Different Types Of Eye Movements Research Articles

Time control of hand movements

Publisher Summary The time control of self-initiated voluntary limb movements is more difficult to assess than that in the oculomotor system, where saccadic and pursuit eye movements are regarded as the products of two independent control systems. The different velocities of the two types of eye movement depend on vestibular and visual inputs as well as on movement amplitude. In contrast to these different types of eye movements, velocity control in the skeletal motor system is continuous, such that limb muscles can produce movements resembling the pursuit or saccadic type of eye movements. In spite of this continuum of possible performances, it is a widely held view that in the skeletal motor system ballistic and ramp movements represents different categories. A difficulty in a comparative analysis of time control in the two systems lies in their different accessibility to examination. Eye movements can be examined in response to visual and vestibular inputs and described in terms of input-output relationships. In reflex studies, this is also possible for limb movements. However, the wide range of input variables and of possible performances of limb movements makes it difficult to explore the control strategies relevant for their performance. A closer understanding of the mechanisms underlying the matching of certain temporal demands for perception and motor control is an intriguing problem for future research.

An improved neural-network model for the neural integrator of the oculomotor system: more realistic neuron behavior.

The discharge rates of premotor, brain-stem neurons that create eye movements modulate in relation to eye velocity yet firing rates of extraocular motoneurons contain both eye-position and eye-velocity signals. The eye-position signal is derived from the eye-velocity command by means of a neural network which functions as a temporal integrator. We have previously proposed a network of lateral-inhibitory neurons that is capable of performing the required integration. That analysis centered on the temporal aspects of the signal processing for a limited class of idealized inputs. All of its cells were identical and carried only the integrated signal. Recordings in the brain stem, however, show that neurons in the region of the neural integrator have a variety of background firing rates, all carry some eye-velocity signal as well as the eye-position signal, and carry the former with different strengths depending on the type of eye movement being made. It was necessary to see if the proposed model could be modified to make its neurons more realistic. By modifying the spatial distribution of afferents to the network, we demonstrate that the same basic model functions properly in spite of afferents with nonuniform background firing rates. To introduce the eye-velocity signal a double-layer network, consisting of inhibitory and excitatory cells, was necessary. By presenting the velocity input to only local regions of this network it was shown that all cells in the network still carried the integrated signal and that its cells could carry different eye-velocity signals for different types of eye movements. Thus, this model stimulates quantitatively and qualitatively, the behavior of neurons seen in the region of the neural integrator.

Cerebral events preceding self-paced and visually triggered saccades. A study of presaccadic potentials

The cerebral potentials preceding self-paced and visually triggered saccadic eye movements were studied using multichannel recording and spatio-temporal mapping techniques, and the contribution to these potentials of stimulus-evoked activity and the electro-oculographic field was investigated. A premotor positivity (PMP) and negativity (PMN) comparable to those associated with movements of the extremities were found with both self-paced and triggered saccades, but there were differences in the amplitude, duration and topography of these potentials in the different types of eye movement. The slope of the PMP was greater for visually triggered than for self-paced saccades and its slope and duration were influenced by the predictability of the triggering stimulus, the slope being greater and the duration shorter with predictable than with unpredictable stimuli. The characteristics of this potential are compatible with an origin from saccade-related and visually sensitive neurons in parietal and occipital cortex and it is suggested than in a visually triggered eye movement, the PMP may be a correlate of visuomotor interactions. A PMN was associated with both self-paced and visually triggered saccades, and in the case of triggered saccades is thought to reflect anticipation of the cuing stimulus in addition to preparatory movement-related activity. When the precise timing of the cuing stimulus was not known by the subject, a PMN still developed but then plateaued until the arrival of the stimulus and execution of the movement. In this situation the PMN therefore appears to reflect an increasing level of arousal and preparedness to move which is then maintained pending the final motor command.

Control of human eye movements: II. a model for the extraocular plant mechanism

Control of eye movements is essential in accomplishing visual or perceptive tasks. The brain and central nervous system process retinal information and send nervous signals to the extraocular muscles, which exert forces that cause the eye to move. A model for the human extraocular plant, which consists of the nervous input signals, the extraocular muscles, the orbit and the globe, is proposed. The derivation is based on anatomical and physiological data as well as experiments concerned with a variety of eye movements under normal and abnormal conditions. The nervous activity controlling eye movements was estimated from electromyography and single unit studies of the extraocular nuclei. The equations describing muscle properties were discussed in a previous paper by the authors; these results were incorporated into the present model. The characteristics of the isolated globe and its visco-elastic interaction with the orbit were computed from length- tension curves and isotonic experiments. Simulations using the resulting representation accurately depicted the isotonic experiments on the isolated globe and on the total extraocular plant, the isometric forces during three different types of eye movements, and the weighted globe experiment. A future paper will show that the model accurately simulates normal eye movements of different types and amplitudes.

Some observations on lambda waves and peripheral stimulation

1. 1. A series of experiments involving different types of eye movements and visual tasks, using 94 normal subjects showed that lambda waves were best seen when the subject looked at a detailed picture with interest. Eye movements were a necessary but not sufficient condition for the production of lambda waves. 2. 2. Comparisons were made of the latency for eye movement lambda waves with the latency of occipital responses to stimulation by flashes of light, and also with the waking K-complexes to light flash and auditory stimulation. The latency measurements of the different types were similar, but the lambda waves showed a slightly longer latency. 3. 3. There was much variation in the shape, amplitude, and incidence of each response to a stimulus, which occurred with all four types of phenomena. Subjects showing a good response to one type of stimulus did not necessarily have a good response to the other types. 4. 4. The different phenomena appeared to have complex wave forms and no direct relationship could be established. However, the fact that on close examination of the wave forms, some of the components appeared common to each of the phenomena, combined with the closeness of the latency measurements, suggest that lambda waves may have more in common with some part of the arousal mechanism than with simple eye movement.