Parallel processing of colors and faces in human ventral visual stream: functional evidence and technical challenges

摘要

Macaque monkeys possess a series of four color-biased regions arranged along the posterior-anterior axis of inferior temporal cortex, with each color region residing ventral and in close proximity to a face patch (Lafer-Sousa and Conway 2013). Moreover, face-selective patches appear to be more robust in the right hemisphere, and color-biased regions more robust in the left hemisphere. Color-biased regions and face patches are also found in humans (Bartels and Zeki 2000; Hadjikhani et al. 1998; Kanwisher 2010), but their spatial relationship to each other and their homology to those found in monkeys is unclear. To test the extent to which inferior temporal cortex is organized similarly in the two species, we sought to address three questions with fMRI experiments in humans: i) How far anteriorly do color-biased activations extend? ii) Do color-biased patches bear a systematic spatial relationship to face-selective patches? iii) Are color-biased regions left-lateralized? We scanned the same human subjects on contrasts designed to identify face-selective and color-biased cortex. Preliminary fMRI data from three subjects suggest that color-biased regions i) are found more anteriorly than previously reported in humans (N=2/3); ii) bear a systematic spatial relationship to face-selective regions; and iii) are somewhat left-lateralized. These results support prior indications of separate pathways for processing surface properties (texture and color) and geometric properties of objects in humans (Cavina-Pratesi et al. 2010). Definitively addressing the functional organization along the full anterior extent of the temporal lobe in humans will require overcoming the substantial susceptibility artifacts caused by the ear canals. Ongoing work is tackling these technical challenges, in an effort to determine the global organizational principles of the ventral visual pathway in humans, and the homologies between humans and macaque monkeys.