Dynamics of visual hand localization in the 24-hour observation of persons working under conditions of additional loads

Examined--by means of a Starkiewicz's hand localizer--were 170 right-hand workers of a paper factory working in conditions of excessive noise and high temperature of the surroundings. Analyzed were 140 persons tested 4 times in the period of each production shift (6.00-14.00; 14.00-22.00, and 22.00-6.00). The analysis showed the maximal efficacy of the visual function of the hand localization in the range of the right-hand and in the course of the night shift in both age groups.     

Pointing response in normal subjects]

Eye-hand open-loop pointing responses were examined in five normal subjects, with visual cues for relative target localization. Pointing errors differed significantly with the position of the target. In some cases, pointing responses in the dark were significantly different from those in the light. Pointing shifts were also significant between the responses immediately after putting the experimental device on and those 15 minutes after. From these results, it was speculated that visual localization and eye-hand coordination may be influenced by the visual context and the passage of time.     

Usefulness of the provocative prism test for studying visual hand localization

Two examples are presented of the behaviour of the visual-hand localization during examination by means of a hand localizer, each eye separately with a provocative prism test and without the prism. The provocative test allows to perform a deeper analysis of the changes of the hand localization. The authors describe the behaviour of the visual-hand localization in 40 examined persons and consider the amount of the localization recoil caused by placing of a prism, the speed of the straightening out the changed localization, in other words a hypercorrected sign of deviation and lateral shifting to the right or left.     

Neck muscle vibration in full cues affects pointing

Vibration of the dorsolateral neck stimulates proprioceptors that are normally active during head movement; this induces a visual illusion of contralateral motion and displacement of a stationary target seen against a homogenous background. The spatial constancy explanation of the illusion argues that it occurs because information about head movement is necessary for accurate egocentric localization of visual objects. Accurate egocentric localization, in turn, is necessary for the success of object-directed motor action, but previous studies failed to find evidence that vibration affects pointing toward visual targets in a normally illuminated, structured field. Our goal was to provide this evidence. Vibration lasting 12 s was applied to either side of the neck while observers (N = 11) pointed at the visual target with an unseen hand. Vibration of the right side of dorsal neck in the illuminated visual field induced a 26-mm lateral bias in pointing responses in comparison to the vibration of the left side. We conclude that the mechanism that takes into account neck proprioceptive signals also operates in full cues. The pointing bias in full cues generally co-occurred with reported stationariness of the visual target, suggesting a conflict between cues used in perception of body-centric position used to guide action, which include neck proprioception, and those used in perception of motion, for which object-relative retinal information is sufficient.     

Mislocalization of peripheral targets during fixation

To investigate the effect of the visual stimulus configuration on localization when oculomotor performance is excluded, we evaluated the errors made when subjects compare the horizontal location of two sequentially presented peripheral targets while looking at a visual or memorized fixation spot. Eye position was monitored by means of an infrared eye tracker. Significant localization errors were observed. As long as the fixation spot stayed on or off during the entire presentation time of both peripheral targets, the localization error did not depend on the presence or absence of the fixation spot. A significant change in the localization error was observed only if the fixation spot was presented together with the first peripheral target but disappeared before the presentation of the second one. The localization error did not depend on: (1) the visual asymmetry (unilateral versus bilateral target presentation); (2) the distribution of visual attention (cued versus non-cued test location); or (3) the time interval between the two targets. These results suggest that the mislocalization observed during fixation is partially due to a mismatch between egocentric and exocentric localization mechanisms.     

Dynamics of visual functions in the conditions of glow and sodium lighting. II. Time of conscious reaction and visual space-hand localization

The authors present the results of investigations performed in 20 young persons with normal sight. A trial of evaluation of the strain of the central nervous system in conditions of various kind of lighting was carried out basing on its close connection with the visual hand localization as well as with the time of the conscious reaction. Analyzed was the behaviour of the quoted functions as the time passed during the morning hours and the results of the examinations obtained in conditions of glow and sodium illumination were compared. They suggest a favourable influence of the sodium light on the discussed functions.     

Some aspects of the current controversy about the treatment of amblyopia

Occlusion has been used for centuries for treating amblyopia but in recent years an intensive debate about the treatment has arisen. The aim of this article is to summarize some of the new aspects of this discussion: on the one hand the effect of occlusion treatment during childhood is being questioned and on the other hand experimental approaches are being tested which are aimed at treating amblyopia in adults. Evidence from own experimental work is presented showing the influence of occlusion on the spatial localization of visual stimuli. A continuation of research on amblyopia and the effect of the therapy is urgently needed.     

Eye movements during rapid pointing under risk

We recorded saccadic eye movements during visually-guided rapid pointing movements under risk. We intended to determine whether saccadic end points are necessarily tied to the goals of rapid pointing movements or whether, when the visual features of a display and the goals of a pointing movement are different, saccades are driven by low-level features of the visual stimulus. Subjects pointed at a stimulus configuration consisting of a target region and a penalty region. Each target hit yielded a gain of points; each penalty hit incurred a loss of points. Late responses were penalized. The luminance of either target or penalty region was indicated by a disk which differed significantly from the background in luminance, while the other region was indicated by a thin circle. In subsequent experiments, we varied the visual salience of the stimulus configuration and found that manual responses followed near-optimal strategies maximizing expected gain, independent of the salience of the target region. We suggest that the final eye position is partially pre-programmed prior to hand movement initiation. While we found that manipulations of the visual salience of the display determined the end point of the initial saccade we also found that subsequent saccades are driven by the goal of the hand movement.     

Evidence for spatially local computations underlying discrimination of periodic patterns in fovea and periphery

Human visual sensitivity for discriminating between, on the one hand stimuli composed of components (F) and (F + 3F) (compound detection), and on the other hand (F + 3F) and (F - 3F) (phase discrimination), was measured as a function both of stimulus contrast and eccentricity. Performance under these particular conditions was found to depend upon whether the (F) or (3F) component was dominant in the pattern. When the (F) component was high in contrast, visual performance was well modelled by an edge-blur discrimination, whereas when the (3F) component was high in contrast, visual performance was well modelled by a contrast discrimination involving local spatial features within each waveform. These conclusions were valid for both foveal and peripheral vision. The finding that these suprathreshold compound stimuli are discriminated on the basis of the local spatial features, and not on differences in their phase spectra as previously thought, allows a reinterpretation of the importance of phase coding in normal vision and of the selective loss of these discriminations that have been previously reported for peripheral vision and in amblyopia.     

Bayesian integration of visual and vestibular signals for heading

Self-motion through an environment involves a composite of signals such as visual and vestibular cues. Building upon previous results showing that visual and vestibular signals combine in a statistically optimal fashion, we investigated the relative weights of visual and vestibular cues during self-motion. This experiment was comprised of three experimental conditions: vestibular alone, visual alone (with four different standard heading values), and visual-vestibular combined. In the combined cue condition, inter-sensory conflicts were introduced (Δ = ±6° or ±10°). Participants performed a 2-interval forced choice task in all conditions and were asked to judge in which of the two intervals they moved more to the right. The cue-conflict condition revealed the relative weights associated with each modality. We found that even when there was a relatively large conflict between the visual and vestibular cues, participants exhibited a statistically optimal reduction in variance. On the other hand, we found that the pattern of results in the unimodal conditions did not predict the weights in the combined cue condition. Specifically, visual-vestibular cue combination was not predicted solely by the reliability of each cue, but rather more weight was given to the vestibular cue.     

Spatial localization of colour and luminance stimuli in human peripheral vision

A variety of studies suggest the localization of objects in three-dimensional space is predominantly the task of the magnocellular (M) system, and conversely that the parvocellular (P) system plays little or no role in localization. However, there are conflicting reports and the goal of this paper was to determine whether spatial localization is predominantly accomplished by one or the other visual system. Both manual pointing and three-target alignment protocols were used to measure localization accuracy for eccentrically presented patches of a sinewave grating. Two general approaches were adopted to activate preferentially one or the other pathway: (1) we varied the spatio-temporal frequency, contrast and chromatic properties of the stimulus to conform with the physiological response properties of either M or P cells; and (2) some measurements were made both with steady fixation and during large saccades, as the latter have been reported to cause selective suppression of the M system [Burr, Morrone & Ross (1994). Nature, 371, 511-513]. Each stimulus was presented at or near its detection contrast threshold, which was determined separately for each visual field location using forced-choice procedures. Using manual pointing, both M- and P-type stimuli were localized to within about 1.3 degrees at retinal eccentricities near 10 degrees. This accuracy was not affected by distractor targets in the peripheral field or temporal uncertainty in stimulus presentation, but was reduced by a similar amount for each stimulus type during saccadic eye movements. Using the alignment task, localization accuracy remained at about 1.3 degrees for P-type stimuli but improved to 0.5 degrees for M-type stimuli. We conclude that both M and P systems play an equally important role in localizing peripheral targets for the purpose of visuo-motor tasks such as pointing, but that the M system may offer an advantage over the P system for the perceptual task of localizing a stimulus relative to nearby targets.     

Focal activation of the feline retina via a suprachoroidal electrode array

This paper presents the results of the first investigations into the use of bipolar electrical stimulation of the retina with a suprachoroidal vision prosthesis, and the effects of different electrode configurations on localization of responses on the primary visual cortex. Cats were implanted with electrodes in the suprachoroidal space, and electrically evoked potentials were recorded on the visual cortex. Responses were elicited to bipolar and monopolar stimuli, with each stimulating electrode coupled with either six-return electrodes, two-return electrodes, or a single-return electrode. The average charge threshold to elicit a response with bipolar stimulation and six-return electrodes was 76.47 ± 8.76 nC. Bipolar stimulation using six-return electrodes evoked responses half the magnitude of those elicited with a single or two-return electrodes. Monopolar stimulation evoked a greater magnitude, and area of cortical activation than bipolar stimulation. This study showed that suprachoroidal, bipolar stimulation can elicit localized activity in the primary visual cortex, with the extent of localization and magnitude of response dependent on the electrode configuration.     

Spatial localization without visual references.

To explain the veridical percept of the spatial ordering of objects and the generation of eye movements to peripheral targets, Lotze (1885 Microcosmos. Edinburgh: T. & T. Clark) proposed that there is a position label (local sign) for each retinal element. To estimate the precision of local sign information, we measured absolute localization thresholds at various eccentricities in the nasal visual field, in the complete absence of visual references. To eliminate perception of the visual surround, observers viewed a large display screen through a neutral density filter (2.0 log unit) in a dark room. The fixation target was extinguished at various times (interstimulus intervals or ISIs) prior to the onset of the test stimulus. In general, our results show that localization thresholds are proportional to the target eccentricity at all ISIs. At each eccentricity, localization thresholds are elevated after the extinction of the visual reference compared to thresholds when the reference is present. However, relative to the referenced threshold, unreferenced thresholds are elevated by a greater proportion at smaller eccentricities than at larger eccentricities. Our threshold vs ISI data can be adequately modeled on the basis of an intrinsic positional uncertainty, which increases with eccentricity, and additive and multiplicative sources of noise. The additive noise appears to reflect primarily the increasing scatter in eye position when the fixation target is extinguished. Our model's estimate of intrinsic positional uncertainty in the isoeccentric direction appears to reflect primarily the intrinsic positional uncertainty of the peripheral retina (the local sign), being very similar to cumulative cone position uncertainty and to the spacing between ON-P beta ganglion cells. In the isoeccentric direction, the estimated precision of the local sign mechanism across eccentricities is slightly better than the precision of saccadic endpoints, suggesting that noise in the motor system must also contribute to the scatter of saccadic endpoints in the isoeccentric direction. Interestingly, in the radial direction, we find a surprising similarity in our observers' positional uncertainty and the precision of saccadic endpoints.     

Visocontrastometry as one of diagnostic criteria for early detection of glaucoma and evaluation of stabilization of glaucomatous process

The relationship between contrast-frequency characteristics of the eye, on the one hand, and visual acuity and peripheral field, photosensitivity in the central visual field, ophthalmic tone, and area of the optic disk neuroretinal zonule, on the other, was for the first time evaluated by regression-correlation analysis. Videograms averaged for groups with consideration for glaucoma stage and changes in visual acuity in each group were compared. The sensitivity and specificity of visocontrastometry for early detection of glaucoma and evaluation of stabilization of the glaucomatous process were assessed. Based on the results, the author formulated her suggestions supplementing the classification of primary glaucoma currently used in Russia.     

Spatial localization in visual impairment

PURPOSE: To investigate self-reported difficulties experienced by visually impaired subjects in real-world tasks requiring judgment of space and distance and to determine whether laboratory measures of spatial localization predict self-reported difficulty with spatial tasks better than traditional measures of visual function, such as visual acuity and contrast sensitivity. METHODS: Forty-two subjects with visual impairment participated. The Spatial Localization Questionnaire (SLQ) was developed to investigate self-reported spatial localization difficulties, and subjects answered the questionnaire as part of the study. Subjects also completed a variety of clinical vision tests (visual acuity, contrast sensitivity, stereo acuity, and reading speed) and laboratory vision tests (vernier acuity, bisection acuity, and visual direction). RESULTS: The SLQ was found to have good validity. Several significant correlations were found between the Rasch analysis ability scores for the questionnaire and the clinical and laboratory vision tests. Using stepwise regression analysis, we found that vernier acuity and contrast sensitivity accounted for 42% of the variance in the Rasch scores (P < 0.001). CONCLUSIONS: The findings indicate that certain subjects with visual impairment have difficulty with real-world spatial tasks, as indicated by the SLQ. Of note, these difficulties were better predicted by vernier acuity (a resolution test) and contrast sensitivity, rather than vernier or bisection bias, which measure localization.     

Spatial localization in normal and amblyopic vision

Spatial localization was investigated for each eye of amblyopic observers using a bisection paradigm. The stimuli were comprised of a grating composed of bright lines, and a test line. The test line was either placed above the grating (bisection-no overlap) or within the row of lines comprising the grating (bisection-with overlap) and thresholds for each bisection task were measured as a function of the fundamental spatial frequency of the grating. Vernier thresholds were also measured. For the nonamblyopic eyes at low spatial frequencies, bisection thresholds were a constant fraction ("Weber" fraction) of the space to be bisected, while at high spatial frequencies thresholds were approximately a constant retinal distance (a hyperacuity). However the spatial localization of an amblyopic eye depends upon both the type of amblyopia, and the stimulus configuration. Specifically, for anisometropic amblyopia, spatial localization (bisection-no overlap) and vernier, when scaled to the resolution losses, were normal. However, spatial adjacency (bisection with overlap), while enhancing the spatial localization of nonamblyopic eyes at high spatial frequencies, markedly elevated thresholds in the amblyopic eyes of anisometropic amblyopes. Strabismic amblyopes on the other hand show disturbances in both spatial localization tasks which can not be accounted for on the basis of reduced resolution. Their results are characterized by an absence of a constant Weber fraction at low spatial frequencies and "crowding" effects at high spatial frequencies. For strabismic amblyopes, the optimal localization thresholds were similar to the Snellen threshold, while for anisometropic amblyopes, the optimal localization thresholds were several times better than the Snellen threshold.     

Neither here nor there: localizing conflicting visual attributes

Natural visual scenes are a rich source of information. Objects often carry luminance, colour, motion, depth and textural cues, each of which can serve to aid detection and localization of the object within a scene. Contemporary neuroscience presumes a modular approach to visual analysis in which each of these attributes are processed within ostensibly independent visual streams and are transmitted to geographically distinct and functionally dedicated centres in visual cortex (van Essen & Maunsell, 1983; Zihl, von Cramon & Mai, 1983; Maunsell & Newsome, 1987; Tootell, Hadjikhani, Mendola, Marrett & Dale, 1998). In the present study we ask how the visual system localizes objects within this framework. Specifically, we investigate how the visual system assigns a unitary location to objects defined by multiple stimulus attributes, where such attributes provide conflicting positional cues. The results show that conflicting sources of visual information can be effortlessly combined to form a global estimate of spatial position, yet, this conflation of visual attributes is achieved at a cost to localization accuracy. Furthermore, our results suggest that the visual system assigns more perceptual weight (Landy, 1993; Landy & Kojima, 2001) to visual attributes which are reliably related to object contours.     

Afferent delays and the mislocalization of perisaccadic stimuli

Determining the precise moment a visual stimulus appears is difficult because visual response latencies vary. This temporal uncertainty could cause localization errors to brief visual targets presented before and during eye movements if the oculomotor system cannot determine the position of the eye at the time the stimulus appeared. We investigated the effect of varying neural processing time on localization accuracy for perisaccadic visual targets that differed in luminance. Although systematic errors in localization were observed, the effect of luminance was surprisingly small. We explore several hypotheses that may explain why processing delays are not more disruptive to localization performance.     

Diagnostic sensitivity/specificity of preattentive vision tests in glaucoma

PURPOSE: Damage to the nerve fiber layer or visual pathway might be expected to reduce the efficiency with which the visual system performs analysis of the ever-changing field of vision. The purpose of this article is to provide a further analysis of previously reported data (Loughman J, Davison P, Flitcroft I, Br J Ophthalmol 2007;91:1493-98.) to: (i) determine the sensitivity and specificity of a test of preattentive vision for glaucoma detection and (ii) provide a cutoff performance level that would serve to distinguish glaucoma in early cases. METHODS: Three groups of observers (glaucoma, suspects, and normals) were examined, using computer-generated flicker, orientation, and vertical displacement targets to assess preattentive visual search (PAVS) efficiency. The task required rapid and accurate localization of a singularity embedded in a field of 119 homogenous distractors on either left or right hand side of a computer monitor. All subjects also completed a choice reaction time task. RESULTS: Receiver operating characteristic curve analysis demonstrates consistently high diagnostic sensitivity and specificity values (significantly above 90% for all tasks) using the raw PAVS data and also for a novel perceptual search index (which improves the diagnostic capacity of the test). Optimal performance cutoff values for each task were also computed. CONCLUSIONS: A test of PAVS efficiency demonstrates high sensitivity and specificity to early glaucoma. Analysis incorporating the perceptual search index confirms the high diagnostic capacity of the test.