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Marzieh Salehi Fadardi, Larry A Abel; Eye movement reaction times and visual task performance in congenital nystagmus in the presence of mental load. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2908.
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© ARVO (1962-2015); The Authors (2016-present)
Longer visual recognition time and latencies of target acquisition (Lt) and saccades (Ls) have been measured in congenital nystagmus (CN). Visually demanding tasks in the presence of stress have been said to make CN worse. We have investigated task performance, Lt and Ls in saccade tasks with low and high mental load in CN and controls.
Eye movements and heart rate (HR) were recorded in 15 CN and 25 normal subjects who were required to respond manually to saccade targets randomly presented. The task was done with low mental load (by itself) and high mental load (with time restriction and mental arithmetic). We compared manual response time (RT), HR, Lt and Ls within subjects and across groups using 2-way mixed ANOVA.
High mental load was evidenced by significantly increased in HR at both groups. The percentage of the trials with saccades towards target did not change across tasks in CN. Eye movement reaction times were significantly longer in CN than normals (Ls: f(1,38)=26.3, p<.001, Lt: f(1,38)=23.12, p<.001) and also at the task with high mental load Ls:f(1,38)=34.7, p<.001, Lt: f(1,38)=7.20, p=.011). The interaction between task and group was not significant for Ls (Mean ± SEM for CN: 254.6±9.9 ms at low and 221±7.4 at high load; for normals: 216.2±6.1 at low and 180.8±4.2 at high load). Similarly, no significant interaction was found between task and group for Lt for CN: 539.7±47.4 at low and 489.8±20.6 at high load; for normal: 375.6±5.8 at low and 413.1±9.3 at high load). There was a significant main effect on manual RT only for group (f(1,38)=9.9, p=.003). The interaction between task and group was significant for RT; CN subjects showed longer RT than normals with high load (for CN: 873.3±47.3 at low and 968.7±32.7 at high load; for normals: 770±25 at low and 801.1±36.6 at high load, f(1,38)=5.02, p=.03).
Both Ls and Lt are prolonged in CN. Task performance degraded in CN with mental load. Possible interactions between task demands and internal state may have affected CN and may have changed the exposure time required to see a target. Further studies are required to investigate the underlying motor and sensory mechanisms involved in both being slow to get on the target and slow to recognize it.
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