will j harrison

all about my active-vision research

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Why is crowding released at the saccade goal? A commentary by van Koningsbruggen and Buonocore

mechanisms behind perisaccadic increase of perception

At the start of 2013, I published a paper in The Journal of Neuroscience showing that, just prior to a saccade, the deleterious effects of crowding are released at the saccade goal. “Crowding” refers to the phenomenon where an object in peripheral vision becomes difficult to recognise when it is closely surrounded by other objects. There’s a demo and a longer explanation of crowding and my previous paper here.

In this week’s issue of the same journal, Martijn van Koningsbruggen and Antimo Buonocore published a Journal Club paper examining the potential cause of a pre-saccadic release of crowding. The paper is behind a paywall here — email me for a copy if you don’t have access. It’s quite interesting to read how others interpret my work, and I think these sorts of commentaries represent and important stage of peer-review that occurs post-publication. Our formal response to this commentary has been published alongside the Journal Club paper, but here I’ll add some more thoughts about van Koningsbruggen and Buonocore’s explanation of our data.

In a nutshell, van Koningsbruggen and Buonocore’s main suggestion is that crowding may be released prior to a saccade because visual attention shifts to the saccade goal before the eyes move. The known relationship between eye movements and visual attention (e.g. Remington, 1980, Deubel et al, 1996) was part of my motivation for running the experiments in the first place. However, I don’t think pre-saccadic shifts of visual attention are adequate to explain our results, especially without a clear definition of “visual attention”. Our formal reply includes a summary of the specific reasons why “visual attention”, as it is used in the cognitive psychology literature, can’t fully account for our data. Depending on the authors’ definition of attention, there might be some explanatory power in their suggestion, but it seems to me that their use of “attention” actually describes an effect, such as a change in identification accuracy, rather than a mechanism, such as a change in the gain response settings of visual neurons.

To play devil’s advocate, I could, for example, argue that previous demonstrations of improved performance at the saccade goal also were the result of pre-saccadic changes in crowding, but have been called “attention” effects. Supporting this hypothetical argument, previous studies on eye movements and attention used stimulus configurations that would have been prone to crowding (e.g. Duebel et al, 1996, Kowler et al, 1995). My intention here is not to argue that this is in fact the case, but instead I’m trying to demonstrate that simply saying that changes in performance are due to “attention” may not necessarily encompass a meaningful explanation of the underlying neural mechanisms driving the changes in performance. Britt Anderson has written a great article about distinguishing “attention” as an effect versus cause in an open access article here.

Van Koningsbruggen and Buonocore bring up a few other interesting points about our study and its limitations which I mostly agree with, so it’s certainly worthwhile to read their article in full.

I’m very interested to carry on these discussions with other researchers, so please feel free to drop me a line or leave a comment here to share your thoughts. [Note that this was originally published on my old Harvard site, and there were a few contributions from people that may be worth reading: http://scholar.harvard.edu/willjharrison/news/why-crowding-released-saccade-goal-commentary-van-koningsbruggen-and-buonocore# ]

References

Our original article showing a release from crowding at the saccade goal:

Harrison, W. J., Mattingley, J. B., & Remington, R. W. (2013). Eye movement targets are released from visual crowding. Journal of Neuroscience, 33(7), 2927–2933. doi:10.1523/JNEUROSCI.4172-12.2013

Van Koningsbruggen and Buonocore’s response:

van Koningsbruggen, M. G., & Buonocore, A. (2013). Mechanisms behind Perisaccadic Increase of Perception. Journal of Neuroscience, 33(13), 11327–11328. doi:10.1523/​JNEUROSCI.1567-13.2013

Other references:

Anderson, B. (2011). There is no such thing as attention. Frontiers in Psychology, 2, 1–8. doi:10.3389/fpsyg.2011.00246

Deubel, H., & Schneider, W. X. (1996). Saccade target selection and object recognition: evidence for a common attentional mechanism. Vision Research, 36(12), 1827–1837.

Kowler, E., Anderson, E., Dosher, B., & Blaser, E. (1995). The role of attention in the programming of saccades. Vision Research, 35(13), 1897–1916.

Remington, R. W. (1980). Attention and saccadic eye movements. Journal of Experimental Psychology: Human Perception and Performance, 6(4), 726–744.

For a great introduction to crowding, as well as a heap of crowding demos, check out:

Pelli, D. G., & Tillman, K. A. (2008). The uncrowded window of object recognition. Nature Neuroscience, 11(10), 1129–1135.