Age-related decline of peripheral visual processing: the role of eye movements

Abstract

Earlier work suggests that the area of space from which useful visual information can be extracted (useful field of view, UFoV) shrinks in old age. We investigated whether this shrinkage, documented previously with a visual search task, extends to a bimanual tracking task. Young and elderly subjects executed two concurrent tracking tasks with their right and left arms. The separation between tracking displays varied from 3 to 35 cm. Subjects were asked to fixate straight ahead (condition FIX) or were free to move their eyes (condition FREE). Eye position was registered. In FREE, young subjects tracked equally well at all display separations. Elderly subjects produced higher tracking errors, and the difference between age groups increased with display separation. Eye movements were comparable across age groups. In FIX, elderly and young subjects tracked less well at large display separations. Seniors again produced higher tracking errors in FIX, but the difference between age groups did not increase reliably with display separation. However, older subjects produced a substantial number of illicit saccades, and when the effect of those saccades was factored out, the difference between young and older subjects' tracking did increase significantly with display separation in FIX. We conclude that the age-related shrinkage of UFoV, previously documented with a visual search task, is observable with a manual tracking task as well. Older subjects seem to partly compensate their deficit by illicit saccades. Since the deficit is similar in both conditions, it may be located downstream from the convergence of retinal and oculomotor signals.

Fig. 1

Schematic drawing of our experimental setup. Black dots represent the cursors that the subjects had to keep centered, and black arrows indicate the possible movement of the two joysticks. The vertical target display areas are plotted in white (for 3 cm display separation) and gray (for 10 and 35 cm display separations). The center cross represents the fixation point; it was displayed only in condition FIX and the white brackets represent the calculated target zone (for exemplary individual and 35 cm display separation)

Fig. 2

a Exemplary tracking performance of young (gray lines) and older (black lines) subject in condition FREE in its original state. Dashed lines represent cursor movements with 3 cm display separation, solid lines represent cursor movements with 35 cm display separation. b Tracking error of young and elderly subjects. Symbols represent means and bars represent the appropriate standard errors. Display separations of 3, 10, and 35 cm are plotted

Fig. 3

Eye movement parameters, with symbols representing mean values and error bars representing the appropriate standard error. Only display separations of 10 and 35 cm are plotted, since data from the 3 cm separation were not unequivocal