DCS Corporation, Alexandria, VA, USA.
DCS Corporation, Alexandria, VA, USA.
Neuroimage. 2024 Sep;298:120781. doi: 10.1016/j.neuroimage.2024.120781. Epub 2024 Aug 9.
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.
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.
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.
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.
迄今为止，视觉神经科学领域的绝大多数研究都被迫采用一种高度受限的视觉系统视角，其中刺激以开环反应的方式进行处理（即，突然呈现刺激，然后引发神经反应）。虽然这种限制使神经科学研究具有高度的构建有效性，但主要结果是采用一种还原论方法来分离视觉感知的组成过程。在电生理学中，在所研究的许多神经过程中，最著名的可以说是 P300 诱发反应。然而，在视觉刺激以闭环方式与神经功能连接的自由观看范式中，对于该成分的实际后果知之甚少。尽管越来越多的证据表明，类似 P300 的神经活动确实会在这种范式中发生，但仍不清楚该反应何时发生，以及哪些行为或环境因素可用于分离该成分。
当前的工作使用卷积网络来解码闭环范式中的自由观看视觉搜索任务期间的神经信号，该范式在开放式虚拟环境中。从解码的活动中，我们构建固定锁定响应曲线，从而能够估计任何 P300 模拟在固定时刻的可变潜伏期。然后，我们使用这些估计值来研究哪些因素可以最好地减少可变潜伏期，从而预测响应的起始时间。我们考虑了可测量的、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）的过程，例如固定持续时间和显着性。我们还考虑了眼跳大小作为反映这两个系统整合的中间因素。
结果表明，在这些因素中，只有眼跳大小才能可靠地确定该任务中 P300 类似活动的起始时间。具体来说，我们发现对于大的眼跳，响应起始的可变性足够小，足以使用传统的整体平均方法进行分析。
结果表明，在闭环、自由观看视觉搜索期间确实会发生 P300 类似活动，同时突出了这种反应的开环版本与其真实世界模拟之间的明显区别。结果还进一步确立了眼跳和眼跳大小作为真实世界视觉处理的关键因素。
