Uta Sailer

Spatial and temporal aspects of eye-hand coordination across different tasks

Abstract. The way in which saccadic eye movements are elicited influences their latency and accuracy. Accordingly, different tasks elicit different types of saccades. Using the tasks steps, gap, memory, scanning and antisaccade, we analyzed combined eye and hand movements to determine whether both motor systems share control strategies. Errors and latencies were measured to examine whether changes in eye motor behavior are reflected in hand motor behavior. Directional and variable errors of eye and hand changed differently according to the tasks. Moreover, errors of the two systems did not correlate for any of the tasks investigated. Contrary to errors, mean latencies of eye movements were organized in the same pattern as hand movements. A correlation of latencies indicates that both motor systems rely on common information to initiate movement. Temporal coupling was stronger for intentional tasks than for reflexive tasks.

Global Effect of a Nearby Distractor on Targeting Eye and Hand Movements

Eye-hand coordination was investigated with the global effect paradigm. In this paradigm, saccades typically land in between the target and a nearby presented distractor, the configurations center of gravity. This so-called global effect, or spatial averaging, is attributed to incomplete target selection. Four experiments demonstrated a similar effect for hand movements; thus, eye and hand are coupled during target selection. However, under some conditions the global effect was different for eye and hand, suggesting that their coupling is not achieved through a shared target representation. Instead, eye and hand seem to use 2 separate target representations that exchange information. The convergent amplitudes of eye and hand with simultaneous execution support this interpretation. Latencies showed a similar converging pattern.

Differential effect of a distractor on primary saccades and perceptual localization.

A distractor presented nearby the target of a goal-directed short latency saccade leads to spatial averaging, that is, the saccade lands between the target and the distractor. This so-called global effect is a characteristic feature of the spatial processing underlying the programming of saccadic eye movements. To determine whether this effect of near distractors on saccade metrics is also reflected in perceptual localization, subjects performed a saccade task and a perceptual localization task using identical, briefly flashed visual stimuli. To make the available visual processing time for saccades and perception more similar, we followed the target with a mask. Without the mask, primary saccades with short latency landed between target and distractor. The distractor had less effect on primary saccades with longer latencies (>200 ms) and did not affect the final eye position after late secondary saccades in the dark. This indicates that the oculomotor system can correctly use information about the target location 200 ms after the target flash even if no visual stimulus is present during this period. Likewise the presence of a distractor did not affect perceptual localization. Under the masking condition a similar global effect occurred for primary saccades with short latencies, but the latency dependence of the global effect was weakened. Secondary saccades and perceptual localization still did not show a global effect. The results suggest that the primary saccade is based on a specific target acquisition process that differs from that used for spatial perception and for the programming of memory-guided corrective saccades.

Impaired temporal prediction and eye-hand coordination in patients with cerebellar lesions.

This study investigated the effect of cerebellar lesions on temporal prediction and coordination in eye and hand movements. Nine patients with cerebellar lesions were compared to controls while they made saccades with and without simultaneous pointing movements towards a target that was either temporally predictable or non-predictable. The direction and amplitude of the target step was always predictable. Patients made much more early and late saccades than controls, but an equal amount of visually triggered saccades. This suggests that inappropriate saccades could be suppressed during the preparation of a goal-directed saccade. Hand movement frequency did not differ between both groups. Thus, cerebellar lesions can induce inappropriate saccades more easily than inappropriate hand movements. Controls, but not patients, generated visually triggered saccades of shorter latencies when the target was temporally predictable. Thus, the patients could not use information about target timing to synchronise visually triggered saccades with the target. They could, however, use this information to improve the suppression of inappropriate saccades. Regarding coordination, patients showed impairments in synchronising saccades with hand movements. Nevertheless, hand movements led to an enhancement of anticipatory saccades in patients as in controls. Moreover, hand movements and temporal predictability affected saccadic accuracy in both groups similarly. These results suggest that cerebellar lesions do not generally prevent access to temporal information on the rhythm of a target sequence or the timing of a planned hand movement. More specifically, the cerebellum seems to be crucial for synchronizing saccades with such learned or planned temporal events.

Implications of distracter effects for the organization of eye movements, hand movements, and perception.

The end positions of eye and hand movements were both drawn towards a distracter that was presented nearby the target. They thus showed a so-called global effect. In contrast, perception was not influenced by the presence of a distracter. These results are discussed with regard to the question whether eye, hand, and perception are based on shared or separate target representations and readout triggers. We conclude that separate representations and readout triggers for eye and hand are the most likely case.

Assessing noise annoyance: an improvement-oriented approach

A concept for practice-oriented assessment of noise annoyance at the workplace is presented. Employees evaluated the noise situation at their workplace by characterizing the loudest noise event with respect to relevant noise characteristics. The results from a first use of the questionnaire for Subjective Evaluation of Noise Characteristics in Office Workplaces (SENO) show (1) a general need for an additional constructive measure of subjective noise annoyance, (2) that evaluation of the loudest noise event is representative for the overall workplace situation, and (3) that coping plays a crucial role and should be explicitly controlled. Finally, examples of how to use SENO for improving the workplace situation are given.

Predictive eye and hand movements are differentially affected by schizophrenia

BackgroundSchizophrenic patients are known to have problems suppressing reflexive eye movements. This is considered to indicate a dysfunction in prefrontal cortex. As the eye and hand motor systems are tightly coupled, we investigated whether predictive hand movements and eye-hand coordination are unimpaired in schizophrenic patients.MethodSaccades and hand movements of 19 patients during an acute schizophrenic episode and 19 controls were measured in a task in which the predictability of target timing was varied.ResultsSchizophrenic patients generated more anticipatory and less visually triggered saccades than controls with both non-predictable and predictable target timing. Anticipatory saccades in the wrong direction were clearly directed towards previous target positions, indicating that they are indicators of erroneous prediction rather than of fixation instability. In contrast to saccades, the number of anticipatory and visually triggered hand movements was the same in patients as in controls. As a consequence, patients took longer to initiate a hand movement after a saccade than controls.ConclusionSchizophrenic patients show increased predictive saccadic activity, but no qualitative changes in predictive saccades. Since prediction itself was not disturbed, the patients’ deficit rather lies in the suppression or gating of anticipatory saccades than in their generation. This may be explained by a selective dysfunction of the basal ganglia oculomotor loop. As predictive hand movements were unimpaired, the problems in eye-hand coordination as expressed by a longer initiation time of hand movements relative to saccades are a direct consequence of impaired predictive saccadic behaviour.

Predictive Pointing Movements and Saccades Toward a Moving Target

Abstract The authors investigated whether and, if so, how velocity information is used to control predictive manual pointing movements and saccades. Participants (N = 6) intercepted an occluded moving target as if it were still visible. They kept their eyes fixated while the target moved. The target traveled over a fixed distance and changed its velocity on the way. The presentation time of the final velocity was varied. Both the eye and the hand overshot the slow target and undershot the fast target, particularly when the duration of the final velocity was short. Thus, responses were biased in the direction of the targets initial velocity. The error seemed to arise because participants did not take their latency into account when aiming at the target. Instead, they strategically aimed farther ahead when the target was fast. Amplitude was also more related to the position of velocity change than to final velocity duration. Both findings suggest that target velocity is not extrapolated but that individuals add an increment to the position of velocity change.

Die Priorisierung von Problemhinweisen in der software-ergonomischen Qualitätssicherung

Im Rahmen software-ergonomischer Qualitatssicherung sind die Ressourcen fur Gestaltung beschrankt. Um die effiziente Bearbeitung zu gewahrleisten, wird die Priorisierung von Problembereichen eines Softwaresystems notig. Es werden zwei Arten der Priorisierung von Problemhinweisen. namlich Priorisierung nach Fehlerkosten und Priorisierung nach Auftretensstabilitat, vorgestellt und empirisch analysiert. Hierbei steht der Aspekt der mentalen Beanspruchung im Zentrum der Uberlegungen. Prinzipiell eignen sich beide Methoden zur Priorisierung und Auswahl der wichtigsten Problembereiche eines Softwaresystems. Ob man sich fur die eine oder andere Methode entscheiden soll, hangt jedoch von verschiedenen Randbedingungen. wie Auftretenshaufigkeit und zeitokonomischen Uberlegungen ab. In jedem Fall kann eine der hier vorgeschlagenen Priorisierungsmethoden den Prozes der software-ergonomischen Qualitatssicherung effizienter gestalten und damit im Ergebnis die mentale Beanspruchung der Benutzer reduzieren.

Saccade-Related Potentials during Eye-Hand Coordination: Effects of Hand Movements on Saccade Preparation

This study investigated the effect of hand movements on behavioral and electrophysiological parameters of saccade preparation. While event-related potentials were recorded in 17 subjects, they performed saccades to a visual target either together with a hand movement in the same direction, a hand movement in the opposite direction, a hand movement to a third, independent direction, or without any accompanying hand movements. Saccade latencies increased with any kind of accompanying hand movement. Both saccade and manual latencies were largest when both movements aimed at opposite directions. In contrast, saccade-related potentials indicating preparatory activity were mainly affected by hand movements in the same direction. The data suggest that concomitant hand movements interfere with saccade preparation, particularly when the two movements involve motor preparations that access the same visual stimulus. This indicates that saccade preparation is continually informed about hand movement preparation.