A relative position code for saccades in dorsal premotor cortex

Previous studies have shown that the parietal reach region (PRR) encodes the two dimensional location of frontoparallel reach targets in an eye centered reference frame in early movement plans (Batista 1999; Snyder et al. 2000). Performing a visually guided reach initially requires the ability to perceive the depth of a target in three dimensional space. Beyond that initial perception, however, reach plans may represent the egocentric distance of the target in different ways. To investigate how a reach target is represented in three dimensions, recordings were made of the spiking activity of PRR neurons from two rhesus macaques trained to fixate and perform memory reaches to targets at different depths. Reach and fixation targets were configured to explore whether neural activity directly reflects egocentric distance as the amplitude of the required motor command, which is the absolute depth of the target, or rather the relative depth of the target with reference to fixation depth. This thesis shows that planning activity in PRR represents the depth of the reach target as a function of disparity and fixation depth, the spatial parameters important for encoding the egocentric distance of a reach goal in an eye centered reference frame. Most PRR neurons were found to be sensitive to the disparity of a reach target (82%), and vergence angle (74%) which determines fixation depth. Most PRR neurons carry both disparity and vergence angle signals, and comparisons of several modulation indices and the information carried in firing rates for each variable show a single homogenous PRR population encodes egocentric distance. The strength of modulation by disparity was maintained across vergence angle, where vergence angle gain modulates disparity tuning while preserving the location of peak tuning features in PRR neurons, which allows the absolute depth of the reach target to be decoded from the population activity. Neural activity in PRR shows a wide range of sensitivity to both target disparity and fixation depth that has never been previously tested in a reach task. The results demonstrate a specific role for PRR neurons in supporting eye-hand coordination when decoupling the effector from the point of gaze.

Neurons in the parietal reach region (PRR) have been implicated in the sensory-to-motor transformation required for reaching toward visually defined targets. The neurons in each cortical hemisphere might be specifically involved in planning movements of just one limb, or the PRR might code reach endpoints generically, independent of which limb will actually move. Previous work has shown that the preferred directions of PRR neurons are similar for right and left limb movements but that the amplitude of modulation may vary greatly. We now test the hypothesis that frames of reference and eye and hand gain field modulations will, like preferred directions, be independent of which hand moves. This was not the case. Many neurons show clear differences in both the frame of reference as well as in direction and strength of gain field modulations, depending on which hand is used to reach. The results suggest that the information that is conveyed from the PRR to areas closer to the motor output (the readout from the PRR) is different for each limb and that individual PRR neurons contribute either to controlling the contralateral-limb or else bimanual-limb control.

The parietal reach region (PRR) is known to be involved in the preparation of visually guided arm movements to single targets. We explored whether PRR encodes only the target of the next movement or, alternatively, also a subsequent goal in a double-reach sequence. Two monkeys were trained to memorize the locations of two peripheral cues and to prepare for a memory-guided delayed double-reach sequence. Upon a GO-signal they had to reach in a predefined order to both remembered target locations without breaking eye fixation. The movement goals were arranged such that either the first or the second target was inside the response field of an isolated neuron. We analyzed the neural activity of single cells in PRR during the late memory period between cue offset and the GO-signal. During this memory period, most PRR cells encoded the first as well as the second goal of the planned reaching sequence. The results indicate that the posterior parietal cortex is involved in the spatial planning of more complex action patterns and represents immediate and subsequent movement goals.

Relationship between eye acceleration and retinal image velocity during foveal smooth pursuit in man and monkey.

Recently, some studies have demonstrated that the dorsomedial pathway is not only involved in arm reaching but also hand grasping. Grasp types can be decoded with multiunit activity (MUA) collected from dorsal premotor cortex (PMd) in dorsomedial pathway. However, these studies analyze and decode the neural activity during the whole grasp period. The precise function of PMd during the movement planning period has not been systematically investigated. In this study, neural signals were collected from a monkey's PMd by microelectrode array when it was performing a grip-specific task. With single neural activity (SUA) analysis, we found that 11.9% of neurons in PMd were selective to gestures during the planning period, which illustrated some neurons in PMd are related to planning. Furthermore, four grasp gesture types prediction were classified using support vector machines model (SVM) and k-nearest neighbor model (kNN) from neuron population activities. The results showed that the gesture classification accuracy reaching 60.8% by SVM and 63.9% by kNN. It infers that grasp planning is modulated by PMd neurons and that the PMd may play a central role in all phases of reach-to-grasp planning action.

Every movement we make represents one of many possible actions. In reaching tasks with multiple targets, dorsal premotor cortex (PMd) appears to represent all possible actions simultaneously. However, in many situations we are not presented with explicit choices. Instead, we must estimate the best action based on noisy information and execute it while still uncertain of our choice. Here we asked how both primary motor cortex (M1) and PMd represented reach direction during a task in which a monkey made reaches based on noisy, uncertain target information. We found that with increased uncertainty, neurons in PMd actually enhanced their representation of unlikely movements throughout both planning and execution. The magnitude of this effect was highly variable across sessions, and was correlated with a measure of the monkeys' behavioral uncertainty. These effects were not present in M1. Our findings suggest that PMd represents and maintains a full distribution of potentially correct actions.

To address the problem of low classification accuracy in existing bioradar sleep staging technology caused by the use of indirect physiological features, research on bioradar sleep eye movement detection is conducted. A synchronous acquisition platform for millimeter-wave bioradar and electrooculogram (EOG)/polysomnography (PSG) is established. Simulated eye movement experiments and real sleep experiments are carried out respectively. In the simulated eye movement experiments, the time-domain cross-correlation coefficient between the eye movement signals detected by the bioradar and the EOG signals exceeds 0.90. The error in the dominant frequency within the frequency domain is less than 0.05 Hz. In the real sleep experiments, eye movement signals consistent with EOG are also detected by the bioradar. These signals exhibit explosive characteristics in the rapid eye movement period, intermittent smooth fluctuation characteristics in the light sleep period, and stable low-amplitude fluctuation characteristics in the deep sleep period. The experimental results indicate that the bioradar can effectively detect and distinguish three typical sleep eye movement events: rapid eye movement, slow eye movement, and no significant eye movement. This provides a new technical approach for bioradar sleep staging, which holds promise for further improving staging accuracy.

Saccadic localisation of targets of various properties has been extensively studied, but rarely for texture-defined figures. In this paper, three experiments that investigate the way information from a texture target is processed in order to provide a signal for eye movement control are presented. Participants made saccades to target regions embedded in a background structure, and the saccade landing position and latency were measured. The textures comprised line elements, with orientations of the lines configured to form the figure and ground. Various orientation profile configurations (Block, Blur, and Cornsweet), were used in order to measure the role of edge profiles in driving eye movements and producing salience. We found that in all cases the visual system is in fact able to effectively segregate a texture figure from the ground in order to accurately plan a saccade to the target-figure. While saccadic latency was the highest for the Blur profile, the mean saccadic landing position was mostly unaffected by the various profiles (Experiment 1). More specifically, we showed that saccades were directed to the centre-of-gravity of the target (Experiment 2). We also found that figures with information of orientation contrast at both the edge and centre of figure (i.e. Block) produced the highest level of saliency in attracting eye movements (Experiment 3). Overall, the results show that saccades are planned on the representation of the whole target shape rather than a local salient region based on orientation contrast cues, and that the various texture profiles were important only to the extent that they affected the time to programme a saccade.

Chapter 12 - Modeling the effects of lexical ambiguity on eye movements during reading

Where we look when we scan visual scenes to obtain an understanding of the 3D world around us is a question of interest for both fundamental and applied research. Recently, it has been shown that depth is an important variable in driving eye movements: the directions of saccades tend to follow depth gradients (Wexler (2008), Janssen (2009)). Whether saccades are aligned with a single depth cue or a combination of depth cues is still unknown. And, in the latter case, it is interesting to ask whether saccades are based on similar combination rules as those that apply to depth perception. Moreover, these scanning eye movements across different depth planes are composed of two distinct components: conjugate shifts of gaze (saccades) and disjunctive movements changing the depth of fixation (vergence). And the same questions about the effect of depth cues still apply to vergence: various studies have reported that vergence is guided by the consciously perceived depth percept, whereas others report that vergence is based on depth cue(s). Here we studied what depth information is used to plan both saccades and vergence. We showed observers surfaces inclined in depth, in which perspective and disparity defined different plane orientations (both small (0°-45°) and large (90°,180°) conflicts). Observers' eye movements were recorded binocularly, while they scanned the surface. After the stimulus presentation, observers reported the perceived surface orientation using a joystick. We found saccade directions and perceived surface orientation use the same pattern of depth cue combination: a weighted linear cue combination for small conflicts and cue dominance for large cue conflicts. The weights assigned to each cue varied across subjects, but were strongly correlated for perception and saccades, within subjects. This correlation was maintained while manipulating cue reliability. Vergence on the other hand was dominated by the disparity cue.

Virtual environments (VE) allow testing complex behaviors in naturalistic settings by combining highly controlled visual stimuli with spatial navigation and other cognitive tasks. They also allow for the recording of eye movements using high-precision eye tracking techniques, which is important in electrophysiological studies examining the response properties of neurons in visual areas of nonhuman primates. However, during virtual navigation, the pattern of retinal stimulation can be highly dynamic which may influence eye movements. Here we examine whether and how eye movement patterns change as a function of dynamic visual stimulation during virtual navigation tasks, relative to standard oculomotor tasks. We trained two rhesus macaques to use a joystick to navigate in a VE to complete two tasks. To contrast VE behavior with classic measurements, the monkeys also performed a simple Cued Saccade task. We used a robust algorithm for rapid classification of saccades, fixations, and smooth pursuits. We then analyzed the kinematics of saccades during all tasks, and specifically during different phases of the VE tasks. We found that fixation to smooth pursuit ratios were smaller in VE tasks (4:5) compared to the Cued Saccade task (7:1), reflecting a more intensive use of smooth pursuit to foveate targets in VE than in a standard visually guided saccade task or during spontaneous fixations. Saccades made to rewarded targets (exploitation) tended to have increased peak velocities compared to saccades made to unrewarded objects (exploration). VE exploitation saccades were 6% slower than saccades to discrete targets in the Cued Saccade task. Virtual environments represent a technological advance in experimental design for nonhuman primates. Here we provide a framework to study the ways that eye movements change between and within static and dynamic displays.

Recordings in the lateral intraparietal area (LIP) reveal that parietal cortex encodes variables related to spatial decision-making, the selection of desirable targets in space. It has been unclear whether parietal cortex is involved in spatial decision-making in general, or whether specific parietal compartments subserve decisions made using specific actions. To test this, we engaged monkeys (Macaca mulatta) in a reward-based decision task in which they selected a target based on its desirability. The animals' choice behavior in this task followed the molar matching law, and in each trial was governed by the desirability of the choice targets. Critically, animals were instructed to make the choice using one of two actions: eye movements (saccades) and arm movements (reaches). We recorded the discharge activity of neurons in area LIP and the parietal reach region (PRR) of the parietal cortex. In line with previous studies, we found that both LIP and PRR encode a reward-based decision variable, the target desirability. Crucially, the target desirability was encoded in LIP at least twice as strongly when choices were made using saccades compared with reaches. In contrast, PRR encoded target desirability only for reaches and not for saccades. These data suggest that decisions can evolve in dedicated parietal circuits in the context of specific actions. This finding supports the hypothesis of an intentional representation of developing decisions in parietal cortex. Furthermore, the close link between the cognitive (decision-related) and bodily (action-related) processes presents a neural contribution to the theories of embodied cognition.

Long-term adaptive changes in primate vestibuloocular reflex. III. Electrophysiological observations in flocculus of normal monkeys.

In the late 1970s/early 1980s, Baddeley and colleagues conducted a series of experiments investigating the role of eye movements in visual working memory. Although only described briefly in a book, these studies have influenced a remarkable number of empirical and theoretical developments in fields ranging from experimental psychology to human neuropsychology to nonhuman primate electrophysiology. This paper presents, in full detail, three critical studies from this series, together with a recently performed study that includes a level of eye movement measurement and control that was not available for the older studies. Together, the results demonstrate several facts about the sensitivity of visuospatial working memory to eye movements. First, it is eye movement control, not movement per se, that produces the disruptive effects. Second, these effects are limited to working memory for locations and do not generalize to visual working memory for shapes. Third, they can be isolated to the storage/maintenance components of working memory (e.g., to the delay period of the delayed-recognition task). These facts have important implications for models of visual working memory.

The major objective of the work is concern about the education community in their mission to be with the majority. The initial stage of the work is to study different mechanism for diagnosing learning disability (LD). Medical diagnosing searching becomes the major problem for movements of relationship among eye and dyslexia. To manage these problems several work have been demonstrated. But still it becomes most important difficulty how to extraction of best features from original data and how to improves the detection result in learning disability (LD). In order overcome these difficulties proposed an efficient wavelet transform (WT) for feature extraction and Adaptive Neuro-Fuzzy Inference System (ANFIS) based classifier dyslexia detection from eye movement signal. Eye movement of children was evaluated using Videooculographic (VOG) techniques. During this process both reading and non-reading tasks were measured based on eye movement of each children. After the measurement of eye movement then extract features using WT, then further the diagnosis of learning disability for classification using ANFIS system. Finally evaluate the performance of ANFIS classifier for dyslexia detection from eye movement signal. Compare to ANN based classification ,proposed ANFIS Classifier are less computational complication and detection result of methods are compared using parameters like accuracy, sensitivity and specificity, it shows that ANFIS Classifier are higher detection result than existing ANN classification