Action planning and the timescale of evidence accumulation

Perceptual decisions are based on the temporal integration of sensory evidence for different states of the outside world. The timescale of this integration process varies widely across behavioral contexts and individuals, and it is diagnostic for the underlying neural mechanisms. In many situations, the decision-maker knows the required mapping between perceptual evidence and motor response (henceforth termed “sensory-motor contingency”) before decision formation. Here, the integrated evidence can be directly translated into a motor plan and, indeed, neural signatures of the integration process are evident as build-up activity in premotor brain regions. In other situations, however, the sensory-motor contingencies are unknown at the time of decision formation. We used behavioral psychophysics and computational modeling to test if knowledge about sensory-motor contingencies affects the timescale of perceptual evidence integration. We asked human observers to perform the same motion discrimination task, with or without trial-to-trial variations of the mapping between perceptual choice and motor response. When the mapping varied, it was either instructed before or after the stimulus presentation. We quantified the timescale of evidence integration under these different sensory-motor mapping conditions by means of two approaches. First, we analyzed subjects’ discrimination threshold as a function of stimulus duration. Second, we fitted a dynamical decision-making model to subjects’ choice behavior. The results from both approaches indicated that observers (i) integrated motion information for several hundred ms, (ii) used a shorter than optimal integration timescale, and (iii) used the same integration timescale under all sensory-motor mappings. We conclude that the mechanisms limiting the timescale of perceptual decisions are largely independent from long-term learning (under fixed mapping) or rapid acquisition (under variable mapping) of sensory-motor contingencies. This conclusion has implications for neurophysiological and neuroimaging studies of perceptual decision-making

Alkali cleavage of α,α-disubstituted β-ketoesters, nitriles and β-diketones

670-671Nucleophilic cleavage of several α,α-disubstituted β-ketoesters, nitriles and β-diketones has been examined. Only alkali hydroxides participated in the reaction yielding substituted esters, nitriles and ketones

Biotransformation of Δ3-carene by <i style="mso-bidi-font-style:normal">Penicillium nigricans</i>

217-222A fungus was isolated from forest soil by selective enrichment method with Δ3-carene as a sole source of carbon and identified as Penicillium nigricans. The isolate was capable of transforming Δ3-carene into neutral [dihydrocarvone, carvone, carveol, (+)-trans-p-mentha-5,8-dien-2-ol and (+)-trans-p-mentha-5,8-dien-2-one] and acidic (perillic acid and 2-hydroxy-p-menth-8-ene-7-oic-acid) metabolic compounds. These compounds were identified based on infrared (IR), proton nuclear magnetic resonance (1H NMR) and mass spectrum (MS) studies. Three pathways have been proposed for the transformation of Δ3-carene into the neutral and acid metabolic compounds based on the study of oxygen consumption by Δ3-carene grown fungal cells. As the different metabolic intermediates of Δ3-carene are much used in the perfume industry, the Δ3-carene, which is abundantly available, can be used as a starting material in the perfume industry by microbial techniques, using this fungal strain