The mystery of visual stability

Date:
June 11, 2020
Source:
Tohoku University
Summary:
We move our eyes several times per second. These fast eye
movements, called saccades, create large image shifts on the
retina -- making our visual system work hard to maintain a stable
perceptual world. Remapping the retinal image compensates for this;
however, errors in actual eye movements cause image shifts, even
with remapping.



FULL STORY ==========================================================================
We move our eyes several times per second. These fast eye movements,
called saccades, create large image shifts on the retina -- making our
visual system work hard to maintain a stable perceptual world. Remapping
the retinal image compensates for this; however, errors in actual eye
movements cause image shifts, even with remapping.


==========================================================================
To do this, our eyes reduce sensitivity to the displacement of visual
stimuli during saccades using a process called Saccadic Suppression of Displacement (SSD). However, SSD remains a mystery to researchers. A
research team at Tohoku University's Research Institute of Electrical Communication, led by Professor Satoshi Shiori, investigated the
mechanisms underlying SSD.

In their psychophysical experiment, an observer first stared at a fixation point for a random duration between 500 and 1300ms. After the fixation
point disappeared, the observer had to shift their eyes to a target disc
at the other side of the monitor. The target disc moved its location
slightly during the observer's saccadic eye movement (about 500 ms), and
the observer was asked to judge the direction of target disc displacement (either left or right).

Researchers varied the target disc contrasts, before and after
saccadic movements separately, to manipulate the retinal input
strength. Furthermore, they analyzed the observer's accuracy to detect displacement at each contrast level.

Interestingly, the results show two distinct contrast effects which
informed us about the involvement of two visual pathways. Higher contrast
in pre-saccadic stimuli enhanced observers' sensitivity to detect visual motion, which is the typical contrast effect on vision. However, an
opposite contrast effect was discovered for post-saccadic visual stimuli: higher contrast led to lower detection sensitivity. The research group
explains the results successfully with a model which includes two major pathways of early vision: parvo-pathway and magno-pathway. In this
model, the signals in the magno-pathway are responsible for detecting displacements while the signals in the parvo-pathway suppress erroneous
motion information across saccades. SSD occurs when parvo- pathway
signals suppress magno-pathway signals immediately after a saccade.

The understanding the mysterious phenomenon, visual stability across
saccades, would help future AI/robots to perceive the world as we do.


========================================================================== Story Source: Materials provided by Tohoku_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Shuhei Takano, Kazumichi Matsumiya, Chia-huei Tseng, Ichiro Kuriki,
Heiner Deubel, Satoshi Shioiri. Displacement detection is suppressed
by the post-saccadic stimulus. Scientific Reports, 2020; 10 (1)
DOI: 10.1038/s41598-020-66216-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200611094213.htm

--- up 20 weeks, 2 days, 2 hours, 34 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)