This is the assignment from 2006. The 2007 assignment will be similar in depth and scope, but on a slightly different topic.
Biological Sciences 330/331, Smith College | Neurophysiology

Sometimes an attractive idea seems to solve a difficult problem, and it quickly becomes the conventional wisdom even though our understanding is incomplete and possibly incorrect. In some cases, the idea remains controversial for many years. The role of synchronous firing of visual neurons to bind together the responses to components of an object is just such an attractive but controversial idea. Visual processing initially breaks up the visual scene into isolated fragments that are detected by many individual neurons in V1 and higher visual areas. Yet visual perception of objects somehow reassembles the isolated fragments into complete objects. The problem of creating a unified percept from the responses of many separate neurons is referred to as "the binding problem." In the early 1990s, a theoretical solution emerged from the work of Wolf Singer and others, who found that neurons responding to portions of the same object fired synchronous action potentials. They suggested that correlated firing could be the mechanism for binding together responses from multiple, dispersed neurons.

The purpose of this assignment:

We will have a class discussion on synchrony and the visual binding problem on Thursday, May 4, 2006. To prepare for the discussion, you are asked to read the articles listed below and to write a thoughtful paper based on the readings. You may discuss the readings and the general topic freely with your classmates, but you must write your paper alone. Papers will be graded on the basis of their insight, thoughtfulness, and clarity. Since the purpose of the paper is to prepare the class for an informed discussion, it is important that both you and your paper be present in class. If you are absent or your paper is late, the paper will receive only a neutral (Pass/Fail) grade.

The readings:

The following readings address the binding problem. Papers 2, 4 and 5b contain experimental evidence that will form the heart of our discussion in class. Be prepared to examine their illustrations carefully and draw conclusions. These three experimental papers should be the heart of the paper that you write. The remaining papers will help you sort out your thinking. You do not have to address them specifically in your writing, but you will want to get ideas from them.

(1) Engel, A.K. et al. (1992) Temporal coding in the visual cortex: new vistas on integration in the nervous system. Trends in Neurosciences 15: 218-226 (excerpt, pages 218-222). [This link and most of the others are available only on the Smith campus.] Singer's proposal for synchrony as the solution to the binding problem. This excerpt explains the hypothesis but omits the experimental examples. You can also see the complete article.

(2) * Kreiter AK (2001) Functional implications of temporal structure in primate cortical information processing. Zoology (Jena) 104: 241-255 Experimental support for Singer's idea, presented more clearly than in the 1992 paper by one of that paper's co-authors.

(3) Shadlen, M.N. & Movshon, J.A. (1999) Synchrony unbound: a critical evaluation of the temporal binding hypothesis. Neuron 24: 67-77. A review skeptical of synchronous firing for visual binding. It is rambling, and not all of its arguments are of equal weight, but it is the paper most often cited in opposition to Singer's proposal. Read it to get its main, most important points.

(4) * Kiper, D.C., Gegenfurtner, K.R. and Movshon, J.A. (1996) Cortical oscillatory responses do not affect visual segmentation. Vision Research 36: 539-544. An experimental test of synchrony's role in binding. An animation of Figure 2 is on our Web site. It will help you understand the experiment. Does the experiment of Figure 2 deal a fatal blow to the synchrony hypothesis?

(5a) Stryker, MP (2001) Drums keep pounding a rhythm in the brain. Science 291: 1506-1507.

(5b) * Fries P, Reynolds JH, Rorie AE, Desimone R (2001) Modulation of oscillatory neuronal synchronization by selective visual attention. Science 291:1560-1563. An experiment that suggests a different role for synchrony. The general point is important for us. Don't get overly tangled in the experimental details, but do try to understand them. We'll discuss them briefly in class. The Perspective by Stryker gives a useful context for the paper and the question we are discussing.

A page of color figures from the papers is also available (Smith campus only).


Your paper and the class discussion:


Write a 5-page paper on the visual binding problem, paying special attention to the experimental evidence in readings 2, 4 and 5b. Use the other readings as background to help you understand and define the issues.

Depending on your own approach as a learner, you may write your paper at several different levels of complexity. Choose the approach that will be the most satisfying, beneficial, and genuine for you. Give your paper one of these titles:

(a) Evidence for and against the role of synchrony in visual binding. Explain the visual binding problem, and then describe and analyze the experiments in readings 2, 4 and 5b in the context of what they show about binding.

(b) An analysis of the visual binding problem and the role of synchronous firing. Consider the experimental evidence, but also add criticism and support based on the arguments advanced in the other papers. For example, does synchrony explain how grouping occurs? If it doesn't, can it create binding?

(c) Resolving the controversy about synchronous firing in visual binding. Enclose your discussion of the evidence in an analytical structure that tries to resolve the opposing views about synchrony and the binding problem. There are many ways of creating an analytical structure, but one example might be: Does synchrony occur in V1 and other visual areas, and is it associated with perceptual grouping? Does forcing synchrony in V1 (Kiper et al.) adequately test the binding hypothesis, and is it a fatal test? Is there another possible role for synchrony in perception? Again, you should feel free to create your own analytical structure.

In writing your paper, be careful to translate ideas from the readings into your own words. Cite the source of major ideas, but in a way that doesn't litter your paper with citations. In citing the articles, use the style of Science and Annual Reviews in which a number in parentheses [eg, (3)] refers to an item in the bibliography. Since we all have the numbered bibliography given above, you do not need to include a bibliography in your paper. The page on Tips for Writing in Neuroscience may be helpful to you.