Control of Predictive Error Correction During a Saccadic Double-Step Task

Abstract

Sharika KM, Ramakrishnan A, Murthy A. Control of predictive error correction during a saccadic double-step task. J Neurophysiol 100: 2757-2770, 2008. First published September 24, 2008 doi:10.1152/jn.90238.2008. We explored the nature of control during error correction using a modified saccadic double-step task in which subjects cancelled the initial saccade to the first target and redirected gaze to a second target. Failure to inhibit was associated with a quick corrective saccade, suggesting that errors and corrections may be planned concurrently. However, because saccade programming constitutes a visual and a motor stage of preparation, the extent to which parallel processing occurs in anticipation of the error is not known. To estimate the time course of error correction, a triple-step condition was introduced that displaced the second target during the error. In these trials, corrective saccades directed at the location of the target prior to the third step suggest motor preparation of the corrective saccade in parallel with the error. To estimate the time course of motor preparation of the corrective saccade, further, we used an accumulator model (LATER) to fit the reaction times to the triple-step stimuli; the best-fit data revealed that the onset of correction could occur even before the start of the error. The estimated start of motor correction was also observed to be delayed as target step delay decreased, suggesting a form of interference between concurrent motor programs. Taken together we interpret these results to indicate that predictive error correction may occur concurrently while the oculomotor system is trying to inhibit an unwanted movement and suggest how inhibitory control and error correction may interact to enable goal-directed behaviors.

Proactive control of sequential saccades in the human supplementary eye field

“…1C), however, the second target stepped to a new location during the first saccade. Participants occasionally made second saccades to the old position of the final target in these trials, consistent with the idea of concurrent planning of the second saccade along with the first saccade (14,15). Importantly, we scored target-shift trials as correct via auditory feedback only when the second saccade foveated the new position of the final target.…”

“…The slope of the ISI vs. RPT is often used as an explicit measure of concurrent planning of sequential saccades (14)(15)(16)(17)(18). Such a measure of RPT, however, is absent in the context of a delayed saccade task in which the second saccade may be concurrently planned along with the first saccade at any point during the hold-time (i.e., the time between the presentation of the initial target and the disappearance of fixation spot).…”

“…We therefore used the distribution of second saccade end points as a proxy of concurrent planning. We have previously reported that the end-point locations of second saccades in target-shift trials vary systematically with RPT, such that the greater the degree of concurrent preparation, the closer the second saccade end points are to the old location of the final target (15). Accordingly, using data from experiment 1, we classified second saccades of target-shift trials based on whether they ended at the old position of the final target ( Fig.…”

“…Intersaccadic interval (ISI), defined as the time between the end of the first saccade and the beginning of the second saccade, has been shown to decrease with increasing concurrent preparation of two saccades (14)(15)(16)(17)(18). Thus, we hypothesized that if concurrent planning of sequential saccades is indeed affected by previous trial type, the ISI of a given no-shift trial should be shorter when preceded by a no-shift trial compared with when preceded by a target-shift trial.…”

“…Performance in a given trial was examined as a function of previous trial type using a parameter that has previously been shown to vary systematically with the reprocessing time (RPT), which is the time available for concurrent preparation of two saccades (14)(15)(16)(17)(18). Intersaccadic interval (ISI), defined as the time between the end of the first saccade and the beginning of the second saccade, has been shown to decrease with increasing concurrent preparation of two saccades (14)(15)(16)(17)(18).…”