Visual Selection and Posterior Parietal Cortex: Effects of Repetitive Transcranial Magnetic Stimulation on Partial Report Analyzed by Bundesen's Theory of Visual Attention
Abstract:Posterior parietal cortex (PPC) may contribute to visual selection by exerting top-down influences on visual processing. To seek direct evidence for this, we used 10 Hz repetitive transcranial magnetic stimulation (rTMS) over right or left PPC in nine healthy volunteers during a partial (selective) report task that allows quantitative assessment of top-down control and other parameters. Participants reported digits in a relevant color ("targets") but not those in an irrelevant color ("nontargets") from a brief… Show more
“…This allowed separate parameters concerning top-down control, sensory effectiveness, and attentional weight to be measured within a single visual task (see Materials and Methods, Data analysis, below). We have previously examined the impact of parietal TMS on Bundesen parameters in this task (Hung et al, 2005). Applying TMS to the left or right human FEF permitted a new comparison between the frontal effects studied here and the parietal effects reported previously (Hung et al, 2005) to further specify the distinct roles of different nodes in the network modulating visual processing.…”
Section: Introductionmentioning
confidence: 77%
“…For blocks with TMS, magnetic stimulation was delivered synchronously with the onset of the stimulus array to be reported (during the partial-report or the color-report control task) in a five-burst train at 10 Hz for 500 ms, with a fixed intensity of 60% of maximum stimulator output (corresponding to 86 -115% of the intensity of the resting motor threshold for participants in this experiment, when the same TMS stimulator was applied over M1 outside the experiment). Previous studies have shown that, with these stimulation parameters, such bursts of TMS are able to induce transient disruptions of neural processing in FEF (Muggleton et al, 2003;O'Shea et al, 2004; for effects of the same TMS protocol in the current paradigm when applied over PPC instead of FEF, see Hung et al, 2005).…”
Section: Methodsmentioning
confidence: 99%
“…The general procedures were modified from a previous study (Duncan et al, 1999) that applied Bundesen's (1990) TVA approach to study effects of permanent brain damage in patients. The exact procedures adhered to those used in our previous parietal TMS study of healthy volunteers (Hung et al, 2005) for the selective partialreport paradigm, being identical to that study in all respects except for the new TMS sites used here [now over left or right FEF, rather than over left or right posterior parietal cortex (PPC)]. Our use of equivalent methods, including identical TMS parameters except for the changed TMS sites, allowed a direct comparison of the present new FEF effects to the PPC effects found previously.…”
Section: Methodsmentioning
confidence: 99%
“…Our use of equivalent methods, including identical TMS parameters except for the changed TMS sites, allowed a direct comparison of the present new FEF effects to the PPC effects found previously. Given the similarity in methods, we summarize the protocol only briefly here; see Hung et al (2005) for further details.…”
Section: Methodsmentioning
confidence: 99%
“…To ensure that any TMS effects on selection by task-relevant color in the above partial-report task could not be due to any effects on gross color perception, we also tested a control task requiring report of stimulus color rather than digit identity (Duncan et al, 1999;Habekost and Bundesen, 2003;Hung et al, 2005). The stimulus array now comprised a single digit in red or green at one of the four possible positions (hence eight display types); these positions were identical to those used in the partial-report task.…”
“…This allowed separate parameters concerning top-down control, sensory effectiveness, and attentional weight to be measured within a single visual task (see Materials and Methods, Data analysis, below). We have previously examined the impact of parietal TMS on Bundesen parameters in this task (Hung et al, 2005). Applying TMS to the left or right human FEF permitted a new comparison between the frontal effects studied here and the parietal effects reported previously (Hung et al, 2005) to further specify the distinct roles of different nodes in the network modulating visual processing.…”
Section: Introductionmentioning
confidence: 77%
“…For blocks with TMS, magnetic stimulation was delivered synchronously with the onset of the stimulus array to be reported (during the partial-report or the color-report control task) in a five-burst train at 10 Hz for 500 ms, with a fixed intensity of 60% of maximum stimulator output (corresponding to 86 -115% of the intensity of the resting motor threshold for participants in this experiment, when the same TMS stimulator was applied over M1 outside the experiment). Previous studies have shown that, with these stimulation parameters, such bursts of TMS are able to induce transient disruptions of neural processing in FEF (Muggleton et al, 2003;O'Shea et al, 2004; for effects of the same TMS protocol in the current paradigm when applied over PPC instead of FEF, see Hung et al, 2005).…”
Section: Methodsmentioning
confidence: 99%
“…The general procedures were modified from a previous study (Duncan et al, 1999) that applied Bundesen's (1990) TVA approach to study effects of permanent brain damage in patients. The exact procedures adhered to those used in our previous parietal TMS study of healthy volunteers (Hung et al, 2005) for the selective partialreport paradigm, being identical to that study in all respects except for the new TMS sites used here [now over left or right FEF, rather than over left or right posterior parietal cortex (PPC)]. Our use of equivalent methods, including identical TMS parameters except for the changed TMS sites, allowed a direct comparison of the present new FEF effects to the PPC effects found previously.…”
Section: Methodsmentioning
confidence: 99%
“…Our use of equivalent methods, including identical TMS parameters except for the changed TMS sites, allowed a direct comparison of the present new FEF effects to the PPC effects found previously. Given the similarity in methods, we summarize the protocol only briefly here; see Hung et al (2005) for further details.…”
Section: Methodsmentioning
confidence: 99%
“…To ensure that any TMS effects on selection by task-relevant color in the above partial-report task could not be due to any effects on gross color perception, we also tested a control task requiring report of stimulus color rather than digit identity (Duncan et al, 1999;Habekost and Bundesen, 2003;Hung et al, 2005). The stimulus array now comprised a single digit in red or green at one of the four possible positions (hence eight display types); these positions were identical to those used in the partial-report task.…”
Predictability in the visual environment provides a powerful cue for efficient processing of scenes and objects. Recently, studies have suggested that the directionality and magnitude of saccade curvature can be informative as to how the visual system processes predictive information. The present study investigated the role of the right posterior parietal cortex (rPPC) in shaping saccade curvatures in the context of predictive and non-predictive visual cues. We used an orienting paradigm that incorporated manipulation of target location predictability and delivered transcranial magnetic stimulation (TMS) over rPPC. Participants were presented with either an informative or uninformative cue to upcoming target locations. Our results showed that rPPC TMS generally increased saccade latency and saccade error rates. Intriguingly, rPPC TMS increased curvatures away from the distractor only when the target location was unpredictable and decreased saccadic errors towards the distractor. These effects on curvature and accuracy were not present when the target location was predictable. These results dissociate the strong contingency between saccade latency and saccade curvature and also indicate that rPPC plays an important role in allocating and suppressing attention to distractors when the target demands visual disambiguation. Furthermore, the present study suggests that, like the frontal eye fields, rPPC is critically involved in determining saccade curvature and the generation of saccadic behaviors under conditions of differing target predictability.
Previous neuroimaging studies have shown that working memory load has marked effects on regional neural activation. However, the mechanism through which working memory load modulates brain connectivity is still unclear. In this study, this issue was addressed using dynamic causal modeling (DCM) based on functional magnetic resonance imaging (fMRI) data. Eighteen normal healthy subjects were scanned while they performed a working memory task with variable memory load, as parameterized by two levels of memory delay and three levels of digit load (number of digits presented in each visual stimulus). Eight regions of interest, i.e., bilateral middle frontal gyrus (MFG), anterior cingulate cortex (ACC), inferior frontal cortex (IFC), and posterior parietal cortex (PPC), were chosen for DCM analyses. Analysis of the behavioral data during the fMRI scan revealed that accuracy decreased as digit load increased. Bayesian inference on model structure indicated that a bilinear DCM in which memory delay was the driving input to bilateral PPC and in which digit load modulated several parieto-frontal connections was the optimal model. Analysis of model parameters showed that higher digit load enhanced connection from L PPC to L IFC, and lower digit load inhibited connection from R PPC to L ACC. These findings suggest that working memory load modulates brain connectivity in a parieto-frontal network, and may reflect altered neuronal processes, e.g., information processing or error monitoring, with the change in working memory load.
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