Lui L L, Bourne J A, Rosa M G P
Department of Physiology, Monash University, 3800 Clayton, VIC, Australia.
Exp Brain Res. 2005 Mar;162(1):100-8. doi: 10.1007/s00221-004-2113-9. Epub 2004 Oct 23.
In order to investigate the neural processes underlying figure-ground segregation on the basis of motion, we studied the responses of neurones in the second visual area (V2) of marmoset monkeys to stimuli that moved against dynamic textured backgrounds. The stimuli were either "solid" bars, which were uniformly darker or lighter than the background's average, or kinetic ("camouflaged") bars, formed by textural elements that matched the spatial and temporal modulation of the background. Camouflaged bars were rendered visible only by the coherent motion of their textural elements. Using solid bars, we subdivided the population of marmoset V2 neurones into motion-selective (uni- and bi-directional units, 73.3% of the sample) and weakly-biased (26.7%) subpopulations. The motion selective subpopulation was further subdivided into cue-invariant neurones (units which demonstrated a similar selectivity for the direction of motion of the solid and camouflaged bars) and non-cue-invariant neurones (units which showed selectivity to the direction of motion of solid bars, but had weak or pandirectional responses to camouflaged bars). Cells with cue-invariant responses to these stimuli were as common in V2 as in the primary visual area (V1; approximately 40% of the population). In V2, neurones with cue-invariant and non-cue-invariant motion selectivity formed distinct populations in terms of classical response properties: cue-invariant neurones were characterized by a sharp axis of motion selectivity and extensive length summation, while the majority of non-cue-invariant neurones had broader motion selectivity and were end-stopped. In the light of previous studies, these different constellations of classical response properties suggest a correlation with more traditionally recognized categories of V2 units and modular compartments. The responses of V2 cells to kinetic stimuli were slightly delayed relative to their responses to luminance-defined stimuli.
为了研究基于运动的图形-背景分离背后的神经过程，我们研究了狨猴第二视觉区（V2）神经元对在动态纹理背景上移动的刺激的反应。刺激物要么是“实心”条，其比背景平均亮度均匀地更暗或更亮，要么是动态（“伪装”）条，由与背景的空间和时间调制相匹配的纹理元素形成。伪装条仅通过其纹理元素的连贯运动才可见。使用实心条，我们将狨猴V2神经元群体细分为运动选择性（单向和双向单元，占样本的73.3%）和弱偏向（26.7%）亚群。运动选择性亚群进一步细分为线索不变神经元（对实心条和伪装条的运动方向表现出相似选择性的单元）和非线索不变神经元（对实心条的运动方向表现出选择性，但对伪装条的反应较弱或呈全方向反应的单元）。对这些刺激具有线索不变反应的细胞在V2中与在初级视觉区（V1；约占群体的40%）中一样常见。在V2中，具有线索不变和非线索不变运动选择性的神经元在经典反应特性方面形成了不同的群体：线索不变神经元的特征是运动选择性轴尖锐且具有广泛的长度总和，而大多数非线索不变神经元具有更广泛的运动选择性且是末端抑制的。根据先前的研究，这些经典反应特性的不同组合表明与更传统认可的V2单元类别和模块化隔室相关。V2细胞对动态刺激的反应相对于它们对亮度定义刺激的反应略有延迟。
