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Scott Reed, Paul Dassonville; Leftward Prism Adaptation Increases Sensitivity to Local Cues in Healthy Individuals. Journal of Vision 2011;11(11):1063. doi: https://doi.org/10.1167/11.11.1063.
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Adaptation to right-shifting prisms has been shown to diminish the symptoms of hemispatial neglect in patients with parietal lesions (Rossetti et al., 1998). In contrast, left-shifting adaptation in healthy individuals has been shown to simulate symptoms of neglect, such as a rightward bias in line bisection tasks (Colent et al., 2000) and a reduction in global interference in the perception of Navon figures (Bultitude & Wood, 2010). The current study tested whether leftward prism adaptation (PA) can also increase local processing biases in healthy individuals. In experiment 1, participants' susceptibility to the rod-and-frame illusion (RFI) was measured before and after prism adaptation. A significant increase in susceptibility to a small frame version of the RFI (thought to be driven primarily by local interactions between the rod and the contours of the frame) was found for leftward PA, whereas rightward PA caused no change in susceptibility. To confirm this effect, experiment 2 was conducted using a more pure measure of local processing: the simultaneous tilt illusion (STI). Again, it was found that illusion susceptibility increased post-adaptation for the left-shifting prism group only. Experiment 3 tested whether PA can also modulate global processing independent of local processing by having participants make a saccade to perceived vertical in the presence of a large tilted frame. A marginally significant result was found in that the leftward PA group was less susceptible to the tilted frame post-adaptation. Results from all 3 experiments suggest that leftward PA in healthy individuals can simulate the local processing bias of neglect patients primarily through increasing sensitivity to local visual cues, and that the attentional effects of PA not only modulate lateral shifts of attention, but also shifts from one level of processing to another.
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