1st and 2nd order stimuli reaction time measures are very sensitive to mild traumatic brain injuries.

Abstract

We investigated the impact of mild traumatic brain injury (mTBI) on visuomotor processing of first and second order contrast using flickering or motion defined sinusoidal gratings. Spatial frequency was 0.5 cpd and temporal frequency was 2 Hz. Flicker consisted in contrast inversion, and motion drifted right or left. Contrast was 12.5% for first and 100% for second order, difference usually observed in perception thresholds, and used to make measures of first and second order comparable. Reaction times (RTs) of 15 adults diagnosed mTBI were compared to those of 15 matched controls. Measurements were obtained at 15 days, 3 months and 12 months after the injury, and at equivalent times for control participants. Detection RTs, for the flicker condition, and direction discrimination RTs, for the motion condition, were measured. For RTs corresponding to correct responses, means, standard deviations (SDs), medians, interquartile ranges (IQRs) were calculated. In general, RTs of mTBI were longer than control subjects as revealed by means (p=0.031) and medians (p=0.037). For mTBI group motion condition, RTs corresponding to 1st order were shorter than those corresponding to 2nd order stimuli (means: p=0.001; medians: p<0.0001). SDs (p=0.031) and IQRs (p=0.040) were larger for mTBI than for control participants. Control group SDs were smaller for detection RTs than for direction discrimination RTs (p=0.007), but IQRs revealed this was true for both groups (p <0.0001). For the mTBI group motion condition, SDs (p=0.047) and IQRs (p=0.013) were larger for 1st than for 2nd order. All these observations were made over the 3 sessions. The use of RT measures, combined with stimulus properties, appear to be a very sensitive method for measuring mTBI-induced visuomotor anomalies. The different stimulus properties allow for fine probing of the underlying mechanisms in conditions where the brain is exposed to mild trauma.

Meeting abstract presented at VSS 2014