Okay, Hello, I am the next presenter, as you know, Hunjae Lee.
The article that I chose is “The Relationship between Saccadic Suppression and Perceptual Stability” by Watson and Krekelberg, 2009 from Current Biology .
Um, I feel somewhat nervous because this is my first presentation as graduate student, even in english. And the former presenter Oakyoon Cha , he is an expert of saccades, So please listen me with generous mind but be awake.
Here is another expert of saccade, comedian, 이경규.
I think everybody know what saccadic eye-movement is. Important question is how can we get perceptual stability in this rapid movement. / Saccadic omission is a phenomenon refers most visual stimuli presented just before and during saccades are not perceived. Saccadic suppression is the reduction in visual sensitivity before and during saccade, so it can removes perisaccadic stimuli from visual processing, and there are many study that this saccadic suppression cause saccadic omission.
But in this research, they have another point of view. The goal of this paper is to investigate whether such a saccadically omitted stimulus nevertheless processed by the early visual system or not.
And the conclusion, haha, so fast ? of course yes. perisaccadic stimuli are processed by the early visual system but cannot reach visual awareness.
Let’s see how they design the experiment
They use the shape contrast effect
This picture tell us all about this illusion in this study.
A circle presented after a line appears elongated orthogonal to the line orientation
Here is demo.
not that good but you can feel it. fixate here.
Experiment 1 has done to test and replicate the basic shape contrast illusion. they check that 250ms can make illusion. 250ms is the duration between the presentation of the line and the test circle and they will make saccades during that time in experiment 2.
This is the conditions in detail. ~~~~
Task was ~~~
and they determine the percentage of trials in which observer perceived the circle to be horizontally elongated.
The main experiment is this second one. Here they moved the places of the stimuli slightly. and the time course like this. with saccadic eyemovement.
First there is initial fixation. and after 1 second target fixation appeared and then initial fixation disappeared. it is the signal to start saccades toward target.
and at that known to be the time window of saccadic suppression inducer line appeared around invisible initial fixation and after 250 ms test circle is presented at target fixation for 100ms
This is the simulated version of the experiment with real time interval.
Task was like this
And Here is the results.
This graph shows that the participants had a significant shape illusion even without awareness of the inducer. It means that, even when saccadic omission was complete, the omitted stimulus affected subsequent perception. This implies that the line was processed at least by higher visual areas responsible for this shape illusion.
The data also show that the shape illusion was reduced for those lines that were reported not to be seen compared to lines that were reported to be seen. This shows that the influence a line effect on visual processing is diminished most when it is not seen. It is saccadic suppressiong but Still suppression is not enough to explain the omission here.
Okay, in this line of study, my additional article is this. “Visual Perception: Saccadic Omission – Suppression or Temporal Masking?” by Ibbotson and Cloherty.
In this paper They based on Watson’s study. that shows inducing line during saccades is processed by relatively higher area.
Actually there are two theory explaining saccadic omission. one is this, An alternative theory, This one suggests that saccadic omission is the result of backward temporal masking, means that visual stimuli present at the time of re-fixation is very strong, and mask, the stimuli presented before or during the saccade.
But backward masking depends on the stronger mask than the stimulus during the saccade. a visual stimulus during the saccade would need to be weak compared to the visual stimulus at re-fixation. But in natural scenes this requirement is frequently challenged.
Look at this photo. The first fixation, X, is on a low contrast step. A saccade is then made across a high contrast riser, Y, and re-fixation occurs on a low contrast step, Z.
(B) So this is neural responses from a visual neuron, without saccadic modulation, around the time of the saccade. There is low-level ongoing activity during fixation at X (black), the response to Y is large (blue) and the response to Z is small (red).
So we cannot think about masking in this case.
with saccadic modulation. Ongoing activity is suppressed around saccade start at X. The response to Y is suppressed and the response at re-fixation, Z, is greatly enhanced Also, the response latencies to stimulation at Y and Z are reduced, thus truncating the response to Y.
However, recent physiological experiments in behaving primates provide a
unifying theory. In primates, there is a modulation of visual sensitivity around the time of saccades This consists of a pre-saccadic reduction and a substantial post-saccadic enhancement of spontaneous neural activity and visual sensitivity. In the medial superior temporal area (MST) of the parietal cortex,
for example, the mean pre-saccadic reduction in visual sensitivity is around 50% and the post-saccadic (or re-fixation) enhancement boosts responses by more than 70% Mean response amplitudes around the time of saccades from 72 MST
neurons in two macaque monkeys Response amplitudes for stimuli delivered prior to the saccade are suppressed compared to the control level
while responses to stimuli delivered after the saccade are enhanced.
Coloured bars indicate periods of significant suppression (blue) and enhancement (red)
So the discussion topics are here.
First early versus late. do perisaccadic stimuli are fully suppresed early area like LGN ? Watson’ s data shows that They not.
Illusion used in the experiment, use spatially seperated line and circle, this position invariant characteristic means that they are processed by relatively large receptive fields such as superior temproal sulcus and inferotemproal cortex, higher area. But still we can think reduced activity from early stage continues to higher area and then saccadic omission occurs. So what do you think?
Second, similar question Retinal versus Extraretinal. what do you think about the mechanism of saccadic omission, retinal, in other words masking ? or extraretinal, suppression ? or both of them ?
Third one is dorsal versus ventral stream. According to Burr, M pathway mainly wires to dorsal stream is suppressed. then Does P pathway and ventral stream relatively survived ? my naive question about this is, then why we cannot perceive the perisaccadic stimuli?
* maybe both two streams are suppressed and it is not fully suppressed
Last two questions are about generalized ideation of saccades.
What do you think of the purpose of saccadic suppression? to get Perceptual stablitiy ? Then what is better strategy? To suppress all of perisaccadic information? Watson who is pro for perisaccadi stimuli are processed by early stage, argue that perisaccadic signals are useful for Perceptual stablitiy. then why ?
Last one, More generally, then, what is suppressed during saccade?
thank you. I am done. please say something.