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Patients that make use of chloroquine or hydroxychloroquine, drugs which are frequently administered for treatment of rheumatoid arthritis, lupus erithromatosus or malaria, may suffer alterations in color vision and in contrast sensitivity. The present work evaluates the visual function of these patients in a joint study of the University of São Paulo (USP), in São Paulo, and of the Federal University of Pará (UFPA), in Belém. Thirty two chloroquine user patients without alterations in the eye fundus exam were evaluated in São Paulo (n=10; aged 38 to 71 years; mean=55,8 years) and in Belém (n=22; aged 20 to 67; mean=40 years). The prescribed accumulated chloroquine dose was 45 to 430 g (mean=213 g; sd = 152 g) for the São Paulo group, and 36 to 540 g (mean=174 g; sd=183 g) for the Belém group. Tests were performed monocularly with corrected eye refractive state. Color discrimination was evaluated using the Cambridge Colour Test (CCT): the color discrimination threshold was measured first in the protan, deutan and tritan axes and, in succession, three MacAdam's ellipses were determined. The patient's color vision was also evaluated with color arrangement tests: the Farnsworth-Munsell 100 Hue (FM100), the Farnsworth-Munsell D15, and the Lanthony Desaturated (D15d) tests. We also measured the contrast sensitivity for black-and-white sine wave grating of twenty two patients. The results were compared with controls without ophthalmologic or neuro-ophthalmologic pathologies. Twenty four patients presented acquired dyschromatopsia. There were cases of selective loss (11 patients) and of diffuse loss (13 patients). Although losses were present in the FM100 there was no correlation between the FM100 error score and the ellipse area measured by the CCT. Moreover, three patients that scored normal in the FM100, failed to reach normal threshold in the CCT. The Lanthony test was less sensitive than the other two tests, since it failed to indicate loss in about half the patients, and the D15 was the least sensitive test, having failed to indicate loss in 9 out of 10 patients. Contrast sensitivity was within normal values for patients submitted to this test. The extent of losses in color discrimination was positively correlated with the accumulated dose. The CCT is recommended for follow up since it provides quantitative data that can be directly interpreted in CIE (Commission Internationalle d'Éclairage) color space.

Keywords: Chloroquine; Retinopathy; Color vision; Contrast sensitivity; Neurotoxicology; Neurobehavioral test battery; Dyschromatopsia

In contrast to the CIE (Commission Internationale de l'Eclairage) colorimetric systems in which colors are specified on the basis of spectrum of light, a system for surface color is displayed by the standard chips. According to the principle by which the standard chips are selected and arranged, we have many different systems. Three representative systems are examined, Munsell, OSA-UCS (Optical Society of America-Uniform Color Scale), and NCA (Natural Color System) of Sweden. Each is a systematization of human cognition of colors, and how we see the difference between two chips j and k plays a different role in each spatial representation. On the basis of observers' assessments, the perceptual difference is scaled as d jk, a numerical value. The structure of each system is quantitatively examined by checking the behavior of d jk. This article is a review of the author's studies in this line.

Keywords: Color vision; colorimetry; psychophysical scaling; multi-dimensional representation

This article presents a brief overview of visual space perception. It begins by noting the significance of visual space perception to broader issues in philosophy and science and observes that the appreciation of visual space perception as a scientific topic is impeded by naïve realism. The second section notes the longstanding interest in the phenomenology of visual space and focuses on one issue, the dissocation between perceived location and perceived shape in visual space. The last section discusses three conceptions of how vision controls action, with special attention to the role of visual space.

Keywords: Visual perception; Space perception; Phenomenology

A framework is proposed for analyzing the perception of motion in depth produced by simple proximal motion patterns of two to four points. The framework includes input structure, perceptual system constraints, and a depth scaling mechanism. The input is relational stimulation described by two proximal dimensions, orientation and separation, that can change or remain constant over the course of a motion pattern. Combinations of change or no-change in these dimensions yield four basic patterns of proximal stimulation: parallel, circular, perspective, and parallax. These primary patterns initiate automatic processing mechanisms - a unity constraint that treats pairs of points as connected and a rigidity constraint that treats the connection as rigid. When the constraints are activated by perspective or parallax patterns, the rigid connection between the points also appears to move in depth. A scaling mechanism governs the degree to which the objects move in depth in order to maintain the perceived rigidity. Although this framework is sufficient to explain perceptions produced by three- and four-point motion patterns in most cases, some patterns require additional configurational factors to supplement the framework. Nevertheless, perceptual qualities such as shrinking, stretching, bending, and folding emerge from the application of the same processing constraints and depth scaling factors as those that produce the perception of rigid objects moving in depth.

Keywords: Perception; Motion; Rigidity; Vectors; Depth

This chapter is about basic conditions of seeing motion (mostly of single objects in the frontoparallel plane). It emphasizes the richness and challenge of phenomena in motion perception. Apart from the distinction between afferent (retinal) and efferent (oculomotor) mechanisms, motion percepts can result from real (object) motion as well as from various forms of apparent motion (stroboscopic or phi motion, induced motion, autokinesis). Further intriguing motion phenomena include motion contrast and assimilation, motion adaptation and aftereffects, and velocity transposition. Finally, anticipatory performance of motion extrapolation is considered as a dynamic case of amodal perceptual completion, indicating that visual motion is closely related to action.

Keywords: Motion perception; Afferent/efferent mechanisms; Oculomotor system; Apparent motion; Velocity transposition; Motion extrapolation

To reach for and grasp an object, its distance, shape and size must be known. In principle, the combination of disparity and motion information could be used to provide this information as the perception of object shape from disparity is biased and the perception of object size from motion is indeterminate. Here we investigate whether the visual system can take advantage of the simultaneous presence of both cues in the control of reaching and grasping. For both real and virtual objects, peak grip aperture scaled with object size and peak wrist velocity scaled with object distance. Kinematic indices, which reflect distance reached and perceived size, showed clear and systematic biases. These biases may be interpreted as arising from the biases in the use of binocular disparity, and the indeterminacy of the information provided by motion. Combining disparity and motion information improved estimates of the width, but not the depth or distance of objects. Overall, these results suggest that accurate metric depth information for the control of prehension is not available from binocular or motion cues, either in isolation or in combination.

Keywords: Prehension; Binocular disparity; Distance perception; Size perception

Binocular cues were considered the prevailing information on specifying depth since the beginning of vision research. In the present study, two perceptual responses, the classical verbal report and a more recent method, open-loop walking, were used to assess the role of binocular information for egocentric distance perception. In two cue conditions environments, full- and reduced-cue, observers judged and walked egocentric distances of stimuli presented at eye-level, under binocular or monocular viewing. Results indicated perceptual constancy for open-loop walking and binocular responses, as well as poor performances under strong degradation on visual information (reduced-cue under monocular viewing), thus presenting evidence to support the fundamental role of binocular information on perception of egocentric distances. Besides that, visually directed actions could be adequate measures of perceived distance, with a better reliability than verbal report, since they were quite free of intrusion of inferential processes and perceptual tendencies. In addition, reduced head movements, side-to-side as well as back and forth deflexion movements, could have contributed to a near perfect coupling between binocular disparity information and open-loop walking responses.

Keywords: Visual perception; Space perception; Motor skills; Walking

Objects appear enlarged in water by less than the 4/3 angular magnification. They usually appear beyond their optical distance and slightly enlarged in linear size, but not in accordance with size-distance invariance (SDI). We investigated whether misperceptions of angular size could explain the discrepancies. Twenty observers viewed targets of various sizes and distances within transparent tanks 40 cm long containing air or water. They judged distance by hidden reaching, and linear or angular size by adjusting the size of a target in air at a further distance. Matched distance was close to physical distance in air and optical distance in water. All size matches were close to true linear size, and were larger in water than in air. Angular size matches were much too small to explain departures from SDI. Size perception under water is best explained by incomplete adaptation to optical distortion, and by the use of various size cues.

Keywords: Underwater effects; Apparent size; Angular size; Apparent distance; Spatial distortion; Adaptation

We assessed temporal modulation visual fields (TMFs) for 91 observers including controls, Parkinson patients and members of the James Bay Cree community of Northern Québec suspected of being chronically exposed to relatively low levels of methyl-mercury. The main goal was to establish the feasibility of using such procedures to rapidly evaluate visual function in a large field study with the James Bay Cree community. The results show clear normal aging effects on TMFs and the pattern of loss differed depending on the flicker rates used. Group data comparisons between the controls and the experimental groups showed significant effects only between the Cree and normal controls in the 40 to 49 year-old age category for the low temporal frequency condition (2 Hz). Examples of individual analysis shows a Cree observer with severe visual field constriction at the 2 Hz condition with a normal visual field at the 16 Hz condition and a reverse pattern was demonstrated for a Parkinson's patient where a visual field constriction was evident only for the 16 Hz condition. The general conclusions are: Such a technique can be used to evaluate the visual consequences of neuropathological disorders and it may lead to dissociation between certain neurotoxic and neurodegenerative effects depending on the parameters used; this technique can be used for a large field study because it is rapid and easily understood and performed by the subjects; the TMF procedure used showed good test-retest correlations; normal aging causes changes in TMF profiles but the changes will show different patterns throughout the visual field depending on the parameters used.

Keywords: Neurotoxicology; Parkinson's disease; Visual fields; Aging; Neurobehavioral tests

We report a new illusion of elasticity in a rigid surface. A square frame is presented behind a concentric occluding cross. When the two surfaces are rotated rigidly, the square frame appears "rubbery", that is, it appears to contract or expand during the rotation. The rubber square illusion is related to a number of other illusory phenomena involving motion and surface stratification. It is generally believed that these phenomena are due to suppression of potentially veridical motion signals at t-junctions signalling occlusions. However, in all previously reported phenomena the effect of t-junctions was confounded with effects due to surface relative motion, spatial integration, or relative contrast. Given that none of these potential confounds applies to our demonstration, the rubber square illusion provides critical evidence that t-junctions are sufficient to cause suppression of the corresponding motion signals.

Keywords: Vision; Motion; Integration; Segmentation; Depth; Illusions

Visual perception is closely related to and associated with the processing of space. Nevertheless, all events occur at some moment in time, and time needs to be processed in the visual mode. After briefly reviewing the many research avenues in which time and vision are linked, this article focuses on the discrimination of visually marked time intervals, emphasizing work from my own laboratory. It presents a theoretical position, that of a single-clock hypothesis, as well as issues and data that show how visual temporal processing can be approached. These issues are partly related to the fact that time is marked by signals from a single source or by signals provided by distanced sources. In the latter case, different questions arise depending on the signals' exact location. It is known that more distance between flashes can result in longer perceived duration (kappa effect). However, the data reported here, involving signals placed on the same vertical plane, show the opposite effect: briefer perceived duration with more distance between flashes. When flashes are located on the same horizontal plane in different hemi-fields, there is also a lateral effect that may influence time judgments.

Keywords: Time perception; Perceived duration; Time markers; Kappa effect

Manual and saccadic reaction times (MRTs and SRTs) are reduced when a warning signal precedes the onset of a target. The decreasing on SRTs observed after the offset of a fixation point has been called the gap effect. Different theories have been proposed to explain it. According to some authors, the offset also allows the saccadic system to generate a separate population of SRTs, the express saccades. Nevertheless there is no agreement about the influence of the offset of a peripheral stimulus on MRT. In two experiments we tested the effects of a peripheral visual offset used as preparatory signal on MRTs to a target after variable intervals. We found a reduction on MRT at short (200-300 ms) and long (1300-2000 ms) intervals after the peripheral offset. MRT distribution shifted toward short latencies, which sometimes formed a separate population. Since MRTs obtained at long intervals were affected by the introduction of catch trials, while MRTs at short intervals were not, we propose that two different mechanisms are involved in the decreasing of MRTs: warning and temporal expectancy. Our data support the hypothesis that the temporal component involved with the preparatory stages for motor responses can be shared by saccadic movements and key press responses, allowing the reduction on motor latencies after the visual offset in the gap paradigm. Our data corroborate the three components model for the gap effect. In our view, the question of the existence or not of a gap effect for manual responses is essentially conceptual.

Keywords: Reaction time; Preparation; Expectancy; Gap effect; Visual offset; Express responses

It is largely accepted that only a few stimuli will be selected and attentively analyzed in a difficult visual search task, but the efficiency of the selection process remains unclear. The present study shows that the processes of selection and analysis are affected by different experimental factors, which contribute additively to the RT. The RT increases as a function of the target-distractor similarity and, as a function of the presence of the background stimuli in the search field. In the target present trials, the presence of the background stimuli increases the RT in 30 ms, independent of target-distractor similarity. In the target absent trials, the effect of the background stimuli is inversely related to target-distractor similarity. The increase in similarity between target and distractor can lead to an increase in the ratio of guessing, compensating or eliminating the increase in RT caused by the presence of the background stimuli. These results are compatible with a model in which the relevant stimuli are selected pre-attentively and then, submitted to an attentive serial analysis.

Keywords: Visual attention; Visual search; Stimuli selection