James W. Bisley

Attention, Intention, and Priority in the Parietal Lobe

For many years there has been a debate about the role of the parietal lobe in the generation of behavior. Does it generate movement plans (intention) or choose objects in the environment for further processing? To answer this, we focus on the lateral intraparietal area (LIP), an area that has been shown to play independent roles in target selection for saccades and the generation of visual attention. Based on results from a variety of tasks, we propose that LIP acts as a priority map in which objects are represented by activity proportional to their behavioral priority. We present evidence to show that the priority map combines bottom-up inputs like a rapid visual response with an array of top-down signals like a saccade plan. The spatial location representing the peak of the map is used by the oculomotor system to target saccades and by the visual system to guide visual attention.

Saccades, salience and attention: the role of the lateral intraparietal area in visual behavior.

Neural activity in the lateral intraparietal area (LIP) has been associated with attention to a location in visual space, and with the intention to make saccadic eye movement. In this study we show that neurons in LIP respond to recently flashed task-irrelevant stimuli and saccade targets brought into the receptive field by a saccade, although they respond much to the same stimuli when they are stable in the environment. LIP neurons respond to the appearance of a flashed distractor even when a monkey is planning a memory-guided delayed saccade elsewhere. We then show that a monkeys attention, as defined by an increase in contrast sensitivity, is pinned to the goal of a memory-guided saccade throughout the delay period, unless a distractor appears, in which case attention transiently moves to the site of the distractor and then returns to the goal of the saccade. LIP neurons respond to both the saccade goal and the distractor, and this activity correlates with the monkeys locus of attention. In particular, the activity of LIP neurons predicts when attention migrates from the distractor back to the saccade goal. We suggest that the activity in LIP provides a salience map that is interpreted by the oculomotor system as a saccade goal when a saccade is appropriate, and simultaneously is used by the visual system to determine the locus of attention.

Activity in the Lateral Intraparietal Area Predicts the Goal and Latency of Saccades in a Free-Viewing Visual Search Task

The purpose of saccadic eye movements is to facilitate vision, by placing the fovea on interesting objects in the environment. Eye movements are not made for reward, and they are rarely restricted. Despite this, most of our knowledge about the neural genesis of eye movements comes from experiments in which specific eye movements are rewarded or restricted. Such experiments have demonstrated that activity in the lateral intraparietal (LIP) area of the monkey correlates with the monkeys planning of a memory-guided saccade or deciding where, on the basis of motion information, to make a saccade. However, other experiments have shown that neural activity in LIP can easily be dissociated from the generation of saccadic eye movements, especially when sophisticated behavioral paradigms dissociate the monkeys locus of attention from the goal of an intended saccade. In this study, we trained monkeys to report the results of a visual search task by making a nontargeting hand movement. Once the task began, the monkeys were entirely free to move their eyes, and rewards were not contingent on the monkeys making specific eye movements. We found that neural activity in LIP predicted not only the goal of the monkeys saccades but also their saccadic latencies.

The role of the lateral intraparietal area of the monkey in the generation of saccades and visuospatial attention.

Abstract: The brain cannot monitor or react towards the entire world at a given time. Instead, using the process of attention, it selects objects in the world for further analysis. Neuronal activity in the monkey intraparietal area has the properties appropriate for a neuronal substrate of attention: instead of all objects being represented in the parietal cortex, only salient objects are. Such objects can be salient because of their physical properties (recently flashed objects or moving objects) or because they can be made important to the animal by virtue of a task. Although lateral intraparietal area (LIP) neurons respond through the delay period of a memory‐guided saccade, they also respond in an enhanced manner to distractors flashed during the delay period of a memory‐guided saccade being generated to a position outside the receptive field. This activity parallels the monkeys psychophysical attentional process: attention is ordinarily pinned at the goal of a memory‐guided saccade, but it shifts briefly to the locus of a task‐irrelevant distractor flashed briefly during the delay period and then returns to the goal. Although neurons in LIP have been implicated as being directly involved in the generation of saccadic eye movements, their activity does not predict where, when, or if a saccade will occur. The ensemble of activity in LIP, however, does accurately describe the locus of attention.

A rapid and precise on-response in posterior parietal cortex.

The activity of neurons in the lateral intraparietal area (LIP) of the monkey predicts the monkeys allocation of spatial attention. We show here that despite being relatively high within the visual hierarchy, neurons in LIP have extremely short and precise visual latencies. Mean latency was 45.2 msec; the timing precision of the onset response was usually better than 4 msec. The majority of neurons had a pause in response after an initial burst, followed by more sustained visual activity. Previous attention allocation had no effect on either the latency or magnitude of the initial burst, but produced clear effects on the magnitude of the later sustained activity. Together, these data indicate that the initial burst in LIP visual response reflects an uncontaminated sensory signal. Information about stimulus onset is transmitted rapidly through the visual system to LIP; the on-response has a higher speed and temporal precision than realized previously. This information could be used to orient attention to novel objects in the visual environment rapidly and reliably.

The neural basis of visual attention

Visual attention is the mechanism the nervous system uses to highlight specific locations, objects or features within the visual field. This can be accomplished by making an eye movement to bring the object onto the fovea (overt attention) or by increased processing of visual information in neurons representing more peripheral regions of the visual field (covert attention). This review will examine two aspects of visual attention: the changes in neural responses within visual cortices due to the allocation of covert attention; and the neural activity in higher cortical areas involved in guiding the allocation of attention. The first section will highlight processes that occur during visual spatial attention and feature‐based attention in cortical visual areas and several related models that have recently been proposed to explain this activity. The second section will focus on the parietofrontal network thought to be involved in targeting eye movements and allocating covert attention. It will describe evidence that the lateral intraparietal area, frontal eye field and superior colliculus are involved in the guidance of visual attention, and describe the priority map model, which is thought to operate in at least several of these areas.

Tactile Feedback Induces Reduced Grasping Force in Robot-Assisted Surgery

Robot-assisted minimally invasive surgery has gained widespread use over the past decade, but the technique is currently operated in the absence of haptic feedback during tissue manipulation. We have developed a complete tactile feedback system, consisting of a piezoresistive force sensor, control system, and pneumatic balloon tactile display, and mounted directly onto a da Vinci surgical robotic system. To evaluate the effect of tactile feedback on robotic manipulation, a group of novices (n = 16) and experts ( n = 4) were asked to perform three blocks of peg transfer tasks with the tactile feedback system in place. Force generated at the end-effectors was measured in all three blocks, but tactile feedback was active only during the middle block. All subjects used higher force when the feedback system was inactive. When active, subjects immediately used substantially less force and still maintained appropriate grip during the task. After the system was again turned off, grip force increased significantly to prefeedback levels. These results demonstrate that robotic manipulations without tactile feedback are done with more force than needed to grasp objects. Therefore, the addition of tactile feedback allows the surgeon to grasp with less force, and may improve control of the robotic system and handling of tissues and other objects.

A Haptic Feedback System for Lower-Limb Prostheses

A haptic feedback system has been developed to provide sensory information to patients with lower-limb prostheses or peripheral neuropathy. Piezoresistive force sensors were mounted against four critical contact points of the foot to collect and relay force information to a system controller, which in turn drives four corresponding pneumatically controlled balloon actuators. The silicone-based balloon actuators were mounted on a cuff worn on the middle thigh, with skin contacts on the posterior, anterior, medial, and lateral surfaces of the thigh. Actuator characterization and human perceptual testing were performed to determine the effectiveness of the system in providing tactile stimuli. The actuators were determined to have a monotonic input pressure-vertical deflection response. Six normal subjects wearing the actuator cuff were able to differentiate inflation patterns, directional stimuli and discriminate between three force levels with 99.0%, 94.8%, and 94.4% accuracy, respectively. With force sensors attached to a shoe insole worn by an operator, subjects were able to correctly indicate the movements of the operator with 95.8% accuracy. These results suggest that the pneumatic haptic feedback system design is a viable method to provide sensory feedback for the lower limbs.

One-Dimensional Dynamics of Attention and Decision Making in LIP

Where we allocate our visual spatial attention depends upon a continual competition between internally generated goals and external distractions. Recently it was shown that single neurons in the macaque lateral intraparietal area (LIP) can predict the amount of time a distractor can shift the locus of spatial attention away from a goal. We propose that this remarkable dynamical correspondence between single neurons and attention can be explained by a network model in which generically high-dimensional firing-rate vectors rapidly decay to a single mode. We find direct experimental evidence for this model, not only in the original attentional task, but also in a very different task involving perceptual decision making. These results confirm a theoretical prediction that slowly varying activity patterns are proportional to spontaneous activity, pose constraints on models of persistent activity, and suggest a network mechanism for the emergence of robust behavioral timing from heterogeneous neuronal populations.

A Multielement Tactile Feedback System for Robot-Assisted Minimally Invasive Surgery

A multi-element tactile feedback (MTF) system has been developed to translate the force distribution, in magnitude and position, from 3times2 sensor arrays on surgical robotic end-effectors to the fingers via 3times2 balloon tactile displays. High detection accuracies from perceptual tests (> 96%) suggest that MTF may be an effective means to improve robotic control.