Periodic Reporting for period 1 - DYSC-EYE-7T (The neural substrate of numerical cognition in dyscalculia revealed by eye tracking and ultra-high field 7T functional magnetic imaging)
Periodo di rendicontazione: 2020-04-01 al 2022-03-31
The ability to quickly estimate the number of enemies or prey has obvious evolutionary benefits and is present in all animals, from insects to humans. This non-symbolic and language independent ability is based on the ‘number sense’ and allows for an immediate and spontaneous perception of numerosity. In humans it predicts formal arithmetical skills: individuals who struggle in discriminating numerosity between two ensembles of items also find learning math more difficult, and this is particularly evident in people with developmental dyscalculia (DD). The overall goal of this action was to investigate how individuals with and without DD perceive numerical quantities and to establish an innovative quantification of numerical processing, based on completely objective, replicable, and non-invasive indices that can be obtained with eye tracking. The action had three objectives that aimed at studying the spontaneous nature of numerical perception by measuring 1) saccadic eye movements, 2) pupil size and 3) its neural correlates with fMRI. By leveraging on a highly interdisciplinary approach that combined psychophysics, eye tracking and imaging techniques to test neurotypical and clinical populations, DYSC-EYE-7T provided insights into the neural mechanisms supporting numerosity perception and their interplay with higher cognitive functions such as attention and working memory. The results shed new light on the neurocognitive substrate of DD and identified new biomarkers to explore numerical cognition that are independent of language and potentially allows for early diagnosis of DD. Earlier identification would allow for earlier interventions that have higher effectiveness, like for most developmental disorders, consequently decreasing the negative impact of this condition on the employment prospects, mental and physical health of the affected individuals, as well as its socioeconomic burden on the society.
This action investigated number perception in individuals with and without dyscalculia by means of psychophysics, eye tracking and fMRI techniques. I found that humans can perform a saccadic eye movement toward the more numerous of two arrays at extremely high speed (only 190 ms) and that pupil size scales with the perceived numerosity of stimuli of identical luminance: pupil constriction and dilation (depending on stimulus luminance) were stronger for patterns with higher numerosity, physical or illusory. These studies suggest that numerosity is a salient and spontaneously detected visual feature that automatically attracts out attention. The observed numerosity-driven fast saccades and pupil modulation suggests that there might be a primitive circuitry that quickly transforms the numerosity information into oculomotor and pupillary responses. In collaborative studies, I also characterized the localization of the cortical areas supporting different aspects of numerical cognition (numerical perception, numerical operations, groupitizing and calculation) relative to anatomical and functional landmarks at high resolution, with 7T and 3T fMRI and multivariate pattern analysis. In addition, I carried out other behavioral studies in individuals with and without dyscalculia. These studies 1) characterized the phenomenon of groupitizing showing that it can be used as an efficient strategy to estimate visual and auditory numerosities; 2) tested how perception of time and number is affected by the distance between the observer and the stimulus, determining the possibility to act on it; 3) characterized visual perception in dyscalculia and found that dyscalculic individuals have excessive visual crowding which prevents them from efficiently segregating individual items in the periphery of the visual field, and impaired global shape perception which may prevent them from successfully group items together; 4) simulated some behavioral signs characterizing dyscalculics’ numerical perception in individuals without dyscalculia by loading participants’ visuo-spatial working memory, suggesting that a common system supporting both visuo-spatial working memory and numerical perception might be disrupted in dyscalculia; 5) explored another branch of mathematics, i.e. geometry, and how perception of geometrical sequences interacts with numerosity perception in primary school children. Altogether these findings contributed to advance the understanding of the mechanisms underlying numerical perception, how they relate to school achievement and to characterize visual perception deficits in dyscalculia.
The results of the action have been disseminated through 15 manuscripts, presentations at 5 conferences, 4 seminars to students at the University of Pisa and Florence, social media [accounts: @EliCastaldi (Twitter), elisa.castaldi.731 (Facebook), elisa-castaldi (LinkedIn)], press releases (e.g. https://rb.gy/j05e01 https://rb.gy/forsmr https://rb.gy/gbjuop https://rb.gy/5ufxjn) podcast (https://rb.gy/q64xdk) and website.
The results of the action have been disseminated through 15 manuscripts, presentations at 5 conferences, 4 seminars to students at the University of Pisa and Florence, social media [accounts: @EliCastaldi (Twitter), elisa.castaldi.731 (Facebook), elisa-castaldi (LinkedIn)], press releases (e.g. https://rb.gy/j05e01 https://rb.gy/forsmr https://rb.gy/gbjuop https://rb.gy/5ufxjn) podcast (https://rb.gy/q64xdk) and website.
The results of current action succeeded in 1) providing a new theoretical framework within which conceptualize the interaction between attention and numerosity perception and 2) identifying new biomarkers to explore numerical cognition. From a theoretical point of view, the results showed that numerosity is an extremely salient visual feature that automatically attracts our attention and gaze, and modulates even basic physiological responses (such as the pupil light response) being intrinsically related to perceptual strength. This behavioral evidence also informs on the neural circuits supporting numerical processing: the numerical content of the image probably accesses a phylogenetically ancient and very simple neural circuit able to process numerosity at extremely high speed and to guide oculomotor responses. From a practical point of view, this action provided new quantitative and easily measurable markers (eye-movement speed and pupil-size modulation) to explore numerical cognition, opening the path to an entire new set of questions to be addressed with these new techniques. In addition to these planned goals, the results of this action also revealed and described the different strategies used to estimate numerosity, the interaction between numerosity perception and the motor system, the importance of numerosity perception for the development of arithmetical and geometrical skills, the visual deficits present in dyscalculia and their possible impact on the development of numerosity perception, the relevance of visuo-spatial working memory resources (in addition to attention) to veridically estimate numerosity. Finally, my studies provided a more precise localization of the cortical areas supporting different aspects of numerical cognition (numerical perception, numerical operations, groupitizing and calculation) relative to anatomical and functional landmarks at high resolution. A deeper comprehension of the neurocognitive and perceptual mechanisms underlying the typical and dysfunctional numerical competence as well as the identification of easily measurable markers sets the basis for more effective rehabilitation/potentiation programs and more efficient educational strategies at school, potentially decreasing the socio-economic impact of low numeracy skills.