- 「脳のセミナー」 special seminar ---

□□ 非線形動力学セミナー 日時： 10月29日（月） PM 1:30　(Mon. Oct. 29, 2007) 場所： ６号館２０２

担当： Ernst Niebur, Ph.D.（Johns Hopkins University）

題目： Binding and border-ownership: The neural basis of perceptual organization in extrastriate cortex

概要： Underlying the seemingly effortless perception of complex visual scenes are sophisticated neuronal computations that are necessary to extract information about the external world from an inherently ambiguous and frequently incomplete set of sensory inputs. One important component of this process is the organization of the visual scene into perceptual objects. At present, it is an unsolved question how the structure this imposes on the visual input is generated by the activity of neural assemblies. We study how neurons represent the assignment of figures elements (edges) to separate visual objects ('border ownership assignment') and how they represent the perceptual binding of different elements to a coherent visual object ('binding problem.')

It was recently found (Zhou et al, J Neurosci. 2000, 20:6594) that individual neurons in extrastriate cortex of awake behaving monkeys represent whether a local contrast edge in their receptive field is part of the visual foreground or the background. In other words, these neurons encode whether the edge is part of the border of one or two visual objects. We present a model of this border ownership coding based on dedicated neural circuits for contour grouping. The results are consistent with neurophysiological and psychophysical findings and the model makes predictions about the hypothetical grouping circuits and the role of feedback. Binding of visual objects has been proposed to be represented by correlated (synchronous) firing of neurons ('binding-by-synchrony hypothesis'). We test this hypothesis by studying responses of pairs of neurons from the visual cortex of macaques when they respond to stimuli that are either part of 1 figure (and thus supposed to be bound together) or two figures (and thus not bound). For each neuron we also determined its border ownership selectivity. In 32 pairs of cells studied we did not find any significant difference between the correlograms for the 1-figure and the 2-figure conditions. However, we found synchronization in the 20 ms range in cell pairs whose members were both border-ownership selective. This synchronization was absent in pairs in which only one member or none was border ownership selective. Because border ownership selectivity implies integration of image context, the observed association of inter-neuron synchronization with border ownership selectivity suggests that the synchronization arises from the connectivity in a network that integrates context information.

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島崎君のJohns Hopkins Univ.でのお師匠．来日にあわせて話して頂きました．

振動子の理論家で，バインディング問題に取り組んでおられます．１５年前に蔵本研に来られたそうです．篠本はそのときにはオックスフォードにいて会わなかったもようです．

アフターセミナーでは，彼がボートを所有しているという話題で盛り上がりました．

院生：「篠本さんもボートを買ったらどうですか」

篠本：「ぼくもボートを買いたいなあ．そのために，まず皆から募金を募ろう」．

彼からJohns Hopkins大学のグッズをもらった島崎君が「ああ，いい指導教官だ」というので，

篠本は「ぼくはあげないからね」と釘を刺しておきました．