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Recent developments in the cognitive neuroscience of number processing.

Saturday, October 01st,   2011 [08:30 - 10:30]

SY_09. Recent developments in the cognitive neuroscience of number processing

Reynvoet, B. 1 & Gevers, W. 2

1 University of Leuven
2 Universite Libre de Bruxelles

A gradual shift can be observed in theories on number processing. For several years, the dominant view has been that the representation of numbers is localized in the parietal cortex. Furthermore, this representation would take the form of a mental number line upon which numbers are oriented from left to right. Today, both the type of representation and its location are again matter of intense debate. For what regards localisation, instead of focusing on the parietal cortex, empirical evidence starts to point towards the frontal cortex as an important region in number processing. Relatedly, it becomes increasingly clear that the representation of numbers cannot be investigated independent from decision making processes. The aim of this symposium is to bring together researchers who, using a variety of different techniques and approaches, illustrate on these new developments in the domain of number processing. Seppe Santens will present computational networks modeling the behavior of subjects in numerical judgment tasks, focusing on the contribution of representational characteristics and decision making. Delphine Sasanguie will focus on similarities and dissimilarities between different cognitive markers of magnitude representation using a Transcranial Magnetic Stimulation (TMS) approach. Paola Previtali will present behavioral research that further investigates the role of working memory processes in the processing of numerical information. She will focus on the interaction between long and short term representations of number processing. Fabrizzio Doricchi and Oliver Lindemann will talk about the relation between quantities and space. Fabrizzio Doricchi will present findings obtained with right brain damaged subjects, whereas Oliver Lindemann is going to present behavioral studies and a fMRI study on this topic. Finally, Roi Cohen Kadosh will present a recent neuroscience technique called transcranial direct current stimulation aimed at improving the performance of subjects in numerical tasks.



SY_09.1 - Judging Quantities

Santens, S. & Verguts, T.

Dept. of Experimental Psychology, Ghent university, Belgium

To understand the cognitive nature of quantities such as number, researchers often investigate how participants perform e.g. magnitude (small / large) or parity (odd / even) judgments. However, computational modelling and behavioral studies conducted in our lab suggest that these tasks might tell us more about how we make decisions than about how we represent quantitative information. Our own work has focused on associations between number, space and physical size. We show how the results fit within our modelling framework.

SY_09.2 - Magnitude representation or decision in the LIPS? Evidence from TMS

Sasanguie, D. 1 , Reynvoet, B. 1 & Goebel, S. M. 2

1 Dept. of Psychology, University of Leuven, Belgium
2 Dept. of Psychology, University of York, UK

Previous studies with Transcranial Magnetic Stimulation (TMS) have shown that stimulation of the parietal cortex can disrupt symbolic number processing. From those experiments alone, however, it cannot be concluded whether the stimulation interfered with representational or decisional stages of number processing as both magnitude processing and response selection have been linked to the parietal cortex. In this study, we conducted a priming task which enabled us to dissociate between representational and decisional effects. Sixteen adults were showed two sequentially presented single digits and had to decide whether they were larger or smaller than five, while being stimulated with repetitive online TMS (rTMS, for 500ms at 10Hz) over the left intraparietal sulcus (LIPS) or the vertex (control site). In addition, the onset of the stimulation was manipulated and was simultaneously administered with either the first or the second digit. The comparison distance effect (i.e. distance between the target and the standard) and the priming distance effect (i.e. distance between sequentially presented targets) were analyzed. Repetitive TMS over the LIPS slowed down the reaction times but the comparison distance effect remained significant. In contrast, the priming distance effect disappeared when the stimulation was administered together with the first stimulus. In general, these results suggest that stimulation over the LIPS interferes with magnitude representations and can delay decisions based on magnitude representations without affecting the decision processes.

SY_09.3 - Working memory and number processing

Previtali, P. 1 , Ginsburg, V. 2 , Vermeiren, A. 2 , Van Dijck, J. 3 & Gevers, W. 2

1 (1) Universita  degli Studi di Milano Bicocca, Italy
2 (2) Universite Libre de Bruxelles (ULB), Belgium
3 Ghent University, Belgium

A well studied indication of the correspondence between numbers and space is the SNARC effect, the observation of an association between small numbers and the left hand side and between large numbers and the right hand side. Recently, a working memory account for these spatial numerical associations was proposed (Van Dijck & Fias, 2011). This account holds that the associations between numbers and space are short term representations that are build during task execution. The aim of our study was to test this assumption. A number of experiments are discussed that illustrate different aspects of the working memory account.

SY_09.4 - The way we look at the Mental Number Line: evidence from the study of patients with right brain damage

Doricchi, F. 1, 2

1 Dipartimento di Psicologia 39, Università degli Studi di Roma “La Sapienza”, Roma Italy
2 Fondazione Santa Lucia - IRCCS, Roma Italy

At the turn of the 19th century, in two Nature issues Francis Galton (1880) first described the introspective reports of humans possessing the strong tendency to see numbers ”raising before the mind’s eye” in “definite and constant arrangements” upon spoken number presentation. Later studies demonstrated that in cultures with left-to-right reading, numbers are prevalently organised along a mental number line (MNL), with small magnitudes located to the left of larger ones. Recently, the possibility that such an introspective arrangement reflects an inherent spatial coding of number magnitudes in the human brain, was apparently endorsed by the bias toward higher numbers displayed by right brain damaged (RBD) patients during the bisection of number intervals, which has been taken as synonymous with spatial-attentional neglect for small numbers on the left side of the MNL. In contrast with this conclusion, we report the results of a series of investigations showing that the numerical bias displayed by RBD patients is functionally and anatomically dissociated from an equivalent attentional bias in visual space. Based on experiments designed to generate a mismatch in the “default” association of small numbers with the left side of space and of high numbers with the right side of space, we demonstrate that RBD have troubles in the mental manipulation of small number magnitudes independently from their mapping on the left or the right side of a mental layout. Parallel studies run in healthy adults and in childrens reveal new properties of the MNL, and support the conclusion that assuming a close phenomenological, functional and anatomical equivalence between orienting in visual space and orienting in mental number space is misleading.

SY_09.5 - Numerical Magnitude Interference in Perception and Action

Lindemann, O. & Krausse, F.

Donders Institute for Brain, Cognition and Behaviour; Nijmegen The Netherlands

Our research aims to investigate the coupling between high-level cognitive processes, such as the reading of meaningful symbols, and low-level processes as involved in visual perception and the control of motor behaviour. The presented studies will focus on the mechanisms underlying the representation of magnitude information in these different domains and their neural substrates. Our behavioural experiments demonstrate that magnitude representations for numbers are functionally linked to size-related codes required for perception and action. This will be illustrated by two types of effects: a numerical size-congruity effect on visual search performances and non-spatial compatibility effects between number stimuli and motor responses. We present furthermore recent fMRI data that aim to explore the neural substrates of such a shared magnitude metric by comparing spatial (i.e., SNARC) and non-spatial number-response compatibility effects. All results will be discussed in the context of recent models on number processing and an embodied approach to mathematical cognition.

SY_09.6 - Experience-dependent plasticity in the brains of Oxford mathematicians

Popescu, T. , Sader, E. , Thomas, A. , Terhune, D. , Cohen Kadosh, K. , Dowker, A. & Cohen Kadosh, R.

Department of Experimental Psychology, University of Oxford, UK

Experience-dependent structural plasticity has been shown to exist as a result of training in various areas of expertise (e.g. playing a musical instrument, juggling or taxi driving), however few of these involved higher cognitive functions such as mathematical cognition. In this study, we investigated the long-term effects of maths training on brain structure. We examined mathematicians and non-mathematicians academics at the University of Oxford; both groups were matched in terms of age, gender and number of years spent in full-time education. All subjects were tested on a broad battery of cognitive abilities (such as IQ, numerical tasks, working memory and social skills), and were MRI scanned in order to examine any anatomical differences between the groups and any correlations between these differences and cognitive performance. The results indicated that mathematical expertise is associated with: 1) better performance also in tasks that are not purely mathematical; 2) an increase as well as a decrease in grey matter in several brain areas. The current results provide insight into one of the less studied areas of cognitive neuroscience - the neurocognitive mechanisms of exceptional mathematical abilities. At the other end of the spectrum, having a clearer picture of how brain structure changes as a result of long-term training in mathematics can also prove important in gaining a better understanding of dyscalculia, a specific learning disability that affects the normal acquisition of numerical skills.

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