Sanchez, D.J. & Reber, P.J. Society for Neuroscience 2009.
The sequence of motor operations involved in performing a procedural task is often difficult to describe verbally even when it can be easily performed after training. Previous research using the serial reaction time task has shown group level dissociations between implicit and explicit perceptual-motor sequence knowledge in amnesic patients and young, healthy participants. Using a new perceptual-motor sequence learning task, we examined the dissociation between performance and explicit sequence knowledge in individual participants.
The task consists of circular cues scrolling vertically towards four ring-shaped targets placed at equidistant horizontal locations. Participants were instructed to press a corresponding key when the cue reached its matching target and were not told that the cues followed a repeating sequence. Each participant was assigned to one of five 12-item sequences. The intervals between cues were gradually shortened across training to maintain a challenging level of difficulty and 20% of training cues were random to minimize explicit knowledge. Test consisted of the five sequences and learning was assessed by comparing error rates from the learned sequence against the novel sequences. Participants were then asked to verbally report any sequence information they may have noticed and completed a recognition test. For the recognition test, the five sequences were shown and participants rated how likely it was that each sequence had been the one practiced.
An analysis of error rates across test indicated that the learned sequence was the sequence with the fewest total errors in 21 of 30 participants. For 20 of these participants, the error rate on the practiced sequence was significantly lower than the four novel sequences at an individual participant level. On the recognition task, only four of 30 participants (13%) gave their practiced sequence the highest rating of the five sequences. In 70% of participants, observation of their motor performance indicated which of the five sequences had been trained while verbal report and recognition of the sequences was at chance across the group.
Practice with a repeating perceptual-motor sequence in this task is shown to produce an implicit representation that identifies which particular sequence was learned in an individual participant even when that participant can neither report nor explicitly recognize the same information. This finding reinforces the encapsulation between implicit and explicit sequence knowledge and further suggests that perceptual-motor sequence information can be encoded and retrieved from the motor system without the awareness of the participant.