Action history and target uncertainty co-determine human reaching direction under time pressure

Given the inaccuracies that are inherent in biological sensory and motor functions, animal sensorimotor control should be probabilistic. Effective neural control systems for movement must estimate the most likely true state of the world on the basis of uncertain sensory information, and to select and execute movements that are most likely to be successful given motor variability. Bayesian inference dictates that if sensory information is ambiguous (e.g. low light conditions), animals should rely more on their past experience of target locations to guide motor planning, and less on their current sensory information about target location. Here we investigated how time pressure affects degree to which the precision of sensory information about a target influences movement direction bias towards previous target locations. We used a paradigm developed by Dekleva et al. (2016) that involved uncertain cues to the location of a hidden target for reaching with movement preparation time strictly controlled. One group of participants (n=10) were required to initiate their reaches within 150-300ms of target presentation, and a second group (n=10) were required to initiate their reaches with 1150-1300ms of target presentation. We found that participants relied more on prior target location information when target precision was reduced under time pressure, which suggests that integration of target uncertainty information according to Bayesian principles is an inherent component of sensorimotor transformation and does not require time-consuming cognitive processes.