Download or read book Color and Motion Processing in Human Cortical Areas MT+, V4, and Vo Investigated by Online Repetitive Transcranial Magnetic Stimulation (TMS) written by Irem Önay and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The visual environment contains a vast amount of information which is encoded efficiently by the visual system through the use of segregated dorsal and ventral streams. This study investigates the interaction between selected areas in the parallel dorsal and ventral pathways with the use of online repetitive TMS. The effects of TMS on two psychophysical tasks were investigated: a global motion task directed at the specialties of dorsal area hMT+ and a color contrast task directed at the specialties of ventral areas VO and V4. In each case, TMS was applied to the selected areas and a control area (vertex). Regions of interest were localized using fMRI. As our global motion task, we used a two-interval speed discrimination task with achromatic random dot kinematograms (RDKs) as stimuli, in which subjects were presented with a reference stimulus in the first interval and a test stimulus in the second interval. Regions of interest were dorsal area hMT+ and ventral area V4. The color contrast discrimination task consisted of isoluminant red stationary RDKs masked by achromatic noise and a similar two-interval design. Regions of interest were ventral area VO and dorsal area hMT+. Tasks were performed without and with TMS. We developed a task using two reference stimuli to avoid learning effects to replace the single fixed reference used in other studies. TMS was always applied during the second (test) interval. In the speed discrimination task, TMS was found to cause a perceived slowing of global motion stimuli, indicated by a significant increase in "test slower than reference" responses. This effect was not area-specific. Reaction times were longer with the TMS of hMT+ and shorter with the TMS of V4 compared to control, however, this difference did not reach significance. In the color contrast discrimination task, TMS did not have an effect on perceived contrast. Reaction times were longer with the TMS of VO and shorter with the TMS of hMT+ compared to control; again, this difference was non-significant. In conclusion, online rTMS was found to slow down motion perception. The trends seen in reaction times indicate a dissociation between dorsal and ventral areas and suggest that these areas exert a level of inhibition on each other. These findings provide insights into the working of dorsal and ventral streams in the visual system and pave the way for future studies." --