We use psychophysics and neuroimaging (fMRI, M-EEG) in adults and children of different cultures and cognitive skills to study the relation between perception and symbolic cognition: on one side, we investigate which aspects of perception act as fundamental building blocks of language-based symbolic cognition; on the other side we study if and how symbolic acquisitions in turn shape perception. Our research spans over two main areas: number processing and word processing. See a brief description of our work as well as some selected pubblications below:
Description: We study the fundamental skill that humans share with other animals to extract and mentally represent discrete and continuous quantities from their physical environment. In particular we study the ability to quantify sets on the basis of their numerosity (the number of objects), its neuronal correlates, it’s development, and it’s role in grounding higher level cognitive skills, such as formal symbolic arithmetic. We also study dyscalculia with the aim of understanding whether and how impaired perceptual quantity-related skills may hinder the ability to properly acquire knowledge and skills in symbolic number processing.
People: M. Piazza, G. Decarli, P. Chagas
Collaborations: S. Dehaene, E. Eger, V. Izard, D. Hyde
M. Piazza, V. De Feo, S. Panzeri, and S. Dehaene. (2018). Cognition, 181, 35-45.
With age and education, children become increasingly accurate in processing numerosity. This developmental trend is often interpreted as a progressive refinement of the mental representation of number. Here we provide empirical and theoretical support for an alternative possibility, the filtering hypothesis, which proposes that development primarily affects the ability to focus on the relevant dimension of number and to avoid interference from irrelevant but often co-varying quantitative dimensions. Data from the same numerical comparison task in adults and children of various levels of numeracy, including Mundurucú Indians and western dyscalculics, show that, as predicted by the filtering hypothesis, age and education primarily increase the ability to focus on number and filter out potentially interfering information on the non-numerical dimensions. These findings can be captured by a minimal computational model where learning consists in the training of a multivariate classifier whose discrimination boundaries get progressively aligned to the task-relevant dimension of number. This view of development has important consequences for education.
Figure 1. The filtering and sharpening hypotheses
Figure 2. Data supporting the filtering hypothesis
M.Piazza, V. Izard, E.Spelke, P.Pica, and S. Dehaene. (2013). Psychological Science, 24(6): 1037-1043.
All humans share a universal, evolutionarily ancient approximate number system (ANS) that estimates and combines the numbers of objects in sets with ratio-limited precision. Interindividual variability in the acuity of the ANS correlates with mathematical achievement, but the causes of this correlation have never been established. We acquired psychophysical measures of ANS acuity in child and adult members of an indigene group in the Amazon, the Mundurucú, who have a very restricted numerical lexicon and highly variable access to mathematics education. By comparing Mundurucú subjects with and without access to schooling, we found that education significantly enhances the acuity with which sets of concrete objects are estimated. These results indicate that culture and education have an important effect on basic number perception. We hypothesize that symbolic and nonsymbolic numerical thinking mutually enhance one another over the course of mathematics instruction.
Description: we study how the meaning of words is stored and retrieved during reading. We are currently using imaging and behavioral methods to test the hypothesis that word meaning is an emergent property of the simultaneous re-activation of both perceptual and more abstract features of the objects implied by the words. Todate we have shown that different features are represented in different cortical regions, and that feature-specific semantic representations emerge very early (by 200 ms) and in parallel during reading. We are currently studying the cortical changes occurring during symbol learning, thus visualizing how the brain supports the emergence of novel semantic representations.
People: M. Piazza, V. Borghesani, S. Viganò
Collaborators: M. Buiatti
V. Borghesani, F. Pedregosa, A. Amadon, E. Eger, M. Buiatti, & M. Piazza. (2016). NeuroImage. 143, 128-140.
The meaning of words referring to concrete items is thought of as a multidimensional representation that includes both perceptual (e.g., average size, prototypical color) and conceptual (e.g., taxonomic class) dimensions. Are these different dimensions coded in different brain regions? In healthy human subjects, we tested the presence of a mapping between the implied real object size (a perceptual dimension) and the taxonomic categories at different levels of specificity (conceptual dimensions) of a series of words, and the patterns of brain activity recorded with functional magnetic resonance imaging in six areas along the ventral occipito–temporal cortical path. Combining multivariate pattern classification and representational similarity analysis, we found that the real object size implied by a word appears to be primarily encoded in early visual regions, while the taxonomic category and sub-categorical cluster in more anterior temporal regions. This anteroposterior gradient of information content indicates that different areas along the ventral stream encode complementary dimensions of the semantic space.
M. Andres, M. Buiatti, C. Finocchiaro, and M. Piazza (2015). Cognition. 134, 174-184.
Electrophysiological and brain imaging studies show a somatotopic activation of the premotor cortex while subjects process action verbs. This somatotopic motor activation has been taken as an indication that the meaning of action verbs is embedded in motor representations.
However, discrepancies in the literature led to the alternative hypothesis that motor representations are activated during the course of a mental imagery process emerging only after the meaning of the action has been accessed. In order to address this issue, we asked participants to decide whether a visually presented verb was concrete or abstract by pressing a button or a pedal (primary task) and then to provide a distinct vocal response to low and high sounds played soon after the verb display (secondary task). Manipulations of the visual display (lower vs. uppercase), verb imageability (concrete vs. abstract), verb meaning (hand vs. foot-related), and response effector (hand vs. foot) allowed us to trace the perceptual, semantic and response stages of verb processing. We capitalized on the psychological refractory period (PRP), which implies that the initiation of the secondary task should be delayed only by those factors that slow down the central decision process in the primary task. In line with this prediction, our results showed that the time cost resulting from the processing of abstract verbs, when compared to concrete verbs, was still observed in the subsequent response to the sounds, whereas the overall advantage of hand over foot responses did not influence sound judgments. Crucially, we also observed a verb effector compatibility effect (i.e., foot-related verbs are responded faster with the foot and hand-related verbs with the hand) that contaminated the performance of the secondary task, providing clear evidence that motor interference from verb meaning occurred during the central decision stage. These results cannot be explained by a mental imagery process that would deploy only during the execution of the response to verb judgments. They rather indicate that the motor activation induced by action verbs accompanies the lexico-semantic processes leading to response selection.