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Christina Konen, Mark Pinsk, Michael Arcaro, Sabine Kastner; Object representations in the dorsal pathway: fMRI adaptation effects in macaque posterior parietal cortex. Journal of Vision 2008;8(6):493. doi: 10.1167/8.6.493.
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The visual system is divided into two separate pathways, which are specialized for functionally distinct tasks (Ungerleider & Mishkin 1982). The dorsal stream is directed into the posterior parietal cortex (PPC) and is associated with visually guided action, while the ventral pathway is directed into the temporal cortex and is involved in object recognition. Using fMRI-adaptation under passive viewing conditions, we previously reported object-selectivity in two topographically organized areas in human PPC (Konen & Kastner 2008). Electrophysiological studies in non-human primates have shown shape-selectivity in neurons of the lateral intraparietal (LIP) area (Sereno & Maunsell 1998). Here, we used fMRI-adaptation in monkeys in order to investigate object-selectivity at a larger scale in PPC. The monkeys were trained to maintain fixation while passively viewing geometric objects such as 2D-objects. At least two areas along the intraparietal sulcus exhibited object adaptation effects, i.e. the signal was reduced when identical objects were presented repetitively compared to an equivalent number of non-repeated objects. One area was located in the lateral bank (LIP) and the other area was located ventral (VIP) in the intraparietal sulcus. The response profiles found in these areas were similar to those in TEO, an area of the ventral stream thought to be critical for object recognition. Taken together, our results indicate object-selectivity in more than just one area of monkey PPC. Importantly, the dorsal object responses were found under passive viewing conditions and thus independent of a behavioral context that required action planning. Furthermore, the findings were strikingly similar as compared to human PPC.
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