Accuracy Of Memory-guided Saccades Research Articles

Effects of eye position on estimates of eye displacement for spatial updating

Neurons in the parietal cortex represent spatial memory of visual stimuli in an eye-centered coordinate frame. To preserve spatial stability across eye movements, spatial memory must be updated during each eye movement. Because eye movement signals in the parietal cortex are known to be modulated by eye position in the orbit, estimates of eye displacement on the basis of these signals could also be influenced by eye position. The present study examined the possible effect of eye position on the accuracy of memory-guided saccades in monkeys following saccades or smooth pursuit during the memory period. The results showed that eye position has a modest effect on saccade localization, suggesting that eye position signal plays a modulatory role in updating visuospatial working memory.

Comparison of performance on memory-guided saccade and delayed spatial match-to-sample tasks in monkeys

To investigate the sources of spatial error in memory-guided saccades (MGS), we have trained monkeys on two different tasks: a MGS task and a delayed spatial match-to-sample (MTS) task. We first tested the effect of introducing a post-saccadic visual feedback on the accuracy of MGS. We found that visual feedback had a pronounced effect on the systematic saccade error, but less of an effect on the variable error. Visual feedback can improve the accuracy of saccadic eye movements over several days, while feedback removal can decrease accuracy in a reversible way. These effects also depend both on target eccentricity and the duration of the memory delay. To test whether saccade error is due to the accuracy of spatial memory storage or arises downstream from that memory, we measured behavioral performance on a spatial MTS task both before and after training with visual feedback. The results showed no significant difference in performance of the MTS task before and after feedback training despite significant changes in MGS accuracy. The results suggest that the accuracy of spatial memory is not the source of the systematic errors that accompany MGS.

Reflexive and Voluntary Saccades in Parkinson's Disease

To evaluate the characteristics of saccadic eye movements in patients with Parkinson's disease(PD). Eye movements of 14 patients with moderate to advanced PD and 12 age-matched controls were recorded with an infrared system. Two kinds of saccade tasks were used: saccade tasks for eliciting reflexive saccades(visually guided saccades in the gap condition) and saccade tasks for eliciting volitional saccades(visually guided saccades, saccades in overlap condition, memory-guided saccades, and anti-saccades). Latency, accuracy, peak velocity, and other parameters of saccades were evaluated. Visually guided saccades and saccades in the gap condition were slightly hypometric in PD patients. Saccades in the short-term overlap condition were not impaired in PD patients. Increased mean latencies and decreased degrees of accuracy of memory-guided saccades, and increased error rates of the memory-guided saccade task were marked in PD patients. Error rates in the anti-saccade task were not increased in PD but the mean saccadic latencies were slightly increased. Reflexive saccades are preserved in PD, whereas memory-guided saccades are markedly impaired. But anti-saccades in a task for eliciting in volitional saccades are not impaired in PD.

Cortical control of spatial memory in humans: the visuooculomotor model.

We review current knowledge of the cortical control of spatial memory, studied using visuooculomotor paradigms. Spatial memory is an essential cognitive process that can be involved in preparing motor responses. Our knowledge of spatial memory in humans recently has progressed thanks to the use of ocular saccades as a convenient model of motor behavior. Accuracy of memory-guided saccades, made to the remembered locations of visual targets, is a reflection of spatial memory. For the performance of memory-guided saccades with brief delays (up to 15-20 seconds), that is, involving short-term spatial memory, lesion studies have shown that the posterior parietal cortex, the dorsolateral prefrontal cortex, and the frontal eye field play significant roles. Studies of memory-guided saccades using transcranial magnetic stimulation have suggested that the right posterior parietal cortex is involved at the initial stage (<300 milliseconds) of visuospatial integration, whereas the dorsolateral prefrontal cortex in both hemispheres controls the following phase of short-term memorization, the frontal eye field mainly serving to trigger saccades. The new concept of a medium-term spatial memory has emerged from a behavioral study of memory-guided saccades in normal subjects, showing a paradoxical spontaneous improvement of spatial memory after delays of approximately 20 seconds. Lesion studies have shown that the parahippocampal cortex could specifically control this medium-term spatial memory. Last, different experimental and clinical arguments suggest that, after a few minutes, the hippocampal formation finally takes over the control of spatial memory for long-term spatial memorization. Therefore, spatial memory involved in the memorization of visual items could be successively controlled by the dorsolateral prefrontal cortex (short-term spatial memory), the parahippocampal cortex (medium-term spatial memory), and the hippocampal formation (long-term spatial memory), depending on specific periods of times. The applicability of this simple visuooculomotor model of spatial memory to other types of stimuli and general motoricity has yet to be confirmed.

Oculomotor Abnormalities in Boys With Tourette Syndrome With and Without ADHD

To assess saccadic eye movements in boys with Tourette syndrome (TS) with and without attention-deficit hyperactivity disorder (ADHD), comparing performance with that of an age-matched group of male controls. Three different saccade tasks (prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and execution of eye movements, including motor response preparation, response inhibition, and working memory. The study included 14 boys with TS without ADHD (TS-only), 11 boys with TS and ADHD (TS+ADHD), and 10 male controls. Latency of prosaccades was prolonged in boys with TS (both with and without ADHD) compared with controls. Variability in prosaccade latency was greater in the groups of boys with TS+ADHD compared with both the TS-only and control groups. Response inhibition errors on both the antisaccade task (directional errors) and memory-guided saccade task (anticipatory errors) were increased in boys with TS+ADHD compared with those with TS-only. There were no significant differences among the three groups in accuracy of memory-guided saccades. Oculomotor findings suggest that TS is associated with delay in initiation of motor response as evidenced by excessive latency on prosaccades. Signs of impaired response inhibition and variability in motor response appear to be associated with the presence of ADHD.

Accuracy of memory-guided saccades.

Accuracy of saccades toward a remembered target positions in the dark (memory-guided saccades) was studied in 11 normal subjects. The subjects were instructed to execute saccades with amplitudes of 20, 40, 60, and 80 degrees, centering on the primary position. Saccades were initially performed for 30 s with visual fixation targets. The targets were then switched off. The subjects continued saccades in the dark with the given amplitude. Most memory-guided saccades overshot the target. Saccades with an amplitude error of 12.7 +/- 7.3 degrees (mean +/- SD) were followed by corrective saccades, while no corrective saccades occurred following saccades with an error of 4.3 +/- 4.0 degrees. The accuracy of initial memory-guided saccades decreased with time. However, the amplitude of the memory-guided saccades was corrected when the error was beyond about 5 degrees. These results suggest that memory-guided saccades are not repetitions of visually guided saccades, but nonvisual error signals relate to the control of eye movements in the dark.