Cortical Networks of color/shape integration in grapheme/color synesthesia

描述（由申请人提供）：本提案旨在澄清字素-颜色联觉领域的两个核心问题。字素-颜色联觉者在观看或思考字母或数字等字素时，会经历一致和自动的颜色感知。核心问题是：1)字素-颜色联觉是否依赖于皮质区域之间的直接解剖投影或间接功能连接；2)联觉感知需要注意的程度。通感研究人员之间存在争议，其中一些人认为通感是由于早期发育过程中皮层修剪不完全造成的（例如，Maurer & Mondloch, 2005; Ramachandran & Hubbard, 2001），而另一些人则认为这是由于所有成年人通常被抑制的连接解除抑制造成的（例如，Grossenbacher & Lovelace, 2001）。越来越多的聚合功能和解剖学证据支持V4颜色选择视觉区域的参与（Hubbard, Arman, Ramachandran, & Boynton, 2005）；Weiss & Fink, 2008)以及下顶叶区域(顶叶内沟和角回，例如，（Rouw & Scholte, 2007; Nunn etal ., 2002）。同样，经颅磁刺激对角回的作用也会减少联觉知觉（Esterman, Verstynen, Ivry, & Robertson, 2006; Muggleton, Tsakanikos, Walsh, & Ward, 2007）。越来越多的证据一致表明，顶叶皮层和V4区都参与联觉知觉，但没有研究阐明这两个区域是如何相互作用的。为了理解联觉并解决关于额外连接或剥夺反馈（或两者都有）的持续争论，有必要绘制在联觉体验过程中涉及的功能回路，并通过视网膜定位定义的视觉皮层和解剖连接（DTI）区域的精确测量来共同记录它。我们将通过IPS定位V1的视觉区域，并测量这些区域的解剖和功能连通性。然后，使用从先前的联觉工作中发展出来的心理物理范式，我们将测试涉及字素-颜色联觉的皮质网络，并定量测量它们对注意力的依赖。更广泛地说，这一建议解决了感知绑定和特征整合的广泛问题，这是感知和认知神经科学和心理学领域的核心问题。联觉知觉不会取代它们的诱导物，而是作为一个额外的特征加入它们。这种联觉并发也很可能是由注意力介导的（见Mattingley， 2009年的评论）。正如Robertson（2003）所提出的那样，联觉为实验测试和分离知觉绑定机制和特征整合提供了一个理想的模型，因为主观联觉经验可以被测量为单个特征（即联觉颜色）的纯粹孤立的现象学经验，而所有刺激属性（即刺激亮度、颜色、大小、对象类型等）保持可测量的恒定。

DESCRIPTION (provided by applicant): This proposal seeks to clarify two central issues in the field of grapheme-color synesthesia. Grapheme-color synesthetes experience consistent and automatic color percepts when viewing or thinking of graphemes such as letters or numbers. The central issues are 1) whether grapheme-color synesthesia relies on direct anatomical projections or indirect functional connectivity between cortical regions and 2) to what extent synesthetic percepts require attention. A debate exists amongst synesthesia researchers, some of whom suggest that synesthesia results from incomplete cortical pruning during early development (e.g., Maurer & Mondloch, 2005; Ramachandran & Hubbard, 2001) and others who suggest it results from disinhibition of connections normally suppressed in all adults (e.g., Grossenbacher & Lovelace, 2001). A growing body of convergent functional and anatomical evidence supports the involvement of color-selective visual area V4 (Hubbard, Arman, Ramachandran, & Boynton, 2005); Weiss & Fink, 2008) and also inferior parietal areas (intraparietal sulcus and angular gyrus, e.g., (Rouw & Scholte, 2007; Nunn et al., 2002). Likewise, TMS to the angular gyrus reliably diminishes synesthetic percepts (Esterman, Verstynen, Ivry, & Robertson, 2006; Muggleton, Tsakanikos, Walsh, & Ward, 2007). This growing corpus of evidence has consistently identified both parietal cortex and area V4 in synesthetic perception but no study has clarified how these two areas might interact if at all. To understand synesthesia and to resolve the ongoing debate of extra connections or disinherited feedback (or both) it is necessary to map the functional circuit involved during synesthetic experience and co-register it with accurate measurements of retinotopically defined areas of visual cortex and anatomical connectivity (DTI). We will retinotopically localize visual areas from V1 through IPS and measure both anatomical and functional connectivity within these regions. Then, using a psychophysical paradigm developed from previous work on synesthesia, we will test the cortical networks involved in grapheme-color synesthesia and quantitatively measure their dependence on attention. More generally, this proposal addresses the broad issues of perceptual binding and feature integration, core issues in the field of perception and cognitive neuroscience and psychology. Synesthetic percepts do not replace their inducers and instead are added to them as an extra feature. This synesthetic concurrent is also most likely mediated by attention (see Mattingley, 2009 for a review). As suggested by Robertson (2003), synesthesia offers an ideal model for experimentally testing and isolating perceptual binding mechanisms and feature integration because a subjective synesthetic experience can be measured as a purely isolated phenomenological experience of a single feature (i.e., synesthetic color) while all stimulus properties (i.e., the stimulus luminance, color, size, object type, etc.) remain measurably constant.