Influence of moving background on line bisection performance in the normal elderly versus patients with hemispatial neglect

Objective: Previous studies have shown that when healthy young participants bisect stationary lines on a moving background (MB) or optokinetic stimulation, they perceive the stationary line moving in the opposite direction of the MB (illusory motion [IM]), and they displace their bisection mark in the direction of the IM. This study attempted to learn whether IM also Influences attentional biases of the healthy elderly and patients with hemispatial neglect. Design: In experiment 1, healthy elderly participants and patients with neglect bisected lines in conditions where IM was absent or present. To better understand the MB dichotomy between the healthy elderly and neglect patients, in experiment 2, participants' eye movements were recorded using an infrared eye tracker. Results: In experiment 1, healthy elderly participants' biases occurred in the opposite direction of MB when IM was present but in the same direction of MB when IM was absent. In contrast, neglect patients' biases occurred in the same direction of MB regardless of conditions. Eye movements reflect the spatial direction of attention. In experiment 2, the healthy elderly participants were able to selectively attend to the line, whereas neglect patients were impaired in that they fixated on the line. Conclusions: These results suggest that the healthy elderly can selectively fixate on a line, and with MB, they perceive the stationary line moving, resulting in a bisection bias in the direction of the IM. In contrast, when there is an MB, the patients with neglect are impaired in that they fixate on the line. Thus, they do not perceive IM; instead, they are primarily influenced by the MB.