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Title: Numbers, space and motion, convergent data about their interaction. Behavioral, electrophysiological and TMS evidence
Authors: Semenza, Carlo
Salillas Perez, Elena
Keywords: number cognition, spatial attention, motion perception, neglect
psychophysics, TMS, ERPs
Issue Date: 18-Apr-2008
Publisher: Università degli studi di Trieste
Abstract: In this thesis five studies on the relationship between numbers and space and between numbers and motion are presented. The introduction of the thesis contains a description of works dealing with the link between numbers and spatial attention. This includes some behavioral data exploring shifts of spatial attention induced by numbers, data from hemispatial neglect and neuroimaging data. We further explore space-number relationship across modalities (vision and audition) and discuss how the semantics of numbers are dependent or independent form the used modality. This includes an study on blind population using the auditory modality. In a second part, the possible relationship between numbers and motion is introduced and discussed. Two papers that bring convergent data about it are provided. In the first one, an interference of the perception of motion into a number comparison process is presented. In the second paper, a neural substrate in the intraparietal sulcus is proposed as a focus of intersection between number and motion processes. Finally, a study with neglect patients explore possible compensatory mechanism of motion in their altered spatial representation of numbers. Amounting evidence exists on the relationship between numbers and space (see introduction). Numbers´ semantics would have the form of a mental number line with spatial characteristics. Fischer and collaborators (2003) showed that a lateralized target presented on the left visual field (LVF) is detected faster after low numbers than after high numbers and a target presented on the right visual field (RVF) is detected faster following a high number than after low numbers. The studies presented here explore these shifts of attention induced by numbers in electrophysiological terms. Event related potentials (ERPs) allow to explore the process underlying this effect: we describe it as a conjunction of attentional sensory and cognitive, more controlled, mechanisms. We test the possibility that the effect extends to the auditory modality both in sighted and in blind individuals. And we show interesting differences between the two populations in the way they manipulate a similar left-to-right number representation. Regarding the link between motion and number processes, we show how rightward motion facilitates a process thought to call the core presentation of numbers: number comparison. We also explore the vertical dimension, in which upward motion has the same facilitatory effects in number comparison. We show how selective attention to motion has effects on the number comparison process and that his effect may be independent of space-location effects. Furthermore, using transcranial magnetic stimulation (TMS), we present evidence of possible common neural networks processing numbers and motion. One area of intersection, we show, is the ventral intraparietal sulcus (VIPS). VIPS has been proposed previously as an area processing motion in humans. We show that besides motion it is implied in number comparison processes. Finally, we use the behavioral paradigm from the third paper to explore possible effects of motion perception in number processing in hemispatial neglect. While several papers show their difficulty in the representation of the “left side” of the mental number line or in its access, we show that this difficulty or misrepresentation can be compensated by the external presentation of leftward coherent motion. Therefore, common attentional processes seem to be acting over external and internal representational space. In summary, the present thesis provides evidence of the space number relationship and describe how they interact through electrophysiological methods. Some tentative conclusions about the modality dependencies of the number-space link can be drawn from the comparison between modalities. Besides, when there is no access to the visual modality, in congenital blindness, we show how a left to right mental number line stands, but its manipulation varies. We propose motion as another process operating over number representation and provide direct evidence of this new link. Finally, we show how motion acts as a compensatory mechanism in neglect.
Description: 2006/2007
NBN: urn:nbn:it:units-7265
Appears in Collections:Scienze storiche, filosofiche, pedagogiche e psicologiche

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