Degrees Of Visual Angle Research Articles

Spatiotemporal visual processing in schizophrenia.

Studies examining visual processing in schizophrenia have provided inconsistent results. In this study, the authors measured static and dynamic visual contrast sensitivity (CS) in patients with schizophrenia (n=20) and control subjects (n=15). Extrapyramidal symptoms were evaluated with the Simpson-Angus scale. In the static condition, the patients with schizophrenia showed reduced CS in the spatial frequency range of 2.9-14.4 cycles per degree of visual angle (c/d). In the dynamic condition, CS loss was present over the whole range tested (0.5-14.4 c/d). Higher Simpson-Angus scores and higher doses of antipsychotic medication were associated with more severe CS deficits. These results suggest that the hypodopaminergic state induced by antipsychotic medication may produce parkinsonian visual impairments in schizophrenia patients.

Instant neural control of a movement signal.

The activity of motor cortex (MI) neurons conveys movement intent sufficiently well to be used as a control signal to operate artificial devices, but until now this has called for extensive training or has been confined to a limited movement repertoire. Here we show how activity from a few (7-30) MI neurons can be decoded into a signal that a monkey is able to use immediately to move a computer cursor to any new position in its workspace (14 degrees x 14 degrees visual angle). Our results, which are based on recordings made by an electrode array that is suitable for human use, indicate that neurally based control of movement may eventually be feasible in paralysed humans.

Stimulus size selectivity and receptive field organization of ectostriatal neurons in the pigeon.

The avian ectostriatum is the telencephalic recipient zone of the tectofugal pathway, which may be homologous to the colliculo-pulvinar-cortical pathway in mammals. The present paper studies the visual response properties and receptive field organization of ectostriatal cells in pigeons with extracellular recording and computer mapping techniques. The results indicate that 90% of ectostriatal cells prefer forward, downward and upward motion of visual stimuli at velocities in the range of 16-128 degrees s(-1). They respond optimally to small stimuli (1-4 degrees visual angle), mostly preferring a target of 2 degrees. Most cells (78.8%) have one excitatory receptive field that usually possesses one or two hotspots, some cells (13.5%) have two excitatory receptive fields each having one or two hotspots, and a few cells (7.7%) have one excitatory receptive field with an unresponsive region in the center. An inhibitory receptive field is not found surrounding the excitatory receptive field in the ectostriatal cells examined. These response properties and receptive field organization may reflect the possible roles of the ectostriatum in stimulus discrimination and visual cognition.

The Limits of Transparent Depth Perception with Restricted Field of View: Application in an Augmented Reality Surgical Microscope

This paper describes an investigation into the effect of reduced field of view and target size in transparent stereo augmented reality systems. Six subjects were asked to identify the maximum disparity limit of correct 3D perception for a random dot target of different sizes, viewed through a transparent scene with a varying field of view (FOV). The results showed that the maximum disparity limit increased linearly up to 25 degrees FOV after which it showed no significant increase for increasing FOV. There was no significant difference in the maximum disparity values obtained using a 4, 8, or 10 degree target. The maximum disparity limit of 5.9 ±1 (mean ± SD) degrees visual angle was used in an equation to predict the range in which correct depth perception occurs for transparent AR in a binocular surgical microscope. We suggest that the optimum image position to give the greatest range for correct 3D depth perception is 25cm when viewing transparent targets behind a transparent real scene.

Reaction time in automated kinetic perimetry: effects of stimulus luminance, eccentricity, and movement direction

Purpose: To determine the effects of stimulus eccentricity and luminance level on the reaction time (RT) of young normal volunteers during automated kinetic campimetry. Methods: We used a specially designed video-campimetric device equipped with a continuous infrared (IR) pupillographic fixation control (Tübingen Computer Campimeter) and recorded reaction times upon presenting horizontally moving small circular stimuli (size 26′; constant angular velocity 2°/s) starting at 16 locations within the central 30°-radius of the visual field. Two different levels of stimulus luminance were used (41.6 cd/m 2 and 110 cd/m 2), while background luminance was 10 cd/m 2. Each stimulus was presented a total of six times in a randomized order. Subjects were 12 healthy young individuals (aged 21–30 years) with normal ophthalmic examinations. An analysis of variance (ANOVA) was performed on the data. Results: RTs showed considerable inter- and intra-individual variation with individual least squares means (LSM, fitted values of a linear model) ranging from 305 to 454 ms, and residual standard deviation (R.S.D.) 66 ms. Reaction times did not differ significantly as a function of stimulus direction ( P>0.6). Higher luminance levels produced significantly reduced reaction times for all stimulus locations and directions (mean reduction: 16 ms; P<0.0001). Reaction times increased with increasing eccentricity, in the mean by 1.8 ms per degree of visual angle, from 365±4 ms (S.E.M.) foveally, to 407±2 ms at 30° eccentricity; ( P<0.0001). Conclusions: Automated kinetic perimetry should be designed to cope with significant, variable interindividual response characteristics. Other stimulus related factors, such as eccentricity or luminance level, have a significant but comparatively small effect on reaction time within the central 30°-radius visual field in healthy young individuals.

Objective visual field testing with functional magnetic resonance imaging

Purpose : To detect cortical retinotopy using the functional magnetic resonance imaging technique at clinical circumstances. Methods : Four normal volunteers were examined. Four experiments were performed on each subject: a ‘central-peripheral’ visual field stimulation and an ‘upper-lower’ visual field stimulation, both for right and left visual hemifields. The checkerboard stimuli, presented on a front projection screen, subtended 3 degrees of visual angle in height and 5 degrees in width. Sequential paradigms alternated rest phases with no checkerboard stimulation and stimulation phases. For the ‘central-peripheral’ visual field stimulation, the checkerboard was presented to either the central or peripheral visual field. During the ‘upper-lower’ visual field stimulation, the checkerboard was presented to either the upper or lower visual field. Results : The central visual field stimulation revealed a broad activated area in the contralateral occipital pole, whereas the peripheral visual field stimulation displayed a more anterior and narrower activated area. The ‘upper-lower’ visual field stimulation revealed broad activated areas covering the contralateral occipital pole. The upper visual field stimulation revealed the center of the cortical activation located inferiorly to lower visual field stimulation. Conclusion : Retinotopical eccentricity in the primary visual cortex is accurately detected using simple visual stimulations partially presented to the central-peripheral visual field. Upper visual field stimulation bordering the horizontal meridian could be differentiated from lower visual field stimulation in the associated visual cortex. This technique may help to evaluate the visual field.

Frequency doubling technology perimetry in retinal diseases--preliminary report.

The role of frequency doubling technology perimetry (FDT) in glaucoma has been promising in speed and simplicity as well as in its high sensitivity and specificity compared to conventional automatic perimetry. In this study, we evaluate the role of frequency doubling technology perimetry (FDT) in a variety of retinal diseases. FDT using full-threshold C-20 mode was performed in thirty-three patients with a variety of retinal diseases [16 cases of rhegmatogenous retinal detachment (RRD), nine cases of age-related maculopathy (AMD) and eight cases of central serous chorioretinopathy (CSCR)]. The fundus was scored by the extent of disease on each quadrant and macular area (central five degree visual angle). Then the retinal scores were compared with the points depressed to 2% on total deviation plots in FDT C-20 full-threshold mode using Spearman's rank correlation method. The correlation was statistically significant in the group of RRD (R = 0.57, P = 0.01), whereas the correlation was not significant in the group of macular diseases (AMD & CSCR, R = 0.47 & 0.32, P = 0.12 & 0.20). In conclusion, our results suggest that FDT might be a useful and simple technique for functional evaluation in RRD, but not in the macular disease group under this scoring system.

Attentional biases in geometric form perception.

This paper reports the operation of robust attentional bias to the top and right during perception of small, single geometric forms. Same/different judgements of successively presented standard and comparison forms are faster when local differences are located at top and right rather than in other regions of the forms. The bias persists when form size is reduced to approximately one degree of visual angle, and it is unaffected by saccadic eye movements and by instructions to attend to other reliably differentiating regions of the forms. Results lend support in various degrees to two of the possible explanations of the bias: (1) a static, skewed distribution of attentional resources around eye fixation; and (2) biased, covert scanning that commences invariably at the top and right of stimulus forms. Origins of the bias in terms of possible left-hemispheric capacity for constructing representations of visual stimuli from parts, as well as in terms of reading experience and prevailing optic flow during locomotion through space are considered. Recent investigations of conditions under which the bias can be maintained or reduced are mentioned.

Depth motion sensitivity functions.

Functions reliably describing perception of motion in depth have been established experimentally by using psychophysical methods of size and distance estimations and threshold measurements. The stimuli were generated with a new hybrid technique yielding an image refresh rate of 1667 Hz. In this way it was possible to generate rapid expansions and contractions of the moving checkerboard pattern constituting the stimulus for depth motion perception. The results showed that perceived size constancy as well as depth impression varied with oscillation frequency. Under the conditions of slow motions (oscillation frequencies around 2 Hz), perfect size constancy was obtained. Above that limit, size constancy systematically decreased, and with oscillation frequencies of about 5 Hz the perceived size constancy was close to zero when small-sized patterns were used. Under the conditions of wide field stimulation (when the pattern subtended 66 degrees of visual angle), the cut-off limit increased to 16 Hz. Since the perception of depth motion amplitudes as well as perceived velocities of the visual object are related to perceived size constancy, the findings have certain implications for theoretical explanations of depth motion perception.

Reading with central scotomas: What can we learn from simulation studies?

Age-related macular degeneration (ARMD) is the leading cause of visual impairment in adults 65 years of age and older. ARMD often results in scotomas affecting the fovea, leading to central field loss. We used simulated scotomas in normally sighted young adults to test the impact of scotoma size and location on reading. We measured reading rate and eye movement patterns and found that the number of letters masked by the scotoma is more important than the size of the scotoma in degrees of visual angle and that forcing subjects to attend below a simulated scotoma results in better reading than when they are forced to attend to either the left or the right.

Reading with central field loss: number of letters masked is more important than the size of the mask in degrees.

When the center of a readers, visual field is blocked from view, reading rates decline and eye movement patterns change. This is true whether the central visual field is blocked artificially (i.e. a mask) or through disease (e.g. a retinal scotoma due to macular degeneration). In past studies, when mask size was defined in terms of the number of letters masked from view, reading rates declined sharply as number of letters masked increased. Patients with larger central scotomas (in degrees of visual angle) also read slower. We sought to determine whether number of letters masked or size of the mask in degrees is the predominant factor affecting reading rates and eye movement behavior. By matching number of letters masked across several mask sizes (and compensating for reduced acuity in the periphery), we found that number of letters masked is the more important factor until mask size is quite large (> or = -7.5 degrees) and number of letters masked from view is more than seven.

Evaluation of CRT Flicker under Office Viewing Conditions

Flicker detection thresholds were assessed for 10 participants with CRT screens of varying luminance, size, viewing angle eccentricity, and ambient illumination. The test conditions were selected to span the range of typical office applications. Under the test conditions, CRT refresh rate was manipulated using a psychophysical method of limits procedure to estimate the 50% Critical Flicker Frequency (CFF) threshold. Results indicate that CFF increases with increasing display luminance, ambient illumination, and display size. CFF also increases with increasing eccentricity up to about 30 degrees of visual angle. These findings confirm and extend previous research and provide a coherent database for development of quantitative image quality models for use by display designers and for display ergonomics technical standards.

Impaired sensitivity to visual contrast in children treated early and continuously for phenylketonuria.

Contrast sensitivity was assessed in 47 children aged 5.4-9.8 years: 12 with phenylketonuria (PKU), six unaffected siblings and 29 children from the general population. Children with PKU, despite early and continuous treatment and despite phenylalanine (Phe) levels within accepted limits, were impaired across the range of spatial frequencies [1.5-18.0 cycles per degree of visual angle (c.p.d.)]. They were most impaired at the next to the highest spatial frequency, where "group' accounted for 70% of the variance in sensitivity to contrast, controlling for acuity, sex, age and test site. Never, at any spatial frequency, was the contrast sensitivity of any PKU subject better than that of his or her sibling. All subjects were tested under conditions of 20/20 vision, with correction if needed. The mean IQ of PKU subjects was 99; IQ was not significantly related to contrast sensitivity performance. We interpret these findings as support for Diamond's hypothesis that moderately elevated plasma Phe levels (3-5 x normal), combined with reduced plasma tyrosine (Tyr), moderately reduce the levels of Tyr reaching the eye and brain, which adversely affects those dopamine neurons that fire and turn over dopamine most rapidly (the dopamine neurons in the retina and those projecting to prefrontal cortex). This would lead to the deficit in contrast sensitivity found here and to the selective deficit in prefrontal cortex cognitive functions previously reported in PKU children under moderately good dietary control.

Visual Field Tunneling in Aviators Induced by Memory Demands

Aviators are required rapidly and accurately to process enormous amounts of visual information located foveally and peripherally. The present study, expanding upon an earlier study (Williams, 1988), required young aviators to process within the framework of a single eye fixation a briefly displayed foveally presented memory load while simultaneously trying to identify common peripheral targets presented on the same display at locations up to 4.5 degrees of visual angle from the fixation point. This task, as well as a character classification task (Williams, 1985, 1988), has been shown to be very difficult for nonaviators: It results in a tendency toward tunnel vision. Limited preliminary measurements of peripheral accuracy suggested that aviators might be less susceptible than nonaviators to this visual tunneling. The present study demonstrated moderate susceptibility to cognitively induced tunneling in aviators when the foveal task was sufficiently difficult and reaction time was the principal dependent measure.

An effect of structured backgrounds on smooth pursuit eye movements in patients with cerebral lesions.

The oculomotor smooth pursuit system is driven by the slip of the target image upon the retina arising from errors in matching eye and target velocities. However, pursuit of an object moving against a structured background causes most retinal flow to be in the direction opposite to target movement. Central mechanisms allow these distracting signals to be overridden effortlessly. To isolate the anatomical substrate of this capacity we studied the effect of the presence of a structured background upon smooth pursuit in 26 patients with focal cerebral lesions. In normal control subjects, studies confirmed that a background has little effect upon pursuit. Eye movements were recorded by the scleral search coil method or by infra-red oculography. The target was a bright spot moving horizontally in a triangular waveform of amplitude +/- 11.25 degrees visual angle, at either 10, 20, 30 or 36.5 degrees/s. Data were collected in darkness and with a structured background: 14 patients showed a significant reduction of gain with a structured background, while the remaining 12 showed little or no effect. Comparison of the location of the cerebral lesions in these two groups suggested that lesions in the inferior parietal cortex (area 40) or in white matter containing parieto-frontal connections result in disruption of pursuit in the presence of a background.

Visual selective attention and mental retardation

Abstract Two experiments are reported that examined differences in the control of visual attention exhibited by two groups of subjects with mental retardation (Down syndrome versus non-Down subjects) and subjects without mental retardation. Subjects took part in a response competition task to examine their ability to restrict attentional focus to a narrow range of the visual field and to see if this ability is sensitive to top-down operations associated with category variables (letter versus number). Subjects saw targets flanked by distractors. The distractors could be identical to targets (2 2 2 or K K K), from the same category as targets (3 2 3 or L K L), or from a different category to targets (L 2 L or 3 K 3). We also manipulated the separation between target and flankers from 0.06 to 2.5 degrees of visual angle. In Experiment 1, subjects responded to either the number 2 or the letter K. Results indicated that both groups of subjects with mental retardation exhibited greater interference at wider sep...

Optic neuritis. Differential losses of luminance and chromatic function near a scotoma.

Visual sensitivity to achromatic and chromatic stimulus flashes was determined at sites just inside, on the boundary and just outside scotomata in 11 patients with recovered optic neuritis. The colour of the flashes and the size of the steady background on which they appeared were such that detection was more likely to be mediated by either the large-diameter, magnocellular fibres or the small-diameter, parvocellular fibres of the anterior visual pathway. The spacing of the test sites ranged from 0.5 degrees to 4 degrees visual angle, depending on the shape and location of the scotomata. The greatest differences in sensitivity were between sites just inside and just outside the scotoma and in response to achromatic stimuli more likely to involve the magnocellular fibres. This effect may be due to the size of magnocellular fibres or to their relatively smaller numbers.

A defective visual pathway in children with reading disability.

The possibility that reading disability in children is associated with visual problems is in dispute. We sought to test the existence of this association by using electrophysiologic techniques to measure the processing of visual information in the magnicellular and parvicellular visual pathways of the brain. Visual evoked potentials were measured with scalp electrodes in children 8 to 11 years old who were normal readers and in those with reading disability. The potentials were measured for targets with low (0.5 cycle per degree of visual angle) and high (4.5 cycles per degree) spatial frequency, surrounded by either a steady background or a uniform-field flickering 12 times per second. A flickering field normally reduces the amplitude and increases the latency of a transient potential evoked by a low-spatial-frequency target, which preferentially excites the magnicellular visual pathway, but has little effect on the response to a high-spatial-frequency target. With a steady background, the latencies of the early components (N1 and P1) of the visual evoked potentials were longer in the reading-disabled children than in the normal readers when the low-spatial-frequency target was used, but not when the high-spatial-frequency target was used. In normal readers, the flickering background increased the latency and reduced the amplitude of the early components, whereas in the reading-disabled children only the amplitude was affected. No differences were observed in either group with the high-spatial-frequency target. The pattern of results suggests that the response of the magnicellular visual pathway is slowed in reading-disabled children, who do not, however, have a general slowing of the visual response. The possibility that there is a cause-and-effect relation between these findings and reading disability will require further study.

Windowlessness in the Workplace

A series of studies was performed to explore the hypothesis that employees in windowless offices compensate for the lack of windows. In Experiment 1, students rated the degree to which they perceived various office features to be substitutes for windows. Analyses revealed four general categories of potential window substitutes: other apertures (e.g., skylights), paintings/art, living things (e.g., plants), and panels (e.g., light panels). Experiment 2 supported the external validity of the data in Experiment 1 in that full-time office workers produced virtually identical ratings of window substitutability. Experiment 3 was a field study of 173 offices. Measurements were made of the number and size of windows, number and size of all potential window substitutes, and size of wall space available for pictures. Size was measured in degrees of visual angle from the office workers' chairs. No evidence was obtained to indicate that any of the features measured were more prevalent or larger in offices without windows. Furthermore, power analyses indicated that the study had sufficient power to find such effects. Experiment 4 was designed to investigate other potential reasons for the use of the items that were examined in Experiment 3. Several reasons, such as space personalization, were found to be perceived by office occupants as more important than the desire to compensate for lack of windows.

Quantitative evaluation of the function of looking at visual target in optokinetic nystagmus.

A new method is presented to qualitatively evaluate the function of OKN which certainly looks at a visual target. Optokinetic stimulation was given to a test subject by projecting stripes with a 5 degrees visual angle width at 30 degrees intervals, which was accelerated by 1 degree/s2 up to 100 degrees/s. The correlation between slow phase and fast phase was computed with our program. Two correlations were mixed in a normal response, one indicated low correlation and the other high correlation. As normal subjects look at wide interval visual targets one by one regardless of the target velocity, low correlation type OKN beats are considered to be those which certainly look at the visual target. In order to quantitatively analyze this type of OKN, approximate regression lines of the low correlation type, [y = ax + b (x: slow phase velocity, y: fast phase amplitude or velocity)], were computed by the minimum square method. In normal subjects, value a indicates low and value b high velocity and their normal limits are determined. The results of cases with central disequilibrium indicate that this analysis provides information of pathological OKN different from that of such conventional parameters as slow phase velocity and number of nystagmus beats.