Abstract：
OBJECTIVE: To date the vast majority of research in the visual neurosciences have been forced to adopt a highly constrained perspective of the vision system in which stimuli are processed in an open-loop reactive fashion (i.e., abrupt stimulus presentation followed by an evoked neural response). While such constraints enable high construct validity for neuroscientific investigation, the primary outcomes have been a reductionistic approach to isolate the component processes of visual perception. In electrophysiology, of the many neural processes studied under this rubric, the most well-known is, arguably, the P300 evoked response. There is, however, relatively little known about the real-world corollary of this component in free-viewing paradigms where visual stimuli are connected to neural function in a closed-loop. While growing evidence suggests that neural activity analogous to the P300 does occur in such paradigms, it is an open question when this response occurs and what behavioral or environmental factors could be used to isolate this component.
METHODS: The current work uses convolutional networks to decode neural signals during a free-viewing visual search task in a closed-loop paradigm within an open-world virtual environment. From the decoded activity we construct fixation-locked response profiles that enable estimations of the variable latency of any P300 analogue around the moment of fixation. We then use these estimates to investigate which factors best reduce variable latency and, thus, predict the onset time of the response. We consider measurable, search-related factors encompassing top-down (i.e., goal driven) and bottom-up (i.e., stimulus driven) processes, such as fixation duration and salience. We also consider saccade size as an intermediate factor reflecting the integration of these two systems.
RESULTS: The results show that of these factors only saccade size reliably determines the onset time of P300 analogous activity for this task. Specifically, we find that for large saccades the variability in response onset is small enough to enable analysis using traditional ensemble averaging methods.
CONCLUSIONS: The results show that P300 analogous activity does occur during closed-loop, free-viewing visual search while highlighting distinct differences between the open-loop version of this response and its real-world analogue. The results also further establish saccades, and saccade size, as a key factor in real-world visual processing.
METHODS: The current work uses convolutional networks to decode neural signals during a free-viewing visual search task in a closed-loop paradigm within an open-world virtual environment. From the decoded activity we construct fixation-locked response profiles that enable estimations of the variable latency of any P300 analogue around the moment of fixation. We then use these estimates to investigate which factors best reduce variable latency and, thus, predict the onset time of the response. We consider measurable, search-related factors encompassing top-down (i.e., goal driven) and bottom-up (i.e., stimulus driven) processes, such as fixation duration and salience. We also consider saccade size as an intermediate factor reflecting the integration of these two systems.
RESULTS: The results show that of these factors only saccade size reliably determines the onset time of P300 analogous activity for this task. Specifically, we find that for large saccades the variability in response onset is small enough to enable analysis using traditional ensemble averaging methods.
CONCLUSIONS: The results show that P300 analogous activity does occur during closed-loop, free-viewing visual search while highlighting distinct differences between the open-loop version of this response and its real-world analogue. The results also further establish saccades, and saccade size, as a key factor in real-world visual processing.
摘要：
目的：迄今为止，视觉神经科学中的绝大多数研究都被迫采用视觉系统的高度约束视角，在视觉系统中，刺激以开环反应方式进行处理（即，突然的刺激表现，然后是诱发的神经反应）。虽然这样的约束使神经科学研究具有很高的结构效度，主要结果是采用简化方法来分离视觉感知的组成部分过程。在电生理学中，在这个主题下研究的许多神经过程中，最著名的是,可以说,P300引起的反应。有,然而,在视觉刺激以闭环方式与神经功能相连的自由观看范式中，对该组件的现实推论知之甚少。虽然越来越多的证据表明，类似于P300的神经活动确实发生在这样的范例中，当这种反应发生时，以及可以使用什么行为或环境因素来分离这种成分，这是一个悬而未决的问题。
方法：当前的工作使用卷积网络在开放世界虚拟环境中以闭环范式的自由观看视觉搜索任务期间解码神经信号。从解码的活动中，我们构建了固定锁定的响应曲线，可以估计固定时刻附近任何P300类似物的可变延迟。然后，我们使用这些估计来调查哪些因素最好地减少可变延迟，因此，预测反应的开始时间。我们认为是可衡量的，与搜索相关的因素包括自上而下(即，目标驱动)和自下而上(即，刺激驱动)过程，如固定持续时间和显着性。我们还认为扫视大小是反映这两个系统集成的中间因素。
结果：结果表明，在这些因素中，只有扫视大小可靠地决定了P300类似活动的开始时间。具体来说,我们发现，对于大型扫视，响应发作的变异性足够小，可以使用传统的集合平均方法进行分析。
结论：结果表明，P300类似活动确实发生在闭环过程中，免费观看视觉搜索，同时突出显示该响应的开环版本与其真实世界模拟之间的明显差异。结果还进一步建立了扫视，和扫视大小，作为现实世界视觉处理的关键因素。
方法：当前的工作使用卷积网络在开放世界虚拟环境中以闭环范式的自由观看视觉搜索任务期间解码神经信号。从解码的活动中，我们构建了固定锁定的响应曲线，可以估计固定时刻附近任何P300类似物的可变延迟。然后，我们使用这些估计来调查哪些因素最好地减少可变延迟，因此，预测反应的开始时间。我们认为是可衡量的，与搜索相关的因素包括自上而下(即，目标驱动)和自下而上(即，刺激驱动)过程，如固定持续时间和显着性。我们还认为扫视大小是反映这两个系统集成的中间因素。
结果：结果表明，在这些因素中，只有扫视大小可靠地决定了P300类似活动的开始时间。具体来说,我们发现，对于大型扫视，响应发作的变异性足够小，可以使用传统的集合平均方法进行分析。
结论：结果表明，P300类似活动确实发生在闭环过程中，免费观看视觉搜索，同时突出显示该响应的开环版本与其真实世界模拟之间的明显差异。结果还进一步建立了扫视，和扫视大小，作为现实世界视觉处理的关键因素。
