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The term priority map is commonly used to describe a map of the visual scene, in which objects and locations are represented by their attentional priority, which itself is a combination of low-level salience and top-down control. The aim of this review is to examine how such a map may be represented at the neuronal level. We propose that there is not a single, common map in the brain, but that a number of cortical areas work together to generate the resultant behavior. Specifically, we suggest that the lateral intraparietal area (LIP) of posterior parietal cortex provides a simple representation of attentional priority, which remaps across saccades, so that there is an apparent allocentric map in a region with retinocentric encoding scheme. We propose that the frontal eye field (FEF) of prefrontal cortex receives the responses from LIP, but can suppress them to control the flow of eye movement behavior, and that the intermediate layers of the superior colliculus (SCi) reflect the final saccade goal. Together, these areas function to guide eye movements and may play a similar role in allocating covert visual attention.

BackgroundThe loss of tactile feedback in minimally invasive robotic surgery remains a major challenge to the expanding field. With visual cue compensation alone, tissue characterization via palpation proves to be immensely difficult. This work evaluates a bimodal vibrotactile system as a means of conveying applied forces to simulate haptic feedback in two sets of studies simulating an artificial palpation task using the da Vinci surgical robot.MethodsSubjects in the first study were tasked with localizing an embedded vessel in a soft tissue phantom using a single-sensor unit. In the second study, subjects localized tumor-like structures using a three-sensor array. In both sets of studies, subjects completed the task under three trial conditions: no feedback, normal force tactile feedback, and hybrid vibrotactile feedback. Recordings of correct localization, incorrect localization, and time-to-completion were used to evaluate performance outcomes.ResultsWith the addition of vibrotactile and pneumatic feedback, significant improvements in the percentage of correct localization attempts were detected (p = 0.0001 and p = 0.0459, respectively) during the first experiment with phantom vessels. Similarly, significant improvements in correct localization were found with the addition of vibrotactile (p = 2.57E-5) and pneumatic significance (p = 8.54E-5) were observed in the second experiment involving tumor phantoms.ConclusionsThis work demonstrates not only the superior benefits of a multi-modal feedback over traditional single-modality feedback, but also the effectiveness of vibration in providing haptic feedback to artificial palpation systems.

When searching a visual scene for a target, we tend not to look at items or locations we have already searched. It is thought that this behavior is driven by an inhibitory tagging mechanism that inhibits responses on priority maps to the relevant items. We hypothesized that this inhibitory tagging signal should be represented as an elevated response in neurons that keep track of stimuli that have been fixated. We recorded from 231 neurons in the frontal eye field (FEF) of 2 male animals performing a visual foraging task, in which they had to find a reward linked to one of five identical targets (Ts) among five distractors. We identified 38 neurons with activity that was significantly greater when the stimulus in the receptive field had been fixated previously in the trial than when it had not been fixated. The response to a fixated object began before the saccade ended, suggesting that this information is remapped. Unlike most FEF neurons, the activity in these cells was not suppressed during active fixation, had minimal motor responses, and did not change through the trial. Yet using traditional classifications from a memory-guided saccade, they were indistinguishable from the rest of the FEF population. We propose that these neurons keep track of any items that have been fixated within the trial and this signal is propagated by remapping. These neurons could be the source of the inhibitory tagging signal to parietal cortex, where a neuronal instantiation of inhibitory tagging is seen.SIGNIFICANCE STATEMENT When we search a scene for an item, we rarely examine the same location twice. It is thought that this is due to a neural mechanism that keeps track of the items at which we have looked. Here we identified a subset of neurons in the frontal eye field that preferentially responded to items that had been fixated earlier in the trial. These responses were remapped, appearing before the saccade even ended, and were not suppressed during maintained fixation. We propose that these neurons keep track of which items have been examined in search and could be the source of feedback that creates the inhibitory tagging seen in parietal cortex.

The enhancement of neuronal responses in many visual areas while animals perform spatial attention tasks has widely been thought to be the neural correlate of visual attention, but it is unclear whether the presence or absence of this modulation contributes to our striking inability to notice changes in change blindness examples. We asked whether neuronal responses in visual area V4 and the lateral intraparietal area (LIP) in posterior parietal cortex could explain the limited ability of subjects to attend multiple items in a display. We trained animals to perform a change detection task in which they had to compare 2 arrays of stimuli separated briefly in time and found that each animal's performance decreased as function of set-size. Neuronal discriminability in V4 was consistent across set-sizes, but decreased for higher set-sizes in LIP. The introduction of a reward bias produced attentional enhancement in V4, but this could not explain the vast improvement in performance, whereas the enhancement in LIP responses could. We suggest that behavioral set-size effects and the marked improvement in performance with focused attention may not be related to response enhancement in V4 but, instead, may occur in or on the way to LIP.

The decision of where to make an eye movement is thought to be driven primarily by responses to stimuli in neurons' receptive fields (RFs) in oculomotor areas, including the frontal eye field (FEF) of prefrontal cortex. It is also thought that a saccade may be generated when the accumulation of this activity in favor of one location or another reaches a threshold. However, in the reading and scene perception fields, it is well known that the properties of the stimulus at the fovea often affect when the eyes leave that stimulus. We propose that if FEF plays a role in generating eye movements, then the identity of the stimulus at fixation should affect the FEF responses so as to reduce the probability of making a saccade when fixating an item of interest. Using a visual foraging task in which animals could make multiple eye movements within a single trial, we found that responses were strongly modulated by the identity of the stimulus at the fovea. Specifically, responses to the stimulus in the RF were suppressed when the animal maintained fixation for longer durations on a stimulus that could be associated with a reward. We suggest that this suppression, which was predicted by models of eye movement behavior, could be a mechanism by which FEF can modulate the temporal flow of saccades based on the importance of the stimulus at the fovea.

BackgroundThe principal objective of the experiment was to analyze the effects of the clutch operation of robotic surgical systems on the performance of the operator. The relative coordinate system introduced by the clutch operation can introduce a visual-perceptual mismatch which can potentially have negative impact on a surgeon's performance. We also assess the impact of the introduction of additional tactile sensory information on reducing the impact of visual-perceptual mismatch on the performance of the operator.MethodsWe asked 45 novice subjects to complete peg transfers using the da Vinci IS 1200 system with grasper-mounted, normal force sensors. The task involves picking up a peg with one of the robotic arms, passing it to the other arm, and then placing it on the opposite side of the view. Subjects were divided into three groups: aligned group (no mismatch), the misaligned group (10 cm z axis mismatch), and the haptics-misaligned group (haptic feedback and z axis mismatch). Each subject performed the task five times, during which the grip force, time of completion, and number of faults were recorded.ResultsCompared to the subjects that performed the tasks using a properly aligned controller/arm configuration, subjects with a single-axis misalignment showed significantly more peg drops (p = 0.011) and longer time to completion (p

IntroductionThe aims of this study were to evaluate (1) grasping forces with the application of a tactile feedback system in vivo and (2) the incidence of tissue damage incurred during robotic tissue manipulation. Robotic-assisted minimally invasive surgery has been shown to be beneficial in a variety of surgical specialties, particularly radical prostatectomy. This innovative surgical tool offers advantages over traditional laparoscopic techniques, such as improved wrist-like maneuverability, stereoscopic video displays, and scaling of surgical gestures to increase precision. A widely cited disadvantage associated with robotic systems is the absence of tactile feedback.Methods and procedureNineteen subjects were categorized into two groups: 5 experts (six or more robotic cases) and 14 novices (five cases or less). The subjects used the da Vinci with integrated tactile feedback to run porcine bowel in the following conditions: (T1: deactivated tactile feedback; T2: activated tactile feedback; and T3: deactivated tactile feedback). The grasping force, incidence of tissue damage, and the correlation of grasping force and tissue damage were analyzed. Tissue damage was evaluated both grossly and histologically by a pathologist blinded to the sample.ResultsTactile feedback resulted in significantly decreased grasping forces for both experts and novices (P  0.05 in all subjects).ConclusionThe in vivo application of integrated tactile feedback in the robotic system demonstrates significantly reduced grasping forces, resulting in significantly less tissue damage. This tactile feedback system may improve surgical outcomes and broaden the use of robotic-assisted minimally invasive surgery.

As our eyes move, we have a strong percept that the world is stable in space and time; however, the signals in cortex coming from the retina change with each eye movement. It is not known how this changing input produces the visual percept we experience, although the predictive remapping of receptive fields has been described as a likely candidate. To explain how remapping accounts for perceptual stability, we examined responses of neurons in the lateral intraparietal area while animals performed a visual foraging task. When a stimulus was brought into the response field of a neuron that exhibited remapping, the onset of the postsaccadic representation occurred shortly after the saccade ends. Whenever a stimulus was taken out of the response field, the presaccadic representation abruptly ended shortly after the eyes stopped moving. In the 38% (20/52) of neurons that exhibited remapping, there was no more than 30 ms between the end of the presaccadic representation and the start of the postsaccadic representation and, in some neurons, and the population as a whole, it was continuous. We conclude by describing how this seamless shift from a presaccadic to postsaccadic representation could contribute to spatial stability and temporal continuity.

Priority maps are winner-take-all neural mechanisms thought to guide the allocation of covert and overt attention. Here, we go beyond this standard definition and argue that priority maps play a much broader role in controlling goal-directed behavior. We start by defining what priority maps are and where they might be found in the brain; we then ask why they exist-the function that they serve. We propose that this function is to communicate a goal state to the different effector systems, thereby guiding behavior. Within this framework, we speculate on how priority maps interact with visual working memory and introduce our common source hypothesis, the suggestion that this goal state is maintained in visual working memory and used to construct all of the priority maps controlling the various motor systems. Finally, we look ahead and suggest questions about priority maps that should be asked next.

Robot-assisted surgery is characterized by a total loss of haptic feedback, requiring surgeons to rely solely on visual cues. A compact, flexible, and lightweight pneumatic balloon tactile display has been developed suitable for mounting on robotic surgical master controls. The tactile display consists of a molded polydimethylsiloxane substrate with cylindrical channels and a spin-coated silicone film that forms the array of balloons. Human perceptual studies were conducted to determine the optimal diameter, spatial resolution, and temporal resolution of the balloon actuator design. A balloon diameter of 3.0 mm provided the highest average accuracy ([greater than or equal to] 95%) while offering five detectable inflation levels. Spatial accuracy in a two-actuator discrimination task reached 100% with 1.5 mm edge-to-edge spacing, and the accuracy of determining the order of two successive stimuli was greater than 90% when the time separation was 100 ms. Design optimization based on the results from this study enables the described tactile display to provide the effective tactile feedback that is otherwise unavailable during robotic surgery. Index Terms--Haptic feedback, haptic perception, robot tactile systems.

We can search for and locate specific objects in our environment by looking for objects with similar features. Object recognition involves stimulus similarity responses in ventral visual areas and task-related responses in prefrontal cortex. We tested whether neurons in the lateral intraparietal area (LIP) of posterior parietal cortex could form an intermediary representation, collating information from object-specific similarity map representations to allow general decisions about whether a stimulus matches the object being looked for. We hypothesized that responses to stimuli would correlate with how similar they are to a sample stimulus. When animals compared two peripheral stimuli to a sample at their fovea, the response to the matching stimulus was similar, independent of the sample identity, but the response to the nonmatch depended on how similar it was to the sample: the more similar, the greater the response to the nonmatch stimulus. These results could not be explained by task difficulty or confidence. We propose that LIP uses its known mechanistic properties to integrate incoming visual information, including that from the ventral stream about object identity, to create a dynamic representation that is concise, low dimensional, and task relevant and that signifies the choice priorities in mental matching behavior. NEW & NOTEWORTHY Studies in object recognition have focused on the ventral stream, in which neurons respond as a function of how similar a stimulus is to their preferred stimulus, and on prefrontal cortex, where neurons indicate which stimulus is being looked for. We found that parietal area LIP uses its known mechanistic properties to form an intermediary representation in this process. This creates a perceptual similarity map that can be used to guide decisions in prefrontal areas. [ABSTRACT FROM AUTHOR]