Functional independence of explicit and implicit motor adjustments

Adaptation to novel visuomotor transformations for example when navigating a cursor on a computer monitor by using a computer mouse, can be explicit or implicit. Explicit adjustments are made when people are informed about the occurrence and the type of a novel visuomotor transformation and intentionally modify their movements. Implicit adjustments, in contrast, are made without reportable knowledge of a novel visuomotor transformation and without a change intention. The relation of implicit adjustments to explicit adjustments needs further clarification. Here we show that these two types of adjustment occur at the same time and remain functionally independent. The size of total adjustment turned out to be the sum of explicit and implicit adjustments measured in isolation, even when both processes produce opposite outcomes. In perspective our results demonstrate that automatic, implicit processes of motor control are not superseded by intentional, explicit ones, but only superposed.     

Adaptation to visuomotor rotations in younger and older adults

Adaptation to a visuomotor rotation is known to be impaired at older adult age. The authors examined whether the impairment is present already at preretirement age and whether it depends on the difficulty of the adaptation task. Moreover, the authors tested predictions of the hypothesis that the age-related impairment pertains primarily to strategic corrections and the explicit knowledge on which they are based but not to the acquisition of an (implicit) internal model of the novel visuomotor transformation. The authors found an age-related impairment of adaptation and explicit knowledge already at preretirement age but no age-related change of aftereffects. With an incremental simplification of the adaptation task, age-related changes were able to be eliminated. Individual differences of the quality of explicit knowledge were associated with differences of adaptation, but not of aftereffects. When age groups were matched by explicit knowledge, age-related impairments of adaptation largely disappeared. However, a reliable difference remained in one of the experiments, suggesting that other processes of adjustment to a visuomotor rotation might be affected by aging as well.     

Implicit and explicit false belief development in preschool children

The ability to represent the mental states of other agents is referred to as Theory of Mind (ToM). A developmental breakthrough in ToM consists of understanding that others can have false beliefs about the world. Recently, infants younger than 2 years of age have been shown to pass novel implicit false belief tasks. However, the processes underlying these tasks and their relation to later‐developing explicit false belief understanding, as well as to other cognitive abilities, are not yet understood. Here, we study a battery of implicit and explicit false belief tasks in 3‐ and 4‐year‐old children, relating their performance to linguistic abilities and executive functions. The present data show a significant developmental change from failing explicit false belief tasks at 3 years of age to passing them at the age of 4, while both age groups pass implicit false belief tasks. This differential developmental trajectory is reflected by the finding that explicit and implicit false belief tasks do not correlate. Further, we demonstrate that explicit false belief tasks correlate with syntactic and executive functions, whereas implicit false belief tasks do not. The study thus indicates that the processes underlying implicit false belief tasks are different from later‐developing explicit false belief understanding. Moreover, our results speak for a critical role of syntactic and executive functions for passing standard explicit false belief tasks in contrast to implicit tasks.     

Implicit and explicit learning: individual differences and IQ

We explored the degree to which individual differences in performance were observed in a group of subjects who worked with two different tasks: one implicit and one explicit. The implicit task was a standard artificial grammar-learning task; the explicit was a series-completion problem-solving task. Substantial individual differences were found between subjects on the explicit task; relatively small individual differences were found on the implicit task. Moreover, performance on the explicit task correlated strongly with intelligence quotient, but performance on the implicit task did not. Data from previous experiments were also found to be in agreement with these results. The findings are presented in the context of a general theory of implicit learning proposed recently by Reber (1989a, in press) that derives from considerations of the evolution of cognitive processes. This evolutionary model argues that unconscious, implicit induction systems are evolutionarily older and antedate conscious, explicit learning processes, and that this antiquity carries with it particular patterns of function that differentiate implicit processes from explicit processes.     

Domain general mechanisms account for imagined transformations of whole body perspective

Three experiments investigated the contribution of domain general processes to imagined transformations of whole body perspective. In a task where participants make left–right judgements about a schematic human figure, reaction times made from the point of view of the figure are longer when the figure does not share the same spatial orientation as the participant and are substantially longer than those made from the participant's own point of view. These phenomena have been attributed to a specialised mechanism for imagined perspective transformations. In the present experiments, the effect of orientation on performance was influenced by factors that affect spatial stimulus–response (S–R) compatibility; it was attenuated with reduced dimensional overlap and reversed by crossed S–R mappings. Performance in a control experiment in which no figure was present suggests that processes moderating S–R mappings may account for the effect of adopting another's point of view. Our findings demonstrate a role for domain general processes in imagined transformations of whole body perspective, imply that egocentric codes for spatial relationships within visually presented bodies are automatically generated, and undermine evidence for a specialised mechanism for imagined perspective transformations.     

Effects of increased complexity of visuo-motor transformations on children's arm movements

The effects of increasing complexity of visuo-motor transformations on movement were examined in 4-, 6-, and 8-year-old children and adults. Participants performed a 'center-out' drawing task under three increasingly complex conditions: (1) Normal transformation: The target, line path and hand position were fully visible, in the horizontal plane, throughout the movement. (2) Aligned transformation: The target and line path were displayed horizontally above the workspace, with vision of the arm/hand occluded. (3) Vertical transformation: The target and line paths were presented on a vertical computer monitor with vision of the arm/hand occluded. Results showed that with increasing age, movements became faster, straighter, and smoother. The 4- and 6-year-old children were more variable in their specification of movement direction than the 8-year-old children and the adults, and were also more affected by the complexity of the transformation. This suggested that besides the complexity of the visual transformation, the familiarity/experienced environment might also play a role in 'sharpening' the transformation maps represented in movement planning.     

The neural correlates of implicit and explicit sequence learning: Interacting networks revealed by the process dissociation procedure

In two H2(15)O PET scan experiments, we investigated the cerebral correlates of explicit and implicit knowledge in a serial reaction time (SRT) task. To do so, we used a novel application of the Process Dissociation Procedure, a behavioral paradigm that makes it possible to separately assess conscious and unconscious contributions to performance during a subsequent sequence generation task. To manipulate the extent to which the repeating sequential pattern was learned explicitly, we varied the pace of the choice reaction time task-a variable that is known to have differential effects on the extent to which sensitivity to sequence structure involves implicit or explicit knowledge. Results showed that activity in the striatum subtends the implicit component of performance during recollection of a learned sequence, whereas the anterior cingulate/mesial prefrontal cortex (ACC/MPFC) supports the explicit component. Most importantly, we found that the ACC/MPFC exerts control on the activity of the striatum during retrieval of the sequence after explicit learning, whereas the activity of these regions is uncoupled when learning had been essentially implicit. These data suggest that implicit learning processes can be successfully controlled by conscious knowledge when learning is essentially explicit. They also supply further evidence for a partial dissociation between the neural substrates supporting conscious and nonconscious components of performance during recollection of a learned sequence.     

The relationship between divided attention and implicit memory: a meta-analysis

This article reports a meta-analysis comparing the size of repetition priming in full and divided-attention (DA) conditions. The main analysis included 38 effect sizes (ES) extracted from 21 empirical studies, for a total of 2074 (full-attention) and 2148 (divided-attention) participants. The mean weighted ES was 0.357 (95% CI = 0.278–0.435), indicating that divided attention produced a small, but significant, negative effect on implicit memory. Overall, the distinction between identification and production priming provided the best fit to empirical data (with the effect of DA being greater for production tests), whereas there was no significant difference between perceptual and conceptual priming. A series of focused contrasts suggested that word-stem completion might be influenced by lexical–conceptual processes, and that perceptual identification might involve a productive component. Implications for current theories of implicit memory are discussed.     

Understanding implicit and explicit attitude change: a systems of reasoning analysis

There is considerable controversy about how to conceptualize implicit and explicit attitudes, reflecting substantial speculation about the mechanisms involved in implicit and explicit attitude formation and change. To investigate this issue, the current work examines the processes by which new attitudes are formed and changed and how these attitudes predict behavior. Five experiments support a systems of reasoning approach to implicit and explicit attitude change. Specifically, explicit attitudes were shaped in a manner consistent with fast-changing processes, were affected by explicit processing goals, and uniquely predicted more deliberate behavioral intentions. Conversely, implicit attitudes reflected an associative system characterized by a slower process of repeated pairings between an attitude object and related evaluations, were unaffected by explicit processing goals, uniquely predicted spontaneous behaviors, and were exclusively affected by associative information about the attitude object that was not available for higher order cognition.     

Ageing affects conceptual but not perceptual memory processes

Whereas age effects commonly occur in tests of explicit memory, tests of implicit memory often show age invariance. In two experiments, the traditional confound between test type (implicit vs explicit) and retrieval process (conceptually driven vs perceptually driven) was removed by using conceptually driven and perceptually driven tests of both implicit and explicit memory. Experiment 1 revealed a significant age effect for conceptually driven retrieval and no age effect for perceptually driven retrieval, regardless of the type of memory being measured. Experiment 2 highlighted a difference between the two age groups in their ability to utilise semantic encoding in a nominally perceptually driven explicit memory test. The paper concludes that although perceptually driven processing is stable over age, particular care must be taken to minimise contamination from conceptually driven retrieval processes in such investigations.     

Impact of Parkinson’s disease and dopaminergic medication on adaptation to explicit and implicit visuomotor perturbations

The capacity to learn new visuomotor associations is fundamental to adaptive motor behavior. Evidence suggests visuomotor learning deficits in Parkinson’s disease (PD). However, the exact nature of these deficits and the ability of dopamine medication to improve them are under-explored. Previous studies suggested that learning driven by large and small movement errors engaged distinct neural mechanisms. Here, we investigated whether PD patients have a generalized impairment in visuomotor learning or selective deficits in learning from large explicit errors which engages cognitive strategies or small imperceptible movement errors involving primarily implicit learning processes. Visuomotor learning skills of non-medicated and medicated patients were assessed in two reaching tasks in which the size of visuospatial errors experienced during learning was manipulated using a novel three-dimensional virtual reality environment. In the explicit perturbation task, the visuomotor perturbation was applied suddenly resulting in large consciously detected initial spatial errors, whereas in the implicit perturbation task, the perturbation was gradually introduced in small undetectable steps such that subjects never experienced large movement errors. A major finding of this study was that PD patients in non-medicated and medicated conditions displayed slower learning rates and smaller adaptation magnitudes than healthy subjects in the explicit perturbation task, but performance similar to healthy controls in the implicit perturbation task. Also, non-medicated patients showed an average reduced deadaptation relative to healthy controls when exposed to the large errors produced by the sudden removal of the perturbation in both the explicit and implicit perturbation tasks. Although dopaminergic medication consistently improved motor signs, it produced a variable impact on learning the explicit perturbation and deadaptation and unexpectedly worsened performance in some patients. Considered together, these results indicate that PD selectively impairs the ability to learn from large consciously detected visuospatial errors. This finding suggests that basal ganglia-related circuits are important neural structures for adaptation to sudden perturbations requiring awareness and high-cost action selection. Dopaminergic treatment may selectively compromise the ability to learn from large explicit movement errors for reasons that remain to be elucidated.     

Ageing affects conceptual but not perceptual memory processes

Whereas age effects commonly occur in tests of explicit memory, tests of implicit memory often show age invariance. In two experiments, the traditional confound between test type (implicit vs explicit) and retrieval process (conceptually driven vs perceptually driven) was removed by using conceptually driven and perceptually driven tests of both implicit and explicit memory. Experiment 1 revealed a significant age effect for conceptually driven retrieval and no age effect for perceptually driven retrieval, regardless of the type of memory being measured. Experiment 2 highlighted a difference between the two age groups in their ability to utilise semantic encoding in a nominally perceptually driven explicit memory test. The paper concludes that although perceptually driven processing is stable over age, particular care must be taken to minimise contamination from conceptually driven retrieval processes in such investigations.     

The effects of weak perturbations on rapid finger oscillations

Movement control can be position based or amplitude based; in the first case the frame of reference is fixed, while in the second case the origin is at the start of each movement so that in series of movements errors are propagated. In movements aimed at a target the kind of control is task dependent, though the majority of findings suggest a stronger weight of amplitude-based control. In rapid finger oscillations which do not require visuo-motor transformations, control turned out to be position based as revealed by a lack of propagation of small shifts of angular position induced by brief mechanical perturbations; the only effect of the perturbations in addition to the immediate mechanical effect on movement amplitude was enhanced myoelectric activity in both agonists and antagonists which showed up with some delay. The finding of position-based control points to the functional importance of the mechanical characteristics of peripheral musculo-skeletal systems in rapid limb oscillations.     

Proximity and distance goals in adult attachment

We used a variant of the Implicit Association Test (IAT) and explicit reports to examine the assumption that attachment anxiety and avoidance are related to proximity and distance goals. Results confirmed that attachment avoidance was associated with a stronger implicit motivation for and positive evaluation of distance goals in attachment relationships. This was found both at the implicit and explicit levels and both in a threat and non‐threat context. Attachment anxiety was associated with proximity goals only when measured explicitly, but not when goal activation was measured implicitly. Our findings highlight the importance of considering both implicit and explicit goal representations when studying motivational processes in the context of attachment, and suggest that the IAT can provide a useful tool for investigating implicit motivational constructs. Copyright © 2008 John Wiley & Sons, Ltd.     

Unitization of Sublexical Components in Implicit Memory for Novel Words

This study examines the role of componential knowledge and unitization processes in implicit memory. In two experiments, subjects studied novel words formed out of morphemes, syllables, or pseudosyllables. They then completed an implicit task requiring a judgment as to which of two items (one old, one new) was a better English word. Experiment 1 replicated previous results showing priming for nonwords formed out of morphemes and syllables but not seudosyllables. This effect was present when orthographic factors were controlled and, unlike explicit (recognition) memory, was equally strong following visual and semantic processing. Experiment 2 showed that little priming was present across a variety of conditions in which the connections between components were altered across study and test. Results are interpreted as evidence for the role of perceptually based activation and integration processes in implicit memory for novel stimuli.     

编码与提取干扰对内隐和外显记忆的非对称性影响

以往研究表明在外显记忆中,编码与提取加工存在着非对称性,但在内隐记忆中,二者的关系并不明确,因此实验采用“学习-再认”范式,考察在编码或提取中分别附加的干扰任务对词汇判断或再认产生的影响。结果证实编码与提取干扰对内隐或外显记忆都具有非对称性的影响,但又存在着差异,即编码干扰会导致随后外显记忆成绩显著减少,而提取干扰对其影响较小,相反,编码干扰对随后内隐测验中启动效应的影响较小,但提取干扰会破坏启动效应,从而为内隐记忆和外显记忆的分离提供了进一步的证据     

A developmental trajectory in implicit memory is revealed by picture fragment completion

Dissociations between performance on implicit and explicit tasks have often been taken as evidence that different neural structures subserve the two types of memory. One such dissociation involves developmental differences that emerge in explicit tasks, but which appear to be absent in implicit tasks. Such findings are consistent with the idea that implicit memory is subserved by a more primitive system that evolves earlier at both phylogenetic and ontogenetic levels. The present paper reviews previous studies that claimed to find evidence that implicit memory is fully developed in very young children. Issues of measurement error, ceiling effects, and insufficient power brought up questions about those studies with respect to the developmental issue. The present study compares performance on implicit (picture fragment completion) and explicit (free recall and recognition) memory tasks with groups ranging in age from 5-28 years. We find a reliable developmental trend in both implicit and explicit performance in which the former cannot be attributed to the operation of explicit memory processes. Thus, we conclude that implicit memory, like explicit memory, develops with age.     

Explicit and motoric dependent measures of geographical slant are dissociable: A reassessment of the findings of Durgin, Hajnal, Li, Tonge, and Stigliani (2010)

Durgin et al. (2010) argued that the apparent accuracy of the palmboard measure of geographical slant is accidental and reflects limitations in wrist flexion that reduce palmboard adjustments by just the right amount given the perceptual overestimations upon which they are based. This account is inconsistent with findings that verbal reports and palmboard adjustments are dissociable. In addition to previous evidence found for such dissociation, Durgin et al. also found verbal/palmboard dissociations in Experiment 2. Experiments 1 and 3 of Durgin et al. lacked verbal reports and instead compared palmboard adjustments to free-hand estimates in the context of small wooden surfaces. These experiments are not relevant to the issue of verbal/palmboard dissociability. Across studies, the accuracy of Durgin et al.'s palmboard implementation is far less than that found by others (Feresin & Agostini, 2007). The design of Durgin et al.'s Experiment 5 misrepresented the experimental conditions of Creem and Proffitt (1998), and consequently, the findings of this study have no bearing on the issue at hand.     

The combination of explicit and implicit learning processes in task control

Summary Two experiments look at the combination of explicit and implicit learning processes on a single task. Subjects are required to control the rate of sugar output in a small sugar production factory while maintaining cordial relations with the union. Experiment 1 investigates whether subjects can learn to control this task, which relies on their knowing about both salient and nonsalient relationships. It looks at how performance on the task relates to explicit verbalisable knowledge (as assessed by written questionnaire). Experiment 2 considers alternative ways of tapping the more implicit aspects of subjects' knowledge.     

A Developmental Trajectory in Implicit Memory is Revealed by Picture Fragment Completion

Dissociations between performance on implicit and explicit tasks have often been taken as evidence that different neural structures subserve the two types of memory. One such dissociation involves developmental differences that emerge in explicit tasks, but which appear to be absent in implicit tasks. Such findings are consistent with the idea that implicit memory is subserved by a more primitive system that evolves earlier at both phylogenetic and ontogenetic levels. The present paper reviews previous studies that claimed to find evidence that implicit memory is fully developed in very young children. Issues of measurement error, ceiling effects, and insufficient power brought up questions about those studies with respect to the developmental issue. The present study compares performance on implicit (picture fragment completion) and explicit (free recall and recognition) memory tasks with groups ranging in age from 5–28 years. We find a reliable developmental trend in both implicit and explicit performance in which the former cannot be attributed to the operation ofexplicit memory processes. Thus, we conclude that implicit memory, like explicit memory, develops with age.