When an action contingently yields the same effect, we form bidirectional action-effect associations that allow us to anticipate the effects of our actions. Importantly, our eyes already move toward the expected future location of our actions' effects in anticipation of them, that is, we perform anticipatory saccades. These anticipatory saccades are linked to a proactive effect-monitoring process that prepares the comparison of expected and actual effect. However, how fast such anticipatory saccades emerge (i.e., how fast learning leads to monitoring) is unknown. To address this question, correct left/right responses were followed by a visual effect either on the same side (response-effect compatible) or on the opposite side (response-effect incompatible). In Experiment 1, action-effect compatibility switched after sequences of four, eight, or 12 trials (randomly allocated; partly predictable environment). In Experiment 2, random trials (two to seven) separated sequences of three, five, or seven experimental trials. Again, action-effect compatibility switched after a sequence of trials and sequences were randomly allocated (unpredictable environment). In both experiments, participants started to perform anticipatory saccades toward future effects after experiencing a new action-effect mapping once/twice (response-effect compatible/incompatible). That is, a single to two action-effect (re-)learning instances were sufficient to develop actioneffect associations that trigger attentional shifts toward the expected future consequences of our actions (i.e., monitoring processes), whereas influences on action selection are only observed after a substantially larger number of (re-)learning instances. These results suggest that monitoring processes modulate the expression of action-effect associations in action planning based on observed action-effect contingencies. Public Significance StatementWhen an action predictably yields a certain consequence, we anticipate the future effect and already move our eyes to where it will appear. These eye movements prepare us for comparing expected and actual consequences of our actions and allow us to adapt if things did not go as planned. Here, we demonstrate that we only need to experience our action and its consequence once to start performing such anticipatory eye movements that guide our subsequent actions.

When an action contingently yields a predictable effect, we form bi-directional action-effect associations that allow us to anticipate both the location and timing of our actions’ effects. This is evident in anticipatory eye movements towards the future effect’s location which are performed earlier when the effect’s delay is short rather than long. Such anticipatory eye movements reflect a proactive process of effect monitoring which prepares a comparison of expected and actual effects. Here, in two online eye tracking experiments, we manipulated effect locations (spatially compatible vs. incompatible in one half) and effect delays (short vs. long) to determine whether in-laboratory effects could be reliably replicated online using participants’ individual webcams. Extending prior research, we further compared irrelevant (Experiment 1) to relevant effects (response to effect feature; Experiment 2). In contrast to prior in-laboratory studies, participants anticipatorily looked towards future effects above chance only when effects were relevant. Post-experiment questions suggested that online-participants intentionally ignore irrelevant information to optimize task performance. Nevertheless, replicating in-laboratory experiments, both for relevant and irrelevant effects, participants’ first saccade towards a future effect occurred earlier for the short rather than the long effect delay. Thus, we demonstrate that anticipatory eye movements reflecting a time-sensitive proactive effect monitoring process can reliably be assessed both in-laboratory as well as online. However, when investigating anticipatory saccade frequencies online, additional aspects like effect relevance have to be considered.