Diurnal variation and practice effects in saccade task performance

Abstract

Saccadic eye movement tasks have been widely used as a probe for measuring cognitive functions in healthy humans as well as in patients with neurological and psychiatric disorders. Circadian variation has been shown to affect multiple aspects of cognitive function especially executive function related to prefrontal cortex. The effects of diurnal variation in saccadic task performance and the dissociation of these effects from repetition or practice effects has not been adequately addressed. In the current study thirty healthy adults performed several saccadic eye movement tasks including visually guided saccades, antisaccades and countermanding saccades in three consecutive sessions. Participants were divided into three groups, with a different starting time of the sequence of the three sessions across groups (morning or afternoon or evening) to examine the effect of diurnal variation (time of day that the tasks were performed) separated from the effect of session repetition (practice effect). The results showed no effect of diurnal variation for all indexes of saccadic eye movement performance including accuracy (antisaccade and countermanding saccade tasks) speed (mean latency in all tasks) and stability (intra-subject standard deviation of latency in all tasks). In contrast, saccadic task repetition significantly improved accuracy, speed and stability of performance indicating the presence of practice effects in these tasks. Finally, linear mixed model analysis confirmed no interaction between diurnal variation and practice effects for all indexes of saccadic eye movement performance. In conclusion our study provides confirmation that saccadic task performance is not affected by diurnal variation related to circadian rhythms. In contrast, short term repetition of these tasks results in significant practice effects.

Keywords: Antisaccade; Countermanding saccade; Gap saccade; Oculomotor tasks; Saccadic latency; Visually guided saccade.

Fig. 1

This figure presents the sequence of events in each of the 4 saccade tasks used in the current study. A: Step saccade task (STP); in this task the central fixation remains for 1-sec and then the peripheral target appears simultaneously with the disappearance of central fixation (target jumps) and the participant saccades to the peripheral target. B: Gap saccade task (GAP); same as the STP task but the central fixation target disappears 200ms before the appearance of the peripheral target. C: antisaccade task (ANT); same as the STP task but the participant is instructed to saccade at the mirror location from that of the peripheral target. D: Go trial of the countermanding (CMN) saccade task; same as the STP task (50% of trials). E: Stop trial of the CMN saccade task; after 40ms or 100ms from the disappearance of the central target and the simultaneous appearance of the peripheral target the central target reappears signaling the participant to stop for executing the saccade to the peripheral target (50% of trials)

Fig. 2

Plots of single participant data (empty circles) for Mean Latency (A, B) and Standard Deviation (SD) of latency (C, D) in the step (STP) saccade task. A and C present the data arranged by time of day while B and D present the same data arranged by repetition. Horizontal lines represent the corresponding group means

Fig. 3

Plots of single participant data (empty circles) for Mean Latency (A, B) and Standard Deviation (SD) of latency (C, D) in the GAP saccade task. A and C present the data arranged by time of day while B and D present the same data arranged by repetition. Horizontal lines represent the corresponding group means

Fig. 4

Plots of single participant data (empty circles) for percent of correct responses (A, B) Mean Latency (C, D) and Standard Deviation (SD) of latency (E, F) in the antisaccade (ANT) task. A, C and E present the data arranged by time of day while B, D and F present the same data arranged by repetition. Horizontal lines represent the corresponding group means

Fig. 5

Plots of single participant data (empty circles) for percent of correct responses (A, B) Mean Latency (C, D) and Standard Deviation (SD) of latency (E, F) in the countermanding saccade task with 40ms stop signal delay (CMN 40ms). A, C and E present the data arranged by time of day while B, D and F present the same data arranged by repetition. Horizontal lines represent the corresponding group means

Fig. 6

Plots of single participant data (empty circles) for percent of correct responses (A, B) Mean Latency (C, D) and Standard Deviation (SD) of latency (E, F) in the countermanding saccade task with 100ms stop signal delay (CMN 100ms). A, C and E present the data arranged by time of day while B, D and F present the same data arranged by repetition. Horizontal lines represent the corresponding group means