2026-03-12T17:17:17Z https://ir.soken.ac.jp/oai

oai:ir.soken.ac.jp:00004091 2023-06-20T15:14:37Z 2:430:22

Localization of regions activated by surface gloss in macaque visual cortex using fMRI Localization of regions activated by surface gloss in macaque visual cortex using fMRI 岡澤, 剛起 オカザワ, ゴウキ OKAZAWA, Gouki 総合研究大学院大学 博士（理学） The surface properties of objects, such as gloss, transparency, and texture, provide important information about the material characteristics of objects in our visual environment. Previous psychophysical studies have revealed that humans can correctly estimate surface properties under various environments. Some recent studies also suggest that humans may utilize simple image statistics to extract the information regarding surface properties. Recently, to uncover neural mechanisms underlying perception of surface properties, some researchers have started to examine brain regions processing surface properties in humans using functional magnetic resonance imaging (fMRI) and have found that higher order visual areas in the ventral visual pathway are responsive to surface properties. To fully understand the neuronal processing, physiological studies using non-human primates are indispensable. Previous imaging and electrophysiological studies have shown that there are cortical regions selectively responding to object shapes, colors, faces etc. in the macaque visual cortex. However, because there have been few reports on the neuronal responses to surface properties in the macaque, we still lack information about where and how surface properties are processed. Thus, in this study, I used functional magnetic resonance imaging (fMRI) to examine the cortical responses to surface properties in the macaque visual cortex. Among various surface properties observed in the real world, I focused on surface gloss which is one of the basic surface properties that can be defined by surface reflectances. To find brain regions responsive to surface gloss, I generated images of glossy and matte objects using computer graphics. I also prepared scrambled images for controls of local spatial patterns by locally randomizing the luminance phases of the images with glossy and matte objects. In total, four conditions, i.e. gloss (G), matte (M), scrambled gloss (SG), and scrambled matte (SM), were prepared. I trained two awake macaque monkeys, whose heads were rigidly fixed by headpost, to fixate on a central fixation spot on the screen in the MRI scanner while the images for each condition were presented. In experiment 1, I contrasted the responses to glossy images with those to matte and scrambled images by using a conjunction analysis (G > M & G > SG & G > SM). Activation was observed along the ventral visual pathway, including V1, V2, V3, V4, and posterior and central regions in the inferior temporal (IT) cortex. In experiment 2, to dissociate the responses to contrasts and gloss, I manipulated the contrasts of images to generate high (H) and low (L) contrast images in both the gloss (G) and scrambled gloss (S) conditions. By computing the effect of gloss on the cortical responses irrelevant to the contrast levels (HG + LG > HS + LS), I found that the responses of these regions were actually modulated by surface gloss and could not be explained by the global contrasts. In the IT cortex, it has been shown that there are regions specialized for individual categories such as faces and objects. Because I found multiple gloss responsive regions in the IT cortex, in experiment 3, I examined the spatial relationships between the face/object responsive regions and the gloss responsive regions observed in the IT cortex. To this end, I conducted a face/object localizer experiment with the same monkeys used in experiment 1 and 2. I found that, although there were partial overlaps, the responses to gloss were distinct from those to faces and objects in the IT cortex. I also confirmed that responses to glossy images were not observed in higher order areas in the dorsal visual pathway (MT+ and intraparietal sulcus), suggesting that the surface gloss is predominantly processed in the ventral visual pathway at least in the passive viewing condition. In summary, these results suggest that image features related to glossy surface are processed along the ventral visual pathway from V1 to specific regions in the IT cortex. This is consistent with previous human fMRI experiments that showed surface properties are processed in the ventral visual pathway. Because the responses to glossy images could not be explained by the contrasts of images, other image features specifically related to surface gloss would be processed in these areas. In the IT cortex, because the gloss responsive regions were distinct from the face and object responsive regions, specialized neural substrates may exist to process surface properties of objects. 総研大甲第1611号 thesis 2013-03-22 application/pdf application/pdf https://ir.soken.ac.jp/record/4091/files/甲1611_要旨.pdf https://ir.soken.ac.jp/record/4091/files/学位論文.pdf https://ir.soken.ac.jp/records/4091 eng