Perception of stationary and moving sound following unilateral cortectomy

The perception of motion is an essential prerequisite to responding adequately to the dynamic aspects of sensory information in the environment. The neural substrates of auditory motion processing are, at present, still a matter of debate. It has been hypothesized that motion information is, as in the visual system, processed separately from other aspects of auditory information, such as stationary location. Here we report data on auditory perception of stationary and motion stimuli from a subject with right-sided resection of the anterior temporal-lobe region including medial aspects of Heschl's gyrus, and from three subjects with unilateral (right-sided or left-sided) hemispherectomy. All these subjects had undergone cortectomy decades earlier. The subjects with hemispherectomy were completely unable to perceive auditory motion, but showed slight to moderate deficits in judging stationary location. The subject with temporal lobectomy exhibited quite similar stationary auditory deficits as found in the subjects with hemispherectomy, but was completely normal in judging auditory motion. Thus, there was a clear dissociation of the effects of unilateral temporal lobectomy and hemispherectomy on auditory motion perception. Collectively, these findings suggest that the unilateral anterior temporal-lobe region plays a significant role in the analysis of stationary, but not moving, sound. One may assume that the cortical “motion network” is distinct from the “stationary network”, and is located either in the most posterior aspects of temporal lobe, or in non-temporal, most likely parietal, areas.     

Dynamic vision based on motion-contrast: changes with age in adults

Data are presented for a computerized test of dynamic vision in a sample of 1006 healthy subjects aged between 20 and 85 years. The test employed a form-from-motion stimulus: i.e., within a random-dot display, Landolt rings of the same average luminance as their surroundings become visible only when the dots within the ring are moved briefly, while those of the surround remain stationary. Thus, detection of gap location is based upon motion contrast (form-from-motion) rather than luminance contrast. With the size and exposure duration of the centrally presented ring held constant, motion contrast was manipulated by varying the percentage (between 20 and 100%) of moving dots within the ring. Subjects reported gap location (left, right, top, bottom). A gradual decline of dynamic vision with age was found for all motion-contrast levels. Beyond 70 years of age, chance-level performance occurred in almost half of the subjects. The data provide the basis for applications including diagnostic screening for glaucoma, visual disturbances in brain-damaged patients, as well as assessment of the dynamic vision of drivers of motor vehicles and athletes.     

Determining the artifact sensitivity of recent pulse oximeters during laboratory benchmarking

This study aimed to investigate and compare the performance of the algorithms contained in the newest generation of pulse oximeters (Masimo SET in IVY2000, Nellcor Oxismart N-3000, Agilent M3 rev. B) against a traditional pulse oximeter (Agilent CMS rel. A.0). The benchmark was performed in an efficient and reproducible way in the laboratory environment using patient signal recordings complemented by a two-hand volunteer motion test. A novel method of creating artifact/reference signal pairs from a clinical database, the noise-mix-composition (NMC), was developed. The new method enabled the simulation of critical clinical situations in a more realistic way than the usual two hand volunteer studies. An advantage of the laboratory tests over live clinical studies was that a continuous saturation reference was available, allowing accurate on-going determination of the SpO2 error. A new quantitative performance measure, the non-performance index (NPI), was developed and applied to the benchmark results. It covers the 3 performance aspects of a pulse oximeter: (1) SpO2 accuracy, (2) pulse rate accuracy and (3) drop out times. These factors were weighted according to clinical importance determined by a survey. During the restricted conditions of steady state and forced motion test on healthy volunteers Masimo/Ivy's pulse oximeter performed best with a 2.6 fold improvement over the conventional technology. Clear improvements were also found for Agilent's M3 (1.6 fold) and Nellcor's N-3000 (1.6 fold). In contrast, the clinically oriented NMC study yielded the best performance improvement--as measured in NPI numbers--for Agilent's M3 rev. B (1.6 fold) and due to more frequent SpO2 errors only 1.5 for Masimo and 1.3 for N-3000. A large difference was found for the dropout rate: the lowest was achieved by Masimo (3.0% of total time), the largest by Nellcor N-3000 (24.1% of total time), a factor which was rated high by clinicians. Very pronounced improvements (between 2.3 and 3.4 fold) on all of the newer devices were found for the pulse rate. The NMC turned out to be a very useful tool for generating a standard signal set for algorithm development and benchmarking purposes that eliminates repetitive clinical testing in early stages. The applicability of its results needs confirmation by clinical live studies.     

Multisensory contributions to the perception of motion

The ability to process motion is crucial for coherent perception and action. While the majority of studies have focused on the unimodal factors that influence motion perception (see, for example, the other chapters in this Special Issue), some researchers have also investigated the extent to which information presented in one sensory modality can affect the perception of motion for stimuli presented in another modality. Although early studies often gave rise to mixed results, the development of increasingly sophisticated psychophysical paradigms are now enabling researchers to determine the spatiotemporal constraints on multisensory interactions in the perception of motion. Recent findings indicate that these interactions stand over-and-above the multisensory interactions documented previously for static stimuli, such as the oft-cited 'ventriloquism' effect. Neuroimaging and neuropsychological studies are also beginning to elucidate the network of neural structures responsible for the processing of motion information in the different sensory modalities, an important first step that will ultimately lead to the determination of the neural substrates underlying these multisensory contributions to motion perception.     

Das Bewegungszentrum in der Lendenwirbels?ule bei Flexion und Extension

Zusammenfassung In zwei lumbalen Segmenten hat man mit der Tomographie die Lage der Bewegungsachse bei Flexion und Extension bestimmt. Es wurde gefunden, daß die Achse im Anschluß an die Bandscheibe liegen kann, aber in der Mehrzahl der Fälle lag die Achse auf bedeutendem Abstand von ihr und immer unterhalb dieser Bandscheibe. In extremen Fällen sah man, daß die Bewegungsachse durch die nächst unterhalb liegende Bandscheibe ging.

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Motion centre in flexion and extension of the lumbar spine

Summary The location of the axis of movement between the vertebrae in two lumbar segments was determined by means of tomography in flexion and extension. It was found that the axis may be situated in the disc or in its immediate vicinity but in the majority of cases it lay outside the disc at considerable distances from it. Then it was always below the disc. In extreme cases the axis was seen to pass through the intervertebral disc of the segment below.

     

Motion detection and correction for dynamic 15O-water myocardial perfusion PET studies

Purpose Patient motion during dynamic PET studies is a well-documented source of errors. The purpose of this study was to investigate the incidence of frame-to-frame motion in dynamic ¹⁵O-water myocardial perfusion PET studies, to test the efficacy of motion correction methods and to study whether implementation of motion correction would have an impact on the perfusion results.Methods We developed a motion detection procedure using external radioactive skin markers and frame-to-frame alignment. To evaluate motion, marker coordinates inside the field of view were determined in each frame for each study. The highest number of frames with identical spatial coordinates during the study were defined as non-moved. Movement was considered present if even one marker changed position, by one pixel/frame compared with reference, in one axis, and such frames were defined as moved. We tested manual, in-house-developed motion correction software and an automatic motion correction using a rigid body point model implemented in MIPAV (Medical Image Processing, Analysis and Visualisation) software. After motion correction, remaining motion was re-analysed. Myocardial blood flow (MBF) values were calculated for both non-corrected and motion-corrected datasets.Results At rest, patient motion was found in 18% of the frames, but during pharmacological stress the fraction increased to 45% and during physical exercise it rose to 80%. Both motion correction algorithms significantly decreased (p<0.006) the number of moved frames and the amplitude of motion (p<0.04). Motion correction significantly increased MBF results during bicycle exercise (p<0.02). At rest or during adenosine infusion, the motion correction had no significant effects on MBF values.Conclusion Significant motion is a common phenomenon in dynamic cardiac studies during adenosine infusion but especially during exercise. Applying motion correction for the data acquired during exercise clearly changed the MBF results, indicating that motion correction is required for these studies.     

Shifting the onset of a moving sound source: a Fröhlich effect in spatial hearing

When observers are presented with a visual target in motion, they typically remember its onset position to be displaced in the direction of motion. The present study investigated a similar effect in the auditory modality. In a dark anechoic environment, an auditory target (short noise pulses) appeared randomly at a peripheral or a central azimuthal position and moved from left to right or from right to left along the frontal horizontal plane. Relative judgments were made to determine the onset position of motion: Employing a two-alternative forced-choice task, listeners compared the onset position of the target to a 2-s visual reference stimulus presented at the left or right of the auditory onset position. In comparison with stationary targets, the onset positions of moving targets were localized as displaced in the direction of motion. The most prominent displacement occurred when the visual reference stimulus was presented after the auditory motion. With the reference stimulus presented before the auditory motion, the displacement was significantly reduced. Moreover, the displacement was stronger with peripheral than with central onset positions. These findings suggest the existence of a potential analogue of the Fröhlich effect in the auditory modality. An auditory spatial attention mechanism is proposed that may have given rise to the observed pattern of results.     

Cognitive and emotional alterations in periadolescent mice exposed to 2 g hypergravity field

The development of the nervous system is a dynamic process where epigenetic factors play a fundamental role. Both ground-based and space research indicate that exposure to an altered gravitational environment affects rodent neurobehavioral profile and stage of development as well as duration of exposure appear to be critical for the observed effects. The behavioral profile of adolescent (28-day-old) male and female CD-1 mice upon acute 2 g exposure was characterized and emotional/anxiety responses (plus-maze), as well as spatial learning performance (Morris water-maze), were assessed respectively 24 and 48 h after hypergravity exposure. Behavioral observation indicated a transient mild sickness associated with hypergravity, with a decrease in spontaneous activity. Rotation per se induced an increase in emotional/anxious responses and a deterioration of spatial learning acquisition, while hypergravity specifically improved flexibility of spatial orientation.     

Effective binocular integration at the midline requires the corpus callosum

To study the role of the corpus callosum (CC) in midline binocular integration, the effects of late callosotomy and congenital CC agenesis on the ability to perceive dichoptic plaid motion was assessed. Coherent motion was well perceived at all locations in the visual field under dioptic viewing but not along the vertical meridian (VM) when the components were dichoptically presented. This deficit was totally abolished in the agenesis subject and reduced in the callosotomized individual when stimulus size was increased beyond the VM. Electrophysiological correlates were also examined by recording visual evoked potentials and these showed that the P1/N2 components were abnormal for small dichoptic stimuli presented on the midline. These findings attest to the importance of the contribution of CC to midline binocular integration and the effects of cerebral plasticity.     

Attenuation of perceived motion smear during vergence and pursuit tracking

When the eyes move, the images of stationary objects sweep across the retina. Despite this motion of the retinal image and the substantial integration of visual signals across time, physically stationary objects typically do not appear to be smeared during eye movements. Previous studies indicated that the extent of perceived motion smear is smaller when a stationary target is presented during pursuit or saccadic eye movements than when comparable motion of the retinal image occurs during steady fixation. In this study, we compared the extent of perceived motion smear for a stationary target during smooth pursuit and vergence eye movements with that for a physically moving target during fixation. For a target duration of 100 ms or longer, perceived motion smear is substantially less when the motion of the retinal image results from vergence or pursuit eye movements than when it results from the motion of a target during fixation. The reduced extent of perceived motion smear during eye movements compared to fixation cannot be accounted for by different spatio-temporal interactions between visual targets or by unequal attention to the moving test spot under these two types of conditions. We attribute the highly similar attenuation of perceived smear during vergence and pursuit to a comparable action of the extra-retinal signals for disjunctive and conjugate eye movements.