## Objectives ## In previous experiments of the current project, we have observed that the interference effect when solving a typical flanker task can vary when participants are instructed to maintain different attentional set over the stimuli set presented. If participants, at the same time they are resolving the main flanker task, have to be ready to detect an infrequent vertical displacement of the target, then the interference effect is significantly reduced. But if the infrequent target must be detected as a horizontal displacement, then the interference effect increases significantly. However, in all the experiments developed until now, these stimuli set were presented separately: in some tasks blocks, the infrequent target was displaced all the times over the vertical axis, whilst in others blocks it was displaced over the horizontal axis. In this new experiment, we aim to confirm the differences observed in the interference effect as a function of these different attentional sets (i.e., attending to the vertical vs. horizontal displacement) are still observed when the same stimuli (i.e., both displacements) are presented in all blocks. Therefore, in different blocks of trials participants will receive different instructions (i.e., different attentional set), but both the vertical and the horizontal infrequent displacements of the target will be presented in all blocks. In addition, we look to explore a forth condition in which participants will be set to detect both the vertical and horizontal infrequent displacement of the target at the same time. ## Hypothesis ## We expect to still observe a significant reduction of the interference effect when participants are set to detect the infrequent vertical displacement of the target, and a significant increment of this effect when the infrequent horizontal displacement must be detected. When the attentional set is instructed to resolve just the main flanker task in all the trials (no matter the target is displaced in any direction from it central position), we anticipate to observe an interference effect close to 55 ms, as in the previous experiments (osf.io/erqv9). Last, when participants must resolve the main flanker task while attempting to detect both the vertical and horizontal displacement, we expect to observe an overall increment in the reaction time and percentage of errors, but the same interference effect size than when resolving just the main flanker task. ## Design and Procedure ## Participants will resolve four experimental blocks of 104 trials each of them. All the blocks will have the same proportion of type of trials. In 72 trials, the target will not be displaced from it central position, in 16 trials the target will be displaced either up or down, whilst in the remaining 16 trials it will be displaced either left or right. Participants will receive four different instructions to resolve each of the four blocks: (a) to respond always to the direction pointed by the target (b) to respond to the direction pointed by the target, except when target appears very displaced either up or down, (c) to respond to the direction pointed by the target, except when target appears very displaced either left or right, and (d) to respond to the direction pointed by the target, except when target appears very displaced in any direction (either up/down or left/right). The sequence of instructions for the four blocks will be selected by permutation per participant, so that across the 24 participants the 24 possibles orders will be selected. Participants will perform a practice block of 24 trials (8 trials with the target not displaced, 8 trials with the vertical displacement, and 8 trials with the horizontal displacement) before each experimental block, with visual feedback to each answer. ## Sample Size ## Using G*Power 3.1.9.2 (Faul, Erdfelder, Lang, & Buchner, 2007), we estimated the minimum sample size in 20 participants, based on the effect size (η2p= .44) of the interaction between Displacement Direction x Task Instruction x Congruency (with RT as dependent variable) observed in the second experiment of the current project, and considering a power of .95 and an alpha error of .05. Then, taking into account this minimum sample size, and in order to have one participant per sequence of blocks, we decided to collect data from 24 participants. If we need to replace one or more participants for atypical or extreme performance, then we will collect additional data until 24 participants complete the expected sample.