Search results for "Percept"
showing 10 items of 3839 documents
Imaging the visual autokinetic illusion with fMRI
2005
During fixation of a stationary, dim light-emitting diode (LED) in complete darkness, a subtle, apparent motion is perceived which is called autokinesis. This autokinetic illusion increases with increasing fixation time. Eleven healthy subjects were examined by fMRI while fixating an LED in darkness for 35 s. BOLD signal changes of the first and the second half of the fixation period were compared. While the stimulus was the same for both periods, perception differed in that autokinesis was more pronounced in the second half. This second half of the period was associated with bilateral activations in the motion-sensitive middle occipito-temporal area known as MT/V5. Our finding suggests tha…
Response repetition vs. response change modulates behavioral and electrophysiological effects of distraction
2004
If stimulation occasionally contains distracting information, behavioral responses to task-relevant aspects of the stimulation are prolonged and more error prone. Additionally, event-related potentials (ERPs) acquired in an auditory distraction paradigm show that the distracting information elicits the components mismatch negativity (MMN), P3a and reorienting negativity (RON). Here, we assess to what extent sequential dependencies in the stimulation influence such indicators of distraction. Data of four experiments were reanalyzed for response repetition and response change trials separately. Behavioral performance on Deviants suggests markedly smaller distraction effects in change compared…
Effects of high doses of toluene on color vision.
1999
High exposure to toluene may cause optic neuropathy and retinopathy, both associated with dyschromatopsia. Another solvent, ethanol, is known to induce acute blue-yellow dyschromatopsia. This study investigated the acute effects of high doses of toluene on color vision. Eight male printshop workers were examined before and after cleaning printing containers with pure toluene. After cleaning, concentrations of toluene in blood were between 3.61 and 7.37 mg/l. Color vision was tested with the Farnsworth panel D-15 test, the Lanthony desaturated panel D-15 test, and the Standard Pseudoisochromatic Plates part 2. For control of possible acute effects, eight workers of a metal-working factory wi…
Neural correlates of disturbed perception of verticality.
2012
Objective: Perception of verticality can be perturbed after cortical stroke. However, a relationship between lesion location and pathologic perception of verticality is still a matter of debate since previous studies revealed contradictory results. Thus, the aim of the current study was to test whether specific cortical lesions were associated with tilts of subjective visual vertical (SVV) and to determine the critical brain areas that cause such tilts in the case of a lesion. Methods: SVV was systematically studied in 54 patients (22 patients with left-sided and 32 patients with right-sided lesions) with acute unilateral strokes, analyzed by modern voxel-wise lesion-behavior mapping techni…
Symmetric bilateral implantation of a distance-dominant diffractive bifocal intraocular lens
2007
To assess visual results after symmetrical bilateral implantation of a distance-dominant bifocal diffractive intraocular lens (IOL).Fernández-Vega Ophthalmological Institute, Oviedo, Spain.Fifty patients had bilateral implantation of a distance-dominant diffractive bifocal 447D IOL (Acri.Tec GmbH) in a prospective study. Monocular and binocular best corrected distance visual acuities and best distance-corrected near visual acuity, binocular best distance-corrected intermediate visual acuity, and distance contrast sensitivity under photopic (85 cd/m(2)) and mesopic (5 cd/m(2)) conditions were determined.At the 6-month postoperative visit, the mean binocular best corrected distance acuity and…
Comparison of the Behavioural Inattention Test and the Catherine Bergego Scale in assessment of hemispatial neglect.
2010
The objective of the study was to correlate visual and behavioural assessments of hemispatial neglect caused by cerebrovascular accident. We assessed 17 consecutive right-hemisphere stroke patients with hemispatial neglect: the Catherine Bergego Scale (CBS) was used to evaluate neglect in spontaneous behaviour and the conventional subtests of the Behavioural Inattention Test (BIT C) were used to assess visual neglect. The proportional severity of both visual and behavioural neglect was calculated in each individual patient. Dissociations were found between mild neglect in visual screening tasks and moderate or severe neglect in behaviour, although in most patients, neglect was equally evide…
Oculovestibular interactions under microgravity.
1993
On a space mission in March 1992 a set of experiments were performed aimed at clarifying the interaction between visual, proprioceptive and vestibular inputs to the equilibrium system. Using the VESTA goggle facility from the European Space Agency we investigated the effect of pure neck receptor stimulation on eye position as measured by the flash afterimage method and on perception of a head-fixed luminous line in space. Space vestibular adaptation processes were measured by rotating pattern perception during prescribed head movements. It was found that static ocular counterrotation does not occur under micro gravity conditions. This result suggests that the neck receptors apparently do no…
Fixation suppression of optokinetic nystagmus modulates cortical visual-vestibular interaction.
2005
Water activation positron emission tomography and statistical group analysis were used to evaluate differences in activation-deactivation patterns during small-field visual motion stimulation, eliciting rightward optokinetic nystagmus and its fixation suppression in 12 healthy volunteers. Bilateral patterns of activation in the visual cortex, including the motion-sensitive area MT/V5, and deactivations in an assembly of vestibular areas (posterior insula, thalamus, anterior cingulate gyrus) during optokinetic nystagmus was markedly diminished or totally absent during its fixation suppression. This finding agrees with the concept of a reciprocal inhibitory interaction between the visual-opto…
Hemispatial neglect reflected on visual memory
2011
PURPOSE Recent studies of hemispatial neglect have revealed both lateralized and nonlateralized attention mechanisms contributing to the syndrome. In addition, neglect patients show impaired spatial working memory and diminished working memory capacity. The aim of this study was to investigate, how neglect would be reflected in their performances in commonly used clinical visual memory tests. METHODS Twelve patients with right hemisphere lesions and left neglect and twelve matched controls were assessed with the Behavioural Inattention Test, the visual reproduction of the WMS-R, the object memory test, the Rey figure test and the list learning test. Visuo-spatial span was explored with the …
Tactile perceptual processes and their relationship to medically unexplained symptoms and health anxiety
2011
Abstract Objective The Somatic Signal Detection Task (SSDT; Lloyd, Manson, Brown and Poliakoff, 2008) is an innovative paradigm to study perceptual processes related to physical symptoms. It allows examining touch illusions as a laboratory analog of medically unexplained symptoms (MUS) according to the cognitive model of MUS proposed by Brown (2004). The present study compared psychopathologic measures of MUS and health anxiety with SSDT parameters. Furthermore, we aimed to define a reliable measurement of tactile perception threshold. Methods 67 participants of a student population reported whether they detected tactile stimuli at their fingertip which were presented in half of the test tr…