Periodic Reporting for period 1 - Freq4Num (The neural signature of numerosity: Tracking the cerebral correlates of numerical and continuous magnitude extraction with a frequency-based approach)
Berichtszeitraum: 2018-03-01 bis 2020-02-29
Mathematical skills are critical in modern societies and their development has considerable financial impact on the GDP per capita. Moreover, mathematical difficulties are a frequent factor in children’s learning difficulties. The ability to handle approximate large quantities has been identified as a building block of mathematical skills. Despite its importance from both a fundamental and an educational perspective, the mechanism behind this ability is still not fully understood. The remaining gap comes from the fact that a set is not only characterized by its number of objects but additionally by nonnumerical features naturally correlating with numerosity (e.g. a more numerous set occupies a larger surface). Most authors agree that humans have an Approximate Number System that specifically processes numerosity. However, a set of objects is not only characterized by its numerosity but also by additional visual information related to its continuous dimensions (e.g. object size). Accordingly, the alternative theory argues that the numerosity is extracted through a weighting of the continuous dimensions of the stimulus. The opposite views cannot be properly tested through classic behavioral and neuroimaging approaches due to the intrinsic correlation between numerosity and continuous dimensions. Freq4Num aims at disentangling the specific cerebral responses to numerosity and to continuous dimensions. This objective will be achieved by adopting an innovative frequency-based approach to specifically measure the neural correlates of both numerical and continuous dimensions, and their potential interaction. More precisely, the project will combine Steady-State Evoked Potentials (SSVEP) paradigms with electro-encephalography (EEG) and Magneto-encephalography (MEG) to 1) test whether the system discriminates numerosity and other continuous dimensions within stimulus sequences, and 2) highlight whether and how the brain builds neural representations of numerosity and continuous dimensions. Freq4Num will considerably develop the career of the experienced researcher by allowing her to bring significant new advances to the field and to foster her independent research skill and international network. The general objective of the project was to understand the spatio-temporal dynamics of the mutual influence of continuous dimensions and numerosity during the processing of visual dot collections.
We first used EEG measurements to fine-tune the frequency-tagging approach to separately measure responses to numerosity as well as to continuous magnitudes. Our findings demonstrated that numerosity can be independently processed at an early stage in the visual cortex, even when completely isolated from other magnitude changes. The similar implicit discrimination for numerosity as for some continuous magnitudes, which correspond to basic visual percepts, shows that both can be extracted independently, hence substantiating the nature of numerosity as a primary feature of the visual scene. Further MEG measurements replicated the same discrimination results but in another modality (MEG vs. EEG). We further showed that early visual regions would be able to discriminate numerosity and some of the continuous magnitudes (total area and convex hull) and the parietal regions may support the persistence of the information over short timescales. The frequency-tagged neuromagnetic responses provide evidence in favor of an automatic feature-based attention spontaneously directed towards numerosity and some continuous magnitude properties related to the whole visual scene. Finally, our results highlighted the role of parietal regions in the early steps of magnitude processing (both numerosity and total area) even in absence of any explicit task and decision making mechanisms. Taken together, our innovative frequency-based approach allowed us to isolate responses to numerosity and to continuous magnitudes bringing new insights to a longstanding debate in the field of numerical cognition. Moreover, implementation of the frequency-tagging approach to MEG revealed the relative contribution of different regions of the brain to automatic magnitude discrimination and to the attentional sustain of these representations over short time scales.
The results of the Freq4Num project have been presented at international conferences (Organisation for Human Brain Mapping, Cognitive Neuroscience Society, the Third Jean Piaget Conference) and national meetings (Belgian FNRS group of contact « Numbers and the Brain », Belgian Association for Psychological Sciences, Belgian Socity for Neurosciences). The work done during the Freq4Num project allowed to bring crucial new insights in the field of numerical cognition, as attested by the publication of the seminal results of the project in an interdisciplinary journal (Proceedings of the National Academy of Sciences). Other important publications were associated to the project consisted in a meta-analysis and in the development of an open methodological tool related to non-symbolic numerical cognition. Further outcomes should be accepted for publication in the upcoming months.
The results of the Freq4Num project have been presented at international conferences (Organisation for Human Brain Mapping, Cognitive Neuroscience Society, the Third Jean Piaget Conference) and national meetings (Belgian FNRS group of contact « Numbers and the Brain », Belgian Association for Psychological Sciences, Belgian Socity for Neurosciences). The work done during the Freq4Num project allowed to bring crucial new insights in the field of numerical cognition, as attested by the publication of the seminal results of the project in an interdisciplinary journal (Proceedings of the National Academy of Sciences). Other important publications were associated to the project consisted in a meta-analysis and in the development of an open methodological tool related to non-symbolic numerical cognition. Further outcomes should be accepted for publication in the upcoming months.
In conclusion, the project has brought crucial new insights on the neuro-cognitive underpinnings of non-symbolic numerical cognition. The frequency-tagging EEG and MEG paradigms of the Freq4Num project succeeded in recording specific responses to number and to nonnumerical dimensions. We demonstrated that when numerosity and the other dimensions are present in stimulus sequences, changes of each are automatically discriminated in early visual cortex, highlighting the status of numerosity as a primary visual feature. The novel approaches we developed are promising candidates for clinical and educational applications, due to their relatively easy and quick implementation. The results of the current project will thus be the ground for further fundamental research in numerical cognition but also for more practical research and implications. Indeed, the frequency-tagging paradigms are well suited to become a biomarker of numerical impairments or to target successful intervention strategies in the future.