Related Experiment Videos
Inhibition of saccade initiation by preceding smooth pursuit
R Kanai1, J N van der Geest, M A Frens
1Department of Neuroscience, EE1579, Erasmus MC, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands.
Abstract:
In this study, we investigated the influence of smooth-pursuit eye movements on saccade initiation in response to a sudden jump of a continuously moving target. We replicated the finding by Tanaka et al. (1998) that saccadic eye movements in the direction opposite to preceding pursuit have longer latencies than those in the same direction. We confirmed that this asymmetry is indeed due to an inhibitory effect of smooth pursuit on saccade initiation in the opposite direction rather than facilitation of saccade initiation in the same direction. The inhibitory effect decreased strongly when subjects knew the jump direction in advance. This supports the notion that the prolonged latencies of backward saccades are not due to orbital mechanics or low-level motor processing. Furthermore, we found that the range of saccade directions inhibited by a pursuit movement is broad, covering all directions that did not have the same horizontal component as the pursuit direction. This is in contrast with the predictions of "Inhibition of Saccade Return" (ISR, Hooge and Frens 2000), which is restricted to a smaller confined area.
Insights
Smooth pursuit eye movements inhibit subsequent saccade initiation, especially in the opposite direction. This effect is reduced when target jump direction is known, suggesting a cognitive rather than mechanical basis.
Area of Science:
- Neuroscience
- Ophthalmology
- Motor Control
Background:
- Smooth-pursuit eye movements track moving objects.
- Saccades are rapid eye movements for visual fixation.
- The interaction between pursuit and saccades influences visual perception and action.
Purpose of the Study:
- To investigate how smooth-pursuit eye movements affect saccade initiation.
- To determine the mechanism behind delayed saccades opposite to pursuit.
- To characterize the directional range of pursuit's inhibitory influence on saccades.
Main Methods:
- Participants performed smooth-pursuit eye movements on a continuously moving target.
- A sudden target jump required a saccadic eye movement.
- Saccade latency and direction were analyzed in relation to preceding pursuit.
Main Results:
- Saccades opposite to pursuit direction showed longer latencies than those in the same direction.
- This latency difference was attributed to smooth pursuit inhibiting backward saccades.
- The inhibitory effect diminished when the jump direction was predictable.
- Inhibition extended broadly, not just to directly opposing saccades, challenging existing models like ISR.
Conclusions:
- Smooth pursuit exerts a significant inhibitory influence on subsequent saccade initiation, particularly for saccades in the opposite direction.
- This inhibition appears to be under cognitive control, as predictability of target motion reduces the effect.
- The broad range of inhibition suggests a more widespread neural mechanism than previously proposed by models like ISR.