Impaired acuity of the approximate number system in 22q11.2 microdeletion syndrome

A magnitude comparison deficit has been frequently observed in velocardiofacial syndrome (Del22q11.2). We hypothesized that this deficit extends to impairments in the acuity of the approximate number system (ANS). Three groups of children aged 8-14 years were investigated: Del22q11.2 children (n = 12), low cognitive ability children (LCA; n = 12), and matched typically developing children (TD; n = 28). All children were assessed with a simple reaction time task and symbolic and nonsymbolic number comparison tasks. To estimate the acuity of the ANS, the Weber fraction (w) was calculated from the nonsymbolic comparison task. The Del22q11.2 group exhibited a significantly higher w compared with the other groups. Importantly, no significant differences were found in w between the TD and LCA groups. The performance pattern of the Del22q11.2 group was similar to the TD group in the symbolic comparison task, and both of these groups had better performance than the LCA group. The impairment of ANS acuity observed in individuals with Del22q11.2 cannot be explained by deficits in general processing speed because no significant group differences were found in the simple reaction time task. These results suggest that lower acuity of the ANS should be added to the behavioral phenotype of Del22q11.2. The absence of impaired ANS acuity in the LCA group is consistent with the hypothesis that number sense is a relatively specific and autonomous domain. Investigations of low ANS acuity in mathematics learning difficulties and Del22q11.2 should be intensified...

The temporal structure of conscious mental states

The brain may work as a space-time machine. On the one hand, time may be spatially represented in neuronal assemblies, i.e., spatially "quantized". On the other, spatially segregated neuronal activity imposes a requirement on temporal integration mechanisms. Both theoretical and empirical evidence supports a model of integration by periodic oscillations. The model assumes two hierarchically organized, oscillatory frequency ranges. Fast oscillations have a period around the gamma range (30 ms) and may be used to define functional temporal states, inside which time relations are not discernible. These time quanta define mental-neural events. At the next level of the hierarchy, events are automatically and sequentially integrated up to a limit of more or less 3 seconds, which defines the slow oscillatory period. Events integrated into a 3 seconds temporal window constitute a semantic unitary subjective experience, the subjective present or now. Time experience is a construct derived from counting the number of events in a given period. Up to 3 seconds, mechanisms of consciousness equate to those of time perception. Subjective experience of continuous time flow is built upon semantic relatedness between different psychological moments.