Optimal and Suboptimal Use of Postsaccadic Vision in Sequences of Saccades

Abstract

Saccades are imprecise, due to sensory and motor noise. To avoid an accumulation of errors during sequences of saccades, a prediction derived from the efference copy can be combined with the reafferent visual feedback to adjust the following eye movement. By varying the information quantity of the visual feedback, we investigated how the reliability of the visual information affects the postsaccadic update in humans. Two elements of the visual scene were manipulated, the saccade target or the background, presented either together or in isolation. We determined the weight of the postsaccadic visual information by measuring the effect of intrasaccadic visual shifts on the following saccade. We confirmed that the weight of visual information evolves with information quantity as predicted for a statistically optimal system. In particular, we found that the visual background alone can guide the postsaccadic update, and that information from target and background are optimally combined. Moreover, these visual weights are adjusted dynamically and on a trial-to-trial basis to the level of visual noise determined by target eccentricity and reaction time. In contrast, we uncovered a dissociation between the visual signals used to update the next planned saccade (main saccade) and those used to generate an involuntary corrective saccade. The latter was exclusively based on visual information about the target, and discarded all information about the background: a suboptimal use of visual evidence.

Revisiting corrective saccades: Role of visual feedback

“…A similar finding has been reported by Munuera et al (2009); they found that the corrective saccade with visual feedback only compensate for 70% of intrasaccadic target jump (20% of 18° target eccentricity) in a modified double-step paradigm. Their following experiment (Morel, Deneve & Baraduc, 2011) also showed incomplete corrections (with gain lower than the main saccade gain). The reason for this incomplete correction is still unknown, though it may again be a time optimal strategy to avoid overshooting because of inherent noise.…”

“…The reason for this incomplete correction is still unknown, though it may again be a time optimal strategy to avoid overshooting because of inherent noise. On the other hand the calculation might also be based not only on the perceived visual error, but also on the predicted visual error (Morel et al, 2011, Vaziri, Diedrichsen & Shadmehr, 2006, Wong & Shelhamer, 2011). …”

“…A forward predictor of motor outcomes could explain 1) concurrent programming of corrective saccades with an initially erroneous saccade during a double-step task (Sharika et al, 2008), 2) saccade adaptation (Wong & Shelhamer, 2011), and 3) combining visual feedback to adjust the next saccade during sequences of saccades (Morel et al, 2011, Munuera et al, 2009). The results of our study using a simple visually-triggered saccade task conform to this forward model hypothesis of error correction.…”

Integration of Retinal and Extraretinal Information across Eye Movements

“…In this context it remains an open question how our findings might translate to more cluttered visual scenes typically encountered in everyday life. Previous studies indicate that the structural gist of background information is indeed taken into account for matching of visual space across saccades [ 44 , 45 ]. Reliability of such information will be more difficult to parameterize and the visuomotor system may additionally incorporate a non-flat prior on (the implausibility of) visual background jumps during eye movements [ 46 ].…”

Neuronal representation of saccadic error in macaque posterior parietal cortex (PPC)

“…It has been reported that in human subjects, up to 20% of secondary saccades were not directed to the saccade target. These secondary saccades were also considered as secondary saccades ( Morel et al, 2011 ). Therefore, we included all secondary saccades for further analysis.…”