Apparatus and Stimulus Design for Producing and Evaluating Binocular Field Effects in Vision

1. Field of Invention

The invention pertains to the field of visual perception, specifically to an arrangement for inducing certain novel and useful perceptions. These perceptions can create special visual effects for films, television, and other forms of entertainment. Also they can be used to evaluate visual dysfunction.

2. Background--Prior Art--FIGS. 1A-1C

It is known that when a human's two eyes see different images, it is possible to arrange the images so as to create a "competition" between the two eyes which can produce novel perceptual effects. In other words, if the two eyes send respective signals representing a pair of images to the visual centers of the brain, the visual centers will try to combine components parts of the two signals into a single perception. However, when the information contained by the images is incompatable, the visual center may selectively inhibit some of the information in forming the perception. This may be described as a "rivalry" between the eyes, though it should be understood that any synthesis or transformation of the information coming from each eye is accomplished by the brain.

FIG. 1A shows a prior-art visual set of images (called "stimuli" by Psychologists), comprising a black line drawing 11 of a multifaceted polygon with a white background surface, and a white line drawing 12 of the same polygon with a black background. These stimuli are paired to form stereoslide 10, which can be viewed stereoscopically to produce the perception of a single image which has a lustrous "gun-metal" surface. This is because the dark and light regions of the stimulus cause competition between the eyes (called binocular rivalry). This example of binocular rivalry was provided by H. von Helmholtz (Handbuch der Physiologischen Optik, 1910, plate IV-Q).

FIG. 1B shows a prior art stereoscopic slide 20 used by W. J. M. Levelt ("Binocular brightness averaging and contour information," British Journal of Psychology, 1965, pp. 1-13). This slide provides the right eye with a view of three black disks (22, 24, 26), while the left eye sees a hollow disk 21, a black disk 23, and a blank area 25 at the corresponding locations of the binocular visual field. When slide 20 is examined through a stereoscope, ring 21 is combined with disk 22, disk 23 is combined with disk 24, and blank area 25 is combined with disk 26. The perception which results is shown in Fig 1C; the viewer will perceive a bright disk at 31 and dark disks at 32 and 33. Using this stimulus configuration and these viewing requirements, Levelt was able to induce an increase in brightness in the immediate neighborhood of the stimulus contours, with the strength of the effect depending upon the size of the stimulus.

Observations by Helmholtz (op. cit.) and by those who preceded him had established that binocular conflict could produce the perception of luster, either when the images were presented by stereoscope or by viewing the objects through colored filters. However, none were accurate in establishing the essential conditions for producing the effect. H. W. Dove (Poggendorffs Ann. LXXXIII, 1850, p. 169) thought that differential refraction by the two eyes created depth cues which caused the images to be seen in different planes. This does not explain why the luster can be seen with black-and-white or monochromatic images. Helmholtz (op. cit., pp. 417-418) thought the luster was produced by a differential level of stimulation (i.e. a difference in brightness) at correponding points on the two eyes. When an observer with normal binocular vision fixates upon a real object, it provides the same brightness level to the corresponding point in each of the eyes. Under the unusual viewing conditions provided by the stereoscope, however, it is possible to provide the corresponding locations with different brightness levels, and Helmholtz thought this was the key factor in producing the perception of luster. As detailed below, the differential level of brightness is a factor in producing luster, but it is not the only factor. If it were, the binocular synthesis of disk 26 with blank area 25 would produce the perception of luster, since there is a brightness differential at corresponding locations of the two retina. In fact, this combination produces the perception of disk 33, which is seen as dark and having no luster. Levelt (op. cit.) described means by which contours would produce local control of brightness. His means included the centering of the stimulus within the field of view, because his analysis found that the local effects were strongest at the fovea. He stated that the strength of the brightness control was determined by the size of the stimulus, and his means for producing local control included the superimposition of the edges of the stimulus object presented to each eye.

Accordingly, one principal object and advantage of the invention is to provide apparatus and means for inducing binocular rivalry (which controls perceptibility of brightness an pattern) by dark borders which are not limited to contours. Further, the apparatus and means induces this rivalry over a larger zone -- such that the perceptual effects are not restricted to the immediate neighborhood of the dark border. These large-scale influences will be referred to as "binocular field effects." Another object and advantage is to provide apparatus and means for inducing effects which are not restricted to foveal vision. A further object is to produce control of brightness where the edges of the images presented to the two eyes need not be coincident, and are not dependent upon the size or shape of the stimulus. The invention produces binocular rivalry using fewer elements than was heretofore available, and produces a greater diversity of effects--in particular, binocular field effects.

Still further objects are to produce special effects in films or with electronic images, to quantify the strength of the binocular field effect, so that abnormalities of vision may be tested, and to provide an optical device which measures the strength of binocular field effect, for use in research, instruction, and testing of adequacy of vision. Further objects and advantages will become apparent from a consideration of the ensuing description, taken in conjunction with the accompanying drawings.

FIG. 1 (A & B) show examples of prior-art stimulus configurations which will produce the perception of luster. FIG. 1C illustrates the perception from viewing FIG. 1B with a stereoscope.

FIG. 2A shows a viewing device and stimuli according to the invention for demonstrating luster; FIG. 2B and FIG. 2C illustrate the perceptual result, in which the disk with a black rim shows luster.

FIG. 3 shows that stimuli which vary in size and position in the visual field will have uniform luster.

FIG. 4 shows various shapes with uniform luster, and shows that colors presented to opposite eyes can produce luster simultaneously.

FIG. 5 shows geometric figures which are bordered by contours, and that certain contours will not induce luster.

FIG. 6 shows that a dark boundary edges can produce luster, and that one color can provide such an edge for another.

FIG. 7 shows a number of disks which differ in thickness of the perimeter rim; the thickness of the rim determines the level of luster.

FIG. 8 shows a number of stimuli which vary in the degree of direct contact between the color zone and the dark boundary; amount of direct contact determines the amount of luster.

FIG. 9 shows a stereo slide which presents the two eyes with line patterns which differ in tilt, and also presents one eye with a hollow ring; the ring determines which is perceived in the zones inside and outside the ring.

FIG. 10 (A to C) illustrates methods for presenting stimulus materials so that luster may be perceived.

FIG. 11 (A & B) illustrates the production of luster by viewing a stimulus configuration with a stereoscope.

FIG. 12 illustrates the use of polarized light to produce the perception of luster.

FIG. 13 shows the design of a stimulus collection which can test the strength of binocular field effect in vision.

FIG. 14 shows design and components of a stereo viewer which can be used to test the strength of binocular field effects.

FIG. 2A illustrates visual stimulus set 51-52, as well as viewing device 40 according to the invention which can be used to produce binocular field effects, including the perceptual experience of a bright, shimmering surface which may be described as "luster."Viewing device 40 is a pair of glasses containing, for the respective lenses, a set of color filters. These glasses provide the wearer with conflicting information about stimulus set 51-52. Viewing device 40 contains a red filter 41 in the left lens and a blue filter 42 in the right lens. For an individual of normal vision, these filters can be reversed without affecting the perception of luster.

Stimulus set 51-52 consists of two disks. Left disk 51 has no line or other border; it is red, as indicated by the vertical scoring. Right disk 52 is also red, and has a blackline border or rim. Disks 51 and 52 may be drawn on a white paper or projected upon a surface suitable for viewing.

When an observer of normal vision views disks 51 and 52 through glasses 40, the resulting perception is shown in Fig 2B. Disk 51 will be perceived as dark disk 61, and disk 52 will be perceived as lustrous disk 62. Lustrous disk 62 is seen as having a shimmering, color-saturated quality, as indicated by the crosses in the illustration, and will appear to float slightly above the page.

This perceptual phenomenon is created because the color filters segregate the image components to the viewer's respective eyes. FIG. 2C illustrates the stimuli and viewing conditions described above, and provides additional detail about the how the glasses provide conflicting information to each of the observer's two eyes. (Note that optical inversions are not reflected by the illustration, and except for the monocular views, the image components are the same as shown in FIG. 2A and 2B.) Through the blue filter, the eye registers image 63, and image 64 is registered through the red filter. In image 63, disk 51 is seen as a dark, virtually black solid disk. Disk 51 cannot be seen through the red filter (in image 64), and so that location is filled with "background" light. The binocular synthesis of the image components from the two eyes results in the perception of a dark, ruddy red disk 61.

As seen through the blue filter (in image 63), disk 52 also is registered as a dark, virtually black disk. However, in image 64 the eye registers disk 52 as a hollow ring, filled inside and outside with bright red color. The perception of the dark boundary line controls and determines the synthesis of information from the two eyes, so that the stimulus material lying inside the boundary (the bright red light) dominates perception. Thus the binocular perception of disk 52, when viewed through glasses 40 will be of a bright, lustrous disk 62. The dark disk being registered upon one eye through the blue filter is inhibited, and will not be perceived by the observer. (Direct demonstration of these perceptual effects are provided in my paper, "Form Light, Form Bright," Neuropsychology Foundation Monographs, 1985, 2-11).

The system in FIG. 2 differs from the demonstrations of Helmholtz and Dove (op. cit.), did not delineate the contribution of a dark perimeter in producing binocular rivalry. It differs from the work of Levelt (op. cit.) in several ways. Levelt stated that a contour would affect the way light is combined at two corresponding parts of the retina. He stated that in the absence of a contour, the two eyes would average the amount of light from corresponding zones, but that a contour would tip the balance, causing the brightness from one eye to dominate the average. He suggested that the influence of the contour was a function of distance -- the dominance of the eye seeing the contour would be less at points lying at a distance from the the contour. In a separate work (On Binocular Rivalry, Institute for Perception RVO-TNO, 1965, pp. 56-57), Levelt states even more explicitly that the strength of the effect is dependent upon the "size of the disk" (the area contained by the contour). In an article entitled "Some demonstrations of the complementary functioning of the eyes," Perception & Psychophysics, 1966, pp. 39-40) he states: ". .the smaller the distance d between the fixation point of an eye and a monocular contour in the field of this eye, the more the weighting coefficient of this eye tends to unity in the point of fixation." Thus Levelt proposed that there is a gradient in the retina, such that a contour has more influence when it is seen by the fovea (in the vicinity of the fixation point) than when it is seen by the edge of the eye.

The present invention provides apparatus and means for achieving nonlocal binocular rivalry, also called "binocular field effects." The stimulus configurations needed to produce these perceptual phenomenon were not available or described until the appearance of my monograph "Form Light, Form Bright," (op. cit.). Further, the range of perceptual effects which are provided by these means is much greater than has been demonstrated for any other form of binocular rivalry. Below, a number of demonstrations are given, with special emphasis on the range and diversity of perceptions which are possible using means which are not limited by local control processes.

The figure shows a stimulus set 71-74, which consists of a plurality of red disks which vary in size and location from a fixation point 70. An observer who views this stimulus collection through red-blue glasses 40 (FIG. 2A), and who looks at fixation point 70 will perceive the forms shown as binocular perception 75. Broken ring 70' shows the approximate boundary of the area seen by the fovea. Perceived disk 76 lies partly within the fovea, so that some parts of the disk are near the center of the fovea and some parts are farther away. This configuration is able to produce binocular field effects, i.e., a broad control of the zone contained by the dark border. In this example, disk 76 will appear a uniform, lustrous red. Similarly, perceived disk 77 will appear as bright as disk 76, even though it lies at a great distance from the fovea. Perceived disk 79 will appear a uniform, lustrous red across the entire surface of the disk, even though the central zones of the disk lie farther from the dark perimeter line than those near the edge. In fact, disks 76-79 will appear uniform and equal in luster irrespective of their size or position in the visual field.

Binocular field effects are able to act at a substantial distance from the border which controls the process. Because of this, the strength of the effect does not depend upon the proximity of the border to the various zones within the form. FIG. 4 shows stimulus set 81-84, consisting of four forms (crescent 81, star 82, arrow 83 and heart 84) which are colored either red (vertical lining) or blue (horizontal lining) and are bordered by a black line. When viewed with red-blue glasses 40 (FIG. 2) they produce binocular perception 85. Red crescent 86 will exhibit the same amount of luster as red star 87, and the luster will be uniform across the surface of each shape. Similarly, blue arrow 88 will exhibit the same amount of luster as blue heart 89, and again the luster will be uniform.

Binocular rivalry is often explained as the domination of one eye over the other. This explanation is inconsistent with the fact that one will be able to perceive red and blue luster simultaneously, as is the case for the stimulus group shown in FIG. 4. The conditions for producing red luster would require that the eye looking through filter 41 would have to dominate perception, and for blue luster to be seen the eye looking through filter 42 would have to be dominant. Since both lustrous colors are seen at the same time, the demonstration shows that binocular field effects can be controlled simultaneously by the appropriate presentation of stimulus elements to the two eyes.

Containment by dark border is an essential element in control of binocular field effects. This is illustrated in Fib 5, where a red hyperbolic 90 (which is partially bounded by contour 91) will not be perceived as having luster even when the stimulus material is positioned so that it falls on the fovea of the eye. As shown at perception field 95, this stimulus will be perceived as a dark, somewhat ruddy-red form 96. Luster will be seen only when the stimulus contours operate to "contain the zone," as is true with contours 93 and 94, which provide containment of hyperbolic shape 92. The field effects produced by these perimeter elements results in the perception of the lustrous hyperbolic shape 97. In general, the amount of luster produced by a dark boundary is a direct function of the extent of containment. Broken or partial boundary lines will have proportionately less influence than will a solid line.

FIG. 6 contains a stimulus set 101-105, which when viewed with glasses 40 (FIG. 2) will be seen as binocular perception 110. Stimulus 101 is a red disk surrounded by a squarish black form, and stimulus 102 is a blue disk surrounded by an amorphous black form. The resulting perception will be lustrous red and blue disks, respectively, as shown in perceived forms 111 and 112. This demonstrates that the boundary of the disk need not be a contour, but can be a dark zone of indefinite dimensions.

Note also that the edge of the form seen by each eye need not be coincident. The red-filtered eye sees a small bright circle surrounded by an amorphous dark form. To the blue-filtered eye the amorphous form appears completely dark -- one does not see any rim at the location which corresponds to the border of the disk seen by the other eye. Thus the control of luster does not depend upon presentation of coincident edges to the two eyes.

The perimeter may contain more than one color, as shown with disk 103 which contains red and blue half-disks, and disk 104 which has a small blue disk set within a larger red disk. When viewed through glasses 40, these disks will show luster, as illustrated with perceived disks 113 and 114. This occurs because each color appears black when it is viewed through the opposite filter--41 or 42 (FIG. 2). The dark appearance of the color provides a "functional boundary" for the color zone which it contains.

As an additional example, red and blue checkerboard 105 contains no black, yet it will appear lustrous as shown by perceived checkerboard 115. The view through red filter 41 provides a perception of red checks surrounded by black checks, the adjacent checks (as seen through the red filter) providing a dark boundary for the red zones they contain. The converse applies to the view through blue filter 42.

The thickness of a perimeter rim can be a factor in the strength of effect. FIG. 7 shows a disk array 121-124 which has individual blue disks whose perimeter lines increase in thickness. Disk 121 does not have a dark boundary line. If this disk is viewed with glasses 40 (FIG. 2) it appears a dark blue-black, with no luster as shown in perceived field 125 at disk 126.

The thin line used for disk 122 induces a slight amount of luster, as shown by perceived disk 127 which is seen as a dark disk surrounded by a bright blue ring just inside the perimeter line. With thicker lines, the luster grows stronger and becomes uniform across the entire disk.

For disks 123 and 124 (medium and thick rims) the luster will look progressively brighter as a function of the thickness of the black rim (but it appears uniform across the surface for each of the disks). At about this thickness a maximum is reached, and the rim can be indefinitely thick (filling the remainder of the visual field) and the luster will not get any brighter.

An additional important factor is the size and continuity of color mass as it relates to direct contact of the functional border. Little or no luster will be produced if the color is broken into small zones, or otherwise fails to make contact with the dark border. In FIG. 8, stimulus set 131-132 (consisting of triangles with blue inserts) will be perceived as triangles 141 and 142 (part of binocular perception 140) when they are viewed with glasses 40 (FIG. 2). Triangle 131 contains a blue insert 133, which is contiguous with the perimeter line. Insert 133 will appear lustrous, as shown at 143 in perception field 140. However, blue insert 134 is not contiguous with the perimeter of triangle 132. As a result, perceived insert 144 will be seen as dark blue-black in color and having no luster.

Most of the red squares in checkerboard 135 do not make contact with the perimeter line, and thus the squares in perceived checkerboard 145 show no luster. The corner squares which make contact with the perimeter on two sides will show some luster. The lack of luster in this case should be contrasted with the luster which is seen in perceived checkerboard 115 (FIG. 6), where there are red and blue squares which can provide functional borders for each other.

Luster is greatest when there is extreme contrast in what is perceived in the zone by the two eyes. This is exactly the opposite of Helmholtz' theory (op. cit.). He proposed that perception of a lustrous surface was due to a differential of brightness or color as seen by the respective eyes, but further specified that the effect would be strongest where the difference was not very great. In fact, it can be shown that the most luster is seen when one eye perceives bright light in the zone contained by the dark border, and the other sees total blackness at that site.

The perception of depth in the image (with the colored form floating slightly above the surface) is not due to binocular disparity in the image. Binocular disparity cues are provided by slight misalignment of the images which are presented to the respective eyes. This is the principle behind the use of stereoscopes and twin-image projection using polarized light (so called "3-D movies") to enhance perception of depth. In the present case there is no misalignment of image components which can produce any disparity. Instead, the current phenomenon is based on a "binocular field effect" to establish the dominance of certain components in the image, and additionally the viewer attributes depth (floating) to the perceived form.

Accordingly, I have found that various viewing conditions and stimulus configurations will produce the perception of luster. The phenomenon may be seen by an observer who has a normal balance of binocular vision, when two basic conditions are met:

(a) the images presented to the respective eyes have regions which differ substantially at corresponding locations in each eye (i.e. one eye seeing bright light and the other seeing darkness at the same location)

(b) the eye which sees the zone of bright light also sees that zone as being surrounded by a dark border

The strength of the luster effect is determined by:

(1) the degree to which the zone is contained or bounded all around by the dark border,

(2) the magnitude of the brightness difference between the two eyes at the location of the dark-bordered zone,

(3) the thickness of the line or other stimulus material which forms the border, and

(4) the presence of direct contact between stimuli having a brightness differential between the two eyes, and the dark border which surrounds the zone containing these stimuli.

Variations in stimulus elements listed above have a role in determining what is perceived, and can be manipulated systematically as a method to control the strength of the perceptual effect. As discussed previously, for a person of normal binocular vision, the location, size, and shape of the bounded zone are not important as factors in determining the strength and uniformity of the luster effects nor is it necessary to have corresponding positioning of the edges presented to the two eyes.

It is also important to note that the binocular field effects are not the exclusive province of brightness or color. Perceptions of patterns (colored and non-colored) can be determined by the binocular field effects. For example, FIG. 9 shows a stereoslide 150 which can be presented to the two eyes using a stereo viewer, polarized light projector, or a related procedure (stereo viewer not shown). Note that the lines shown in the illustration are meant to portray the actual lines of the stimulus--color is not represented in this particular case.

The right eye sees diagonal lines 151 and the left eye sees lines 152. The left eye also sees a hollow ring 153.

Binocular perception 160 contains elements from each of the eyes. The viewer will perceive a ring 163, and the perception of this ring will determine what is seen inside and outside the zone contained by the ring. Perceived pattern 162 inside the ring is perceptually derived from pattern 152 (which is presented to the same eye that sees ring 153). Perceived pattern 161 outside the ring is perceptually derived from pattern 151. This pattern was presented to the right eye, which is not provided with a view of ring 153. Thus, perception in the zones inside and outside perceived ring 153 are determined by the selective presentation of the stimulus ring to one eye but not the other.

The design of the pattern for showing binocular field effects will depend somewhat on the method of segregation of the images. If a stereoscope is used, the stimulus slide will look approximately like that of FIG. 9, and the lines of the stimulus, as well as the background can be in black and white, or any color combination.

The resulting perception will be a composite in which the lines and background color are segregated according to whether they fall inside or outside the zone contained by the perimeter line. Mixing of line and color elements from the two images is minimal.

If the stimuli are projected upon a screen using polarized light, then patterns 151 and 152 (as well as ring 153) will be separated on the film which is used to make the projection, but the images will be superimposed upon the screen, and then resegregated by the use of polarized filters placed in front of the two eyes like glasses.

If the segregation of images is to be accomplished with colored filters, as with glasses 40 (FIG. 2), then patterns 151 and 152 (as well as ring 153) must be drawn superimposed, and in color--e.g. with pattern 151 drawn using red lines, and pattern 152 and ring 153 drawn using blue lines. The red lines will appear black when they are viewed through blue filter 42 (FIG. 2), and they cannot be seen through red filter 41 (FIG. 2). Conversely, the blue lines will be seen as black when viewed through the red filter (41), but cannot be seen through the blue filter 42. The combined perception 160 will be approximately black and white, and the effect of the perceived perimeter in inducing binocular field effects is manifested by the selective perception of one pattern inside the perimeter, and the other pattern outside the perimeter.

This particular effect depends on a relatively even balance of overall pattern-strength, and the effect is strongest where the rivalrous patterns would be seen as a patch-work quilt were it not for the presence of the hollow ring.

It should be clear that the invention is a specification of the devices and stimulus conditions for producing zonal control of binocular field effects. By the selective presentation of separate images to the two eyes, it is possible to provide one eye and not the other with stimulus material which allow it to dominate the competition between the eyes and to determine the final perception. In particular, where one eye sees a dark boundary and the other does not, the observer will generally perceive whatever material is contained by that boundary, as seen by the eye which is able to see the boundary.

The brightness enhancement (i.e. luster) phenomenon represents a special case of the more general effect. If stimulus material is presented in black and white, then a dark border seen by one eye will create an enhancement of brightness in the zone contained by the perimeter. If that area has color which can be seen by the eye which sees the perimeter, then the color will be seen as being saturated and having a lustrous glow. If that zone is filled with a pattern--lines, dots, or whatever, then the perception inside the perimeter will be of that pattern, and patterned material from the other eye will be inhibited.

It should be clear, therefore, that the factors which determine the strength of luster also determine the control of pattern perception. Thickness of the perimeter line, the degree to which it "contains" a given zone, the relative balance of material in the respective eyes, and the contiguity of material within the zone and the boundary are all factors in determining the strength of effect. While they are specified most completely with respect to luster, it should be clear that they apply also in relation to perception of patterns.

The medium which is used to present an image is not critical, so long as the perceptual relationships described above are preserved. As illustrated in FIG. 10A, the stimulus elements can be printed on a page or any other suitable viewing surface 170. Any method of pigmentation of the surface, such as photographic printing, lithography, or xerography, can provide suitable stimulus elements. Likewise, the stimulus elements can be hand-drawn or constructed by lamination or other method of fabrication.

FIG. 10B shows the stimulus elements being presented on an electronic device 180. This might correspond to a standard television or computer monitor, but would also include other methods of electronic display, such as a liquid crystal display, light-emitting diode array, a plasma display or other device designed to provide a viewable image. Although a still frame is illustrated, the perceptual effects can be produced with moving images as well.

FIG. 10C shows the stimulus elements being projected upon a screen 191 so that they may be viewed. The projection device 190 can be a film-transparency projector, an opaque projector, a video-image projector, or a laser projection device. Again, the images thus projected can be still-frame or can be in motion.

Given the diverse displays which are possible, for simplicity, the phrase "presented to the observer" should be understood to comprise any suitable method for presenting two images stereoscopically to a human (or other animal) who views the images.

An essential precondition for producing the perceptual effects is the use of viewing conditions which provide the two eyes with different images. Various methods will serve this purpose, e.g.

a. constructing an image using colors, and then using colored filters to restrict what can be seen by each eye,

b. presenting each eye with separate images using a stereo

scope or similar device, and

c. projecting two images upon a screen using polarized light, and then using polarized filters to restrict what can be seen by each eye. The use of colored filters has been illustrated in FIGS. 2-8 and in FIG. 10. Additional consideration of the other two methods will now be presented.

The stimulus elements can be presented to the two eyes using a stereoscope 250, as shown in FIG. 11A. With such a device, one would provide the stimulus elements to the two eyes using a special slide, represented in FIG. 11B by stereoslide 260. The left side 270 contains stimulus set 271-274, a collection of four shapes, specifically: green mushroom 271, yellow arrow 272, black circle 273, and black rectangle 274. The right side 280 contains stimulus set 281-284, a corresponding collection of four shapes, specifically: black mushroom 281, black arrow 282, yellow circle 283, and green rectangle 284. Each colored shape on the left or right has a corresponding black shape on the opposite side of the slide.

When stereoslide 260 is viewed in stereoscope 250, stimulus set 271-274 is seen as an image in the left eye, and stimulus set 281-284 forms an image in the right eye. Therefore, for each colored shape which is seen by the left eye, there is a matching black shape (at that same location in the field of view) which is seen by the right eye. Similarly, the colored shapes which are seen by the right eye have a black pair-mate which is presented to the left eye at the corresponding site. A person of normal binocular vision will synthesize the information from the two eyes, and will see binocular field 290, containing perceived shapes 291-294. In the illustration shown in FIG. 11B, all the shapes will be seen as having luster.

Using the stereoscope, one has greater latitude in the selection of colors. When using colored filters to produce the perceptual effects (glasses 40 of FIG. 2), it is necessary to use specific colors for the stimulus elements which match the filtration properties of the glasses. This is not necessary with the stereoscope; any color can be used, such as the green, violet, and yellow shown in stereoslide 260.

The stereoscopic display can be still-frame, or moving. The device for producing the stereoscopic display can use any of the methods described above, including video or other electronic imaging system.

FIG. 12 illustrates a method for producing binocular field effects using polarized light projection and polarized filters as a device for sorting the image components to the respective eyes. Projector 300 makes use of prior art methods for projecting two images upon a screen using light with two kinds of polarity. Light polarities 301 and 302 are indicated by wavy and broken lines. Stimulus elements (contained in a stereoslide or as pair-frames on movie film) are projected upon a viewing surface 305, and the result of that projection can be seen as stimulus set 310.

The polarity of the light is preserved as it is reflected from viewing surface 305, and is selectively filtered by polarized glasses 320 being worn by the viewer. Glasses 320 use lens filters which are of different polarity--i.e. lens 321 allows polarized light 301 to pass through, but not polarized light 302, and vice versa for lens 322. Thus glasses 320 resegregate the stimulus material to reflect what was contained by the paired-frames being projected. The effect is the same as if a stereoscope were being used, and this method of display has the additional latitude for color selection described above.

It should be noted that the perceptual phenomenon being described here is not the same as the standard depth effect produced in "3-D" movies. The standard depth enhancement depends on the creation of binocular disparity in two images -slight misalignment of the edges of the stimulus elements. While the binocular field effects being described in this application produce some enhancement of depth, it is a separate and independent phenomenon. The perceptual effects described according to my invention do not require any binocular disparity.

Commercial uses for the invention include the creation of special effects in various forms of entertainment and advertising. Also, the mere demonstration of the perceptual phenomena will be of importance for research and instruction, and thus the design of the materials for these purposes should be included in a discussion of utility. An important benefit may be provided in the testing of patients being evaluated for binocular dysfunction. While the particulars for application may include a wide variety of uses, I will focus on the testing of visual dysfunction, and special effects for entertainment.

There are various ways in which defective binocular vision might be tested. One method is to systematically vary the amount of light which is delivered from the zone contained by the dark border. A graded sequence of stimuli can be used, as illustrated in FIG. 13, which shows a collection of disks 331-335d, as they would be designed for viewing through red-blue glasses 40 (FIG. 2).

The disks can be printed, painted, or otherwise constructed so that the disks without a rim are all the same color-brightness. The upper set of disks (which have a rim) are a graded sequence of brightness levels. Disk 331 is the same brightness as all four unrimmed disks 335a-335d. Disks 332, 333, and 334 are progressively less bright, but are the exact same color hue as all the other disks. One method of creating this stimulus collection is to use multiple layers of a color film, so the amount of light reflected or transmitted from the stimulus surface is determined by the number of layers of film. With this method, disk 331 might be created by a single film layer, 332 using two layers, etc.

When stimulus array 331-335d is viewed using glasses 40 (FIG. 2), one sees binocular perception 340, consisting of the corresponding perceived disks 341-345d. Disks 345a-345d are seen as being dark, and having a ruddy-red color. The upper set of four disks are seen as having luster, but the amount of brightness enhancement is offset proportional to the initial brightness of the stimulus. One disk among the perceived set will be seen as most equal to the lower comparison disk. In this illustration, perceived disk 343 is seen as most equal for a person of normal vision. A person with weak binocular field effect will select disk 341 or 342 as being equivalent to the lower comparison disk, depending on the degree of dysfunction. An individual with abnormally strong binocular field strength would select disk 344.

It should be clear that the four levels of brightness used in FIG. 13 are for purposes of illustration. Any practical visual test should have more brightness steps to provide better measurment of the strength of binocular field effects.

When using color filters as a means of segregating the visual images, it is essential that the colors of the image be well balanced in relation to the filters being used for viewing. In the case of enhanced brightness, the effect will be diminished substantially if the eye which perceives the boundary is able to see a difference in shading between the interior of the form and the background. The overall effect may be lost where the color used to create the stimuli has not been carefully selected with regard to the glasses. The best field effects are seen if the colored zone is virtually invisible when viewed through one of the glasses, and looks quite dark when viewed through the other. For some applications, "process printing," mixing four preselected colors in various proportions, can be used with success. However, there is always the risk that the color will involve a mix which diminishes the effect. Thus, where the stimulus material is to be printed, the best results are achieved by the use of "direct printing" methods, where one selects the exact colors of ink to be used.

A graded set of masks can be used to control the brightness of the stimulus array. The disks could be made using the same color color brightness for all the stimulus elements, and then the rimmed disks can be overlayed with a 0%, 20%, 40% or 80% mask. The dark mask serves as a counterbalance to the enhancement of brightness created by the rim (i.e. luster), and one of the masked stimuli will appear most like the dark comparison disk which has no rim.

Because of the color-balance discussed above, it is essential that the mask be color neutral. While the ink used for press-on density gradients is nominally black, in fact it may have enough hue of its own to modify perception of the color in that zone. In such a case none of the masked stimuli look quite like the comparison member.

One such device is a specially constructed stereo viewer, shown as 350 in FIG. 14A. The viewer uses special slides which presents stimulus forms which may vary in size, shape, thickness of dark boundary, and other factors which may be of significance in relation to the strength of binocular field effect. Composite slide 400 is one such slide; it is shown in position for viewing within device 350, and the components of the slide are shown separately in FIG. 14B.

The slide composite is designed to allow adjustment of the amount of light which is delivered from the zone contained by the boundary. By varying the amount of light shown in that zone, one can counterbalance the effect of the boundary in inducing luster, and so can arrive at a measurement of the strength of the binocular field influence for any given observer.

As shown in FIG. 14A, the device uses reflected light to illuminate the face of the slide. The light source is indicated (but not shown) at 360. At the viewing plane of the device, composite slide 400 is used for presentation of the visual stimuli.

Key elements for control of luminance are shown in FIG. 14B. The front layer 410 of composite slide 400 has a white surface which is seen as a background to the forms which are printed, painted or otherwise constructed upon the surface. A hole 411 is cut to remove the area contained by the perimeter line, so that the slide now can serve as a mask to selectively allow the transmission of light from the rear of the device, provided by light source 370, wherein the light can pass only through the zone contained by the perimeter.

The stimulus slide must be coated or laminated on the back side with a completely opaque layer to prevent the transmission of light at other sites, this layer being shown at 420 in Fig 14B, with the corresponding hole at 421. A polarized light filter 430 is bonded to each of the stimulus slides, or can be mounted as a separate component in the device. It is important that the components of the slide be relatively thin, and sandwiched tightly to prevent the perception of a depth differential between the background surface and the light transmitting surface which is formed by the holes. Proper diffusion and angling of light also will be essential in this respect.

Control of the amount of transmitted light is accomplished by the positioning of two polarizing filters--filter 430, shown in FIG. 14B, and filter 500, shown in FIG. 14A and 14B. The relative angular position of filters 430 and 500 determines the amount of light which can pass. Filter 500 is designed so that is can be rotated, thus changing the angular position between the filters, and controlling the amount of light which passes through them.

As has been previously discussed, the color balance can be critical to the perception and comparison being required. Adjustment of these factors can be accomplished by careful selection of component materials, color adjustment of the light sources, or the use of a restricted range of wavelengths (so called monochromatic light), for making the tests.

An alternative method would be to adjust the electrical power being delivered to the light source, and measure the amount of current needed to achieve a match of brightness (or other field strength comparison). Again, color balance becomes an issue since the spectral properties of the source will change at different current loads.

A major advantage of the device shown in FIG. 14 is relative simplicity. One can interchange the composite slides and vary all the stimulus parameters described above--perimeter thickness, size of form, etc. The cut-out design allows automatic adjustment for the size and shape of the form. After testing the patient by adjusting the light being delivered to one eye, the device can be turned over to evaluate the other monocular system. However, for the most critical work it would be advisable to use transmitted light for the background as well as the foreground, with multiple-masks and appropriate optics for synthesizing the components for viewing. Additionally, an advanced system should allow adjustment of background illumination as well as the light being delivered from the comparison stimulus. With either approach the illumination must be even.

The methods described in this application can be used to create special perceptual effects in visual material which can be presented in diverse ways. FIGS. 10, 11, and 12 show several applications of the invention, but are inadequate to show the impact of these special effects upon perception. Creation of a color luster is especially interesting -- the color has a ghost-like luminescent quality, and appears to float slightly above the viewing surface. This can be used in motion pictures, television, or books (FIGS. 10a-c) to produce a dazzling array of surrealistic effects which would be suitable for science fiction and fantasy entertainment. The effects could be used for children's cartoon shows, where the special glasses could become part of the fun. In any medium where visual images can be presented, there is the potential for producing special effects which can serve to entertain, inform, or provide additional influence of attention.

Thus it is seen that, according to the invention I have provided an useful analysis of essential devices and stimulus design for producing these perceptual effects. The devices which serve this purpose include:

a. presenting separate images using a stereoscope or similar device,

b. projecting two images upon a screen using polarized light, and then using polarized filters to restrict what can be seen by each eye, and

c. constructing an image using colors, and then using colored filters to restrict what can be seen by each eye.

With respect to stimulus design, I have described the configurations which create the binocular field effects. Stated in the most general terms, it is necessary for one eye to perceive light or light-patterns in a zone of the visual field, and to perceive a dark boundary surrounding that zone. The other eye cannot perceive the light or light-pattern in the correponding zone, nor the presence of a dark boundary to that zone. When these conditions are met, the eye which perceives the boundary will dominate binocular perception, and the person perceives the stimulus material which is contained by the boundary rather than the visual stimulus provided at that location by the other eye.

The reader will see that I have given explicit information as to the devices and stimulus configurations which are needed for producing binocular field effects, and this is the first valid description of the means for producing these effects. Indeed, the existence of extended (nonlocal) control of brightness and contour perception was not known prior to my own disclosure of this phenomenon in my monoagraph ("Form Light, Form Bright," op cit.)

While the foregoing description contains many specifies, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of several preferred embodiments. Other ramifications will occur to those skilled in the art. Accordingly, the scope of the invention should be determined by the appended claims and their legal equivalents.