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S Dehaene

Publications and source records attributed to S Dehaene.

At least 55 records · Page 3Linked to original sources
PubMed1996

Brain processing of native and foreign languages.

We used positron emission tomography to study brain activity in adults while they were listening to stories in their native language, in a second language acquired after the age of seven, and in a third unknown language. Several areas, similar to those previously observed in monolinguals, were activated by the native but not by the second language. Both the second and the unknown language yielded distinct left-hemispheric activations in areas specialized for phonological processing, which were not engaged by a backward speech control task. These results indicate that some brain areas are shaped by early exposure to the maternal language, and are not necessarily activated by the processing of a second language to which they have been exposed for a limited time later in life.

Adult↗
PubMed1996

Cerebral activations during number multiplication and comparison: a PET study.

Positron emission tomography was used to examine the cerebral networks underlying number comparison and multiplication in eight normal volunteers. Cerebral blood flow was measured within anatomical regions of interest defined in each subject using magnetic resonance imaging. Three conditions were used: rest with eyes closed, mental multiplication of pairs of arabic digits and larger-smaller comparison of the same pairs. Both multiplication and comparison activated the left and right lateral occipital cortices, the left precentral gyrus, and the supplementary motor area. Beyond these common activations, multiplication activated also the left and right inferior parietal gyri, the left fusiform and lingual gyri, and the right cuneus. Relative to comparison, multiplication also yielded superior activity in the left lenticular nucleus and in Brodmann's area 8, and induced a hemispheric asymmetry in the activation of the precentral and inferior frontal gyri. Conversely, relative to multiplication, comparison yielded superior activity in the right superior temporal gyrus, the left and right middle temporal gyri, the right superior frontal gyrus, and the right inferior frontal gyrus. These results underline the role of bilateral inferior parietal regions in number processing and suggest that multiplication and comparison may rest on partially distinct networks.

Adult↗
PubMed1996

Impairments of number processing induced by prenatal alcohol exposure.

Prenatal alcohol exposure causes a variety of cognitive deficits, notably in mathematics and higher order processes such as abstraction. An exploratory battery was developed to examine specific types of number processing impairments in 29 adolescent and adult patients with Fetal Alcohol Syndrome (FAS) and Fetal Alcohol Effects (FAE) relative to controls matched for age, gender, and educational level. The battery included 11 tests: number reading and writing, exact calculation (addition, multiplication, subtraction), approximate calculation (selecting a plausible result for an operation), number comparison, proximity judgment, and cognitive estimation. The results indicated particular difficulties in calculation and estimation tests, with intact number reading and writing ability. The greatest impairment was found in the cognitive estimation test, which is sensitive to frontal lobe lesions. The patterns of deficit described may reflect either the diffuseness of brain damage incurred from prenatal alcohol exposure, or a cumulative deficit in comprehension which may be important for the acquisition of higher-order mathematical abilities.

Adolescent↗
PubMed1995

Electrophysiological evidence for category-specific word processing in the normal human brain.

Selective impairment of word categories such as nouns vs verbs has suggested a regional representation of lexical knowledge in the human brain. The time course of visual word processing was investigated using event-related potentials (ERPs) in normal adults. Subjects performed a word classification task with five categories of stimuli: animal names, verbs, numerals, proper names and meaningless consonant strings. A bilateral posterior ERP difference between words and consonants first appeared 192 ms following stimulus onset, probably reflecting the construction of the visual word form. Category-specific ERP differences began to appear around 260 ms. There was a left temporo-parietal negativity for animal names and verbs, a left inferior temporal negativity for proper names, and a bilateral positivity for numerals. These results provide a bilateral parietal positivity evidence for timing and coarse localization of category-specific word processing in the normal human brain.

Adult↗
PubMed1995

Attention, automaticity, and levels of representation in number processing.

Participants performed same-different judgments for pairs of numerals in 2 conditions: numerical matching (responding "same" to pairs such as 2-TWO), or physical matching (responding "different" to pairs such as 2-TWO). In most cases, a distance effect was obtained, with the different responses being slower when the 2 numbers were numerically close together (e.g., 1-2) than when they were further apart (e.g., 1-8). This indicates that numbers were automatically converted mentally into quantities, even when the participants had been told to attend exclusively to their physical characteristics. As postulated by several models of number processing, (e.g., Dehaene, 1992; McCloskey, 1992) Arabic and verbal numerals thus appear to converge toward a common semantic representation of quantities. However, the present results suggest that an asemantic transcoding route might allow for a direct mapping of Arabic and verbal numbers, perhaps by means of a common phonological representation.

Adolescent↗
PubMed1994

Speed and cerebral correlates of syllable discrimination in infants.

The remarkable linguistic abilities of human neonates are well documented. Young infants can discriminate phonemes even if they are not used in their native language, an ability which regresses during the first year of life. This ability to discriminate is often studied by repeating a stimulus for several minutes until some behavioural response of the infant habituates, and later examining whether the response recovers when the stimulus is changed. This method, however, does not reveal how fast infants can detect phonetic changes, nor what brain mechanisms are involved. We describe here high-density recordings of event-related potentials in three-month-old infants listening to syllables whose first consonants differed in place of articulation. Two processing stages, corresponding to an increasingly refined analysis of the auditory input, were identified and localised to the temporal lobes. A late frontal response to novelty was also observed. The infant brain recognizes a phonetic change in less than 400 ms.

Adult↗
PubMed1994

Amnesia for arithmetic facts: a single case study.

We report the case of an anarithmetic patient with a selective deficit of memory for elementary arithmetic facts, who produced, for instance, "25" in answer to "4 x 5." The patient showed good language comprehension and production abilities, had minimal number transcoding difficulties, and mastered normally multidigit arithmetic procedures. She was submitted to a series of calculation, verification, and number classification tasks. The arithmetic deficit was evident in both recognition and recall tasks, was consistent across testing sessions, and did not vary as a function of the format used for presentation of the problems. The patient failed even when only implicit access to arithmetic facts was expected: In a timed addition verification task, she did not show a normal inhibition effect when rejecting addition problems in which the proposed result was the product of the two operands (e.g., "3 + 4 = 12"). We suggest that the deficit resulted from a specific and permanent degradation of some connections and nodes in arithmetic long-term memory.

Adult↗
PubMed1994

Attentional networks.

Recent brain-imaging and neurophysiological data indicate that attention is neither a property of a single brain area, nor of the entire brain. While attentional effects seem mediated by a relative amplification of blood flow and electrical activity in the cortical areas processing the attended computation, the details of how this is done through enhancement of attended or suppression of unattended items, or both, appear to depend on the task and brain-area studied. The origins of these amplification effects are to be found in specialized cortical areas of the frontal and parietal lobes that have been described as the anterior and posterior attention systems. These results represent substantial progress in the effort to determine how brain activity is regulated through attention. While many philosophical and practical issues remain in developing an understanding of attentional regulation, the new tools available should provide the basis for progress.

Animals↗
PubMed1994

Dissociable mechanisms of subitizing and counting: neuropsychological evidence from simultanagnosic patients.

Do people have to count to determine visual numerosity, or is there a fast "subitizing" procedure dedicated to small sets of 1-3 items? Numerosity naming time and errors were measured in 5 simultanagnosic patients who suffered from severe difficulties in serial counting. Although these patients made close to 100% errors in quantifying sets comprising more than 3 items, they were excellent at quantifying sets of 1, 2, and sometimes 3 items. Their performances in visual search tasks suggested that they suffered from a deficit of serial visual exploration, due to a fundamental inability to use spatial tags to keep track of previously explored locations. The present data suggest that the patients' preserved subitizing abilities were based not on serial processing but rather on a parallel algorithm dedicated to small numerosities. Several ways in which this parallel subitizing algorithm might function are discussed.

Adult↗
PubMed1994

Number words and number non-words. A case of deep dyslexia extending to Arabic numerals.

Although the ability to process numerical symbols may be considered a special case of more general linguistic abilities, deficits affecting numbers and words are usually interpreted within entirely independent frameworks. We report a patient presenting typical deep dyslexia, as confirmed in a series of word and non-word reading tasks. Moreover, the main features of his deficit extended to arabic numerals. The patient was equally unable to read aloud non-words and unfamiliar numerals, whereas he performed significantly better with real words and familiar arabic numerals such as famous dates or brands of cars. Additionally, familiar numerals and words yielded qualitatively similar errors, as did unfamiliar numerals and non-words. This contrasting performance with familiar and unfamiliar numerals seems incompatible with any single-route model of number reading. It is rather consistent with the existence of two routes for number reading: a 'surface' route mapping any digit string into a word sequence according to language-specific rules; and a 'deep' semantic route functioning only with familiar items that possess a specific lexical entry. We therefore suggest that number reading is architecturally similar to word reading, although these two processes probably rest on functionally and anatomically distinct pathways.

Adult↗
PubMed1994

Selective deficit of visual size perception: two cases of hemimicropsia.

Hemimicropsia is a rare disorder of visual perception characterized by an apparent reduction of the size of objects when presented in one hemifield. We report two cases of hemimicropsia resulting from focal brain lesions. The first patient was an art teacher and could accurately depict his abnormal visual perception. He subsequently died and his brain was examined post mortem. In the second patient, micropsia was assessed by a quantified size comparison task. The size of a given object is normally perceived as constant across any spatial position. Hemimicropsia may thus be considered a limited violation of the size constancy principle. Behavioural and anatomical data are discussed in relation to the neural basis of visual object perception in humans.

Autopsy↗
PubMed1992

Cross-linguistic regularities in the frequency of number words.

We examine the frequency of numerals and ordinals in seven different languages and/or cultures. Many cross-cultural and cross-linguistic patterns are identified. The most striking is a decrease of frequency with numerical magnitude, with local increases for reference numerals such as 10, 12, 15, 20, 50 or 100. Four explanations are considered for this effect: sampling artifacts, notational regularities, environmental biases and psychological limitations on number representations. The psychological explanation, which appeals to a Fechnerian encoding of numerical magnitudes and to the existence of numerical points of reference, accounts for most of the data. Our finding also has practical importance since it reveals the frequent confound of two experimental variables: numerical magnitude and numeral frequency.

Adult↗
PubMed1992

Varieties of numerical abilities.

This paper provides a tutorial introduction to numerical cognition, with a review of essential findings and current points of debate. A tacit hypothesis in cognitive arithmetic is that numerical abilities derive from human linguistic competence. One aim of this special issue is to confront this hypothesis with current knowledge of number representations in animals, infants, normal and gifted adults, and brain-lesioned patients. First, the historical evolution of number notations is presented, together with the mental processes for calculating and transcoding from one notation to another. While these domains are well described by formal symbol-processing models, this paper argues that such is not the case for two other domains of numerical competence: quantification and approximation. The evidence for counting, subitizing and numerosity estimation in infants, children, adults and animals is critically examined. Data are also presented which suggest a specialization for processing approximate numerical quantities in animals and humans. A synthesis of these findings is proposed in the form of a triple-code model, which assumes that numbers are mentally manipulated in an arabic, verbal or analogical magnitude code depending on the requested mental operation. Only the analogical magnitude representation seems available to animals and preverbal infants.

Aptitude↗
PubMed1991

Two mental calculation systems: a case study of severe acalculia with preserved approximation.

We report the case of an aphasic and acalculic patient with selective preservation of approximation abilities. The patient's deficit was so severe that he judged 2 + 2 = 5 to be correct, illustrating a radical impairment in exact calculation. However, he easily rejected grossly false additions such as 2 + 2 = 9, therefore demonstrating a preserved knowledge of the approximate result. The dissociation between impaired exact processing and preserved approximation was identified in several numerical tasks: solving and verifying arithmetical operations, number reading, short-term memory, number comparison, parity judgement, and number knowledge. We suggest the existence of two distinct number-processing routes in the normal subject. One route permits exact number representation, memory and calculation using symbolic notation. The other route allows for approximate computations using an analog representation of quantities.

Adult↗
PubMed1990

Is numerical comparison digital? Analogical and symbolic effects in two-digit number comparison.

Do Ss compare multidigit numbers digit by digit (symbolic model) or do they compute the whole magnitude of the numbers before comparing them (holistic model)? In 4 experiments of timed 2-digit number comparisons with a fixed standard, the findings of Hinrichs, Yurko, and Hu (1981) were extended with French Ss. Reaction times (RTs) decreased with target-standard distance, with discontinuities at the boundaries of the standard's decade appearing only with standards 55 and 66 but not with 65. The data are compatible with the holistic model. A symbolic interference model that posits the simultaneous comparison of decades and units can also account for the results. To separate the 2 models, the decades and units digits of target numbers were presented asynchronously in Experiment 4. Contrary to the prediction of the interference model, presenting the units before the decades did not change the influence of units on RTs. Pros and cons of the holistic model are discussed.

Adult↗
PubMed1989

Neuronal models of cognitive functions.

Understanding the neural bases of cognition has become a scientifically tractable problem, and neurally plausible models are proposed to establish a causal link between biological structure and cognitive function. To this end, levels of organization have to be defined within the functional architecture of neuronal systems. Transitions from any one of these interacting levels to the next are viewed in an evolutionary perspective. They are assumed to involve: (1) the production of multiple transient variations and (2) the selection of some of them by higher levels via the interaction with the outside world. The time-scale of these "evolutions" is expected to differ from one level to the other. In the course of development and in the adult this internal evolution is epigenetic and does not require alteration of the structure of the genome. A selective stabilization (and elimination) of synaptic connections by spontaneous and/or evoked activity in developing neuronal networks is postulated to contribute to the shaping of the adult connectivity within an envelope of genetically encoded forms. At a higher level, models of mental representations, as states of activity of defined populations of neurons, are discussed in terms of statistical physics, and their storage is viewed as a process of selection among variable and transient pre-representations. Theoretical models illustrate that cognitive functions such as short-term memory and handling of temporal sequences may be constrained by "microscopic" physical parameters. Finally, speculations are offered about plausible neuronal models and selectionist implementations of intentions.

Animals↗
PubMed1989

The psychophysics of numerical comparison: a reexamination of apparently incompatible data.

Reaction-time studies of numerical comparison have used essentially two paradigms: classification, in which a target number must be labelled "larger" or "smaller" in comparison to a fixed standard, and selection, in which the larger (or smaller) number of a pair must be picked out. In previous studies, classification has yielded only a distance effect in RTs, whereas selection has also revealed magnitude (or minimum) and congruity effects. We used two experiments with two-digit number comparisons to find the reason for this discrepancy. In Experiment 1, we used a variant of the classification task with the standard changing on each trial. RTs increased along with the standard for "smaller" responses and decreased along with the standard for "larger" responses, in a manner reminiscent of magnitude and congruity effects. In Experiment 2, we again used classification, but the fixed standard 75 was not at the center of the range of target numbers (20, 21, ... 99). Close to the standard, RTs were faster for "larger" than for "smaller" responses, again a congruity effect. Our data show that magnitude and congruity effects can be obtained with two-digit numbers in classification as well as in selection tasks. A single equation, which implies that numbers are compared with respect to reference points at both ends of the continuum, describes the results from both tasks.

Adolescent↗