Psychological Sciences Research Institute (IPSY), UC Louvain, Louvain-la-Neuve, Belgium.
Institute of Neuroscience (IONS), UC Louvain, Brussels, Belgium.
PLoS One. 2019 Jan 25;14(1):e0210503. doi: 10.1371/journal.pone.0210503. eCollection 2019.
Vision begins with the encoding of contrast at specific orientations. Several works showed that humans identify their conspecifics best based on the horizontally-oriented information contained in the face image; this range conveys the main morphological features of the face. In contrast, the vertical structure of the eye region seems to deliver optimal cues to gaze direction. The present work investigates whether the human face processing system flexibly tunes to vertical information contained in the eye region when processing gaze direction. Alternatively, face processing may invariantly rely on the horizontal range, supporting the domain specificity of orientation tuning for faces and the gateway role of horizontal content to access any type of facial information. Participants judged the gaze direction of faces staring at a range of lateral positions. They additionally performed an identification task with upright and inverted face stimuli. Across tasks, stimuli were filtered to selectively reveal horizontal (H), vertical (V), or combined (HV) information. Most participants identified faces better based on horizontal than vertical information confirming the horizontal tuning of face identification. In contrast, they showed a vertically-tuned sensitivity to gaze direction. The logistic functions fitting the "left" and "right" response proportion as a function of gaze direction were indeed steeper when based on vertical than on horizontal information. The finding of a vertically-tuned processing of gaze direction favours the hypothesis that visual encoding of face information flexibly switches to the orientation channel carrying the cues most relevant to the task at hand. It suggests that horizontal structure, though predominant in the face stimulus, is not a mandatory gateway for efficient face processing. The present evidence may help better understand how visual signals travel the visual system to enable rich and complex representations of naturalistic stimuli such as faces.
视觉始于特定方向对比度的编码。有几项研究表明，人类根据面部图像中包含的水平方向信息识别同类个体的能力最佳；这个范围传达了面部的主要形态特征。相比之下，眼部区域的垂直结构似乎为注视方向提供了最佳线索。本研究旨在探讨当处理注视方向时，人类面部处理系统是否灵活地调整眼部区域的垂直信息。或者，面部处理可能不变地依赖于水平范围，支持面向调谐的领域特异性和水平内容的门户作用，以访问任何类型的面部信息。参与者判断注视着一系列侧面位置的面孔的注视方向。他们还使用直立和倒置的面孔刺激执行了识别任务。在所有任务中，刺激都经过过滤，以选择性地揭示水平（H）、垂直（V）或组合（HV）信息。大多数参与者基于水平信息识别面孔的能力优于垂直信息，证实了面孔识别的水平调谐。相比之下，他们对注视方向表现出垂直调谐的敏感性。当基于垂直信息而非水平信息拟合“左”和“右”响应比例作为注视方向函数的逻辑函数时，其斜率确实更大。注视方向的垂直调谐处理的发现有利于这样一种假设，即面部信息的视觉编码灵活地切换到携带与手头任务最相关线索的方向通道。这表明，尽管水平结构在面部刺激中占主导地位，但它不是高效面部处理的强制性门户。现有证据可能有助于更好地理解视觉信号如何在视觉系统中传播，以实现对自然刺激（如面部）的丰富而复杂的表示。
