Zamboni Elisa, Makin Alexis D J, Bertamini Marco, Morland Antony B
University of Nottingham, School of Psychology, Nottingham, United Kingdom; University of York, Department of Psychology, York YO10 5DD, United Kingdom; University of York, York Neuroimaging Centre, York, United Kingdom.
University of Liverpool, Department of Psychological Sciences, Liverpool, United Kingdom.
Neuroimage. 2024 Aug 15;297:120760. doi: 10.1016/j.neuroimage.2024.120760. Epub 2024 Jul 26.
Identifying and segmenting objects in an image is generally achieved effortlessly and is facilitated by the presence of symmetry: a principle of perceptual organisation used to interpret sensory inputs from the retina into meaningful representations. However, while imaging studies show evidence of symmetry selective responses across extrastriate visual areas in the human brain, whether symmetry is processed automatically is still under debate. We used functional Magnetic Resonance Imaging (fMRI) to study the response to and representation of two types of symmetry: reflection and rotation. Dot pattern stimuli were presented to 15 human participants (10 female) under stimulus-relevant (symmetry) and stimulus-irrelevant (luminance) task conditions. Our results show that symmetry-selective responses emerge from area V3 and extend throughout extrastriate visual areas. This response is largely maintained when participants engage in the stimulus irrelevant task, suggesting an automaticity to processing visual symmetry. Our multi-voxel pattern analysis (MVPA) results extend these findings by suggesting that not only spatial organisation of responses to symmetrical patterns can be distinguished from that of non-symmetrical (random) patterns, but also that representation of reflection and rotation symmetry can be differentiated in extrastriate and object-selective visual areas. Moreover, task demands did not affect the neural representation of the symmetry information. Intriguingly, our MVPA results show an interesting dissociation: representation of luminance (stimulus irrelevant feature) is maintained in visual cortex only when task relevant, while information of the spatial configuration of the stimuli is available across task conditions. This speaks in favour of the automaticity for processing perceptual organisation: extrastriate visual areas compute and represent global, spatial properties irrespective of the task at hand.
识别和分割图像中的物体通常毫不费力，并且由于对称性的存在而变得更加容易：对称性是一种用于将来自视网膜的感官输入解释为有意义表征的知觉组织原则。然而，尽管成像研究显示人类大脑中纹外视觉区域存在对称性选择性反应的证据，但对称性是否会自动得到处理仍存在争议。我们使用功能磁共振成像（fMRI）来研究对两种对称性的反应和表征：反射对称和旋转对称。在与刺激相关（对称性）和与刺激无关（亮度）的任务条件下，向15名人类参与者（10名女性）呈现点阵图案刺激。我们的结果表明，对称性选择性反应从V3区域出现，并延伸到整个纹外视觉区域。当参与者进行与刺激无关的任务时，这种反应在很大程度上得以维持，这表明视觉对称性的处理具有自动性。我们的多体素模式分析（MVPA）结果扩展了这些发现，表明不仅对对称图案的反应的空间组织可以与非对称（随机）图案的反应的空间组织区分开来，而且反射对称和旋转对称的表征在纹外和物体选择性视觉区域也可以区分。此外，任务需求并不影响对称性信息的神经表征。有趣的是，我们的MVPA结果显示出一种有趣的分离：只有在与任务相关时，亮度（与刺激无关的特征）的表征才会保留在视觉皮层中，而刺激的空间配置信息在不同任务条件下都可以获得。这支持了知觉组织处理的自动性：纹外视觉区域计算并表征全局的空间属性，而与手头的任务无关。
