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.