Action-related intentional effects in a visual search task

Contains fulltext : 63712.pdf (publisher's version ) (Open Access)The aim of the current study was to test if visual features relevant to the task are processed more efficiently at an early, presumably parallel, level, compared to irrelevant target features. Subjects either had to grasp or point at a target. It was hypothesised that since orientation, in contrast to colour, is relevant to the action of grasping, enhancement of orientation-discrimination performance should be selective. The visual search task required searching for a conjunction of a particular colour and orientation. Subjects viewed stimuli on a screen while their gaze was tracked to determine the targeting of the first saccade. Target - distractor discriminability and set size were manipulated. In experiment 1, the difficulty of colour and orientation search was matched so that subjects would make 50% errors in feature search. In experiment 2, the colour contrast of target and distractors was decreased. There were two levels of set size of the search display. Enhanced orientation discrimination (relative to colour) was found for the condition in which subjects grasped the target compared to the condition in which they pointed towards the target. The action effect was most prominent in the small set-size, high-discriminability condition, and weakest in the large set-size, low-discriminability condition, with intermediate effects for the other two conditions. Action intention selectively enhances the processing of a behaviourally relevant feature. Signal detection modeling indicates that our results can be explained on the basis of an enhancement of an early and possibly parallel stage of feature processing.1 p

Zur Trainierbarkeit der vestibulo-okulären Präzision

Der Begriff des „vestibulären Trainings“ wird oft als Komponente des sog. „Propriozeptionstrainings“ verwendet. Jüngeren Untersuchungen zufolge muss allerdings hinterfragt werden, inwieweit die vestibuläre Funktion tatsächlich trainierbar ist. In der vorliegenden Studie sollten Rückschlüsse auf die spezifische Trainierbarkeit der vestibulären Funktion anhand standardisierter vestibulo-okulärer Parameter unter verschiedenen dynamischen Bedingungen abgeleitet werden. Im Vestibularisstimulationsgerät der Universität Tübingen wurde das Präzisionsniveau des vestibulo-okulären Reflexes (VOR-Gain) während mono- und multiaxialer sinusoidaler Drehbeschleunigungen videonystagmographisch erfasst (System: 2D-VOG, Fa. SMI). Es wurden Kunstturner der nationalen Leistungsspitze (n = 11, 17-25 J, Trainingsumfang: 25-32 Std/Wo.), D-Kader-Nachwuchsturner (n = 9, 10-13 J., Trainingsumfang: 20 Std./Wo.), D-Kader Trampolinturner (n = 8, 10-13 J., Trainingsumfang: 6-8 Std./Wo.) und eine Kontrolle von Nichtsportlern (n = 10, 11-13 J.) im Rahmen eines Querschnittsdesigns geprüft. Die Gruppe der D-Kader-Turner wurde außerdem im Rahmen einer Längsschnittstudie nach einer vollständigen Trainingspause von 3 Wochen (Messzeitpunkt 2; MZ2), sowie nach 3 Jahren fortgeführten sportartspezifischen Trainings erneut untersucht (MZ3), ebenso die Kontrollgruppe. Die monoaxialen Drehtests erfolgten in horizontaler und vertikaler Ebene mit 0,4 Hz und 0,2 Hz bei ωmax von je 25°/s und mit je 0,1 Hz bei ωmax von 25°/s und 50°/s. Die multiaxialen Tests beinhalteten Schraubensalto- und Doppelschraubensaltosimulationen mit 0,1 Hz (ωmax:113°/s). Die nystagmographische Auswertung erfolgte anhand der Spezialsoftware LabView Vortex IIIc; National Instruments. Im Intrasubject-Vergleich fanden sich fast ausschließlich hochsignifikante Korrelationen zwischen den Einzeltests jedes MZ (p <0,01, Pearson). Weder im Gruppenvergleich noch im Rahmen der Längsschnittuntersuchung konnten jedoch signifikante Verbesserungen der vestibulären Präzision seitens der Sportler festgestellt werden (Wilcoxon; Mann-Whitney-U). Die Ergebnisse können somit eine trainingsabhängige Verbesserung der vestibulo-okulären Präzision nicht belegen, sondern weisen auf ein eher individuell determiniertes und im untersuchten Altersgang weitgehend stabiles Reflexniveau hin

Are there Correlations Between Vertical VOR and Multiaxial Spatial Orientation?

Stangl et al. [1] describe differences of vestibulo-ocular reflex (VOR) gain in groups of athletes accustomed to rotational movements. The authors suggest that the physiological purpose of these differences is to enable better spatial orientation during whole body rotations. Is the reverse possible: to use the VOR gain to estimate an individual’s per-rotatory spatial orientation ability? To answer this question, we looked for differences of the VOR gains in a group of high-performance gymnasts (gym) versus a group of non-athletes (control). The results from the gymnasts were also examined for correlations with a rank of their individual perrotatory spatial orientation (PSO) abilities, performed by their coaches. The subjects’ (gym: n = 9, age: 10–13 years, control: n = 10, age: 11–12 years) eye movements were recorded using a video nystagmography system (SMI). They were seated with head fixed in a software controlled multi-axial whole body rotator. The test included 4 horizontal and 4 vertical sinusoidal whole body rotations with various frequencies and peak velocities (0.4, 0.2 and 0.1 Hz at 25/s; 0.1 Hz at 50/s). VOR gain was calculated as the ratio of the amplitude of the best-fit sine wave for the slow-component eye velocity to the amplitude of the stimulus velocity. The PSO ranking list was based on the independent estimation of three coaches, who work with the group of gymnasts daily. The results showed clear gain differences between the 4 tests (the higher the speed or frequency, the higher the gains). It was not possible to show group differences between groups for either horizontal or during vertical rotations. But there were clear inter-individual differences in both groups, characterized through high significant individual stability (individual correlations between the tests mostly with p<0.01 [Pearson]). All the individual coach rankings showed also significant correlations [p<0.05, Spearman]). The analysis of correlations between vertical gains and PSO showed a clear and significant correlation (0.4Hz: rS=0.647, p=0.109; 0.2Hz: rS=0.786, p=0.036; 0.1Hz@25/s: rS=0.619, p=0.102; 0.1Hz@25/s: rS=0.821, p=0.023). Horizontal motion did not show any correlations with PSO. Differences in VOR gain in subjects accustomed to rotational movements could not be confirmed. Correlations between the various tests for each subject show they are stable indicators of VOR response. Correlations between vertical VOR-gains and PSO of the athletes could indicate a link between VOR parameters and individual per-rotatory multi-axial orientation abilities

Human self-motion sensitivity to visual yaw rotations

Whilst moving through the environment humans use vision to discriminate different self-motion intensities and to control their action, e.g. maintaining balance or controlling a vehicle. Yet, the way different intensities of the visual sensory stimulus affect motion sensitivity is still an open question. In this study we investigate human sensitivity to visually induced circular self-motion perception (vection) around the vertical (yaw) axis. The experiment is conducted on a motion platform equipped with a projection screen (70 x 90 degrees FoV). Stimuli consist of a realistic virtual environment (360 degrees panoramic color picture of a forest) rotating at constant velocity around participants’ head. Visual rotations are terminated by participants only after vection arises. Vection is facilitated by the use of mechanical vibrations of the participant’s seat. In a two-interval forced choice task, participants discriminate a reference velocity from a comparison velocity (adjusted in amplitude after every presentation) by indicating which rotation felt stronger. Motion sensitivity is measured as the smallest perceivable change in stimulus velocity (differential threshold) for 8 participants at 5 rotation velocities (5, 15, 30, 45 and 60 deg/s). Differential thresholds for circular vection increase with stimulus intensity, following a trend best described by a power law with an exponent of 0.64. The time necessary for vection to arise is significantly longer for the first stimulus presentation (average 11.6 s) than for the second (9.1 s), and does not depend on stimulus velocity. Results suggest that lower sensitivity (i.e. higher differential thresholds) for increasing velocities reflects prior expectations of small rotations, more common than large rotations during everyday experience. A probabilistic model is proposed that combines sensory information with prior knowledge of the expected motion in a statistically optimal fashion. Results also suggest that vection rise is facilitated by a recent exposure

Visual Vestibular Interactions for Self Motion Estimation

Accurate perception of self-motion through cluttered environments involves a coordinated set of sensorimotor processes that encode and compare information from visual, vestibular, proprioceptive, motor-corollary, and cognitive inputs. Our goal was to investigate the visual and vestibular cues to the direction of linear self-motion (heading direction). In the vestibular experiment, blindfolded participants were given two distinct forward linear translations, using a Stewart Platform, with identical acceleration profiles. One motion was a standard heading direction, while the test heading was randomly varied using the method of constant stimuli. The participants judged in which interval they moved further towards the right. In the visual-alone condition, participants were presented with two intervals of radial optic flow stimuli and judged which of the two intervals represented a pattern of optic flow consistent with more rightward self-motion. From participants’ responses, we compute psychometric functions fo r both experiments, from which we can calculate the participant’s uncertainty in heading direction estimates

Human sensitivity to different motion intensities

Sensory information processes leading to human self-motion perception have been modelled in the past in terms of visual and inertial stimulations and their interactions. The models, validated through many psychophysical experiments, rely on the assumption that our sensitivity to supra-threshold self-motion is not affected by motion intensity. In other words, the relationship between motion stimulus intensity and human sensitivity to motion is assumed to be linear. However, recent studies have shown that this relationship is non-linear, in particular at higher motion intensity. Therefore, the implementation of nonlinearities in the computational models of human motion perception would increase their accuracy over a wider range of motion stimulus intensity. Here we test human sensitivity for sinusoidal yaw rotation in darkness at frequencies of 0.5 Hz and 1 Hz and velocity amplitudes ranging between 0 and 90 deg/s. In a two interval force choice experimental paradigm, subjects undergo two consecutive rotations in the same direction for each trial. One of these movements is repeated unchanged in every trial, while the other systematically varies in amplitude. Subjects are asked to report after each trial which one of the two movements was stronger. An adaptive staircase adjusts the motion for every trial to identify the smallest detectable change in stimulus intensity (differential threshold). Results show a power law relationship between differential thresholds and stimulus intensity, meaning that sensitivity decreases as motion becomes stronger. No frequency effect is observed. These findings are of particular interest for the field of vehicle motion simulation, where knowledge about self-motion perception is widely exploited to overcome the physical limitations of motion-based simulators. Furthermore, the identification of perceptual nonlinearities in multisensory stimulation will guide future work into understanding the neural mechanisms responsible for self-motion perception

Visual Pursuit in Gymnasts

In comparison with non-athletes, there is little doubt that gymnasts have better spatial orientation during complex sport-specific movements, like double or triple “twisting somersaults” or similar exercises. An understanding of the specific processes of spatial training and their function in a higher level of multi-axial spatial orientation remains unclear. One must consider the role that motor learning in any sensorimotor system contributing to orientation might play, e.g. smooth pursuit. Are there measurable differences in the dynamics of these behaviors between gymnasts and non-athletes due to their respective levels of training? We sought to investigate the relationship between smooth pursuit performance and the spatial orientation needed during fast multi-axial whole body rotations. The subjects’ (gym: n = 9, age: 10–12 years, control: n = 10, age: 10–12 years) smooth pursuit eye movements were recorded using a monocular video nystagmography system (SMI). They were seated in the dark with head and body fixed. The stimulus was a laser target moving horizontally with a sinusoidal velocity profile. Maximum stimulus velocities of 60/s, 120/s, 140/s, 160/s, were used, with a short break between tests. The gymnast group was tested again after a three-week break in their gymnastic training. Pursuit gain was calculated as the ratio of the amplitude of the best-fit sine wave for the slow-component eye velocity to the amplitude of the stimulus velocity. Any additional training effect on pursuit velocity, e.g. video games, could be excluded. Although in both groups the gains were reduced with higher maximum stimulus velocity, the results show significantly higher gains for the gymnasts during the 120/s test (gain ± s.d., gym.:0.23±0.10, n=9, control: 0.14±0.08, n=10; p=0.022, Z=-2.289, Mann-Whitney-U) and 140/s (gain ± s.d., gym.:0.19±0.12, n=9, control: 0.08±0.05, n=10; p=0.010, Z=-2.536, Mann-Whitney-U). For 60/s and 160/s there was only a tendency toward higher gains for the gymnasts. After the break in training, the gymnasts gains were significantly reduced at 120/s and 140 /s (120/s: 0.20±0.09, n=9; p=0.028, Z=-2.198; 140/s: 0.12±0.07, n=9; p=0.033, Z=-2.136, Wilcoxon). There was also a clear reduction at 60/s and 160/s, but not significant. Smooth pursuit in healthy humans shows a saturation (gain>0.8, binocular) of approximately 100/s [1]. So tests with peak velocities of 120/s and 140/s are clearly above this saturation level. The results demonstrate that high-performance gymnasts show a training-dependent modification of their maximum velocity for smooth pursuit

Vestibulo-Ocular Reflex Eye Movements During Multiaxial Whole Body Rotations

Vestibulo-ocular reex (VOR) responses of humans to whole body rotations are well known. Along with other parameters, the “VOR-gain” (eye velocity / head velocity) may be used to evaluate the functional status of the VOR. Although VOR gain is known to show great individual variability, we sought to determine whether the adaptive plasticity of VOR gain may give insight about individual strategies for optimal spatial orientation. The question of whether the oculomotor responses would be different between a group of experts (“gym” - high performance gymnasts), with a high degree of spatial abilities, and a control group of non-athletes (“control”), was of particular interest. The subjects' (gym: n = 9, age: 10–12 years, control: n = 10, age: 10–12 years) eye movements were recorded using a video nystagmography system (SMI). They were seated with head xed in a software controlled multiaxial whole body rotator. The test consisted of a combination of a two simultaneous sinusoidal 360 rotations about the pitch and yaw axes, followed by the reverse motion, simulating movements of “twisting somersaults”. The maximum velocity was 113 deg/s in each axis, and duration was 10 sec for the whole test (0.1 Hz). Each subject was rst rotated without knowledge of the nature of the stimulus, followed by a repetition where the subjects knew the same test would occur. This was compared to a standard sinusoidal monoaxial (horizontal) test (0.1 Hz, 100 deg/s). Although correctly directed eye movements were observed during all phases of the whole body rotation (including in a companion study with double twists), initial comparisons were performed on the horizontal components of eye movements and whole body rotation. The results show no signicant difference between the gymnasts and controls for the sinusoidal test (gain s.d.,gym.:0.48 0.06, n=9, non.:0.45 0.14, n=9; p=.565, Z=-.575, Mann-Whitney-U), and the rst (w/o prior knowledge) multiaxial stimulus (gym.:0.48 0.05, n=8; non.:0.47 0.07, n=9; p=.596, Z=-.531, Mann-Whitney-U). For the second (prior knowledge) multiaxial stimulus, the difference was signicant ((gym.:0.39 0.05, n=6; non.:0.45 0.06, n=6; p=.037, Z=-2.085, Mann-Whitney-U). Finding no difference for the tests without expectations of the stimulus show that the reexive response has not been adapted in this context. But the signicant difference following preparation of the stimulus shows the gymnasts suppress even reexive eye movements. This is consistent with the companion poster indicating that gymnasts may rely heavily on visual orientation mechanisms at the expense of vestibular responses, both cognitive and oculomotor

Comparing vestibulo-ocular eye movement characteristics with coaches' rankings of spatial orientation aptitudes in gymnasts

Visual orientation during head- and self-motion without retinal image slips requires efficient gaze stabilizing oculomotor functions that support unblurred retinal function. These mechanisms are driven by different sensor systems, such as vestibular afferents (vestibulo-ocular reflex - VOR) or retinal afferents (optokinetic reflex - OKR) to generate reflexive eye movements that continuously compensate for 3-dimensional head motions in space. High-level athletes trained in sports that involve fast and complex rotational movements (i.e., gymnasts) have a highly developed capability of efficiently orienting while executing such complex movements. This spatial orientation ability can, to a certain extend be learned. However, one's intrinsic aptitude for easily coping with such multiaxial orientation challenges seems to be specific to each individual. It is not clear which role the individual level of VOR precision plays within the possible factors that determine such individual aptitudes. The aim of the present study is to examine to what extend the individual level of VOR correlates with individual aptitude to cope with multiaxial spatial orientation challenges as required in gymnastics. For this we used a method to evaluate the individual aptitude for multiaxial spatial orientation during actively performed maneuvers in competitive gymnasts by exploiting the accumulated expertise of coaches. We directly compared these expert-rating measures to individual VOR characteristics. The results indicate relationships between these ratings and the response of the vertical VOR in gymnasts