Tuning the speed - accuracy trade - off to maximize reward rate 1 in multisensory decision - making

40 For decisions made under time pressure, effective decision making based on 41 uncertain or ambiguous evidence requires efficient accumulation of evidence 42 over time, as well as appropriately balancing speed and accuracy, known as the 43 speed/accuracy trade-off. For simple unimodal stimuli, previous studies have 44 shown that human subjects set their speed/accuracy trade-off to maximize 45 reward rate. We extend this analysis to situations in which information is 46 provided by multiple sensory modalities. Analyzing previously collected data (J. subjects adjust their speed/accuracy trade-off to produce near-optimal reward 49 rates. This trade-off can change rapidly across trials according to the sensory 50 modalities involved, suggesting that it is represented by neural population codes 51 rather than implemented by slow neuronal mechanisms such as gradual changes 52 in synaptic weights. Furthermore, we show that deviations from the optimal 53 speed/accuracy trade-off can be explained by assuming an incomplete gradient-54 based learning of these trade-offs.