Response-mode shifts during sequence learning of macaque monkeys.

Incidental sequence learning has been conceptualized as involving a shift from stimulus-based to plan-based performance (e.g., Tubauet et al. in Journal of Experimental Psychology: General 136:43-63, 2007). We analyzed the response time (RT) data of two macaque monkeys that were trained for thousands of trials on a sequential reaching task in a study by Matsuzaka et al. in Journal of Neurophysiology 97, 1819-1832 (2007). The animals learned to respond predictively to a repeating 3-element sequence. During a transitional period, RT distributions were bimodal, indicating that the animals alternated between two processing modes. An analysis of trial-to-trial mode shifting probabilities provided preliminary evidence for a strategic process.