The Time-Course of Numerical-Spatial Interactions Edward M. Hubbard1, Mariagrazia Ranzini1,2, Manuela Piazza1,3 and Stanislas Dehaene1,4 1.INSERM Unit 562, Gif-Sur-Yvette, France 2. Dipartimento di Psicologia, Università di Pavia, Italy 3. CIMeC, Università di Trento, Italy, 4. Collège de France, Paris, France

ERP Results

Introduction • Behavioral, neuroimaging and patient data suggests fundamental connections between numbers and space in the intraparietal sulcus (for recent reviews see refs. 1,2). • Our previous fMRI studies3,4 have demonstrated functional overlap between numerical and spatial processes in parietal and frontal cortex. • However, it is unclear if these effects are due to bottom-up or top-down processes; fMRI lacks the temporal resolution to explore this question. • Non-informative number cues can elicit shifts of attention5,6, with smaller numbers leading to facilitation for left sided targets, and larger numbers leading to facilitation for right sided targets. • To explore the time-course of numerical-spatial interactions, we measured ERPs in a standard cuing paradigm (non-informative arrows) and a number cuing paradigm (noninformative digits). • Overlap between numerical and spatial processes should be reflected in similar ERPs.

Arrows

Scalp Topography Numbers

Methods • We explored the event-related components related to shifts of attention due to noninformative arrow and number cues. • We tested 20 subjects, but rejected 5 due to excessive blinks, movement and/or equipment malfunction. • Task: detection of a left or right sided dot with dominant hand. • Cues: left/right arrows; small/large numbers (two numerical magnitudes: 1,2 / 8,9) • Delay: 300/400/500 ms • Number of trials: 396 (1/3 arrows and 2/3 numbers, 66 trials for each arrow, 132 for each numerical condition) and 10% catch trials. • EEG collected with 256 channel EGI system. • Lowpass filtered at 30 Hz, standard eye-blink and artifact detection.

Arrows vs. Numbers Interactions Between Numerical Magnitude and Hemisphere

Attention-Related ERP Components

Conclusions

attention7-9

Previous ERP studies of have identified several components related to shifts of attention. Here, we investigated two main components: • EDAN (early directing attention negativity): at about 200-400ms after cue onset from posterior sites over hemisphere contralateral to the direction indicated by the cue. • ADAN (anterior directing attention negativity): at 300-500ms after the cue onset from anterior sites over the hemisphere contralateral to the cue direction.

Numerical Magnitude Effects Behavioral Results Arrows

F(1,14) = 1.183, p = 0.295

Numbers

F(1,14) = 3.852, p = 0.070

• The EDAN and ADAN components are present even for non-informative arrow cues, suggesting that such cues are automatically processed (see also ref. 10). • Similar, although weaker and slightly delayed, effects for numbers demonstrate that numerical-spatial interactions elicit the same ERP components as shifts of attention (see also ref. 11). • These results further suggest that numbers are automatically treated as lying on a left-toright oriented number line (see refs 1,2). • The scalp distributions suggest that arrows may elicit shifts of attention in a more direct, bottom-up fashion than do numbers, which require an intermediate step of translating from numerical magnitude to space (see also refs. 12,13). • In combination with previous fMRI evidence, we suggest that these effects are mediated by parietal and frontal regions involved in shifts of attention, including hLIP and hFEF.

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