TMS can reveal contrasting functions of the dorsal and ventral visual processing streams

Abstract

. (2006) 'TMS can reveal contrasting functions of the dorsal and ventral visual processing streams.', Experimental brain research., 175 (4). pp. 618-625. Further information on publisher's website:https://doi.org/10.1007/s00221-006-0582-8Publisher's copyright statement:The original publication is available at www.springerlink.com Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract:In order to investigate the functional specificity of the dorsal and ventral visual processing steams we used transcranial magnetic stimulation (TMS) to briefly disrupt one or the other while subjects performed three tasks, involving discrimination of colour or shape or relative position. TMS was delivered over right posterior parietal cortex (PPC) or right lateral occipital (LO) cortex, regions known to have visuospatial and object processing properties respectively. LO but not PPC stimulation had a significant effect on reaction time when subjects were asked to make a discrimination of relative shape. PPC stimulation had a significant effect when subjects were asked to discriminate relative position of the same shapes. Stimulation of LO also lengthened reaction times on the position task. There were no effects of stimulation at either site on colour discrimination. Results are discussed within the framework of how the dorsal stream and ventral stream are dissociated following their damage in neurological patients and possible ways in which they may interact in the normal brain.

Time course of the involvement of the ventral and dorsal visual processing streams in a visuospatial task

“…The distance discrimination task directly replicated that used by Ellison & Cowey (2006), in which subjects had to judge which of two eccentric and identical green (11 cd/m 2 ) squares (1º x 1º in size, 5º to the left of the vertical midline) in the left hemifield was closer to a third identical square at the fixation point. One square (either the top or the bottom) was always 3º above or below the horizontal midline.…”

“…Two sites of stimulation were used, as by Ellison & Cowey (2006), a right ventral stream site (LO) and a right dorsal stream site (PPC). The dorsal site was chosen as an area of posterior parietal cortex (PPC) known to be involved in difficult conjunction visual search tasks that engage dorsal functions, and was identified by using a hunting procedure with the hard conjunction task, as described in Ashbridge et al (1997).…”

“…A previous transcranial magnetic stimulation (TMS) study (Ellison & Cowey, 2006) showed that both the dorsal and ventral cortical visual processing streams are involved in the processing of a task in which judgement of relative spatial position is required. In order to determine whether both streams are active in a parallel or serial manner, a double pulse TMS (20Hz) experiment was carried out to expose peaks of disruption, indicative of when each of the areas under investigation is most potently involved.…”

“…Avidan et al, 2003), although there is also evidence that both may be involved in the processing of a common task (Ellison & Cowey, 2006). This could indicate that some aspects of processing may be common to both streams and/or that there may be some interaction between the areas.…”

“…A previous paper (Ellison & Cowey, 2006) investigated this paradoxical dichotomy and discovered that there was a clear dissociation between the two streams when processing a shape task, with only right lateral occipital (LO) cortex being involved but not right posterior parietal cortex (PPC). However, counter-intuitively, both right LO and PPC were involved in the processing of a visuospatial task concerning the relative position of items in the frontal plane.…”