Search results for "visual"
showing 10 items of 7386 documents
Visuospatial attention shifts by gaze and arrow cues: an ERP study.
2007
Orienting of visual attention can be automatically triggered not only by illumination changes occurring in the visual periphery but also by centrally presented gaze and arrow cues. We investigated whether the automatic shifts of visuospatial attention triggered by centrally displayed gaze and arrow cues rely on the same neural systems. To this end we measured event-related potentials (ERPs) time-locked to the cue and target onsets while the participants (n=17) performed a spatial cuing task. In the task, the participants detected and responded to laterally presented targets preceded by centrally presented, non-predictive, gaze or arrow cues. Manual reaction times and target-triggered ERP da…
Functional Magnetic Resonance Imaging Activations of Cortical Eye Fields during Saccades, Smooth Pursuit, and Optokinetic Nystagmus
2009
Saccades, smooth pursuit, and optokinetic nystagmus (OKN) are three basic eye movements in our ocular motor repertoire that enable us to explore the visual field. These eye movements are cortically controlled in different cortical eye fields, including the frontal eye fields (FEF) and parietal eye fields (PEF), as well as the motion-sensitive visual area MT+/V5. It is not known if this cortical control is organized in parallel cortico-cortical networks or in adjacent subregions of one system. Nor do we know where the specific eye fields are exactly located. Functional magnetic resonance imaging (fMRI) was used to investigate these open questions about the FEF, PEF, and MT+/V5. Activations o…
Inhibitory interhemispheric visuovisual interaction in motion perception.
2003
Findings of an earlier functional magnetic resonance imaging (fMRI) study that coherent motion stimulation of the right or left visual hemifield exhibited negative signal changes (deactivations) in the primary visual cortex and the lateral geniculate nucleus contralateral to the stimulated hemisphere were evaluated to determine the functional significance of this contralateral inhibition of the visual system. Fourteen subjects participated in a psychophysical study on the perception of single object motion (0.4 degrees /s) in one visual hemifield with or without concurrent coherent motion stimulation of the contralateral hemifield. Mean detection times for horizontal object motion (0.5 +/- …
Electrophysiological signatures of masked transposition priming in a same-different task: Evidence with strings of letters vs. pseudoletters
2012
Research on masked transposed-letter priming (i.e., jugde-JUDGE triggers a faster response than jupte-JUDGE) has become a key phenomenon to reveal how the brain encodes letter position. Recent behavioural evidence suggests that the mechanism responsible for position coding in a masked priming procedure works with familiar "object" identities (e.g., letters, digits, symbols) but not with unfamiliar object identities (e.g., pseudoletters). Here we used event-related potentials (ERPs) to explore the time course of masked transposition priming of letters vs. pseudoletters in a cue-target same-different matching task. Target stimuli were preceded by a masked prime that could be: (i) identical to…
Anatomical correlate of positive spontaneous visual phenomena: a voxelwise lesion study.
2010
Objectives: Visual phenomena such as phosphenes, photopsias, or complex visual hallucinations occur in patients with lesions affecting the occipital, parietal, or temporal lobe. Whether these phenomena are provoked by lesions in specific anatomical regions is still uncertain. To determine which brain regions might be involved in such visual phenomena, we used new brain imaging and lesion analysis tools that allow a direct comparison with control patients. Methods: Visual phenomena were investigated in a total of 23 patients with acute infarctions along the visual pathways (6 patients with left-sided and 17 patients with right-sided lesions). Results: Ten of these 23 patients (43%) reported …
fMRI signal increases and decreases in cortical areas during small-field optokinetic stimulation and central fixation
2001
Small-field optokinetic nystagmus (OKN) was performed in seven healthy volunteers in order to analyze the activation and deactivation patterns of visual motion, ocular motor, and multisensory vestibular cortex areas by means of fMRI during coherent visual motion stimulation. BOLD signal decreases (deactivations) were found in the first and second long insular gyri and retroinsular areas (the human homologue of the parietoinsular vestibular cortex and the visual posterior sylvian area in the monkey) of both hemispheres, extending into the transverse temporal gyrus and inferior-anterior parts of the superior temporal gyrus (BA 22), and the precentral gyri at two separate sites (BA 4 and 6). F…
Visual tracking combined with hand-tracking improves time perception of moving stimuli
2014
A number of studies have shown that performing a secondary task while executing a time-judgment task impairs performance on the latter task. However, this turns out not to be the case for certain motor secondary tasks. We show that concomitant secondary motor tasks involving pointing, when performed during a time-judgment task, can actually improve our time-judgment abilities. We compared adult participants' performance in a time-of-movement paradigm with visual pursuit-only and with visual pursuit plus hand pursuit. Rather than interfering with their estimation of stimulus movement duration, the addition of hand pursuit significantly improved their judgment. In addition, we considered the …
Evidence for cortical visual substitution of chronic bilateral vestibular failure (an fMRI study).
2007
Bilateral vestibular failure (BVF) is a rare disorder of the labyrinth or the eighth cranial nerve which has various aetiologies. BVF patients suffer from unsteadiness of gait combined with blurred vision due to oscillopsia. Functional MRI (fMRI) in healthy subjects has shown that stimulation of the visual system induces an activation of the visual cortex and ocular motor areas bilaterally as well as simultaneous deactivations of multisensory vestibular cortex areas. Our question was whether the chronic absence of bilateral vestibular input (BVF) causes a plastic cortical reorganization of the above-described visual-vestibular interaction. We used fMRI to measure the differential effects of…
Accommodation Responds to Optical Vergence and Not Defocus Blur Alone.
2017
Purpose To determine whether changes in wavefront spherical curvature (optical vergence) are a directional cue for accommodation. Methods Nine subjects participated in this experiment. The accommodation response to a monochromatic target was measured continuously with a custom-made adaptive optics system while astigmatism and higher-order aberrations were corrected in real time. There were two experimental open-loop conditions: vergence-driven condition, where the deformable mirror provided sinusoidal changes in defocus at the retina between -1 and +1 diopters (D) at 0.2 Hz; and blur-driven condition, in which the level of defocus at the retina was always 0 D, but a sinusoidal defocus blur …
Position but not color deviants result in visual mismatch negativity in an active oddball task.
2009
Changes in the visual environment might be detected automatically. This function is provided by the sensory systems and showed, for instance, by the pop-out phenomenon. Automatic change detection is also observable within visual oddball paradigms, where rare changes are introduced in an irrelevant stimulus feature; the detection of deviant stimuli is accompanied by a negative component (so-called visual mismatch negativity) in the human event-related brain potential. In this study, the deviating stimulus feature was embedded in a task-relevant object presented in the focus of attention. With this, visual mismatch negativity was observable only with position deviants presented in the upper v…