Fig. 2

Experimental design and structure of the ASRT task. (A) In the ASRT task, participants had to press keys corresponding to the location of the target stimulus (dog’s head), where every second trial was part of an 8-element probabilistic sequence. Random elements were inserted among pattern elements to form the sequence (e.g., 2-r-4-r-3-r-1, where numbers indicate the location of pattern trials from left to right, and r represents random positions). (B) The task was self-paced, therefore stimulus presentation time was not fixed. In case of a correct response, the target stimulus disappeared, and the next stimulus appeared after a 120 ms response-stimulus interval. In case of an incorrect response, the target stimulus remained on the screen until the first correct response. (C) Formation of triplets in the task. Pattern elements are represented by blue backgrounds (they appear consistently in the same position throughout the task), and random elements are represented by red backgrounds (they appear randomly in one of the four possible positions). Every trial can be identified as the third element of three consecutive trials (a triplet) in a sliding window manner. The probabilistic sequence structure results in some triplets occurring with a higher frequency (high-probability triplets, 62.5% of all trials) than others (low-probability triplets, 37.5% of all trials). Statistical learning is operationalized as the performance improvement in high-probability trials compared to low-probability trials. Ten repetitions of the 8-element sequence (80 trials) make up one block of the task. (D) The formation of high-probability triplets could have involved the occurrence of either two pattern trials with one random trial between them, which was the case in 50% of trials; or two random trials with one pattern trial between them, which occurred in 12.5% of trials. In total, 62.5% of all trials constituted the final element of a high-probability triplet, while the remaining 37.5% were the final elements of a low-probability triplet. (E) The experiment consisted of a learning phase, where participants were exposed to the same sequence (Sequence A) for a total of 1200 trials (divided into 3 bins of 400 trials each for analyses). The learning phase was followed by a delay of 45 min on average, where participants filled out questionnaires. Then, in the interference phase, participants first practiced Sequence A again in Bin 4. In Bin 5, the underlying sequence was changed without warning to the reversed version of the original sequence (Sequence B). Lastly, in Bin 6, participants were again presented with Sequence A.