| Although the eyes and the heart perform widely different functions, each receives neural input from the autonomic nervous system. This investigation explored the relationship between ocular and cardiovascular behavior. Experiment 1 demonstrated behavioral covariation between the oculomotor and cardiovascular systems at an individual level. Each of three young adults participated in four experimental sessions. During each session, subjects were exposed to a variety of autonomic demands. Dark vergence and dark focus indexed the oculomotor resting states, and parameters derived from the autoregressive spectral decomposition of variations in inter-beat intervals (IBIs) indexed cardiovascular activity. Both dark vergence and dark focus tended to be nearer during sympathetic dominance of the heart than during parasympathetic dominance, within-subjects variations in cardiovascular parameters could predict dark focus, and between-subjects variations in inter-beat intervals could predict dark vergence. To determine if an oculomotor manipulation can influence cardiovascular behavior, 17 young adults engaged in a near reading task in Experiment 2. In general, cardiovascular parameters covaried with oculomotor changes: in those subjects who experienced oculomotor adaptation, IBIs and high frequency variations in IBIs decreased, and low frequency variations and the ratio of low frequency power to high frequency power tended to increase during the near reading. These shifts indicate an acute shift away from parasympathetic dominance of the heart. Subjects who did not experience oculomotor changes exhibited fewer and smaller cardiovascular effects. These experiments confirm that behavioral covariation between the oculomotor and cardiovascular systems exists on a within-subjects basis. Manipulations designed to influence either system also influence the other. This linkage may have practical consequences for visual performance under stressful conditions and for cardiovascular consequences of prolonged near work. |
