Amanda Ellison

Complementary localization and lateralization of orienting and motor attention

It is widely agreed that the right posterior parietal cortex has a preeminent role in visuospatial and orienting attention. A number of lines of evidence suggest that although orienting and the preparation of oculomotor responses are dissociable from each other, the two are intimately related. If this is true, then it should be possible to identify other attentional mechanisms tied to other response modalities. We used repetitive transcranial magnetic stimulation (rTMS) to demonstrate the existence of a distinct anterior parietal mechanism of motor attention. The critical area for motor attention is anterior to the one concerned with orienting, and it is lateralized to the left hemisphere in humans.

Task–specific impairments and enhancements induced by magnetic stimulation of human visual area V5

Transcranial magnetic stimulation (TMS) can be used to simulate the effects of highly circumscribed brain damage permanently present in some neuropsychological patients, by reversibly disrupting the normal functioning of the cortical area to which it is applied. By using TMS we attempted to recreate deficits similar to those reported in a motion–blind patient and to assess the specificity of deficits when TMS is applied over human area V5. We used six visual search tasks and showed that subjects were impaired in a motion but not a form ‘pop–out’ task when TMS was applied over V5. When motion was present, but irrelevant, or when attention to colour and form were required, TMS applied to V5 enhanced performance. When attention to motion was required in a motion––form conjunction search task, irrespective of whether the target was moving or stationary, TMS disrupted performance. These data suggest that attention to different visual attributes involves mutual inhibition between different extrastriate visual areas.

The role of the parietal cortex in visual attention - hemispheric asymmetries and the effects of learning: a magnetic stimulation study

Our previous studies of the role of the parietal cortex in visual learning and attention showed that the right parietal cortex is required for normal performance on conjunction visual search tasks but that its role depends on whether subjects are naive or trained on the task. Here we extend these findings in two Experiments. Experiment 1 shows that magnetic stimulation of the left parietal cortex also impairs performance (measured as reaction time) on conjunction visual search tasks, but only when the target is present in the right (contralateral) visual field. Stimulation of the same region on a feature detection task speeds up performance significantly when the target is in the left (ipsilateral) visual field. Experiment 2 explores further the role of the right parietal cortex in learning conjunction search tasks. Stimulation of the right parietal cortex in subjects who had already trained on some visual search tasks did not impair performance on a novel motion/form conjunction task even though the search was clearly serial. Stimulation of area V5, however, severely disrupted performance on the same task. These data indicate that the role of the parietal cortex may change much earlier in the course of training than initially thought.

The role of V5/MT+ in the control of catching movements: an rTMS study.

Milner and Goodale described a model which distinguishes between two visual streams in the brain. It is claimed that the ventral stream serves object recognition (i.e. vision for perception), and the dorsal streams provides visual information for the guidance of action (i.e. vision for action). This model is supported by evidence from the domain of spatial vision, but it remains unclear how motion vision fits into that model. More specifically, it is unclear how the motion complex V5/MT contributes to vision for perception and vision for action. We addressed this question in an earlier study with the V5-lesioned patient LM. Can a motion-blind patient reach for moving objects? We found that she is not only impaired in perceptual tasks but also in catching, suggesting a role for V5/MT+ in vision for both perception and action. However, LMs lesion goes beyond V5/MT+ into more dorsal regions. It is thus possible, that the catching deficit was not produced by damage to V5/MT+ itself. In this case, one would expect that selective interference with V5/MT+ would have no effect on catching. In the present study we tested this prediction by applying rTMS over V5/MT+ of the left hemisphere while healthy subjects were either performing a catching or a reaching task. We found that V5-TMS reduced the speed of the catching but not the reaching response. These results confirm that V5/MT+ is not only involved in perceptual but also in visuomotor tasks.

The parietal cortex in visual search: a visuomotor hypothesis

Publisher Summary This chapter examines whether right posterior parietal cortex (rPPC) is important in any difficult visual search task irrespective of the need for feature binding. The chapter questions the prevailing view that rPPC makes its contribution only in relation to the visual aspects of search. The motivation for raising this question lies in the anatomy and physiology of the PPC. It is poised between the visual and motor cortices. Physiologically, PPC neurons do not posses the receptive field properties that would be consistent with a higher visuo–visual role. Thus, the hypothesis that the contribution of rPPC to search lies in visuo–motor transformations is proposed. To discriminate between the visuo–visual and visuo–motor accounts of the role of PPC in search, repetitive transcranial magnetic stimulation (rTMS) is used to selectively disrupt visual search performance in four experiments. First, the difficulty of feature tasks that did not require binding and conjunction tasks that did is manipulated and then the spatial requirements of target detection, the set size to be searched, and finally the visuomotor requirements of the task are manipulated.

The role of transcranial magnetic stimulation (TMS) in studies of vision, attention and cognition.

Transcranial magnetic stimulation (TMS) can be conceptualized as a virtual lesion technique, capable of disrupting organized cortical activity, transiently and reversibly. The technique combines good spatial and temporal resolution and, moreover, because it represents an interference technique, can be said to have excellent functional resolution. The following is a review and discussion of the contribution which TMS has made to the study of vision, attention, development and plasticity and speech and language.

Visual Exploration Training Is No Better than Attention Training for Treating Hemianopia.

Patients with homonymous visual field defects experience disabling functional impairments as a consequence of their visual loss. Compensatory visual exploration training aims to improve the searching skills of these patients in order to help them to cope more effectively. However, until now the efficacy of this training has not been compared to that of a control intervention. Given that exploration training uses the visual search paradigm, which is known to require visual attention, in this study the efficacy of the technique was compared with training that requires visual attention but not exploration. Participants completed either exploration training (n = 21), or attention training followed by exploration training (n = 21). Assessment of the visual field, visual search, reading and activities of daily living were performed before and after each intervention that the participants completed. The results revealed that both the exploration training and the attention training led to significant improvements in most of the visual tasks. For most of the tasks exploration training did not prove superior to attention training, and for reading both types of intervention failed to yield any benefits. The results indicate that attention plays a large role in the rehabilitation of homonymous visual field defects.

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

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 visuo-spatial 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.

Auditory verbal hallucinations as atypical inner speech monitoring, and the potential of neurostimulation as a treatment option

Highlights • We discuss ‘inner speech’ theories of auditory verbal hallucinations.• Atypical self-monitoring may lead to the experience of inner speech as external.• We summarize research into the use of neurostimulation to treat hallucinations.• Effects of neurostimulation may be due to modulation of self-monitoring networks.

Both egocentric and allocentric cues support spatial priming in visual search

The perception-action model proposes that vision for perception and vision for action are subserved by two separate cortical systems, the ventral and dorsal streams, respectively [Milner, A. D., & Goodale, M. A. (1995). The visual brain in action (1st ed.). Oxford: Oxford University Press; Milner, A. D., & Goodale, M. A. (2006). The visual brain in action (2nd ed.). Oxford: Oxford University Press Inc.]. The dorsal stream codes spatial information egocentrically, that is, relative to the observer. Egocentric representations are argued to be highly transient; therefore, it might be expected that egocentric information cannot be used for spatial memory tasks, even when the visual information only needs to be retained for a few seconds. Here, by applying a spatial priming paradigm to a visual search task, we investigated whether short-term spatial memory can use egocentric information. Spatial priming manifests itself in speeded detection times for a target when that target appears in the same location it previously appeared in. Target locations can be defined in either egocentric or allocentric (i.e. relative to other items in the display) frames of reference; however, it is unclear which of these are used in spatial priming, or if both are. Our results show that both allocentric and egocentric cues were used in spatial priming, and that egocentric cues were in fact more effective than allocentric cues for short-term priming. We conclude that egocentric information can persist for several seconds; a conclusion which is at odds with the assumption of the perception-action model that egocentric representations are highly transient.