Validation of the Continuous Tracking Paradigm for Studying Implicit Motor Learning

A continuous pursuit-tracking task is the typical experimental paradigm to investigate implicit motor learning. Implicit motor learning is proven by a greater improvement in tracking of a repeated segment of a target path compared to random segments ( Pew, 1974 ). Recently, doubts about the validity of results obtained with this paradigm have been raised. Improved tracking of a repeated segment might simply be due to the characteristics of that particular segment. In response to these doubts, we seek to improve the continuous tracking task. Therefore, we computed a pool of 37 distinct target segments. Participants (N = 36) practiced the tracking task, each one with a unique repeated segment in the middle and varying outer segments, all taken from the pool of segments. After five practice blocks of 36 trials each, a test block was performed where the repeated middle segment was replaced with a random segment. The tracking performance on the repeated segment was better than on random segments. Furthermore, we assume that learning was implicit, because participants’ answers to a posttest interview showed they were largely unaware of a repeated segment within the curves.

Implicit learning of a repeated segment in continuous tracking: A reappraisal

Several prior studies (e.g., Shea, Wulf, Whitacre, & Park, 2001; Wulf & Schmidt, 1997) have apparently demonstrated implicit learning of a repeated segment in continuous-tracking tasks. In two conceptual replications of these studies, we failed to reproduce the original findings. However, these findings were reproduced in a third experiment, in which we used the same repeated segment as that used in the Wulf et al. studies. Analyses of the velocity and the acceleration of the target suggests that this repeated segment could be easier to track than the random segments serving as control, accounting for the results of Wulf and collaborators. Overall these experiments suggest that learning a repeated segment in continuous-tracking tasks may be much more difficult than learning from a repeated sequence in conventional serial reaction time tasks. A possible explanation for this difference is outlined.

A repeated segment on the mouse Y chromosome is composed of retroviral-related, Y-enriched and Y-specific sequences.

We report the isolation and characterization of two recombinant clones containing DNA derived from the Y chromosome of the C57BL/10 inbred mouse strain. Both clones were isolated from a lambda phage library derived from a partial EcoRI digest of C57BL/10 male DNA using the murine retrovirus M720. Characterization of these clones showed they were derived from a repeated segment present on the C57BL/10J Y chromosome that contains sequences found elsewhere in the genome. In addition, one clone contained a sequence, designated YB10, that is unique to the Y chromosome and present in approximately 500 copies on the C57BL/10J Y chromosome. Analysis of Southern blots containing DNAs prepared from females and males of representative species from four subgenera of Mus probed with pYB10 and the 3'LTR from one of the Y-associated retroviruses (MuRVY) revealed that, with the exception of a single fragment observed in both female and male DNA of Mus saxicola, hybridization to pYB10 was observed only to male DNA of the species Mus spretus, Mus hortulanus, Mus musculus, Mus domesticus and Mus abbotti. In addition, the pattern and intensity of hybridization to YB10 and the MuRVY-LTR indicated that sequence of divergence was followed by amplification of Y chromosome sequences containing YB10 and MuRVY. The divergence and amplification occurred separately in each of the ancestral lineages leading to M. spretus, M. hortulanus, M. abbotti, M. musculus and M. domesticus. We suggest that acquisition and amplification of DNA sequences by the mammalian Y chromosome has contributed to its evolution and may imply that the mammalian Y chromosome is evolving at a faster rate than the rest of the genome.