Effects of adaptation on numerosity decoding in the human brain D Aagten-Murphy1, E Castaldi2, M Tosetti3, D Burr1, M C Morrone4 |
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1University of Florence, Italy |
| Psychophysical studies suggest that the perception of numerosity is susceptible to adaptation. Neuroimaging studies have reported habituation of BOLD signals in the intra-parietal sulcus (IPS), a region clearly involved in the representation of number. Here we tested whether adapting to a dot-pattern of specific numerosity can selectively modify neural coding for numerosity, measuring BOLD responses from all of visual cortex after adaption with a novel paradigm (verified psychophysically). Unlike standard BOLD habituation, we spaced adaptor and test stimuli 20 seconds apart to disentangle their BOLD responses. We then applied multivariate pattern classifiers (SVM) to the BOLD responses to random-dot patterns (20-80 dots, equated for total contrast energy), before and after adaptation to 80 dots. Before adaptation, classifiers for IPS – but not V1 – accurately discriminated numerosity over the whole range. Classifiers applied to post-adaptation trials also decoded numerosity accurately in IPS. However, pre-adaptation classifiers failed to classify accurately post-adaption responses, with systematic misclassifications. All results are consistent with the notion that adaptation to number selectively affects higher-order representations of numerosity magnitude rather than early visual areas. |
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