Effects of Chronic Alcohol Use Disorder on the Visual Tilt Illusion

Rationale: Among the serious consequences of alcohol use disorder (AUD) is the reduced ability to process visual information. It is also generally agreed that AUD tends to occur with disturbed excitation–inhibition (EI) balance in the central nervous system. Thus, a specific visual behavioral probe could directly qualify the EI dysfunction in patients with AUD. The tilt illusion (TI) is a paradigmatic example of contextual influences on perception of central target. The phenomenon shows a characteristic dependence on the angle between the inducing surround stimulus and the central target test. For small angles, there is a repulsion effect; for larger angles, there is a smaller attraction effect. The center-surround inhibition in tilt repulsion is considered to come from spatial orientational interactions between orientation-tuned neurons in the primary visual cortex (V1), and tilt attraction is from higher-level effects of orientation processing in the visual information processing.Objectives: The present study focuses on visual spatial information processing and explores whether chronic AUD patients in abstinence period exhibited abnormal TI compared with healthy controls.Methods: The participants are 30 male volunteers (20–46 years old) divided into two groups: the study group consists of 15 clinically diagnosed AUD patients undergoing abstinence from alcohol, and the control group consists of 15 healthy volunteers. The TI consists of a center target surround with an annulus (both target and annulus are sinusoidal grating with spatial frequency = 2 cycles per degree). The visual angle between center and surround is a variable restricted to 0°, ±15°, ±30°, or ±75°. For measuring the TI, participants have to report whether the center target grating orientation tilted clockwise or counterclockwise from the internal vertical orientation by pressing corresponding keys on the computer keyboard. No feedback is provided regarding response correctness.Results: The results reveal significantly weaker tilt repulsion effect under surround orientation ±15° (p < 0.05) and higher lapse rate (attention limitation index) under all tested surround orientations (all ps < 0.05) in patients with chronic AUD compared with health controls.Conclusions: These results provide psychophysical evidence that visual perception of center-contextual stimuli is different between AUD and healthy control groups.

Estimation of Line Orientation Depends on the Set of Additional Images

The orientation of the lines, to which additional inclined lines could adjoin, was estimated. We have found a distortion in estimation of lines orientation by 1—2° (tilt illusion) when additional lines were presented, depending on a set of additional lines. For different observers, in the case of the presence of additional lines with a difference in orientation between the lines of up to 12°, both the effect of attraction (the lines seemed to be turned towards the additional) and the effect of repulsion could be detected. With a larger difference, only the repulsive effect is revealed. The discrepancy in the dependences can be explained by the difference in the visual acuity of observers associated with the size of the smallest receptive fields of striatal cortex neurons

Visual Deficiency in Wallenberg’s Syndrome

The aim of this case report of a 47-year-old woman who suffered from acute right-sided medullar ischemic stroke was to define the range of visual impairment in Wallenberg’s syndrome (WS). The patient complained of unbearable environmental tilt and rotating visual perception. On examination, 11 months following the stroke, the patient manifested rightsided postural inclination and gaze ipsipulsion. The fixation in primary position was unstable, after a conjugate ipsipulsion ensued, spontaneous corrective saccades and a horizontal-rotational jerking nystagmus beating away from the side of the lesion were generated. Monocular visual acuity (right eye: 0.4 logMAR distance and 0.2 logMAR near; left eye: 0.1 logMAR distance and 0.0 logMAR near) was significantly better than binocular (0.63 logMAR distance and near). Fluent reading was impossible. Contralateral smooth pursuits were more impaired. Saccades were defective manifesting right hypermetria and left hypometria. Visual field was constricted to central 10 – 20°. A diagnosis of Wallenberg’s syndrome was made. Occlusion was prescribed. Review of literature demonstrated lack of evidence-based guidelines for ophthalmic assessment and treatment of visual impairment in WS. Oculomotor abnormalities, oscillopsia and tilt illusion cause significant impact to daily life. Early post-stroke ophthalmological evaluation is thus mandatory in order to offer timing treatment.

Room tilt illusion and subclavian steal – a case report

Background Room tilt illusion (RTI) is a rare symptom of higher vestibular dysfunction, consisting of a transient vertical rotation of the visual scene in the sagittal or coronal plane, most often 90o or 180o, without any alteration in shape, size and color of objects. Case presentation A 63-year-old woman with a history of hypertension and chronic obstructive pulmonary disease went through an uncomplicated aortobifemoral graft surgery due to aortoiliac occlusive disease. Post-operatively she experienced five episodes, lasting from 10 to 30 min, with RTI; 90o forward rotation of the visual scene in the sagittal plane. Work-up revealed subclavian steal grade 3, and transient ischemia of the central vestibular system of the brainstem was the presumed mechanism. Conclusion The course of episodic RTIs is often benign, but RTI may represent ischemia in the posterior cerebral circulation. Both stroke and otoneurologic workup are recommended. To our knowledge, this is the first case of RTI associated with subclavian steal reported.

Interference in Tilt-Illusion stimuli: A simple illustration

The relevance of relative phase for addition of amplitude spectra was demonstrated by comparing theeffect of three phase differences, 0, π/2 = 90 degrees, and π = 180 degrees, with two theoretical amplitudespectra displaced relative to each other as they would if they represented stimuli of different orientations.Differences in phase cause the amplitudes in the combined stimulus to be reduced relative to the sum ofamplitudes in the two spectra. Because the reductions are most pronounced where the spectra overlap, inthe case of partially overlapping spectra this may cause the two spectra to be effectively shifted away fromeach other. In the case where the spectra belong to stimuli of different orientations such shifts may cause theapparent angle between two stimuli to increase. This may be consistent with the Tilt Illusion. In which caseit may be possible to account for this illusion based on the stimuli without implicating the visual system.