will j harrison

all about my active-vision research

me publications

Eye movement targets are released from visual crowding.

Here’s a link to my recent Journal of Neuroscience article, coauthored by my PhD advisors Jason Mattingley and Roger Remington. We tested whether a target closely surrounded by distractors becomes easier to identify just before an eye movement is executed toward the target.

To explain the main findings in the paper briefly, consider the following. Look at the top cross on the left, and, without moving your eyes, see if you can identify the second letter in the string of letters at the far right. Now try identifying the letter in the second row while looking at the bottom cross.

crowdDemo

You’ll probably find it very difficult (impossible?) to identify the second letter in the top row, but it’ll be much easier to identify the same letter in the bottom row. The difference in difficulty can’t simply be due to the distance of each letter from the fixation cross, because the distance of each letter is the same. So, in the top row, there is some sort of interaction between the letters making it difficult to distinguish one from another. The difficulty recognising something in peripheral vision when it’s surrounded by clutter is referred to as “crowding”.

Back to my study. I had participants try to identify a crowded object. In half the trials, they kept their eyes still on a specific place, like the cross above, and they had great difficulty identifying the target as we expected. In the other half of the trials, the participants were required to make a saccadic eye movement toward the crowded target. Using an eye tracker, I was able to switch off the target prior to the start of each eye movement, so that the participants never saw the target after they moved their eyes. I found that, when participants had to identify the crowded target while also preparing an eye movement towards it, their ability to identify the target improved significantly. What’s most important about my findings is that this improved target recognition began before their eyes moved! So, preparing to make an eye movement resulted in better identification of a crowded target, effectively giving the participants a “sneak peak” of what’s in their peripheral vision even before their eyes moved. Pretty neat.

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