterministic or probabilistic sequences under single- or dual-task conditions. Experiment 1 showed that learning of a probabilistic structure was not impaired over a first session by performing a counting task, but that such an interference arose over a second session, when the knowledge was tested under single-task conditions. In contrast, the effects of the secondary task arose earlier for participants exposed to deterministic sequences. This difference between deterministic and probabilistic sequences disappeared in Experiment 2, where the counting task was performed on tones associated to the locations. Comparisons between sessions indicated that the secondary task affected not only the expression but also the acquisition of sequence learning, and that greater interference was observed in those conditions that yielded more explicit knowledge. These results suggest that the effects of a dual task on the measures of implicit sequence learning may be partly due to the intrusion of explicit knowledge and partly due to the disruption of the sequence produced by the inclusion of random events.

Attentional load and implicit sequence learning

A widely employed conceptualization of implicit learning hypothesizes that it makes minimal demands on attentional resources. This conjecture was investigated by comparing learning under single-task and dual-task conditions in the sequential reaction time (SRT) task. Participants learned probabilistic sequences, with dual-task participants additionally having to perform a counting task using stimuli that were targets in the SRT display. Both groups were then tested for sequence knowledge under single-task (Experiments 1 and 2) or dual-task (Experiment 3) conditions. Participants also completed a free generation task (Experiments 2 and 3) under inclusion or exclusion conditions to determine if sequence knowledge was conscious or unconscious in terms of its access to intentional control. The experiments revealed that the secondary task impaired sequence learning and that sequence knowledge was consciously accessible. These findings disconfirm both the notion that implicit learning is able to proceed normally under conditions of divided attention, and that the acquired knowledge is inaccessible to consciousness. A unitary framework for conceptualizing implicit and explicit learning is proposed.

The generation of conscious awareness in an incidental learning situation

The purpose of the present experiments was to investigate the generation of conscious awareness (i.e., of verbal report) in an incidental learning situation. While the single-system account assumes that all markers of learning, verbal or nonverbal, index the same underlying knowledge representation, multiple-systems accounts grant verbal report a special status as a marker of learning because they assume that the nonverbal and verbal effects of learning rely on different memory representations. We tested these two accounts in two experiments in which we held the amount of learning in the nonverbal memory system constant while manipulating independent variables aimed at affecting learning in the declarative system. The results of both experiments revealed significant differences in verbal report between experimental conditions, but no significant differences in response times. Overall, these results provide clear evidence in favor of the multiple-systems account.

The Influence of Grammatical, Local, and Organizational Redundancy on Implicit Learning: An Analysis Using Information Theory

People behave as if they know the structure of their environment. Because people rarely study that structure explicitly, several theorists have postulated an implicit learning system that abstracts that structure automatically. An alternative view is that people respond to local structure that derives from global structure. Measures are developed that quantify structure in a set of stimuli, in individual stimuli, and in encoded stimuli. The authors apply the measures to examine serial recall for sequences of colors generated using a stationary Markov grammar. They demonstrate that the 3 kinds of redundancy are confounded and show that the memorial advantage for grammatical stimuli reflects participants' use of local expressions of grammatical structure to aid learning.

Intentional control and implicit sequence learning

Sequence knowledge acquired by repeated exposure to targets in a speeded localization task was studied in 3 experiments that sought to test A. Destrebecqz and A. Cleeremans's (2001, 2003) claim that, under certain circumstances, the expression of such sequence knowledge cannot be brought under intentional control. In Experiment 1 participants were trained on either a deterministic or a probabilistic sequence and then performed a free-generation test under either inclusion or exclusion instructions. Participants were found to be capable of both expressing (inclusion) and avoiding expressing (exclusion) sequence knowledge. These results were confirmed in Experiment 2 with a more exact replication of Destrebecqz and Cleeremans's methodology. In Experiment 3 participants performed a trial-by-trial generation test under both inclusion and exclusion conditions after a much longer period of training. All the findings are consistent with the proposal that information acquired during sequence learning is explicit in nature.