Visual mislocalization during double-step saccades

Abstract

Visual objects presented briefly at the time of saccade onset appear compressed toward the saccade target. Compression strength depends on the presentation of a visual saccade target signal and is strongly reduced during the second saccade of a double-step saccade sequence (Zimmermann et al., 2014b). Here, I tested whether perisaccadic compression is linked to saccade planning by contrasting two double-step paradigms. In the same-direction double-step paradigm, subjects were required to perform two rightward 10° saccades successively. At various times around execution of the saccade sequence a probe dot was briefly flashed. Subjects had to localize the position of the probe dot after they had completed both saccades. I found compression of visual space only at the time of the first but not at the time of the second saccade. In the reverse-direction paradigm, subjects performed first a rightward 10° saccade followed by a leftward 10° saccade back to initial fixation. In this paradigm compression was found in similar magnitude during both saccades. Analysis of the saccade parameters did not reveal indications of saccade sequence preplanning in this paradigm. I therefore conclude that saccade planning, rather than saccade execution factors, is involved in perisaccadic compression.

The Concurrent Programming of Saccades

“…Furthermore, findings from within and between word/object saccade sequences show a similar flexibility in saccade parallel programming to that reported here, also with a dependency upon saccade latency [46, 47, 48, 49]. It is interesting to note in the context of visual space compression [32, 33] that our results would suggest that the compression of visual space around the onset of the second saccade would only be found, or rather be found more strongly, in trials with greater evidence of parallel programming [but see 50]. This would be expected to occur in the RV sequences but more specifically we would suggest that the extent of visual space compression would increase on a trial-by-trial basis depending on the extent of parallel programming.…”

“…Landing positions of first saccades are prone to averaging between target positions when two saccades are required with the second target location also influencing the trajectories of their movements [3, 18, 19]. Parallel programming of saccades is also suggested from a consideration of the effect of making sequences of saccades on the compression of visual space [32, 33]…”

Visual space curves before eye movements

“…location. This observation is in agreement with the orthogonal mislocalization of flashed stimuli away from a stationary saccade target (15,16). As expected, a larger variance was observed for the initial locus of gaze (6.84 deg²) when compared to the variance associated with the compressed locus of gaze (2.12 deg²).…”

“…the frequent mislocalization of flashed stimuli away from a stationary target (15,16), (ii). the neural computations and architecture that causes cells in the extrastriate cortex to shift orthogonal to the presumed saccade direction (7,8) and (iii).…”

Proof of Concept of Novel Visuo-Spatial-Motor Fall Prevention Training for Old People

“…Visuo-spatial-motor training is to strengthen the connection of eyes with motor areas of the brain [75,132]. In addition, blinks contribute to the instability of a gaze during fixation because the eyes after a blink are not at the same spot [133][134][135][136][137][138][139][140]. Post-saccadic target blanking affects the detection of stimulus displacements across saccades in this way: Displacement detection is improved by blanks between views [133,137,138,141,142].…”