Relationships between feature search and mobility performance in persons with severe visual impairment.

PURPOSE: Because visual search requires both the ability to discriminate visual features and the ability to process information in a large field of view, the association between feature search and mobility of visually impaired (VI) subjects was studied.

METHODS: Forty-four subjects with severe visual impairment participated in the study. Feature search performance (2 x 2 deg square target amid 1 x 1 deg square distracters) was measured for 8- to 16- and 32-item set-sizes on 10 x 10, 20 x 20, and 40 x 40 deg fields. Mobility was evaluated on indoor high-density obstacle courses under photopic and mesopic illumination.

RESULTS: In feature search, VI subjects were slower and made more errors than normal subjects, but they searched in a parallel fashion. On the mobility task, VI subjects walked slower and made more obstacle contacts than age-matched normal controls. In VI subjects, performances on feature search and mobility tasks were significantly associated, with 37.5% to 66.9 of variations in the mobility measurements being accounted for by visual search speed.

CONCLUSIONS: Feature search reaction time can be a good predictor of VI patients' mobility.