Dear all
I am reading the literature about the ‘centre of gravity’ of saccade and ‘averaging saccade’. The concepts of these two terms are alike. The ‘centre of gravity’ is that targets are surrounded by non-targets, and the saccades, instead of landing at the designated target, land in the midst of the whole configuration [Kowler, E. (2011). Eye movements: the past 25 years. Vision Research, 51(13), 1457–1483]. The ‘saccade averaging’ is that two adjoining stimuli in the same hemifield evoke a short-latency saccade, the saccade tends to land on an intermediate location between these stimuli. [Heeman, J., Theeuwes, J., & Van Der Stigchel, S. (2014). The time course of top-down control on saccade averaging. Vision Research, 100, 29–37]. Besides, in some literature, the saccade averaging is known as the ‘global effect’. Are the concepts of these three terms identical?
Thanks in advance.
Hi,
Basically, all three terms refer to the same phenomenon: the observation of systematic saccade endpoint deviations towards a central location within a stimulus configuration consisting of multiple, nearby visual targets/distractors.
The origin/use of the three different terms can be attributed to the different levels at which the phenomenon has been/is being described.
The term ‚center of gravity‘ refers to the fact that respective saccades are executed towards the so called center of gravity of the respective stimulus configuration.
The term ‚averaging saccade‘ or ‚saccade averaging‘ refers to the notion of oculomotor averaging. The concept of averaging is reflected both at the behavioral and neuronal level and further conveys a theoretical assumption concerning the mechanism underlying the computation of respective saccade vectors. At the behavioral level, respective saccades roughly land at an averaged, intermediate location in between the stimuli causing the oculomotor competition (roughly, because saccade endpoints vary as a function of specific features of the stimulus configuration, such as the relative size and saliency of the stimuli, etc.). At the neuronal level, the phenomenon has been linked to an averaging of the population activity associated with the different visual stimuli (i.e. the formation of an intermediate activity hub) within oculomotor maps such as the Superior Colliculi (however, at what processing stage such averaging ultimately occurs is not finally resolved).
The term ‚global effect‘ refers to the notion that respective saccades are thought to be of reflexive nature and are influenced by the global configuration of the visual scene (rather than by a specific local target). Also, respective saccades have been described as to arise from a coarse (or global) visual processing.
peace
Luca Wollenberg
Dear Luca Wollenberg
Thanks for your answer. Your answer is very exciting to me. Can I ask a few questions based on your answer?
First, regarding the averaging saccade, you mentioned the saccade endpoint involving a function of specific features of the stimulus configuration, such as the relative size and saliency of the stimuli. Do you think that the salience of biological stimuli (e.g., emotional body) would likely affect the averaging saccade (i.e., the endpoint of the saccade)?
Second, can you suggest relevant literature about averaging saccades to support the ideas that you refer to?
Third, you pointed out that the processing stage where averaging occurs is not ultimately being resolved. Can you say a little more about this?
Thanks in advance,
Best regards
Chen
Hi Hsin-Yuan Chen
ad question #1:
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The global effect has been typically considered to be a low-level/bottom-up oculomotor phenomenon, i.e. mainly driven by the mere visual input. However, there has been more and more evidence that the global effect is susceptible to modulations by top-down processing/higher-order signals. Still, even though I am not much into the literature of visual processing of biological visual stimuli, I am rather skeptical about a systematic influence of biological/emotionally arousing stimuli if they are being strictly controlled for the low-level saliency of their visual features. As of now, I am also not aware of any literature suggesting a specific role for biological stimuli with regard to the global effect. But maybe you have an indication for believing so?
ad question #2:
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here are two relatively recent and hollistic review papers on the global effect where you can find references to the different aspects I mentioned in my response:
Van der Stigchel, S., & Nijboer, T. C. (2011). The global effect: what determines where the eyes land. Journal of Eye Movement Research, 4(2), 1-13.
Vitu, F. (2008). About the global effect and the critical role of retinal eccentricity: Implications for eye movements in reading. Journal of Eye Movement Research, 2(3), 1-18.
this is my most recent publication investigating the deployment of visual attention before averaging saccades, where you can find many references to and discussion of various aspects of the global effect along with some new exciting insights:
Wollenberg, L., Deubel, H., & Szinte, M. (2018). Visual attention is not deployed at the endpoint of averaging saccades. PLoS biology, 16(6), e2006548.
I guess having a look at those papers gives you a good headstart into the literature...
ad question #3:
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you can find various references concerning the neuronal aspect of averaging in the papers mentioned above...
Dear Luca Wollenberg
Thanks for your response. I am not much into neural aspects of the phenomenon of the saccade. The idea of using a global effect to investigate biological stimuli is led that the specific feature on the salience of stimuli on the global effect. So far I have not gotten sufficient literature to propose the idea that biological stimuli affect the change of the global effect. I am still working on them. If I cannot find any evidence to support my proposition, I can reject the hypothesis that the global effect is affected by the salience of biological stimuli. I am reading the article you offered. The articles are good. Unfortunately, I found they did not directly discuss high-level oculomotor phenomenon much. Even if an article is engaged in the issue, the point mentioned is that it does not have a direct relationship between the global effect and biological stimuli. Moreover, I will try to seek the references you mentioned above concerning the neuronal aspect of averaging.
Best regards
Chen
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