Stimulus-salience and the timecourse of saccade trajectory deviations

The deviation of a saccade trajectory is a measure of the oculomotor competition evoked by a distractor. The aim of the present study was to investigate the impact of stimulus-salience on the time-course of saccade trajectory deviations to get a better insight into how stimulus-salience influences oculomotor competition over time. Two experiments were performed in which participants were required to make a vertical saccade to a target presented in an array of nontarget line elements and one additional distractor. The distractor varied in salience, where salience was defined by an orientation contrast relative to the surrounding nontargets. In Experiment 2, target-distractor similarity was additionally manipulated. In both Experiments 1 and 2, the results revealed that the eyes deviated towards the irrelevant distractor and did so more when the distractor was salient compared to when it was not salient. Critically, salience influenced performance only when people were fast to elicit an eye movement and had no effect when saccade latencies were long. Target-distractor similarity did not influence this pattern. These results show that the impact of salience in the visual system is transient. © 2012 ARVO

The impact of predictive cues and visual working memory on dynamic oculomotor selection

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DEVELOPMENT OF A CLASSIFICATION SYSTEM ON ANKLE-JOINT STIFFNESS

AIM OF THE PROJECT Aim of the project is to develop a classification system for the ankle stiffness in sideward rotations of the fool. MOTIVATION In a previous study (1) a classification system for (running) shoes has been developed on the aspects stability and shock absorption based on a mechanical test protocol. If corresponding features can be quantified for the (lower) legs of the runner, running shoes can be more carefully selected. For example, a runner with less stiff ankles may need shoes which have high stabilizing properties, whereas runners with stable ankles may ask for (more) shock absorbency of their shoes. Consequently, classification systems may contribute to the reduction and /or prevention of running-related injuries. In the present project we have focused ourselves on the stiffness of the ankle. Method: An apparatus has been constructed to quantify the resistance of the foot against sideward rotations. The foot of a person to be tested in a sitting position is placed on a platform and fixed by a special technique. The lower leg is kept in vertical position by straps. The leg is allowed to rotate and translate to some extent around and along the vertical axis of the lower leg. By rotating the platform, the foot can be moved through plantar/dorsal flexion, abduction/adduction and inward/outward rotation. In the first two planes of motion discrete positions of the foot are prescribed while the inward/outward motion is imposed in a motor-driven way. The axes of rotation can be adjusted to individual differences. The axial load on the lower leg can be varied in discrete steps. In this project, the moment of force (M) as a function of rotation (Φ) is measured during inversion/aversion cycle in two positions of the foot, viz. neutral position (0 degrees flexion, 0 degrees adduction) and flexed position (20 degrees plantar flexion, 10 degrees adduction) without axial loading of the tibia. At present, the left ankles of a group of 14 volunteers without ankle complaints and 6 with ankle complaints are measured. Results and Discussion:Based on the specific and reproducible non-linear M- Φ relationship several parameters are deduced such as primary stiffness, mobility, and secondary stiffness for aversion and inversion. One of the results is that in both foot positions the primary stiffness shows to be linear related to the mobility ( a higher stiffness results in a lower mobility.) In the flexed position the primary stiffness is less than in neutral foot position. Using the primary stiffness results of the “sound” group in the flexed foot position a starting classification is made in terms of “stiff”, “neutral”, and “lax”. Depiction of the results of the “injured” ankles in this classification shows that most of these ankles belong to the “lax” category. Biomechanical and epidemiological studies are necessary to evaluate the ultimate effects of combinated foot/shoe classifications

Oculomotor Evidence for Top-Down Control following the Initial Saccade

The goal of the current study was to investigate how salience-driven and goal-driven processes unfold during visual search over multiple eye movements. Eye movements were recorded while observers searched for a target, which was located on (Experiment 1) or defined as (Experiment 2) a specific orientation singleton. This singleton could either be the most, medium, or least salient element in the display. Results were analyzed as a function of response time separately for initial and second eye movements. Irrespective of the search task, initial saccades elicited shortly after the onset of the search display were primarily salience-driven whereas initial saccades elicited after approximately 250 ms were completely unaffected by salience. Initial saccades were increasingly guided in line with task requirements with increasing response times. Second saccades were completely unaffected by salience and were consistently goal-driven, irrespective of response time. These results suggest that stimulus-salience affects the visual system only briefly after a visual image enters the brain and has no effect thereafter

The time course of exogenous and endogenous control of covert attention

Studies of eye-movements and manual response have established that rapid overt selection is largely exogenously driven toward salient stimuli, whereas slower selection is largely endogenously driven to relevant objects. We use the N2pc, an event-related potential index of covert attention, to demonstrate that this time course reflects an underlying pattern in the deployment of covert attention. We find that shifts of attention that occur soon after the onset of a visual search array are directed toward salient, task-irrelevant visual stimuli and are associated with slow responses to the target. In contrast, slower shifts are target-directed and are associated with fast responses. The time course of exogenous and endogenous control provides a framework in which some inconsistent results in the capture literature might be reconciled; capture may occur when attention is rapidly deployed

Interferometry with Bose-Einstein Condensates in Microgravity

Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Due to their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this paper we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far-field of a double-slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.Comment: 8 pages, 3 figures; 8 pages of supporting materia