Fig 1.
Structure of the ASRT and the experiment.
(A) The target stimulus appeared in one of the four possible positions. In the learning phase, only black-and-white stimuli appeared. During the retrieval phase, sometimes yellow stimuli appeared on the screen, which the participants in the dual-task group had to count, while the participants in the single-task group were told to ignore them. (B) High- and low-probability triplets. High-probability triplets (three consecutive elements) can be formed by two patterns (P) and one random element (r) or occasionally, by two random and one pattern elements. (C) Experimental design. In the learning phase, both groups of participants practiced single-task ASRT. After 24 hours, all participants completed five more blocks of single-task ASRT. Then the single-task group completed 18 blocks of single-task ASRT, whereas the dual-task group completed 15 blocks of dual-task ASRT and three blocks of single-task ASRT (one block after every five dual-task blocks).
Table 1.
Comparison of the two groups on age, years of education, handedness, working memory and short term memory performance.
Fig 2.
Learning scores of the two groups during the learning and the retrieval phase.
The vertical axis represents the learning scores (the difference between RTs for high- and low-probability triplets) in ms, and the horizontal axis represents the nine units of five blocks of the learning phase (block 1–45) and the four units of five blocks of the retrieval phase (blocks 1–5, blocks 6–10, blocks 12–16, blocks 18–22). The black line represents the learning scores of the dual-task group, and the grey line the learning scores of the single-task group. The squared block units represent the test blocks, i.e., when the secondary task was also performed by the dual-task group. The error bars represent the standard error of the mean. At the beginning of the retrieval phase, stable statistical knowledge was detected in blocks 1–5. The statistical knowledge remained stable in the later parts of the retrieval phase, even during the test blocks, and no difference was found between groups in terms of learning scores. We found similar results with standardized scores.
Fig 3.
The learning scores of (A) the test blocks and (B) control blocks of the retrieval phase.
The horizontal axes represent the two groups. The vertical axes indicate the learning scores (RTs for the low-probability triplets minus RTs for the high-probability triplets, the blocks collapsed together). The error bars signal the standard error of the mean. The learning scores of the two groups did not differ in the test blocks or the control blocks. We found similar results with standardized scores. n.s.: p > .05.
Fig 4.
Overall RTs in the test blocks.
The horizontal axis represents the three units of test blocks, and the vertical axis the average RTs. The error bars signal the standard error of the mean. Participants were faster in the test blocks in the single-task group, revealing that the dual-task affected the average RTs. *: p < .05.
Fig 5.
Overall RTs between the test and control blocks in (A) the dual-task group and (B) single-task group.
The horizontal axis represents the two types of blocks, and the vertical axis the average RTs. The error bars signal the standard error of the mean. Participants in the dual-task group were faster in the control blocks compared to the test blocks. This pattern was not confirmed in the single-task group, revealing that the dual-task affected the average RTs. n.s.: p > .05; *: p < .05.