Saccadic impairment in chronic traumatic brain injury: examining the influence of cognitive load and injury severity

Figures & data

Table 1. Participant characteristics.

	Control	Mild TBI	Moderate-Severe TBI	p^a
N	26	20	15	–
Female, # (%)	19 (73.1%)	10 (50.0%)	6 (40.0%)	0.09
Age in years, Mean (SD)	33.46 (9.45)	37.05 (10.26)	37.07 (12.86)	0.43
Years education, Mean (SD)	16.86 (1.93)	15.75 (3.91)	15.20 (2.14)	0.15
Estimated premorbid IQ, Mean (SD)	107.00 (11.07)	108.60 (9.80)	112.27 (8.64)	0.28
Neurobehavioral Symptom Inventory score, Mean (SD)	8.81 (10.06)	28.35 (14.82)	27.47 (11.48)	< 0.001 (C < M,MS)
Glasgow Outcome Scale-Extended, Mean (SD)	7.81 (0.49)	6.65 (1.27)	6.21 (1.42)	< 0.001 (C < M,MS)
Months Since Injury, Mean (SD)	–	39.30 (33.24)	57.27 (42.44)	0.17
Race/Ethnicity				0.11
Black, # (%)	10 (38.5%)	3 (15.0%)	1 (6.7%)
White, # (%)	11 (42.3%)	12 (60.0%)	13 (86.7%)
Hispanic/Latino, # (%)	2 (7.7%)	2 (10.0%)	0 (0.0%)
Asian, # (%)	2 (7.7%)	3 (15.0%)	0 (0.0%)
Other, # (%)	1 (3.8%)	0 (0.0%)	1 (6.7%)
Cause of Injury				0.58
Motor vehicle accident, # (%)	–	9 (45.0%)	8 (53.3%)
Sports participation, # (%)	–	3 (15.0%)	4 (26.7%)
Fall, # (%)	–	3 (15.0%)	2 (13.3%)
Assault/Combat, # (%)	–	3 (15.0%)	0 (0.0%)
Military Training, # (%)	–	1 (5.0%)	1 (6.7%)
Other, # (%)	–	1 (5.0%)	0 (0.0%)

Note: C = Control Group. M = Mild TBI Group. MS = Moderate-Severe TBI Group.

^a Statistical significance of ANOVA or chi-square, as appropriate.

Table 2. Neuropsychological test performance in control and TBI groups.

	Control		Mild TBI		Moderate-Severe TBI
	M	SD	M	SD	M	SD	p^a
Global Cognition (t)	51.39	5.48	50.48	5.74	52.53	6.74	0.60
Trail Making Test A (t)	45.69	8.94	49.30	10.20	49.33	14.39	0.44
Trail Making Test B (t)	46.42	9.90	49.85	11.01	51.80	11.53	0.27
HVLT-R Short Delay (t)	47.50	8.35	47.40	9.23	47.67	12.24	1.00
HVLT-R Long Delay (t)	49.77	7.97	45.25	10.58	46.93	13.53	0.34
HVLT-R Recognition (t)	52.42	7.62	49.05	10.96	50.67	11.30	0.52
Digit Span Forward (SS)	10.08	2.28	10.15	2.54	10.67	2.61	0.74
Digit Span Backward (SS)	9.96	2.55	10.15	3.13	10.80	2.54	0.64
Digit Span Sequencing (SS)	10.35	2.76	9.85	2.60	11.53	3.00	0.20
Symbol Search (SS)	10.35	2.70	10.15	2.56	10.93	3.24	0.70
Coding (SS)	11.58	2.86	9.90	2.63	9.80	3.59	0.09

Note: M = mean. SD = standard deviation. t = age-corrected t score. SS = age-corrected scaled score.

^a Statistical significance of ANOVA.

Figure 1. Saccadic target detection in the Fusion n-Back Test. Task was performed across multiple conditions: Low Load (Simple Response Time; press a single button [all target circles were white]), Moderate Load (0-Back/Colour Discrimination; press a button representing green vs. blue current target circle) and High Load (1-Back/Working Memory; press a button representing same vs. different colour of current target circle relative to the previous target circle).

Figure 2. Saccadic RT on the Fusion n-Back Test by group, cue type and cognitive load. mTBI = Mild TBI; Mod-Sev TBI = Moderate-Severe TBI. Error bars represent SE. Main effect of Group was significant, p = 0.04, η_p² = 0.11; pairwise between-group differences are noted with * for p < .05 and ^ for p < 0.10. Significant effects were also present for Cue (η_p² = 0.07, p = 0.03), Load (η_p² = 0.12, p = 0.002); and a Group*Load interaction (η_p² = 0.09, p = 0.048); pairwise comparisons not shown. For the Mild TBI and Moderate-Severe TBI groups only, saccadic RT was significantly slower in the high load (1-Back) condition than in the low (Simple RT) and moderate (0-Back) load conditions (p ≤ 0.03 for all).

Figure 3. Overall Saccadic RT on the Fusion n-Back Test by group. mTBI = Mild TBI; Mod-Sev TBI = Moderate-Severe TBI. Error bars represent SE. Main effect of Group was significant, p = 0.04, η_p² = 0.11.

Figure 4. Manual RT on the Fusion n-Back Test by group,  cue type and cognitive load. mTBI = Mild TBI; Mod-Sev TBI = Moderate-Severe TBI. Error bars represent SE. No significant main effect or interaction was demonstrated for group. Significant main effects were present for cue (η_p² = 0.13, p < .001) and load (η_p² = 0.17, p < .001); pairwise comparisons not shown.