A pupillary and eye movement investigation of functional deficits in multiple object tracking following mild traumatic brain injury.

The ability to maintain visual attention to track multiple moving objects has been reported to be impaired in individuals with mild traumatic brain injury (mTBI). We investigated whether deficits in multiple object tracking (MOT) following mTBI is associated with behavioral markers of attention, particularly cognitively driven pupillary dilation responses and eye movement patterns. Thirty-five adults were recruited. Pupillary responses and eye movements were tracked while participants performed a MOT task in which the duration of tracking (five and ten seconds), number of target dots (three, four, and five), and number of distractor dots (three, six, and nine) were independent variables. Patients with mTBI had reduced pupil dilation when tracking a high number of target dots (four dots: Mean difference [MD] = 0.79, p < 0.001; five dots: MD = 0.67, p < 0.001) compared to controls. Similarly, patients with mTBI had reduced pupil dilation when the number of distractor dots increased (six distractors: MD = 0.43, p < 0.001; nine distractors: MD = 0.46, p < 0.001) compared to controls. A reduction in pupil dilation observed in patients with mTBI may reflect a limitation in the mental capacity to meet increasing cognitive demands. Eye movement analysis showed that patients with mTBI made significantly more fixations (and with reduced fixation durations), consistent with a local tracking strategy, than controls. In conclusion, tracking pupil response and eye movements while tracking multiple moving objects provided an indication of possible factors that contributed to the poor performance among patients with mTBI.