Zaksas D, Bisley J W, Pasternak T
Department of Neurobiology and Anatomy and Center for Visual Science, University of Rochester, New York 14642, USA.
J Neurophysiol. 2001 Aug;86(2):912-21. doi: 10.1152/jn.2001.86.2.912.
We asked if the information about stimulus motion used in a visual working-memory task is localized in space. Monkeys compared the directions of two moving random-dot stimuli, sample and test, separated by a temporal delay and reported whether the stimuli moved in the same or in different directions. By presenting the two comparison stimuli in separate locations in the visual field, we determined whether information about stimulus direction was spatially localized during the storage and retrieval/comparison components of the task. Two psychophysical measures of direction discrimination provided nearly identical estimates of the critical spatial separation between sample and test stimuli that lead to a loss in threshold. Direction range thresholds measured with dot stimuli consisting of a range of local directional vectors were affected by spatial separation when a random-motion mask was introduced during the delay into the location of the upcoming test. The selective masking at the test location suggests that the information about the remembered direction was localized and available at that location. Direction difference thresholds, measured with coherently moving random dots, were also affected by separation between the two comparison stimuli. The separation at which performance was affected in both tasks increased with retinal eccentricity in parallel with the increase in receptive-field size in neurons in cortical area MT. The loss with transfer of visual information between different spatial locations suggests a contribution of cortical areas with localized receptive fields to the performance of the memory task. The similarity in the spatial scale of the storage mechanism derived psychophysically and the receptive field size of neurons in area MT suggest that MT neurons are central to this task.
我们探究了视觉工作记忆任务中所使用的关于刺激运动的信息是否在空间上具有定位性。猴子比较两个移动的随机点刺激（样本和测试刺激）的方向，这两个刺激之间存在时间延迟，猴子要报告这两个刺激的运动方向是相同还是不同。通过在视野中的不同位置呈现这两个比较刺激，我们确定了在任务的存储以及检索/比较阶段，关于刺激方向的信息在空间上是否具有定位性。两种方向辨别心理物理学测量方法得出了几乎相同的关键空间间隔估计值，该间隔是样本刺激和测试刺激之间导致阈值损失的间隔。当在延迟期间在即将到来的测试刺激的位置引入随机运动掩模时，由一系列局部方向矢量组成的点刺激所测量的方向范围阈值会受到空间间隔的影响。在测试位置的选择性掩蔽表明，关于记忆方向的信息在该位置具有定位性且可用。用连贯移动的随机点测量的方向差异阈值也受到两个比较刺激之间间隔的影响。在这两项任务中，影响表现的间隔随着视网膜离心率的增加而增加，这与皮层区域MT中神经元感受野大小的增加是平行的。视觉信息在不同空间位置之间传递时的损失表明，具有局部感受野的皮层区域对记忆任务的表现有贡献。从心理物理学得出的存储机制空间尺度与MT区域中神经元感受野大小的相似性表明，MT神经元对于这项任务至关重要。
