Vicario's Illusion of Sloping Steps Reexamined

Perception ◽  
1987 ◽  
Vol 16 (5) ◽  
pp. 671-675
Author(s):  
Paola Bressan
Keyword(s):  
Visual Field ◽  
Visual Angle

If a few parallel horizontal rows of dots are set diagonally, like steps, across the visual field, the inner rows appear not to be horizontal but sloping up to one side; the effect holds as long as the vertical distances between the rows do not exceed a given visual angle. This illusion, described by Vicario in 1978, was never explained. An experiment is reported in which the illusion was still visible at row separations well in excess of the spatial limits originally considered, provided the stimulus elements were enlarged. The maximum illusion was obtained for length ratios (interrow distance to size of dots) identical to those which have been shown to produce the largest effects in a number of illusions of area and length. This suggests that Vicario's illusion is similar to other illusions of extent, and that it can be explained by a neural extent-coding model.

Dynamic Perception of Computer Generated Visual Information in an Altitude Control Task

1982 ◽  
Vol 26 (10) ◽  
pp. 890-894
Author(s):  
Tamara Mitchell
Keyword(s):  
Visual Field ◽  
Visual Information ◽  
Visual Angle ◽  
Control Task ◽  
Altitude Control

Investigations were conducted to determine what size (visual angle) of objects and where in the forward visual field objects should be placed to provide maximum effectiveness in a simple altitude control task. Two experiments placed between 7 and 9 degrees below the horizon enabled significantly better altitude control and induced the least tendency to drift in altitude. The two experiments investigated targets ranging from 2 to 20 degrees in horizontal visual angle. This variable did not prove to significantly affect altitude control or altitude drift. Subject variance was significant in both experiments.

Binocular Masking Induced by a Moving Object

1965 ◽  
Vol 17 (2) ◽  
pp. 97-109 ◽  
Author(s):  
G. C. Grindley ◽  
Valerie Townsend
Keyword(s):  
Visual Field ◽  
Qualitative Study ◽  
Visual Angle ◽  
Moving Object ◽  
The Other ◽  
Visual Phenomena

Movement in a part of either of two binocular fields can, under some conditions, produce temporary obliteration of the corresponding part of the other field. This paper is a mainly qualitative study of this rather surprising phenomenon. The effect is found to increase from the fovea to the periphery, to be greatest at a velocity of about 20° visual angle per sec. and to vary with the orientation of the fixation point in the visual field. Some further lines of research designed to elucidate the relation of the effect described here to certain other visual phenomena are suggested.

Aberrations of the Human Eye across the Horizontal Visual Field

2007 ◽  
Vol 364-366 ◽  
pp. 1207-1210
Author(s):  
Wei Quan ◽  
Gui Cai Song ◽  
Fu Yun Liu ◽  
Zhao Qi Wang
Keyword(s):  
Visual Field ◽  
Wave Front ◽  
Visual Angle ◽  
Second Order ◽  
Third Order ◽  
Human Eye ◽  
The Third ◽  
Human Eyes

Aberrations of the human eyes in the horizontal visual field were measured with modified Hartmann-Shack wave front sensor. The characteristic of third to tenth order Zernike aberration rms both temporally and nasally out to 50° is as follows: considerable differences occur among subjects in the pattern of aberrations, particularly for the dominating second-order aberrations; the third to tenth order Zernike aberrations increase with the visual angle, but the increscent magnitude decreases as the Zernike order increases; in despite of imperfect symmetry, the increscent magnitude is the same on the whole; the third-order Zernike aberrations increases up to 2 times from 0° to ±50° visual angle, the forth-order up to 1.8 times, and the fifth to tenth order up to 1.7~1.3 times.

scholarly journals THE VISUAL ACUITY OF THE HONEY BEE

1929 ◽  
Vol 12 (6) ◽  
pp. 727-760 ◽  
Author(s):  
Selig Hecht ◽  
Ernst Wolf
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Honey Bee ◽  
Visual Angle ◽  
Distribution Curve ◽  
Angular Separation ◽  
Maximum Density ◽  
Resolving Power ◽  
Apical Angle ◽  
Human Eye

1. Bees respond by a characteristic reflex to a movement in their visual field. By confining the field to a series of parallel dark and luminous bars it is possible to determine the size of bar to which the bees respond under different conditions and in this way to measure the resolving power or visual acuity of the eye. The maximum visual acuity of the bee is lower than the lowest human visual acuity. Under similar, maximal conditions the fineness of resolution of the human eye is about 100 times that of the bee. 2. The eye of the bee is a mosaic composed of hexagonal pyramids of variable apical angle. The size of this angle determines the angular separation between adjacent ommatidia and therefore sets the structural limits to the resolving power of the eye. It is found that the visual angle corresponding to the maximum visual acuity as found experimentally is identical with the structural angular separation of adjacent ommatidia in the region of maximum density of ommatidia population. When this region of maximum ommatidia population is rendered non-functional by being covered with an opaque paint, the maximum visual acuity then corresponds to the angular separation of those remaining ommatidia which now constitute the maximum density of population. 3. The angular separation of adjacent ommatidia is much smaller in the vertical (dorso-ventral) axis than in the horizontal (anterio-posterior) axis. The experimentally found visual acuity varies correspondingly. From this and other experiments as well as from the shape of the eye itself, it is shown that the bee's eye is essentially an instrument for uni-directional visual resolution, functional along the dorso-ventral axis. The resolution of the visual pattern is therefore determined by the vertical angular separation of those ocular elements situated in the region of maximum density of ommatidia population. 4. The visual acuity of the bee varies with the illumination in much the same way that it does for the human eye. It is low at low illuminations; as the intensity of illumination increases it increases at first slowly and then rapidly; and finally at high intensities it becomes constant. The resolving power of a structure like the bee's eye depends on the distance which separates the discrete receiving elements. The data then mean that at low illuminations the distance between receiving elements is large and that this distance decreases as the illumination increases. Since such a moving system cannot be true anatomically it must be interpreted functionally. It is therefore proposed that the threshold of the various ommatidia are not the same but that they vary as any other characteristic of a population. The visual acuity will then depend on the distance apart of those elements whose thresholds are such that they are functional at the particular illumination under investigation. Taking due consideration of the angular separation of ommatidia it is possible to derive a distribution curve for the thresholds of the ommatidia which resembles the usual probability curves, and which describes the data with complete fidelity.

Effects of Laterality and Visual Angle on Time Judgments: A Phenomenological Investigation of Time Durations

1984 ◽  
Vol 58 (1) ◽  
pp. 307-310
Author(s):  
Evans Mandes
Keyword(s):  
Visual Field ◽  
Response Bias ◽  
Visual Angle ◽  
Left Visual Field ◽  
Time Duration ◽  
Experimental Conditions ◽  
Undergraduate Class

20 students from an undergraduate class participated in an experiment designed to study the effects of laterality and visual angle on time judgments. Using a standard two-field tachistoscope, subjects were exposed to two experimental conditions, (1) stimulus cards with a single red or blue dot in the center and several dots clustered on both sides near the center and equidistant from it (visual angle of .6°) and (2) stimulus cards with a single red or blue dot in the center and several dots clustered on both sides away from the center on the edge of the card (visual angle of 2.6°). Five cards containing a single red or blue dot were used to control for response bias. The subjects were asked to indicate whether they saw dots in the left, right, or both fields, and whether they perceived a time duration between fields. No difference in time duration exisited, however, as all cards were exposed to both fields for equal durations. The predictions that the judged duration of dot patterns would be more accurate favoring the left visual-field and more accurate where the distance between the point of fixation and stimulus was larger were supported.

scholarly journals ON THE RELATION BETWEEN MEASUREMENTS OF INTENSITY DISCRIMINATION AND OF VISUAL ACUITY IN THE HONEY BEE

1933 ◽  
Vol 16 (5) ◽  
pp. 773-786 ◽  
Author(s):  
Ernst Wolf
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Honey Bee ◽  
Visual Angle ◽  
Constant Level ◽  
Intensity Discrimination ◽  
Direct Test ◽  
Discrimination Power ◽  
Consistent Manner

1. Bees respond by a characteristic reflex to a movement of their visual field. By confining the field to a series of parallel stripes of two alternating different brightnesses it is possible to determine for any width of stripe, at any brightness of one of the two sets of stripes, the brightness of the second at which the bee will first respond to a displacement of the field. Thus the relations between visual acuity and intensity discrimination can be studied. 2. For each width of stripe and visual angle subtended by the stripe the discrimination power of the bee's eye for different brightnesses was studied. For each visual acuity the intensity discrimination varies with illumination in a characteristic, consistent manner. The discrimination is poor at low illuminations; as the intensity of illumination increases the discrimination increases, and reaches a constant level at high illuminations. 3. From the intensity discrimination curves obtained at different visual acuities, visual acuity curves can be reconstructed for different values of ΔI/I. The curves thus obtained are identical in form with the curve found previously by direct test for the relation between visual acuity and illumination.

Relation of the Aubert-Foerster Phenomenon to Manifest Anxiety

1977 ◽  
Vol 44 (3) ◽  
pp. 699-702 ◽  
Author(s):  
Kaiser A. Sarwar
Keyword(s):  
Visual Field ◽  
Visual Angle ◽  
Anxiety States ◽  
Manifest Anxiety

The relation of the increase in distance to narrowing of the visual angle was investigated with 20 subjects in high and low anxiety states. Stimuli were introduced from the periphery, and readings were taken at the limits of sharp perception of figures. The investigation partially confirmed that increase in distance resulted in narrowing of the visual field for the group low in anxiety. However, the visual angles were greater for the group high in anxiety.

Processing of Alphabetic Information Presented in the Fovea or the Periphery: Functional Visual Field and Cognitive Load

Perception ◽  
1981 ◽  
Vol 10 (6) ◽  
pp. 645-650 ◽  
Author(s):  
Leonard J Williams ◽  
Lester A Lefton
Keyword(s):  
Reaction Time ◽  
Visual Field ◽  
Cognitive Load ◽  
Visual Angle ◽  
Load Level ◽  
Retinal Eccentricity ◽  
Time Study ◽  
Low Level ◽  
The Past ◽  
Level Information

In a tachistoscopic reaction-time study that required subjects to respond ‘same’ or ‘different’ to vertically arrayed letter pairs, it was found that cognitive load (level of required match) and retinal eccentricity were both potent variables. It seems that subjects can process low-level information (physical matches) quite effectively out to at least 7 deg visual angle from fixation, in either direction. It was also demonstrated that higher-level processing may proceed fairly efficiently out to at least 4 deg from fixation. These estimates suggest that the abilities of the information processor to deal effectively with the periphery may have been underestimated in the past.

scholarly journals Processing of Threat-related Information Outside the Focus of Visual Attention

2005 ◽  
Vol 8 (1) ◽  
pp. 3-11 ◽  
Author(s):  
Manuel G. Calvo ◽  
M. Dolores Castillo
Keyword(s):  
Visual Field ◽  
Cognitive Bias ◽  
Visual Angle ◽  
Response Times ◽  
Right Visual Field ◽  
Probe Word ◽  
Decision Task ◽  
Privileged Access ◽  
Related Information ◽  
The Right

This study investigates whether threat-related words are especially likely to be perceived in unattended locations of the visual field. Threat-related, positive, and neutral words were presented at fixation as probes in a lexical decision task. The probe word was preceded by 2 simultaneous prime words (1 foveal, i.e., at fixation; 1 parafoveal, i.e., 2.2 deg. of visual angle from fixation), which were presented for 150 ms, one of which was either identical or unrelated to the probe. Results showed significant facilitation in lexical response times only for the probe threat words when primed parafoveally by an identical word presented in the right visual field. We conclude that threat-related words have privileged access to processing outside the focus of attention. This reveals a cognitive bias in the preferential, parallel processing of information that is important for adaptation.

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