Effects of adaptation on numerosity decoding in the human brain

Abstract

Psychophysical studies have shown that numerosity is a sensory attribute susceptible to adaptation. Neuroimaging studies have reported that, at least for relatively low numbers, numerosity can be accurately discriminated in the intra-parietal sulcus. Here we developed a novel rapid adaptation paradigm where adapting and test stimuli are separated by pauses sufficient to dissociate their BOLD activity. We used multivariate pattern recognition to classify brain activity evoked by non-symbolic numbers over a wide range (20–80), both before and after psychophysical adaptation to the highest numerosity. Adaptation caused underestimation of all lower numerosities, and decreased slightly the average BOLD responses in V1 and IPS. Using support vector machine, we showed that the BOLD response of IPS, but not in V1, classified numerosity well, both when tested before and after adaptation. However, there was no transfer from training pre-adaptation responses to testing post-adaptation, and vice versa, indicating that adaptation changes the neuronal representation of the numerosity. Interestingly, decoding was more accurate after adaptation, and the amount of improvement correlated with the amount of perceptual underestimation of numerosity across subjects. These results suggest that numerosity adaptation acts directly on IPS, rather than indirectly via other low-level stimulus parameters analysis, and that adaptation improves the capacity to discriminate numerosity.

Processing number and length in the parietal cortex: Sharing resources, not a common code

“…While this strategy is commonly used in studies on numerosity perception, it does not control for differences in the total amount and distribution of contrast energy across numerosities, which is likely to affect early visual responses. This factor may indeed likely account for the early visual cortex activation results in this and other studies, also potentially suggested by a previous fMRI study on numerosity perception, which, after equating the contrast energy of the stimuli, could successfully decode numerosity in parietal but not early visual cortex (Castaldi et al, 2016).…”

Mapping numerical perception and operations in relation to functional and anatomical landmarks of human parietal cortex

“…However, independent of the execution of such numerical operations, enhanced activity for numbers as opposed to letters or colors was also to a lesser extent measured in HIPS during an orthogonal target detection task (Eger et al, 2003). Moreover, parietal regions were reported to habituate to repeated presentation of the same numerical quantity and show numerical distance-dependent recovery of activity for deviant numbers Cantlon et al, 2006;Ansari et al, 2006b) to some extent even across formats (Piazza et al, 2007;Vogel et al, 2017), to encode numerical quantity in multi-voxel patterns of evoked activity (Borghesani et al, 2018;Bulthé et al, 2014;Castaldi et al, 2016Castaldi et al, , 2019Cavdaroglu and Knops, 2018;Damarla and Just, 2013;Eger et al, 2009Eger et al, , 2015Lasne et al, 2018) and to contain topographically organized numerosity maps (Harvey et al, 2013;Dumoulin, 2017a, 2017b).…”

Evidence for a Posterior Parietal Cortex Contribution to Spatial but not Temporal Numerosity Perception

“…Hence, common BOLD increase in numerical tasks does not necessarily imply that the underlying representation for different formats and modes is the same. Yet, human imaging studies using multi-voxel pattern analysis (MVPA) endorse simultaneous numerosity encoding independent of response/task related processing (Bulthé et al, 2014;Castaldi et al, 2016;Dormal et al, 2010;Eger et al, 2013Eger et al, , 2009). Based on BOLD signal patterns from PPC these authors were able to decode the numerosities seen by the participants using MVPA.…”