Seeing trees but not the forest: limited perception of large configurations in PD

To learn if Parkinson's disease (PD) is associated with a restricted attentional "floodlight."

Different visual tasks may have different attentional requirements. Focused attention may be needed for some tasks; other tasks demand spatially distributed attention. Neglect after right cortical injury and dopamine depletion may limit the area over which attention can be spread. Although subjects with PD have dopamine depletion and can perform poorly on tests of visuospatial function, it is unclear if their attentional floodlight is restricted.

Eleven subjects with PD and 11 control subjects viewed different-sized letters on five printed stimulus sheets, 43 x 56 cm. On each sheet, four different large letters (14 cm2) were composed of four different medium-sized letters (2.5 cm2), which in turn were composed of four different small letters (0.4 cm2). Stimulus sheets were presented at 30- and 75-cm viewing distances. Subjects named "all the letters they could see."

Subjects with PD named small- and medium-sized letters comparably to control subjects, but PD subjects named fewer large letters than control subjects (control = 65.68%, PD = 24.55%; group-by-letter-size interaction, p < 0.05). Subjects with PD who had undergone stereotactic pallidotomy named more letters than prepallidotomy PD subjects (p = 0.05).

PD may affect the patient's ability to perceive large spatial configurations. As global configurations in subjects may be perceived preferentially over local patterns, it is possible that DA depletion induces an aberrant perceptual-attentional bias, such that patients have a narrowed attentional floodlight.