@misc{oai:ir.soken.ac.jp:00004091,
 author = {岡澤, 剛起 and オカザワ, ゴウキ and OKAZAWA, Gouki},
 month = {2016-02-26, 2013-11-26},
 note = {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},
 title = {Localization of regions activated by surface gloss in macaque visual cortex using fMRI},
 year = {}
}