Anticipation and Synchronization

In Nakatani et al.'s '05 paper in the Journal of Cognitive Neuroscience, they describe a peculiar EEG pattern in subjects experiencing a phenomenon known as "attentional blink." Attentional blink occurs when perceivers can only report one of two target images that are presented in quick succession. This is usually found in conditions of high processing load, such as those demanding of both early and higher visual processing.

Attentional blink is often studied in a paradigm where a sequence of images are presented in rapid succession, for about 100 msec each. Subjects have to detect the presence of two specific images within the sequence. When the target images are present and separated by more than 5 intervening distractor images, both targets are detected without much difficulty. When the two images are presented directly after one another (no intervening images) they can also be reported without much difficulty. However, when the targets are separated by between 1 and 4 intervening images, the second target is usually missed!

What happens during this time, when participants are essentially blind? No one really knows. One explanation is that this "attentional blink" is actually the switch cost associated with task switching between looking for target 1 and looking for target 2 (also known as switching the "attentional set"). Accordingly, several studies implicate the areas responsible for working memory: right posterior parietal, cingular, and left temporal/frontal regions. Further, when the second target was detected, subjects showed a large area of phase coherence in the gamma range (30-80 Hz) throughout the task, suggesting that this synchronized activity might reflect differences in attentional focus, which subsequently translate into improved target detection.

The frequency range of 30-80 Hz has many other relationships with visual attention: synchrony within this band has been implicated in object detection, memory retention, readiness, and consciousness. The authors propose that it may be involved in anticipatory processing, or as functioning something like a "procedural buffer" which can be used to alleviate some of the switch costs associated with changing attentional set.

Sure enough, the authors found increased baseline levels of synchrony in the experimental group (which had to find 2 targets) compared to the control group (which had to find only 1). Interestingly, global synchronization involving more than 188 different electrodes also appeared every 300-500 msec, even before the presentation of the first target, in those participants that were able to detect the second target. The authors suggest that this global, long-range synchrony may be a mechanism by which information is transmitted quickly from occipital to frontal areas, and that cycles of synchrony may correspond to processes such as visual "filter reconfiguration or, alternatively, a memory operation."

The authors continue to say that "the real challenge, rather than looking for traces of endogenous versus exogenous control mechanisms, might be to investigate how a system that is switching continuously between different intrinsic states of phase synchrony is able to adjust these rhythms in coordination with external events." Along those lines, one really interesting thing about this pattern of EEG activity is that it could be caused by a very slow oscillation (2-3 Hz) modulating a much faster rhythm (38-43 Hz). If these are actually two separable components, the slower oscillation could be a good candidate for synchronization with events in the external world (such as expectation of a target).

Of course, then we enter into the infinite regress often associated with assigning "agency" to brain functions: what then modulates the slower signal?

Related Posts:
Active Maintenance and The Visual Refresh Rate
Synchrony vs Polychrony
Hypnotic Lullabies


Anonymous Anonymous said...

This topic of cortical synchrony is fascinating. I've got some experience in computer design and data networks, so I understand the concept in the context of electronic hardware. Wetware synchrony is a little harder for me to grok. Thanks for helping to tease the tangles apart.

1/23/2006 02:50:00 PM  
Blogger Chris Chatham said...

glad i could help - there's a lot of disagreement on what the role of synchrony might be in cortical processing, no matter how "clear" I might falsely portray it ;)

i have some friends reading steven strogatz's "sync" right now - a really fascinating book if you're interested in how universal synchronization really is, both in the data networks you work with, the brain networks I work with, and all kinds of other mechanical, quantum, and biological systems...

1/23/2006 03:17:00 PM  
Anonymous Tim said...

On a slightly unrelated note, but since you are obviously interested in neural networks and connectionism, I'd encourage you to look at Brad Wyble's model of the attentional blink. It is definitely not perfect, and cheats a bit on the type-token distinction, but is an interesting relation between this post and your posts on neural networks.

PS: after my last comment, I realized you are a student of Munakata's -- I worked with Jay McClelland this past summer on some of his work with Timothy Rogers about the semantic system.

1/23/2006 06:05:00 PM  
Blogger Chris Chatham said...

tim - thanks for the pointer, I will *definitely* check it out.

Your background with McClelland makes me a little self-conscious about my comments on ANN's; I'm just now taking O'Reilly and Munakata's class on neural networks, so please chime in whenever you see inaccuracies (or anything of the kind) ...

Thanks for the tip - keep 'em coming :)

1/23/2006 06:23:00 PM  
Anonymous Christophe said...

Truly fascinating indeed! Chris, I've been wondering about what is your source of information for your blog posts? Is there, for example, a directory of recently published papers in cognitive science?

1/25/2006 02:59:00 PM  
Blogger Chris Chatham said...

I check a variety of sources (eurekalert, biopsychology news, the cognitive neuroscience mailing list) but most of my favorite stuff comes from either browsing the big psychology journals, talks that are given here at CU Boulder, or personal recommendations like Tim's.

The number of recently published papers in cog sci would be enormous, although such a directory would probably be useful!

1/25/2006 03:26:00 PM  
Blogger Chris Chatham said...

Here's some synchronicity for you: I just found a directory of new papers related to complexity. Looks like good post material...

1/26/2006 06:54:00 PM  

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