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Smooth pursuit and saccadic tracking eye movements are affected by attention in young infants
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SMOOTH
PURSUIT AND SACCADIC TRACKING EYE MOVEMENTS AFFECTED BY ATTENTION IN YOUNG INFANTS
ARE
John E. Richards Felecia Halley Department of Psychology University of South Carolina Columbia, SC 29208
In infants, moving visual stimuli are initially tracked almost exclusively with saccadic eye movements, and smooth pursuit eye movements increase in number and quality over the first six months of life. The effects of attention status on the tracking of visual stimuli was studied in 8, 14, 20 and 26 week old infants, using heart rate (HR) changes as an index of attention level. Infants were presented with a small sinusoidal moving stimulus that ranged in speed from 4 to 24 degrees per sec. EOG was used to record eye movements, and smooth pursuit and saccadic eye movements were distinguished in the raw EOG record. Sustained attention was defined as occurring following a significant HR deceleration; stimulus orienting any period prior to sustained attention; attention termination as the return of HR to its prestimulus level following sustained attention. There was a gradual increase in the level of smooth pursuit tracking across these ages. Saccadic tracking was fairly good at all ages, but accuracy of pursuit increased for both saccadic and smooth pursuit eye movements. Saccadic tracking was enhanced in the phases of stimulus orienting and sustained attention, and poorest during attention disengagement. This was particularly true in the two older ages at the fastest stimulus speeds, in which during attention a decrease in the amount of smooth pursuit tracking was replaced by an increase in saccadic tracking. Smooth pursuit tracking was also affected by attention and age. The older age infants engaged in smooth pursuit tracking at higher speeds during attention but not during inattention. Thus it appears that attention acts to increase the infant’s focus on the moving target. Attention has its largest effect on tracking behavior at the older two ages, enhancing smooth pursuit for faster speeds and resulting in saccadic tracking when the smooth pursuit system is insufficient to track the stimulus. This pattern of results is consistent with a model positing a primitive saccadic-based tracking system existing in the neonate, the gradual emergence of the neural systems necessary for smooth pursuit tracking at 2 months, the continuing development of the smooth pursuit tracking system for several months, and the rapid emergence of an attention-influenced cortical system affecting tracking from 2 to 6 months.
SMOOTH
PURSUIT AND SACCADIC TRACKING EYE MOVEMENTS AFFECTED BY ATTENTION IN YOUNG INFANTS
ARE
John E. Richards Felecia Halley Department of Psychology University of South Carolina Columbia, SC 29208
In infants, moving visual stimuli are initially tracked almost exclusively with saccadic eye movements, and smooth pursuit eye movements increase in number and quality over the first six months of life. The effects of attention status on the tracking of visual stimuli was studied in 8, 14, 20 and 26 week old infants, using heart rate (HR) changes as an index of attention level. Infants were presented with a small sinusoidal moving stimulus that ranged in speed from 4 to 24 degrees per sec. EOG was used to record eye movements, and smooth pursuit and saccadic eye movements were distinguished in the raw EOG record. Sustained attention was defined as occurring following a significant HR deceleration; stimulus orienting any period prior to sustained attention; attention termination as the return of HR to its prestimulus level following sustained attention. There was a gradual increase in the level of smooth pursuit tracking across these ages. Saccadic tracking was fairly good at all ages, but accuracy of pursuit increased for both saccadic and smooth pursuit eye movements. Saccadic tracking was enhanced in the phases of stimulus orienting and sustained attention, and poorest during attention disengagement. This was particularly true in the two older ages at the fastest stimulus speeds, in which during attention a decrease in the amount of smooth pursuit tracking was replaced by an increase in saccadic tracking. Smooth pursuit tracking was also affected by attention and age. The older age infants engaged in smooth pursuit tracking at higher speeds during attention but not during inattention. Thus it appears that attention acts to increase the infant’s focus on the moving target. Attention has its largest effect on tracking behavior at the older two ages, enhancing smooth pursuit for faster speeds and resulting in saccadic tracking when the smooth pursuit system is insufficient to track the stimulus. This pattern of results is consistent with a model positing a primitive saccadic-based tracking system existing in the neonate, the gradual emergence of the neural systems necessary for smooth pursuit tracking at 2 months, the continuing development of the smooth pursuit tracking system for several months, and the rapid emergence of an attention-influenced cortical system affecting tracking from 2 to 6 months.