Zwei Wege zur Paritätsentscheidung: eine fMRT-Studie zur Notations-/Modalitätsspezifität in der Zahlenverarbeitung

Introduction: According to Dehaene and Cohen (1995) as well as Dehaene et al. (2003), numbers are processed depending on notation, modality and task. Three codes are claimed to build a network of functional and anatomical number representations. First, an abstract semantic magnitude representation is assumed to be connected bilaterally to the horizontal intraparietal sulcus. Second, verbal formats as well as multiplication and arithmetical fact retrieval are supposed to be represented in left hemispheric perisylvic areals. Last, parity decision and the visual number form are presumed to be connected to inferior occipito-temporal junction, on the left side for arabic numerals, on the right side for written number words. But the idea of the connection between the parity decision and the visual number form is only based on one reaction time experiment by Dehaene (1992). Investigations on the MARC-Effect also show verbal-linguistic influences on the parity decision (Willmes & Iversen, 1995). Therfore a second route for processing which is notation- and modality dependent could be assumed. The parity decision as well as the direct comparision of notations and modalities in number processing has rarely been examined in fMRI studies. Our experiment is supposed to find new arguments for two routes to take the parity decision.Methodes: In a fMRI study we investigated sixteen healthy volunteers in a magnitude comparison and a parity decision task in three input formats (arabic numerals, written and spoken number words). The decision was taken mentally in the first run and by response keys in the second run.Results: Notation- and modality-specificity: Visual stimuli produced bilateral activations of the inferior occipito-temporal junction. The activations were similar in the magnitude comparison task but lateralized in the parity decision task: Activations for arabic numerals were stronger in the right hemisphere, where as activations for written number words were stronger in the left hemisphere. Auditory stimuli produced activations in the perisylvic areals as well as the superior temporal lobe in both tasks. But only in the parity decision task could additional activations be found in the posterior part of the middle temporal lobe (BA 21). Activations in the horizontal part of the intraparietal sulcus could neither be found by comparing different notations nor by comparing modalities. Task-specifity: In general, during the parity decision task, stronger activations were measured than during the magnitude comparison task. The lateralization tendencies towards a certain hemisphere mentioned above could not be seen in the direct comparison of the tasks. The spoken number words, on the other hand, again showed activations of the posterior part of the left hemisperic middle temporal lobe. Response-specificity: No additional activations to the presumed somatomotoric and somatosensoric cortex activations have been found. Conclusion: Our results generally support the hypothesis of a number of specific representation located in the horizontal part of the intraparietal sulcus as assumed by Eger et al. (2003) and Dehaene (2003). Furthermore, the lateralization tendencies for the different stimuli in the parity decision task underline a functional connection between the parity decision and the inferior occipito-temporal junction as postulated by Dehaene (1992). The perisylvic activations for spoken number words can be seen as the representation of the auditive-verbal code. Therefore our results so far support the triple-code model of Dehaene and Cohen (1995). Additionally, an activation of the posterior part of the left hemisperic middle temporal lobe could be found for auditory stimuli during the parity decision task only. This activation could be the anatomical connection to the verbal-linguistic component of parity as decribed before by the Odd- and MARC-effect. Therefore this areal could be a second route for the representation of parity. An interindividual preference between the visual number form and this verbal representation is assumed. Further investigations should take place.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2007

Author dc:creator

• Becher, Hans Hartmut

Contributors dc:contributor

• Willmes-von Hinckeldey, Klaus

• info:eu-repo/classification/ddc/150
• Parität
• NMR-Tomographie
• Psychologie
• Zahlenverarbeitung
• fMRT
• Größenvergleich
• number processing
• fMRI
• parity
• magnitude comparison

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123319%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61683