Betül Beyza Cengil^1,2, Huseyin Boyaci^1,3; ¹Bilkent University, ²Social Sciences University of Ankara, ³Justus Liebig University Giessen

In this study, we employ the century-old Poffenberger paradigm to investigate the effects of expectation on visuospatial interactions. In the Poffenberger paradigm, participants respond to a constant and lateralized visual stimulus using either their ipsilateral or contralateral hand, and their response times (RTs) are recorded. The differences in RTs between ipsilateral and contralateral trials are attributed to the cost of interhemispheric transfer based on the shared contralaterality principle in the visual and motor systems: ipsilateral responses require uncrossed visuospatial interactions, whereas contralateral responses require crossed visuospatial interactions. In our design, participants (n = 20) responded to briefly presented lateralized visual stimuli with their ipsilateral or contralateral hand depending on the stimulus characteristics (e.g., an X or an I). Furthermore, prior to the target stimulus, we provided a centrally presented cue indicating which visual stimulus was more likely to appear in that trial with a certain level of congruency (e.g., 100%, 80% or 50%). Whereas the side of the presentation was randomized. Thus, we manipulated the expectations about ipsilateral and contralateral responses irrespective of the visual hemifield and hand. Results showed a main effect of expectation. Post hoc analyses revealed that participants were statistically significantly faster in congruent trials (RT = 529 ms) compared to incongruent trials (RT = 579 ms) and no-expectation trials (RT = 547 ms), and slower in incongruent trials compared to no-expectation trials. There was also an interaction between congruency (congruent, incongruent) and response type (ipsilateral, contralateral): violations of contralateral response expectations increased the RTs more than violations of ipsilateral response expectations. Control experiments demonstrated that the effect could not be attributed solely to visual processing of the stimulus. These results show that expectations can affect the temporal dynamics of visuomotor interactions in speeded tasks.