Symposium
Memory for serial order: Theory and application
Steve Majerus (1,2) and Wim Fias (3)
(1) ULiège; (2) Fonds de la Recherche Scientifique FRS-FNRS; (3) UGent
Processing and memorizing the serial order of information (events, words, numbers) is a fundamental ability of our cognitive system. Yet, we know very little about the way the serial order information is represented, both over the short-term and the long-term. In this symposium, we will present recent advancements in our understanding of the cognitive and neural substrates of memory for serial order, and discuss the broader implications of serial order memory deficits.
Speaker 1: The neural substrate of serial order coding in working memory
Giulia Cristoforetti (1), Muhammet Ikbal Sahan (1), Jean-Philippe van Dijck (1,2), Steve Majerus (3) and Wim Fias (1)
(1) UGent; (2) Thomas More University of Applied Science; (3) ULiège
Serial order in WM is grounded in the spatial attention system. Spatial coding occurs spontaneously in verbal WM and ordinal position produces spatial biases; begin elements are associated with the left side of the space, end elements with the right side (van Dijck et al., 2011). We investigated the neural substrate of serial order coding in WM, detecting brain regions that contain information about the ordinal structure of the information memorized in a serial order sequence. Evidence showed that the intraparietal sulcus (IPS) is involved in ordinal information coding (Majerus et al., 2009) and in spatial attention (Husain et al., 2007). Also, the hippocampus preserves the temporal order of events (Davachi and DuBrow, 2015) and it is involved in spatial memory (Eichembaum, 2014). 28 adult healthy participants performed a serial order WM task in an event-related fMRI setting. A classifier was trained to distinguish activation patterns associated with the retrieval of an item at the beginning or at the end of a sequence in the anterior and posterior bilateral IPS and bilateral hippocampus. We observed that multivariate neural patterns in the left anterior IPS, right anterior IPS (hIP3), left dentate gyrus were able to discriminate between retrieved items (begin vs end). These regions are both linked to serial order coding and spatial processing. Therefore, the results are consistent with the account of spatial coding in serial order WM.
Speaker 2: The developmental neural substrate of serial order learning
Steve Majerus (1,2), Laura Ordonez Magro (3), Arnaud Szmalec (3) and Lucie Attout (1,2)
(1) ULiège; (2) Fonds de la Recherche Scientifique FNRS-FRS; (3) UCLouvain
Hebb repetition learning is a fundamental learning mechanism for sequential knowledge such as language. However, still little is known about its development. This fMRI study examined the developmental neural substrates of Hebb repetition learning and its relation with reading abilities in a group of 49 children aged from 6 to 12 years. In the scanner, the children carried out an immediate serial recall task for syllables sequences of which some sequences were repeated several times over the course of the session (Hebb repetition sequences). We observed that the rate of Hebb repetition learning was associated with modulation of activity in the medial temporal lobe. Importantly, for the age range studied here, learning-related medial temporal lobe modulation was independent of the age of the children. Furthermore, we observed an association between regular and irregular word reading abilities and the neural substrates of Hebb repetition learning. This study suggests that the functional neural substrates of long-term memory for serial order, as instantiated by Hebb repetition learning, do not undergo significant maturational changes in school age children, and could be sustained mainly by implicit sequential learning mechanisms (procedural memory) considered to be fully developed at an early age. Importantly, the neural substrates of Hebb learning remain significant determinants of learning abilities such as reading.
Speaker 3: Reading direction influences order processing in verbal working memory
Vesal Rasoulzadeh (1), Jean-Philippe van Dijck (1,2) and Wim Fias (1)
(1) UGent; (2) Thomas More University of Applied Sciences
The ability to maintain sequence of items in working memory (WM) is important for major cognitive tasks, like language and reasoning. Previous research suggests that serial order WM is grounded in spatial attention. It was shown that sequential information is spatially organized in mental space and retrieval of an item from serial order WM induces a covert spatial shift of attention depending on the position of the item in the sequence. The spatial organization of the serial information is suggested to be influenced by reading/writing direction. In this study, we found behavioral and neural indication (based on recorded EEG data) for the right-to-left organization of serially presented items in Iranian population with right-to-left reading/writing direction. After sequential loading of four letters to WM, when participants retrieved the earliest (last) letter in the sequence, they were faster (slower) to detect a target (a dot) on the right than left visual hemi-field. In ERPs locked to the retrieval of items in the sequence, two components associated with orienting of spatial attention were elicited: EDAN (early directing attention negativity) in posterior and ADAN (anterior directing attention negativity) anterior areas. These components are characterized by larger negativity in Contralateral hemisphere relative to where the cue directs attention (i.e., left hemisphere was implicated when the first letter from the sequence was selected). Our results substantiate the right-to-left organization of serial information in Iranian population at behavioral and neural level. This emphasize the influence of literacy and reading/writing direction on mental organization of sequential information.
Speaker 4: Spatial patterning in working memory as a determinant for mathematical proficiency
Jean-Philippe van Dijck (1,2), Krzysztof Cipora (3) and Wim Fias (2)
(1) Thomas More; (2) UGent; (3) University of Tübingen, Germany
Research suggests that efficient calculation depends on a proper mental representation of numbers. This representation is constructed in working memory (WM) and takes the shape of a horizontal mental number line. A popular task to measure the strength of this spatial representation is parity judgment, where subjects typically respond faster with left to small numbers and with right to large numbers (the SNARC effect). Studies investigating the link between SNARC and mathematics provide inconsistent results. This is mainly because most studies did not take measurement reliability into account or because narrow measures of mathematics were used. In 4 experiments we investigated the relationship between SNARC and mathematics by optimizing reliability and by considering mathematics as a broad construct (word problems, arithmetic, fractions…). In EXP1, we increased reliability by recruiting a heterogeneous (in age and mathematical background) sample. In EXP2, we boosted between-subject variability by manipulating the degree in which numbers have to be processed implicitly. In EXP3, we tested a broader range of math domains. Finally, in EXP4, we manipulated the degree in which WM is involved in the spatial coding. The strength of the spatial coding has no predictive value for any math domain, except when WM was involved. In this case, the degree of spatial coding was positively related to the overall math score. These observations suggest that organizing our WM in a spatial fashion has positive effects on our mathematical thinking. This has important theoretical implications and can be informative in the context of mathematical learning difficulties.
