Gatsby Computational Neuroscience Unit Alexandra House, 17 Queen Square, LONDON, WC1N 3AR, UK, Tel: +44 (0) 20 7679 1176, Fax +44 (0) 20 7679 1173 abla@gatsby.ucl.ac.uk, www.gatsby.ucl.ac.uk   ABSTRACTS Venue B10 Seminar Room, Alexandra House, 17 Queen Square London, WC1N 3AR Supported by The Gatsby Foundation |Index|Objective|Attendees|Programme|Travel information|Accommodation| Acetylcholine and Norepinephrine as Uncertainly Signals in Attentional Tasks Angela Yu Gatsby Unit, University College London, UK The neuromodulators acetylcholine and norepinephrine have long been supposed as being critically involved in attentional processes; however, there is little consensus on their precise computational functions.  We propose that these neuromodulators act as uncertainty signals: acetylcholine reports expected uncertainty, coming from known variability or indeterminancy within a behavioural context; norepinephrine signals unexpected uncertainty, as when sensory observations strongly contradict expectations.  A precise interaction between these formally distinct sorts of uncertainty is proposed as controlling attentional selection, enabling near-optimal cortical inference and learning.  We illustrate these ideas using a novel task that generalizes well-studied attentional paradigms known to interact with acetylcholine and norepinephrine.  The model replicates and explains existent data, as well as making novel physiological, behavioural, and pharmacological predictions.  In particular, simulations of pharmacological intervention, affecting either or both neuromodulators, reveal their part-opponent, part-synergistic interaction.