Visual filtering and covert orienting in persons with Down syndrome

A forced-choice reaction time (RT) task was used to examine the efficiency of visual filtering (the inhibition of processing of irrelevant stimuli) an d covert orienting (shifts of visual attention independent of eye movement) components of attention in persons with Down syndrome (n = 20) and childre n of average intelligence (n = 20) matched for mental age (MA) (average MA = approximately 5.4 years). Conditions varied with regard to presence or ab sence of distracters, and the validity (valid, invalid, or neutral) of loca tion cues. Contrary to expectations, persons with Down syndrome and MA-marc hed children of average intelligence at approximately age 5 showed similar patterns of performance on a task that required filtering distracting stimu li and searching for relevant information in the visual field. Both groups responded more efficiently to a target preceded by a valid cue as compared to a target preceded by an invalid or neutral cue. In addition, performance was more efficient with a target that was presented without irrelevant inf ormation as compared to one that was flanked on either side by extraneous, nontarget information and therefore necessitated filtering for efficient pe rformance. These two findings indicate that: (1) disengaging from the locat ion of an incorrect cue, and then searching for, locating, and responding t o a target requires more time and attention than simply locating and respon ding to a target that has been validly cued; and (2) processing and respond ing to a target flanked by extraneous information entails filtering, and th erefore requires more time and resources than simply responding to a target without distracters. In general, the development of visual reflexive, cove rt orienting, and filtering are intact in persons with Down syndrome relati ve to their level of functioning at an MA level of approximately 5 years, a period that is critical in the development of attentional processes.