Looking for goal-relevant objects in our various environments is one of the most ubiquitous tasks the human visual system has to accomplish. Visual search is guided by a number of separable selective-attention mechanisms that can be categorized as bottom-up driven – guidance by salient physical properties of the current stimuli – or top-down controlled – guidance by observers' “online” knowledge of search-critical object properties. In addition, observers' expectations based on past experience also play also a significant role in goal-directed visual (...) selection. Because sensory environments are typically stable, it is beneficial for the visual system to extract and learn the environmental regularities that are predictive of the target stimulus. This perspective article is concerned with one of these predictive mechanisms: statistical context learning of consistent spatial patterns of target and distractor items in visual search. We review recent studies on context learning and its adaptability to incorporate consistent changes, with the aim to provide new directions to the study of processes involved in the acquisition of search-guiding context memories and their adaptation to consistent contextual changes – from a three-pronged, psychological, computational, and neurobiological perspective. (shrink)

This paper suggests that time could have a much richer mathematical structure than that of the real numbers. Clark & Read (1984) argue that a hypertask (uncountably many tasks done in a finite length of time) cannot be performed. Assuming that time takes values in the real numbers, we give a trivial proof of this. If we instead take the surreal numbers as a model of time, then not only are hypertasks possible but so is an ultratask (a sequence which (...) includes one task done for each ordinal number—thus a proper class of them). We argue that the surreal numbers are in some respects a better model of the temporal continuum than the real numbers as defined in mainstream mathematics, and that surreal time and hypertasks are mathematically possible. (shrink)

Recent studies indicate that mammalian chromosomes contain discretecis‐acting loci that control replication timing, mitotic condensation, and stability of entire chromosomes. Disruption of the large non‐coding RNA gene ASAR6 results in late replication, an under‐condensed appearance during mitosis, and structural instability of human chromosome 6. Similarly, disruption of the mouse Xist gene in adult somatic cells results in a late replication and instability phenotype on the X chromosome. ASAR6 shares many characteristics with Xist, including random mono‐allelic expression and asynchronous replication timing. (...) Additional “chromosome engineering” studies indicate that certain chromosome rearrangements affecting many different chromosomes display this abnormal replication and instability phenotype. These observations suggest that all mammalian chromosomes contain “inactivation/stability centers” that control proper replication, condensation, and stability of individual chromosomes. Therefore, mammalian chromosomes contain four types ofcis‐acting elements, origins, telomeres, centromeres, and “inactivation/stability centers”, all functioning to ensure proper replication, condensation, segregation, and stability of individual chromosomes. (shrink)

The work [11] deals with questions of first-order definability in algebraic function fields. In particular, it exhibits new cases in which the field of constant functions is definable, and it investigates the phenomenon of definable transcendental elements. We fix some of its proofs and make additional observations concerning definable closure in these fields.

This volume brings together original research that throws new light on how standards of behavior for medical practitioners are articulated in different religious, social, and political contexts.