Differential impact of sensory uncertainty in blocked versus trial-interleaved contexts when feedforward and feedback processes co-occur

Theories of human motor learning commonly assume that the degree to which movement plans are adjusted in response to movement errors scales with the precision of sensory feedback received regarding their success. However, support for such models has mainly come from experiments that limit the amount of correction that can occur within an ongoing movement. In contrast, we have recently shown that when this restriction is relaxed, and both within-movement and between-movement corrections co-occur, movement plans undergo large and abrupt changes that are strongly correlated with the degree of sensory uncertainty present on the previous trial and are insensitive to the magnitude and direction of the experienced movement error. Here, we show that the presence of these abrupt and error-insensitive changes are only observed when different levels of sensory uncertainty are interleaved pseudo-randomly on a trial-by-trial basis, and are absent when sensory uncertainty levels vary across blocks of trials. These results suggest that the co-occurrence of within-movement and between-movement corrections is not the only important aspect of our earlier study that challenged traditional models of motor learning under uncertainty.