Research report
Architecture of a gain controller in the pursuit system

https://doi.org/10.1016/S0166-4328(96)89078-4Get rights and content

Abstract

A monkey can pursue faster target oscillations if they appear during ongoing smooth pursuit than if they appear while the monkey is fixating a stationary target. Others have proposed a switch in the pursuit circuit to account for this bistable sensitivity to high frequency targets. It is hypothesized that the switch is closed only during pursuit, permitting the retinal motion signal to pass through the circuit at full gain. Losses in pursuit gain caused by certain cortical lesions do mimic the effect of a switch jammed open. To explore this gain adjustment mechanism further, we measured in monkeys the smooth eye movements in response to a high frequency sinusoidal target (called ‘humm’) presented under a variety of testing conditions. Pursuit gain measured in response to this humm was not merely bistable. Rather, a graded gain modulation of the pursuit system was possible. Furthermore, the gain adjustment had some directional sensitivity to it, enhancing the response to humm along one axis more than the other. In exploring the factors which gated the gain adjustment, it appeared that the movement of the eyes and not the image motion that occurs during pursuit was paramount for enhancing pursuit gain. Gain was not enhanced by saccadic but only by smooth pursuit tracking movements. Finally, gain could be modulated somewhat by covert signals such as the expectation of future smooth pursuit movements.

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  • Cited by (21)

    • The neuronal basis of on-line visual control in smooth pursuit eye movements

      2015, Vision Research
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      Previous studies provided abundant evidence that initial pursuit gain, which is based on open-loop control, is highly influenced by the visual properties of target motion (Krauzlis & Lisberger, 1994; Lisberger & Westbrook, 1985; Lisberger et al., 1981; Tychsen & Lisberger, 1986). The visuomotor gain associated with the initial pursuit is variable, which depends on ongoing behavioral states or cognitive factors (Barnes, 2008; Keating & Pierre, 1996; Krauzlis & Miles, 1996; Tabata, Miura, & Kawano, 2005; Tabata et al., 2006). For example, the initial pursuit response evoked by visual target motion is enhanced when the subjects anticipated the tracking of a moving target.

    • Neural activity in the frontal pursuit area does not underlie pursuit target selection

      2011, Vision Research
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      These findings are not conclusive, but they are sufficient to keep open the question of whether the buildup activity in FPA neurons facilitates pursuit generally or only in their preferred directions. One final related point is that our results could account for the behavioral observation that subjects exhibit an increase in pursuit gain during fixation when they expect that they will be pursuing soon (Keating & Pierre, 1996; Kodaka & Kawano, 2003; Tabata et al., 2005, 2006, 2008). In these experiments, the expectation of upcoming pursuit increases the gain of the pursuit system, similar to the increase in gain that is observed during pursuit itself (Schwartz & Lisberger, 1994).

    • MSTd neurons during ocular following and smooth pursuit perturbation

      2008, Progress in Brain Research
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      It is small during fixation and increases monotonically with higher constant pursuit velocities. This reflects a nonlinear mechanism and has been called dynamic gain control (Schwartz and Lisberger, 1994; Keating and Pierre, 1996). Several structures at the cortical, brainstem, and cerebellar levels are involved in the generation of these eye movements.

    • Neural activity in cortical areas MST and FEF in relation to smooth pursuit gain control

      2008, Progress in Brain Research
      Citation Excerpt :

      The FEF–NRTP–DV pathway implements the DGC mechanism. As shown in several studies (e.g., Keating and Pierre, 1996; Churchland and Lisberger, 2002), the feedforward gain depends linearly on tracking velocity, therefore retinal slip is multiplied by a rectified linear function of the internal estimate of eye velocity (rectification is justified by the fact that the gain is independent of the direction of target motion). Figure 1(b) shows typical responses associated with DGC which are reproduced correctly by the proposed model.

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