Saccadic Adaptation and Visual Function

Saccadic eye movements are used to quickly and accurately orient our fovea within our visual field to obtain detailed information from the visual world. The accuracy of these movements is maintained throughout life despite constant pressure on oculomotor muscles and neuronal structures by growth and aging; this maintenance appears to be a product of an adaptive mechanism that continuously accounts for observed errors in saccade targeting, and is referred to as saccadic adaptation. Saccadic adaptation has long been considered a pure oculomotor learning phenomenon but recent studies have shown that saccadic adaptation not only maintains the function of the oculomotor system, but also significantly contributes to the calibration of other motor systems and even to visual function. When participants’ saccades are adapted to consistent visual error, significant transfer of adaptation occurs to pointing or reaching towards visual targets and to the perceptual localization of visual probes. Saccadic adaptation can even affect the estimation of the extents of an object during fixation. Thus, saccadic adaptation affects visual function. Conversely, while it has long been held that saccadic adaptation is driven by visual error, recent studies suggest that the process of adaptation takes into account not only the visual position of the target after the saccade but also a prediction of that location based on motor re-efference, such that it operates on the mismatch with the prediction rather than the visual error itself.
Although the interaction of saccadic adaptation with motor and visual function has been firmly established, there are many open questions in this area of research. For instance, the role of attention in this process is not well understood. This includes the contribution of visual attention to the effects of saccadic adaptation on visual function as well as the way in which visual attention is altered by the adaptation process. Furthermore, previous studies have demonstrated that visual-functional changes following saccadic adaptation depend on a variety of factors that includes, but is not limited to, the type of saccade performed (in particular, voluntary vs. reactive saccades), the type of adaptation performed (i.e., forward vs. backward adaptation), or the position and visual features of the visual target. It is also an open question which neural systems support the observed interaction. Saccadic adaptation is known to strongly depend on cerebellar function, but the visual effects of adaptation suggest the involvement of cortical areas, possibly driven by cerebellar feedback loops. Shedding light on the neural mechanisms that mediate these influences will allow us to develop a more comprehensive understanding of the oculomotor system and its relationship with visual perception. Such understanding may lead to the development of novel interventions for clinical oculomotor conditions.