Arnaud Destrebecqz

Can sequence learning be implicit?: New evidence with the process dissociation procedure

Can we learn without awareness? Although this issue has been extensively explored through studies of implicit learning, there is currently no agreement about the extent to which knowledge can be acquired and projected onto performance in an unconscious way. The controversy, like that surrounding implicit memory, seems to be at least in part attributable to unquestioned acceptance of the unrealistic assumption that tasks are process-pure—that is, that a given task exclusively involves either implicit or explicit knowledge. Methods such as the process dissociation procedure (PDP, Jacoby, 1991) have been developed to overcome the conceptual limitations of the process purity assumption but have seldom been used in the context of implicit learning research. In this paper, we show how the PDP can be applied to a free generation task so as to disentangle explicit and implicit sequence learning. Our results indicate that subjects who are denied preparation to the next stimulus nevertheless exhibit knowledge of the sequence through their reaction time performance despite remaining unable (1) to project this knowledge in a recognition task and (2) to refrain from expressing their knowledge when specifically instructed to do so. These findings provide strong evidence that sequence learning can be unconscious.

Learned material content and acquisition level modulate cerebral reactivation during posttraining rapid-eye-movements sleep

We have previously shown that several brain areas are activated both during sequence learning at wake and during subsequent rapid-eye-movements (REM) sleep (Nat. Neurosci. 3 (2000) 831-836), suggesting that REM sleep participates in the reprocessing of recent memory traces in humans. However, the nature of the reprocessed information remains open. Here, we show that regional cerebral reactivation during posttraining REM sleep is not merely related to the acquisition of basic visuomotor skills during prior practice of the serial reaction time task, but rather to the implicit acquisition of the probabilistic rules that defined stimulus sequences. Moreover, functional connections between the reactivated cuneus and the striatum--the latter being critical for implicit sequence learning--are reinforced during REM sleep after practice on a probabilistic rather than on a random sequence of stimuli. Our results therefore support the hypothesis that REM sleep is deeply involved in the reprocessing and optimization of the high-order information contained in the material to be learned. In addition, we show that the level of acquisition of probabilistic rules attained prior to sleep is correlated to the increase in regional cerebral blood flow during subsequent REM sleep. This suggests that posttraining cerebral reactivation is modulated by the strength of the memory traces developed during the learning episode. Our data provide the first experimental evidence for a link between behavioral performance and cerebral reactivation during REM sleep.

Striatum forever, despite sequence learning variability : A random effect analysis of PET data

This PET study is concerned with the what, where, and how of implicit sequence learning. In contrast with previous studies imaging the serial reaction time (SRT) task, the sequence of successive locations was determined by a probabilistic finite‐state grammar. The implicit acquisition of statistical relationships between serially ordered elements (i.e., what) was studied scan by scan, aiming to evidence the brain areas (i.e., where) specifically involved in the implicit processing of this core component of sequential higher‐order knowledge. As behavioural results demonstrate between‐ and within‐subjects variability in the implicit acquisition of sequential knowledge through practice, functional PET data were modelled using a random‐effect model analysis (i.e., how) to account for both sources of behavioural variability. First, two mean condition images were created per subject depending on the presence or not of implicit sequential knowledge at the time of each of the 12 scans. Next, direct comparison of these mean condition images provided the brain areas involved in sequential knowledge processing. Using this approach, we have shown that the striatum is involved in more than simple pairwise associations and that it has the capacity to process higher‐order knowledge. We suggest that the striatum is not only involved in the implicit automatization of serial information through prefrontal cortex‐caudate nucleus networks, but also that it plays a significant role for the selection of the most appropriate responses in the context created by both the current and previous stimuli, thus contributing to better efficiency and faster response preparation in the SRT task. Hum. Brain Mapping 10:179–194, 2000.

Dissociating the Effects of Automatic Activation and Explicit Expectancy on Reaction Times in a Simple Associative Learning Task

After repeated associations between two events, E1 and E2, responses to E2 can be facilitated either because participants consciously expect E2 to occur after E1 or because E1 automatically activates the response to E2, or because of both. In this article, the authors report on 4 experiments designed to pit the influence of these 2 factors against each other. The authors found that the fastest responses to a target in a reaction time paradigm occurred when automatic activation was highest and conscious expectancy lowest. These results, when considered together with previous findings indicating that, under most conditions, the relation between expectancy and reaction times is in the opposite direction, are indicative of a reversed association-an interaction pattern that J. C. Dunn and K. Kirsner (1988) demonstrated to be the only one that unambiguously points to the involvement of independent processes.

Implicit change identification: a replication of Fernandez-Duque and Thornton (2003).

Using a simple change detection task involving vertical and horizontal stimuli, I. M. Thornton and D. Fernandez-Duque (2000) showed that the implicit detection of a change in the orientation of an item influences performance in a subsequent orientation judgment task. However, S. R. Mitroff, D. J. Simons, and S. L. Franconeri (2002) were not able to replicate this finding after correcting for confounds and thus attributed Thornton and Fernandez-Duques results to methodological artifacts. Because Mitroff et al.s failure to replicate might in turn have stemmed from several methodological differences between their study and those of Thornton and Fernandez-Duque (2000) and Fernandez-Duque and Thornton, the current authors set out to conduct a further replication in which they corrected all known methodological biases identified so far. The results suggest that implicit change detection indeed occurs: Peoples conscious decisions about the orientation of an item appear to be influenced by previous undetected changes in the orientation of other items in the display. Implications of this finding in light of current theories of visual awareness are discussed.

Cerebral correlates of explicit sequence learning.

Using positron emission tomography (PET) and regional cerebral blood flow (rCBF) measurements, we investigated the cerebral correlates of consciousness in a sequence learning task through a novel application of the Process Dissociation Procedure, a behavioral paradigm that makes it possible to separately assess conscious and unconscious contributions to performance. Results show that the metabolic response in the anterior cingulate/mesial prefrontal cortex (ACC/MPFC) is exclusively and specifically correlated with the explicit component of performance during recollection of a learned sequence. This suggests a significant role for the ACC/MPFC in the explicit processing of sequential material.

Effects of age and practice in sequence learning: A graded account of ageing, learning, and control

The influence of age and practice level was investigated in sequence learning by testing young, middle-aged, and older participants, who first performed a serial reaction time (SRT) task, either after a short or a long training phase (15 vs. 30 training blocks). Unknown to them, successive stimuli followed a repeating pattern. After training, participants performed a sequence generation task under inclusion and exclusion instructions, and a recognition task. SRT and generation data indicate (1) preserved learning and generation abilities in ageing and (2) beneficial effects of extended practice. By contrast, recognition data suggest that ageing tends to impair discrimination performance. Implications of these findings for understanding the effects of age and practice on the ability to control sequential knowledge are discussed in terms of the involvement of gradual representations of sequence structure.

Methods for studying unconscious learning

One has to face numerous difficulties when trying to establish a dissociation between conscious and unconscious knowledge. In this paper, we review several of these problems as well as the different methodological solutions that have been proposed to address them. We suggest that each of the different methodological solutions offered refers to a different operational definition of consciousness, and present empirical examples of sequence learning studies in which these different procedures were applied to differentiate between implicit and explicit knowledge acquisition. We also show how the use of a sensitive behavioral method, the process dissociation procedure, confers a distinctive advantage in brain-imaging studies when aiming to delineate the neural correlates of conscious and unconscious processes in sequence learning.

The influence of temporal factors on automatic priming and conscious expectancy in a simple reaction time task.

In a previous study, we reported a dissociation between subjective expectancy and motor behaviour in a simple associative learning task (Perruchet, Cleeremans, & Destrebecqz, 2006). According to previous conditioning studies (Clark, Manns, & Squire, 2001), this dissociation is observed when the to-be-associated events coterminate and thus overlap in time (a training regimen called delay conditioning), but not when they are separated by a temporal delay (trace conditioning). In this latter situation indeed, there tends to be a direct relationship between subjective expectancy and behaviour. In this study, we further investigated this issue in a series of experiments where conscious and unconscious components of performance were pitted against each other. In Experiments 1–3, participants performed a simple reaction time task in which a preparatory signal (a tone) either overlapped with or terminated earlier than the imperative stimulus (a visual target presented in 50% of the trials). After each response, participants also had to state how much they expected the imperative stimulus to be displayed on the next trial. Results indicate that reaction times tend to decrease when the tone is consistently followed by the visual target across successive trials, whereas conscious expectancy for the target decreases at the same time. Importantly, we systematically found that the temporal relationship between the tone and the target failed to influence performance. In a fourth experiment, we examined whether these results extend to a two-choice reaction time task. To our surprise, we observed a direct relationship between subjective expectancies and reaction time in that situation. We nevertheless observed that the introduction of a delay between the tone and the target had, once again, no effect on performance.

Intuitive decision making in complex situations: Somatic markers in an artificial grammar learning task

In this article, we explore the extent to which implicit learning is subtended by somatic markers, as evidenced by skin conductance measures. On each trial, subjects were asked to decide which “word” from a pair of “words” was the “correct” one. Unknown to the subjects, each “word” of a pair was constructed using a different set of rules (Grammar Aand Grammar B). A (monetary) reward was given if the subject chose the “word” from Grammar A. Choosing the Grammar B word resulted in (monetary) punishment. Skin conductance was measured during each of 100 trials. After each set of 10 trials, the subjects were asked how they selected the “correct word.” Task performance increased long before the subjects could even formulate a single relevant rule. In this preconceptual phase of the experiment, skin conductance was larger before incorrect than before correct choices. Thus, it was shown that artificial grammar learning is accompanied by a somatic marker, possibly “warning” the subject of the incorrect decision.