Where you come from, and where you’re going: attention and action in manual aiming
Sandoval Similä, Sebastián Jonas
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The way we act upon the world influences our visual perception of it. For instance, previous work has found visual perceptual enhancement at the targets of upcoming saccades (e.g. Deubel & Schneider, 1996) and pointing movements (e.g. Deubel, Schneider, & Paprotta, 1998). Visual perceptual enhancement has also been found along the trajectories of manual movements (Festman, Adam, Pratt, & Fischer, 2013a, 2013b), but the area surrounding static hands have also been found to receive perceptual enhancement (Reed, Grubb, & Steele, 2006). The initial question addressed by the present thesis was whether the preparation of a manual movement would also induce perceptual enhancement at the effector location (i.e. the movement’s start point). In other words, do people not only attend where they are going, but also where they are coming from? To address this question, the novel aspect of our task was that participants not only had to select the movement target, but also the moving hand. Across the eight experiments of the present thesis we applied variations on a popular experimental task, asking our participants to conduct pointing movements and studying how this influenced their allocation of visuospatial attention. This was measured by recording whether they could successfully identify a discrimination target (DT), with the discrimination rates at different locations taken to index the amount of attention allocated there. Our first four experiments found evidence for enhancement at the starting point of a movement, but this effect was inconsistent and appeared to compete with other mechanisms for orienting attention. For example, our first experiment found enhancement only at the target location, which may have been induced by having used predictable locations for the DT, whereas Experiment 4 found only an enhancement at both hands, static and responding, which might have been due to the ability to plan the movements in advance. Since in each trial in Experiment 4 participants had to execute one movement out of only two possibilities, this may have allowed them to pre-program both movements before each trial and execute them from memory. In Experiment 5 we increased the number of potential movement targets in order to increase the difficulty of target selection and reduce movement predictability, while also lowering the DT presentation times. Under this more challenging paradigm we found perceptual enhancement only at the movement target, but also that the perceptual task was too difficult for half of our participants. Did we fail to induce enhancement at multiple locations because of the specific task our participants were executing, or due to a general inability to do so within this more challenging version of the experimental paradigm? To address this question we decided to test whether we could still induce perceptual enhancement at two locations within these experimental parameters, but attempting to replicate the work of Baldauf, Wolf and Deubel (2006). They had reported that carrying out pointing sequences resulted in parallel allocation of attention to all movement targets before movement onset. We repeatedly failed to find any enhancement at any location, even when we increased the presentation times to durations used in the earlier experiments. In our final experiment we mounted a more direct replication of Baldauf et al (2006), and we also conducted a preliminary calibration stage in which we attempted to adjust the DT’s presentation time to each participant’s level of ability by assessing their perceptual performance. This calibration was only successful in a third of our participants, with the majority still finding the perceptual task too challenging within the range of exposure times used. Furthermore, even amongst those participants selected for their good perceptual performance in the calibration task, we found visual enhancement only at the first movement target during the two-step pointing sequence. This calls into question not only the general replicability of the work of Baldauf et al. (2006), but also Deubel et al. (1998). On the whole, our findings suggest that although the pattern of attentional allocation is influenced by action planning, including the starting point of a movement, this is but one of many competing factors. Furthermore they call into question the general replicability of previous high-profile results, and call for a greater acknowledgement and investigation of the possible role of extensive practice in yielding some of the results found in the literature. The thesis concludes with suggestions for future work.