Event-related potentials (ERPs) were recorded from the scalp to investigate a long-standing controversy in auditory attention research, namely when the 'breakthrough of the unattended' takes place in the human brain. Nine subjects classified visual stimuli appearing 300 ms after task-irrelevant standard tones (80%, i.e. P = 0.8) or novel sounds (20%, i.e. P = 0.2) into odd/even categories. After the recording session, subjects scored the novel sounds as to whether they had any particular meaning (identifiable) or were perceived as a burst of noise (non-identifiable), and performance and ERPs were analysed according to this classification. A control condition, in which the visual stimuli were presented with no sounds, showed that subjects covertly monitored the task-irrelevant sounds during visual task-performance, and a further condition, in which the auditory and visual stimuli appeared regardless of each other, made it possible to trace the processing of the distracters during allocation of attention outside the auditory environment. Results yielded identical N1-enhancement for the two types of novel sounds, indicating similar attention switching triggered to these two types of unexpected sounds. However, there was a stronger orientating of attention towards identifiable novel sounds, as indicated both by behavioural distraction and by larger novelty-P3. Furthermore, this stronger orientating of attention was due to the sounds being contingent on the visual stimuli, as no increase in novelty-P3 to identifiable novel sounds was observed in the control condition, in which the sounds occurred outside the attentional set. Therefore, provided that the N1-enhancement reflects a call for focal attention, and novelty-P3 the effective orientating of attention towards the eliciting sounds, the present results suggest that semantic analysis of significant sounds occurs after a transitory switch of attention towards the eliciting stimuli. Moreover, as the novelty-P3 increase in amplitude was observed only when subjects covertly monitored the sounds, the present data suggest that semantic analysis of irrelevant sounds depends on the top-down cognitive influences of the attentional set.

On the domain of two-sided assignment markets with agents' reservation values, the nucleolus is axiomatized as the unique solution that satisfies consistency with respect to Owen's reduced game and symmetry of maximum complaints of the two sides. As an adjunt, we obtain a geometric characterization of the nucleolus by means of a strong form of the bisection property that characterizes the intersection between the core and the kernel of a coalitional game in Maschler et al. (1979).

The existence of von Neumann-Morgenstern solutions (stable sets) for assignment games has been an unsolved question since Shapley and Shubik [11].For each optimal matching between buyers and sellers, Shubik [12] proposed considering the union of the core of the game and the core of the subgames that are compatible with this matching. We prove in the present paper that this set is the unique stable set for the assignment game that excludes thirdparty payments with respect to a fixed optimal matching. Moreover, the stable sets that we characterize, as well as any other stable set of the assignment game, have a lattice structure with respect to the same partial order usually defined on the core.

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