Postural responses to specific types of long-term memory during visually induced roll self-motion.

A large body of research has shown that visually induced self-motion (vection) and cognitive processing may interfere with each other. The aim of this study was to assess the interactive effects of a visual motion inducing vection (uniform motion in roll) versus a visual motion without vection (non-uniform motion) and long-term memory processing using the characteristics of standing posture (quiet stance). As the level of interference may be related to the nature of the cognitive tasks used, we examined the effect of visual motion on a memory task which requires a spatial process (episodic recollection) versus a memory task which does not require this process (semantic comparisons). Results confirm data of the literature showing that compensatory postural response in the same direction as background motion. Repeatedly watching visual uniform motion or increasing the cognitive load with a memory task did not decrease postural deviations. Finally, participants were differentially controlling their balance according to the memory task but this difference was significant only in the vection condition and in the plane of background motion. Increased sway regularity (decreased entropy) combined with decreased postural stability (increase variance) during vection for the episodic task would indicate an ineffective postural control. The different interference of episodic and semantic memory on posture during visual motion is consistent with the involvement of spatial processes during episodic memory recollection. It can be suggested that spatial disorientation due to visual roll motion preferentially interferes with spatial cognitive tasks, as spatial tasks can draw on resources expended to control posture.

The Interaction Between Long-Term Memory and Postural Control: Different Effects of Episodic and Semantic Tasks.

The aim of this experiment was to investigate the postural response to specific types of long-term memory (episodic vs. semantic) in young adults performing an unperturbed upright stance. Although a similar level of steadiness (mean distance) was observed, dual tasking induced a higher velocity, more energy in the higher frequency range (power spectral density), and less regularity (sample entropy) compared with a simple postural task. Moreover, mean velocity was always greater in the semantic than in the episodic task. The differences in postural control during dual tasking may result from the types of processes involved in the memory task. Findings suggest a spatial process sharing between posture and episodic memory.

An implicit spatial memory alignment effect.

The memory alignment effect is the advantage of reasoning from a perspective which is aligned with the frame of reference used to encode an environment in memory. It usually occurs when participants have to consciously take a perspective to perform a spatial memory task. The present experiment assesses whether the memory alignment effect can occur without requiring to consciously take a given perspective, when the misaligned perspective is only perceptively provided. In others words, does the memory alignment effect still arise when it is only implicitly prompted? Thirty participants learned a sequence of four objects' positions in a room from a north-as-up survey perspective. During the testing phase, they had to point to the direction of a target object from another object ('the reference') with a fixed north-up orientation. The background behind the reference object displayed either a uniform color (control condition) or a misaligned ground-level perspective. The latter displayed a reference object's position information which was either congruent with the studied environment (congruent misaligned condition) or incongruent (incongruent misaligned condition). Mean pointing errors were higher in the congruent misaligned condition than in the control condition, whereas the incongruent misaligned condition did not differ from the control one. The present study shows that the memory alignment effect can arise without requiring a conscious misaligned perspective taking. Moreover, the perceived misaligned perspective must share the same spatial content as the memorized spatial representation in order to induce an alignment effect.

Mutual interferences between automatic ongoing spatial-updating with self-motion and source recall.

Recent models suggest that spatial updating of position with self-motion is a key component of remembering. In the first experiment, participants simultaneously performed a spatial task and a source recall. In the spatial task, blindfolded participants rotated to a new orientation and then pointed to an object's position. They pointed either from their new orientation (in the updating condition), or as if they were still in their starting orientation (in the ignoring condition). In the updating condition, participants had to accurately integrate their own movement whereas, in the ignoring condition, they had to ignore it. If spatial updating and episodic memory rely on the same network, only the updating condition should interfere with source recall. Results are in line with this prediction. A second experiment using a semantic memory task instead of source recall showed no interference effect. These results suggest that episodic memory and spatial updating are functionally linked.

Sensory-motor properties of past actions bias memory in a recognition task.

The aim of this study was to show that sensory-motor consequences of past actions form part of memory trace components cued by current experience. In a first task participants had to learn a list of words. Then in a guessing task they played against the computer. Finally, in a recognition task, they had to judge if the words were or were not present in the learning task. Words appeared either in the colour associated with success or failure in the guessing task, or in a non-informative colour. In the first experiment, results show that when the words to be judged were in the colour associated with success, participants answered faster and produced more "old" responses than when the words to be judged were in the colour associated with failure in the previous task. Moreover, when the words to be judged were in the colour associated with failure, participants were slower and produced less "old" responses than when the words were in a colour not informative of success or failure. The second experiment confirms that the results obtained in Experiment 1 were linked to the sensory-motor consequences of past actions associated with the colour and not to the colour itself.

Differential hippocampal and retrosplenial involvement in egocentric-updating, rotation, and allocentric processing during online spatial encoding: an fMRI study.

The way new spatial information is encoded seems to be crucial in disentangling the role of decisive regions within the spatial memory network (i.e., hippocampus, parahippocampal, parietal, retrosplenial,…). Several data sources converge to suggest that the hippocampus is not always involved or indeed necessary for allocentric processing. Hippocampal involvement in spatial coding could reflect the integration of new information generated by "online" self-related changes. In this fMRI study, the participants started by encoding several object locations in a virtual reality environment and then performed a pointing task. Allocentric encoding was maximized by using a survey perspective and an object-to-object pointing task. Two egocentric encoding conditions were used, involving self-related changes processed under a first-person perspective and implicating a self-to-object pointing task. The Egocentric-updating condition involved navigation whereas the Egocentric with rotation only condition involved orientation changes only. Conjunction analysis of spatial encoding conditions revealed a wide activation of the occipito-parieto-frontal network and several medio-temporal structures. Interestingly, only the cuneal areas were significantly more recruited by the allocentric encoding in comparison to other spatial conditions. Moreover, the enhancement of hippocampal activation was found during Egocentric-updating encoding whereas the retrosplenial activation was observed during the Egocentric with rotation only condition. Hence, in some circumstances, hippocampal and retrosplenial structures-known for being involved in allocentric environmental coding-demonstrate preferential involvement in the egocentric coding of space. These results indicate that the raw differentiation between allocentric versus egocentric representation seems to no longer be sufficient in understanding the complexity of the mechanisms involved during spatial encoding.

Ongoing egocentric spatial processing during learning of non-spatial information results in temporal-parietal activity during retrieval.

Deficits in amnesic patients suggest that spatial cognition and episodic memory are intimately related. Among the different types of spatial processing, the allocentric, relying on the hippocampal formation, and the egocentric-updated, relying on parieto-temporal connections have both been considered to functionally underlie episodic memory encoding and retrieval. We explore the cerebral correlates underlying the episodic retrieval of words previously learnt outside the magnet while performing different spatial processes, allocentric and egocentric-updated. Subsequently and during fMRI, participants performed an episodic word recognition task. Data processing revealed that the correct recognition of words learnt in egocentric-updated condition enhanced activity of the medial and lateral parietal, as well as temporal cortices. No additional regions were activated in the present study by retrieving words learnt in allocentric condition. This study sheds new light on the functional links between episodic memory and spatial processing: The temporo-parietal network is confirmed to be crucial in episodic memory in healthy participants and could be linked to the egocentric-updated process.

Bias in self-motion perceived speed can enhance episodic memory.

Prior experiences of a stimulus facilitate reprocessing of that stimulus on a subsequent occasion. This relative ease and speed with which information is processed is defined as fluency and can constitute a basis for memory judgment. Fluency can also be manipulated on line by perceptual bias (e.g., levels of noise), leading to an increase in recognition for items processed more fluently (e.g., items with less noise). Previous experiments using Remember-Know paradigm have shown an impact of perceptual fluency only on familiarity and not on recollection. Recent episodic memory models have postulated a strong link between episodic memory and spatial processes, especially with egocentric updating (Gomez et al. in Acta Psychol 132(3):221-227, 2009). The present experiment was conducted to determine whether self-motion fluency affects recognition performance and particularly has an impact on "Remember" responses. Thirty participants learned a 4-min path movie and then had to recognize among short paths if they were part of the learned path, followed by a Remember-Know procedure for recognized items. Self-motion fluency was manipulated with the presence of nimble acceleration applied on a small part of the recognition paths. Results show that the presence of a self-motion fluency increases significantly the proportion of remember responses solely on learned paths. This study spotlights for the first time a specific fluency effect on recollection and indicates an implication of egocentric-updating processing in episodic memory retrieval.

Global precedence effect in audition and vision: evidence for similar cognitive styles across modalities.

This study aimed to provide evidence for a Global Precedence Effect (GPE) in both vision and audition modalities. In order to parallel Navon's paradigm, a novel auditory task was designed in which hierarchical auditory stimuli were used to involve local and global processing. Participants were asked to process auditory and visual hierarchical patterns at the local or global level. In both modalities, a global-over-local advantage and a global interference on local processing were found. The other compelling result is a significant correlation between these effects across modalities. Evidence that the same participants exhibit similar processing style across modalities strongly supports the idea of a cognitive style to process information and common processing principle in perception.

Egocentric-updating during navigation facilitates episodic memory retrieval.

Influential models suggest that spatial processing is essential for episodic memory [O'Keefe, J., & Nadel, L. (1978). The hippocampus as a cognitive map. London: Oxford University Press]. However, although several types of spatial relations exist, such as allocentric (i.e. object-to-object relations), egocentric (i.e. static object-to-self relations) or egocentric updated on navigation information (i.e. self-to-environment relations in a dynamic way), usually only allocentric representations are described as potentially subserving episodic memory [Nadel, L., & Moscovitch, M. (1998). Hippocampal contributions to cortical plasticity. Neuropharmacology, 37(4-5), 431-439]. This study proposes to confront the allocentric representation hypothesis with an egocentric updated with self-motion representation hypothesis. In the present study, we explored retrieval performance in relation to these two types of spatial processing levels during learning. Episodic remembering has been assessed through Remember responses in a recall and in a recognition task, combined with a "Remember-Know-Guess" paradigm [Gardiner, J. M. (2001). Episodic memory and autonoetic consciousness: A first-person approach. Philosophical Transactions of the Royal Society B: Biological Sciences, 356(1413), 1351-1361] to assess the autonoetic level of responses. Our results show that retrieval performance was significantly higher when encoding was performed in the egocentric-updated condition. Although egocentric updated with self-motion and allocentric representations are not mutually exclusive, these results suggest that egocentric updating processing facilitates remember responses more than allocentric processing. The results are discussed according to Burgess and colleagues' model of episodic memory [Burgess, N., Becker, S., King, J. A., & O'Keefe, J. (2001). Memory for events and their spatial context: models and experiments. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 356(1413), 1493-1503].