Current Problems of Visual Research

The effects of colour adaptation and stimulus size on white perception as a function of eccentricity in man

The present investigation was designed to study the effect of area and exposure time of stimulus upon the fusion time of visual sensation. In the dark room two flashes of light were presented successively at an identical location for equal brief durations. Two kinds of thresholds were measured. One of them Was the threshold of fusion and this was defined as. the longest time internal between the two stimuli which produced a single impression (tf), and the other was the threshold of separation and this was defined as the shortest time interval which produced an impression that the second stimulus appeared after the complete disappearance of the first stimulus, i. e., the shortest time interval for perceiving dark interval between the stimuli (ts). So the present experiment was different from the flicker experiment in several points. Using the monocular and foveal vision, the following results were obtained.1. As the area of stimulus was enlarged, ts became smaller. But after ts reached its minimum value at some area, it remained approximately constant within some range of area, then it increased when the area was further enlarged. The value of tf was much smaller than ts, and, in addition, tf became smaller when the stimulus area was enlarged.2. As the exposure time of stimulus was lengthened, ts became smaller.3. Regardless of the length of the exposure time, tf remained approximately constant.4. Presenting two stimuli in differentloci successively, the threshold of simultaneity (tsi) was measured for comparable time interval to the above tf. The threshold of simultaneity was defined as the longest time interval that both stimuli appeared simultaneously. It was found that tsi increased in proportion to the logarithm of the visual angle between the stimuli within 19 degrees of visual angle. When both the visual angle and the perceived distance between the stimuli were held constant, the value of tsi remained the same, regardless of the variation in the objective distance between the stimuli on the one hand and the observing distance on the other.

To determine the relationship between intersession test repeatability in static perimetry and the degree of local sensitivity reduction in patients with retinitis pigmentosa (RP). Visual field data were obtained from 27 patients with RP using FASTPAC 30-2 of the Humphrey Field Analyzer and stimulus sizes III and V. Each test was repeated at two subsequent visits after an initial practice session. An intersession sensitivity difference was defined for each patient at each measured point in the visual field by subtracting the sensitivity value obtained during session 2 from the value obtained during session 3 at the corresponding test location. In addition, the mean sensitivity value for sessions 2 and 3 was determined at each location for each patient. Bland-Altman plots of intersession sensitivity differences as a function of mean sensitivities showed that test-retest variability was greatest at test regions with sensitivities of approximately 10 dB, with lower variability at locations with higher or lower sensitivity. The pattern of findings was similar for sizes III and V stimuli. The mean intersession sensitivity difference was +0.26 dB for stimulus size III and +0.45 dB for stimulus size V, representing a small improvement in sensitivity from session 2 to session 3. Intersession repeatability of visual field measurements in patients with RP is nonmonotonically related to the magnitude of the sensitivity loss. Therefore, apparent changes in visual field sensitivity as a result of time or treatment should be evaluated in light of the degree of the expected variability at particular sensitivity levels.

To study how rod- and cone-driven responses depend on stimulus size in normal subjects and patients with retinitis pigmentosa (RP), and to show that comparisons between responses to full-field (FF) and smaller stimuli can be useful in diagnosing and monitoring disorders of the peripheral retina without the need for lengthy dark adaptation periods. The triple silent substitution technique was used to isolate L-cone-, M-cone- and rod-driven ERGs with 19, 18 and 33% photoreceptor contrasts, respectively, under identical mean luminance conditions. Experiments were conducted on five normal subjects and three RP patients. ERGs on control subjects were recorded at nine different temporal frequencies (between 2 and 60Hz) for five different stimulus sizes: FF, 70°, 60°, 50° and 40° diameter circular stimuli. Experiments on RP patients involved rod- and L-cone-driven ERG measurements with FF and 40° stimuli at 8 and 48Hz. Response amplitudes were defined as those of the first harmonic component after Fourier analysis. In normal subjects, rod-driven responses displayed a fundamentally different behavior than cone-driven responses, particularly at low temporal frequencies. At low and intermediate temporal frequencies (≤12Hz), rod-driven signals increased by a factor of about four when measured with smaller stimuli. In contrast, L- and M-cone-driven responses in this frequency region did not change substantially with stimulus size. At high temporal frequencies (≥24Hz), both rod- and cone-driven response amplitudes decreased with decreasing stimulus size. Signals obtained from rod-isolating stimuli under these conditions are likely artefactual. Interestingly, in RP patients, both rod-driven and L-cone-driven ERGs were similar using 40° and FF stimuli. The increased responses with smaller stimuli in normal subjects to rod-isolating stimuli indicate that a fundamentally different mechanism drives the ERGs in comparison with the cone-driven responses. We propose that the increased responses are caused by stray light stimulating the peripheral retina, thereby allowing peripheral rod-driven function to be studied using the triple silent substitution technique at photopic luminances. The method is effective in studying impaired peripheral rod- and cone- function in RP patients.

Standard automated perimetry (SAP) visual field (VF) results are more repeatable using Goldmann stimulus size V (size V) in eyes with moderate/severe deficits due to glaucoma. There are few reports relating VFs using stimulus size V and III, typically used in the clinic for glaucoma, and none for non-arteritic anterior ischemic optic neuropathy (NAION). We hypothesized that we could compare and relate the VFs with both stimuli for glaucoma and NAION. We utilized 1992 same-day pairs of size III and size V SAP VFs using the 24-2 strategy for eyes with glaucoma or NAION. We explored the optimal threshold to censor the raw sensitivities, prior to calculating age-standardized total deviations (TDs). We determined the mean and standard deviation of the differences among all TD pairs. We computed a line of best fit to determine closeness to the line of unity. The ideal censoring conversion threshold was 21 decibel (dB) for size III and 24 dB for size V. The difference between size V and size III censored (0.0 ± 1.9 dB) and uncensored (0.4 ± 2.6 dB) TD pairings highly correlate with each other (r2 = 0.70, P < 0.001). The line of best fit from these pairings has a slope of 0.92, which is close to that of the line of unity (m = 1). Censoring plus age correction is a valid method of comparison between size III and size V SAP VFs with moderate to severe VF loss due to optic nerve disorders. Size III and size V TDs are comparable in clinical practice.

Effective binocular integration at the midline requires the corpus callosum

Previous research suggests that the right visual field advantage on the lexical decision task occurs independent of the visual quality of stimuli [Chiarello, C., Senehi, J., & Soulier, M. (1986). Viewing conditions and hemisphere asymmetry for the lexical decision. Neuropsychologia, 24(4), 521–529]. However, previous studies examining these effects have had methodological limitations that were addressed and controlled for in the present study. Participants performed a divided visual field, lexical decision task for words that varied in size (Experiment 1) and visibility (Experiment 2). Results showed a quality by visual field interaction effect. In both experiments, response times were faster for targets presented to the right visual field in the high quality (i.e., large font, high visibility) conditions; however, visual quality resulted in no differences for targets presented to the left visual field. Furthermore, this quality by visual field interaction effect was only observed when the target was a word. These results suggest that the left hemisphere advantage for lexical decision depends on the perceptual quality of targets, consistent with an early stage of processing account of hemispheric asymmetry during lexical decision. Findings are discussed within the context of word recognition and decision-based models.

PurposeCurrent clinical perimetric test paradigms present stimuli randomly to various locations across the visual field (VF), inherently introducing spatial uncertainty, which reduces contrast sensitivity. In the present study, we determined the extent to which spatial uncertainty affects contrast sensitivity in glaucoma patients by minimizing spatial uncertainty through attentional cueing.MethodsSix patients with open-angle glaucoma and six healthy subjects underwent laboratory-based psychophysical testing to measure contrast sensitivity at preselected locations at two eccentricities (9.5° and 17.5°) with two stimulus sizes (Goldmann sizes III and V) under different cueing conditions: 1, 2, 4, or 8 points verbally cued. Method of Constant Stimuli and a single-interval forced-choice procedure were used to generate frequency of seeing (FOS) curves at locations with and without VF defects.ResultsAt locations with VF defects, cueing minimizes spatial uncertainty and improves sensitivity under all conditions. The effect of cueing was maximal when one point was cued, and rapidly diminished when more points were cued (no change to baseline with 8 points cued). The slope of the FOS curve steepened with reduced spatial uncertainty. Locations with normal sensitivity in glaucomatous eyes had similar performance to that of healthy subjects. There was a systematic increase in uncertainty with the depth of VF loss.ConclusionsSensitivity measurements across the VF are negatively affected by spatial uncertainty, which increases with greater VF loss. Minimizing uncertainty can improve sensitivity at locations of deficit.Translational RelevanceCurrent perimetric techniques introduce spatial uncertainty and may therefore underestimate sensitivity in regions of VF loss.

The purpose of the present study was to further clarify the role of stimulus exposure time as a variable which affects responses to projective material. Presentation of the standard Rorschach cards over a series of exposure times, ranging from .03 sec. to unlimited exposure, constituted a systematically controlled range of perceptual conditions with stimuli known to have rich and useful personality correlates. In an earlier tachistoscopic smdy Stein (1949) demonstrated different patterns of response as a function of exposure time of Rorschach cards; however, the small sample used (17 Ss who responded under ascending exposure order) limited the generality of his results, and no evaluation of perceptual modes, independent of the experimental conditions, was reported. Stein's study explored the clinical usefulness of a tachistoscopic Rorschach technique by applying it to the analysis of several individual cases. A later study by Stein and Meer (1954) pointed to the usefulness of the tachistoscopic Rorschach technique in discriminating between Ss of high and low creative ability. In the view of chis author, the experimental design used in the present study invites consideration of what perceptual processes may accompany the physically manipulated conditions of minimal and sustained exposure of the stimulus. When an external stimulus is exposed very briefly, the opportunity for the perceiver to base his reactions on an interaction with the stimulus is relatively limited, and he is thereby forced to rely largely upon subjective factors and his immediate, brief perception of the stimulus. Some of the contributing factors which the perceiver may bring to the experimental situation are those of cognitive structure, personality structure, motivational states, and past learning. As exposure time of the external stimulus is increased, more time is available during which interaction between perceiver and stimulus can occur. As there is increased opportunity to investigate the stimulus at slower tachistoscopic speeds, more information can be obtained from the sc~mulus, and there is more time for corrections in perception. While the experimental situation thus varies systematically in the opportunity for interaction, it does not of course follow that all Ss will respond equally to the increased possibilities for interaction with the stimulus at longer exposure times. The present article will be limited to a report and discussion of the more formal aspects of Ror'This article is based upon a doctoral dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the School of Education of New York University, 1956. The author is indebted to Professor John 1. Sullivan for his direction of the research. An abridged account of the study was presented at the Sixty-Sixth Annual Convention of the American Psychological Association, 1958.

Delphi perimetry is a method of visual field examination which produces a statistical estimation of the visual field by testing only four critical points of the central visual field. This study was performed to evaluate this technique for the detection of glaucomatous field loss. Patients with glaucoma and ocular hypertension underwent Delphi perimetry and Humphrey visual field analysis (HVFA) program 24-2. The visual field results of both examination were compared. Of 262 eyes from 199 patients, 120 eyes showed glaucomatous defects by HVFA and 142 were normal. Delphi perimetry showed abnormal visual fields in 107 eyes, 13 of which were false-positive results as Humphrey visual fields were normal. Delphi classified 155 fields as normal, of which 26 were false negatives as Humphrey visual fields showed glaucomatous defects. Therefore, the sensitivity of Delphi perimetry for the detection of glaucomatous visual field defect was 78% and the specificity was 91%. In the 26 false-negative eyes, the most common defect missed was an isolated paracentral scotoma or an early nasal step. Furthermore, 27 of the 94 glaucomatous eyes classified as abnormal by Delphi had defects estimated by Delphi perimetry that corresponded poorly to the field loss demonstrated by Humphrey visual field analysis. Therefore, qualitative sensitivity and specificity of Delphi perimetry for producing an accurate representation of the location, extent and defect depth of glaucomatous visual field loss would be 48.8% and 72% respectively. In this study Delphi perimetry failed to give an accurate statistical estimation of the visual field in an unacceptably high number of cases; therefore, it cannot be recommended for clinical use.

The authors sought to verify computer simulation of visual fields by comparing thresholds of real and corresponding simulated visual fields. Four patients with stable glaucomatous visual fields and three patients with progressing glaucomatous visual fields were chosen for the study. Visual fields had been recorded at 6-month intervals for 5 to 7.5 years. A previously described computer simulation program was used to generate a corresponding simulated visual field for each of the real fields. Twenty different levels of response variability and long-term variability were used in the simulations. Pointwise sensitivity differences between real and simulated fields were calculated. The average difference and 95% interval of the differences were analyzed for the different simulation conditions, for the pointwise sensitivities in the real patient fields, and to determine whether the field was stable or progressing. In almost all simulation conditions, the average pointwise sensitivity differences ranged from -1 to 1 dB and were not significantly different among different simulation conditions. The 95% interval of the average difference increased significantly with response variability, whereas long-term variability failed to show any apparent effect. Average pointwise differences and the 95% intervals were greatest in locations where the real-patient field had reduced sensitivity of 14 dB or worse. The simulation program provided good estimates of visual field sensitivities. Increasing amounts of response, but not long-term variability, produced a linear increase in the variability of threshold sensitivities. This finding implies that short-term rather than long-term fluctuation is the most important factor determining the variability of thresholds.

Perception Matches Selectivity in the Human Anterior Color Center

Glaucoma is characterized by pressure-induced damage to retinal ganglion cells (RGC) leading to progressively irreversible vision loss. Progression of visual field changes and retinal nerve fibre layer (RNFL) thinning are monitored with standard automated perimetry (SAP) and optical coherence tomography (OCT), respectively. In early glaucoma, it is difficult to interpret these tests because up to 20–50% of RGCs can be lost before characteristic visual field defects manifest. As such, there is a nonlinear relationship between anatomy and function, that is, the number of functioning RGCs and visual field (Harwerth et al. 2010). A commonly proposed explanation for this nonlinear relationship is the redundancy among RGC axons. RGCs have overlapping receptive fields, and therefore, sub-threshold cell losses could be compensated for by other RGCs that share the same functional retinal area (Kerrigan-Baumrind et al. 2000). Here, we discuss histological evidence that supports RGC redundancy as this may impact interpretation of visual field defects in early glaucoma. Optic nerve head injections of horseradish peroxidase (HRP) demonstrate a consistent topographic organization of RGC axonal bundles (Fig. 1A, Minckler 1980). This organization explains the arcuate nerve fibre bundle defects and corresponding Bjerrum scotomas seen in moderate and severe glaucoma. However, the linear arrangement of nerve fibre bundles may not provide sufficient anatomic resolution to explain visual field changes in early glaucoma. Additionally, in serial sections of HRP-labelled retina, Minckler consistently found unlabelled RGCs intermixed with labelled RGCs. There are immense overlap and variability in RGCs’ receptive fields. A single retinal laser burn of 100 μm width resulted in axonal degeneration in over 75% of one quadrant of the lamina cribrosa (Ryu & Minckler 1983). Furthermore, a fraction of axonal fibres actually pass through neighbouring fibre bundles, thus arborizing the topographic organization of the individual nerve bundles (Fig. 1B). In other words, there is a sub-population of RGC axons that take a meandering course to the optic disc and adhere only loosely to the expected retinotopic organization (Ogden 1983). These findings explain how a focal defect in the retina can become much more ramified downstream. Any spatial point in the visual field may be widely distributed and represented by multiple points at the optic nerve head. If one point of the nerve head sustains damage, the corresponding area in visual field can still be intact due to other ‘collaterals’. This explains the heterogeneous spectrum of visual field changes seen in early glaucoma. Only when a wider area of damage occurs at the optic nerve head will the visual field defects appear more definite and better correspond to the traditionally illustrated topography of the retinal nerve fibre array. Early stage glaucoma is difficult to detect and correlate with visual field testing. Non-specific visual field defects may be dismissed as non-glaucomatous for not fitting the classic patterns, and up to two-thirds of visual field defects disappear upon retesting. Given these histological findings and clinical variability, we encourage careful consideration when evaluating visual field defects that may at first seem to be non-glaucomatous.

BackgroundThe dorsal parietal visual system plays an important role in self-motion perception and spatial cognition. It also strongly responds to visual inputs from the lower visual field. Postural control is modified in a process called sensory reweighting based on the reliability of available sensory sources. The question of whether visual stimuli presented to either the lower or upper visual field affect postural control and sensory reweighting has not been resolved. Research questionDo visual stimuli presented to the lower and upper visual fields affect postural control and sensory reweighting? MethodsTwenty-nine healthy young adults participated in the study. Four conditions (full visual field, upper visual field, lower visual field, and no optic flow condition) were simulated in a VR environment using a head-mounted display. The optic flow stimuli used were swarms of small white spheres originating from the central point of the visual field, moving radially towards the periphery, and expanding across the scene. Participants were instructed to stand quietly for 50 s under each visual condition. Using force plate signals, we measured the center of pressure (COP) signal in the horizontal plane and calculated its 95 % ellipse area, root mean square (RMS) deviations, the mean velocity, and power spectral density (PSD). ResultsOptic flow in the full and lower visual fields produced significantly smaller 95 % ellipse area and RMS of COP in the anterior-posterior direction compared to optic flow in the upper visual field. Furthermore, the PSD of the lower frequency band (0–0.3 Hz) was decreased and that of higher frequency bands (0.3–1 Hz and 1–3 Hz) was increased for the lower compared to the upper visual field. SignificanceVisual feedback affects static postural control more when presented in the lower visual field compared to the upper visual field.

The representation of the visual field in the ventral lateral geniculate nucleus (LGNv) was studied in rats anesthetized with urethane by recording the response of single units to visual stimulation. Receptive fields of LGNv units were plotted on a campimeter, 60 cm in diameter, which was placed 30 cm from the contralateral eye. LGNv neurons responded mainly to stimulation of the contralateral eye with on-tonic characteristics. Few neurons responded only to stimulation of the ipsilateral eye and no binocular interaction was observed. Retinotopic organization was clearly seen in the LGNv; the nasal visual fields were represented dorsally, the temporal fields ventrally, and the upper to lower visual fields were in the rostrolateral to caudomedial parts of the LGNv. A given point in the visual field is represented along a line running through the LGNv in a rostrocaudal direction. Almost the entire horizontal extent of the contralateral visual field was represented in the LGNv, whereas vertically the visual field between 40 degrees above and 20 degrees below the distribution axis was represented. The major axis of the strip of the visual field containing all the RF centers, which is referred to as the distribution axis, inclined nasally up and temporally down at an angle of 10.4 degrees to the 0 degree horizontal meridian line. The representation of the distribution axis in the retina was in accordance with the major axis of retinal ganglion cell distribution (Fukuda, '77; Schober and Gruschka, '77).