Rueckert Linda, McFadden Harvey Gene
Department of Psychology, Northeastern Illinois University, Chicago, IL 60625, USA.
Laterality. 2004 Oct;9(4):421-32. doi: 10.1080/13576500342000257.
Previous studies have shown that neglect patients exhibit a crossover effect on free vision line-bisection tasks; they place the cross mark too far right for long lines, but too far left for short lines. This is partially determined by the relative line length within a block of testing. The purpose of the present study was to determine whether the crossover that has been observed in normal participants might also be due to the context in which the line is presented. All participants were tested on the free vision Landmark task, in which they were shown a line that had been correctly bisected, and asked whether the cross mark appeared to be too far to the left or too far to the right. In Study 1 half of the participants were exposed only to short lines (1-8 cm) and half were exposed only to long lines (8-28 cm). Unlike the results for neglect patients, performance appeared to be influenced only by the actual length of the line, not the relative length. In Study 2 the background on which the lines were presented was manipulated. For half of the trials the line appeared on the standard US legal-sized paper. For the other half the width of the background was doubled. Unexpectedly, no crossover occurred for the wide field width. The results of Study 1 suggest that normal participants may be less influenced by context than neglect patients. The results of Study 2 suggest that the crossover effect may be influenced by some type of interaction between the line itself and the background on which it is presented.
