Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS


DYNAMICS OF MEMORY Streszczenie raportu

Project ID: 515499
Źródło dofinansowania: FP6-MOBILITY
Kraj: Belgium

Final Activity Report Summary - DYNAMICS OF MEMORY (Dynamics of memory: the notion of representation revisited)

In our initial project, we proposed to revisit the notion of representation as an emergent process by suggesting that it is not the invariants that are represented, but rather the dynamical patterns of activation, organised in neural networks, that makes it possible for the system to reach invariance. The work we have undertaken was to study the process of organisation of information in memory, seen as a dynamical process which characterises representations along a continuum between implicit and explicit knowledge. In this perspective, we have explored four issues: (1) the respective implication of implicit and explicit knowledge at different levels of organisation of the cognitive system, and its determinant, (2) an epistemological concern of the role of time in the process of consolidation of representations in memory and their access in the field of consciousness, (3) a behavioural signature of the involvement of implicit learning in movement, and (4) the dynamical properties of motor memory and the modelling of their computationnal principles.

1. The respective implication of implicit and explicit knowledge at different levels of organisation of the cognitive system, and its determinant.
In this context, we have revisited the importance of time in the information processing of explicit knowledge of an action. To do so, we have carried out an experiment to examine the relation between the intention to perform an action and the subject's conscious experience of subsequently making that action. These amount to pre-constructive and re-constructive aspects of action awareness, respectively. To do this, we combined several existing paradigms. The first relies on the influence of expectancy judgment on the subjective report and its modulation by time delays. The second concerns the relation between on-line motor control and conscious experience in visuomotor adjustment of reaching movements following unpredictable lateral target displacements. In our task, participants (1) expressed their expectancy of the occurrence of a target shift during the upcoming movement, (2) reached to point at a virtual target as quickly and accurately as possible before returning to the start position, and (3) reproduced the spatial path of the movement they had just made as accurately as possible. The expectancy of the target shift, and the ensuing reproduction of the trajectory adjustment evoked by the target shift measure the pre-constuctive, intentional and re-constructive, motoric aspects of action awareness respectively. The relative importance of these two aspects was investigated by introducing timing delays at two key points in the task. Adding a 6 s delay between expectancy judgment and the start of the trial or between the initial movement and the reproduced path weakened influence of expectancy on movement reproduction and boosted the proportion of sensory evidence version of what actually happened. That is, the conscious experience of actions is strongly influenced by prior thoughts, but only over a short time scale. On the other hand, neither expectancy nor delays have impinged on the adjustment movement to the target displacement, that is motor awareness is not involved in motor control processes. Thus, the awareness of our own actions is a dynamic, and relatively flexible mixture of what we think we will do, and what our body actually does, emphasising the role of time in the mixture of consciousness.

2. An epistemological concern of the role of time in the process of consolidation of representations in memory and their access in the field of consciousness.
Here, we have provided an overview of different studies in order to highlight the assumption that time plays a central role in consciousness, at different levels and in different aspects of information processing. Subliminal perception experiments demonstrate that stimuli presented too briefly to enter conscious awareness are nevertheless processed to some extent. Implicit learning, implicit memory, and conditioning studies suggest that the extent to which memory traces are available for verbal report and for cognitive control is likewise dependent on the time available for processing during acquisition. Differences in the time available for processing also determine not only the extent to which one becomes conscious of action, but also provides the basis for making attributions of authorship to experienced acts. In this paper, we offer a brief overview of these different findings and suggest that they can all be understood based on the fact that consciousness takes time. From this perspective, the availability of representations to conscious awareness depends on the quality of these representations - the extent to which they are strong, stable in time, and distinctive. High-quality representations occur when processes of global competition have had sufficient time to operate so as to make the system settle into the best possible interpretation of the input. Such processes implement global constraint satisfaction and critically depend on re-entrant processing, through which representations can be further enriched by high-level constraints.

3. A behavioural signature of the involvement of implicit learning in a continuous tracking movement
Furthermore, we are currently conducting an experiment in order to work on the question of a behavioural signature of implicit learning in continuous-tracking tasks of a repeated segment intermixed with random segments. The preceding studies that have used this paradigm, analysed the discrepancy between the target and the tracker, and have demonstrated contradictory results concerning the involvement of implicit learning in the continuous tracking of the repeated segment. We think that implicit learning can play an important role at the motor level, which is impossible to be studied if one focuses the analysis just on the discrepancy between the tracker and the target. In our experiment, kinematics recording will enable us to analyse velocity and acceleration profiles of the movement in order to study the involvement of implicit learning in the motor aspects of the repeated segment.

4. Psychological hysteresis in sudden awareness: a functional correlate of recurrent processing
In this study we explored the idea that sudden motor awareness emerges as the result of global competition biased by top-down modulation, which implements global constraint satisfaction. The contents of conscious experience at some point in time thus reflect the application of the brain's knowledge on the current situation so as to yield the most adapted representations in the service of action. Such processes in turn critically depend on recurrent, or reentrant processing. Subjects carried out a reaching movement, which was disturbed by a haptic arm on some trials. Participants (1) pointed at the target as accurately as possible before returning to the start position, making a visuomotor adjustment to the target if required and (2) reproduced the spatial path of the movement they had just made, as accurately as possible, to give an indication of their awareness of the pointing movement. We analysed the spatial disparity between the initial and the reproduced movements on those with a movement disturbance. In this framework, we assume that once a recurrent neural activity due to the disturbance has reached a certain threshold, the visuomotor adjustment is suddenly consciously perceived so that the conscious activity may show hysteresis -as Libet (1973) has claimed-since the activity is probably held above a threshold to some extent by some mechanism, such as loops with positive feedback. This activity corresponds to the neural correlates of consciousness (NCC). Introducing a minimalist dynamics model, we highlight the computational principles of the conscious perception process.

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