2. Methods :

1. Now that the two basic terms have been defined, it is possible to proceed to the description of the main illusion discussed in this document: An X-colored background, surrounding a neutral colored spot, creates an illusion of an X-colored spot, after replacing the original image with a neutral field. For example, a gray spot on a green background will create an illusion of a green spot on a magenta background (Figure 3). In other words, this process describes a method of inducing an illusion of the original color of the background, within the area of the spot, on a neutral field. Furthermore, it is possible to add green light to the neutral background of the Actual Secondary Image, thus canceling the magenta background of the Perceived Secondary Image, resulting in a "flipped" secondary image – the original colors of the spot and the background are switched. The present day theory explains the Visionary Illusion by tying together the mentioned illusions of Afterimages (AI) and Simultaneous Contrast (SC), into what could be called a superposition of the two, and most research has focused on attempts to determine in which order: Two possible routes were described by Anstis et al. and Ferree and Rand [3], and are shown in Figure 4. occur. They attempted to prove this statement by cancelling-out each one of them in turn, using the King and Wertheimer neutralizing effects stated above, and showing that the illusion still existed. Ferre and Rand claim that only the mechanism SC  AI exists (red in Figure 4), rather than AI  SC (blue in Figure 4). Anstis opposes this idea, claiming that the intensity and decay time of the background color behaved differently than those of the spot (e.g. the spot's illusion lasted longer than the background's illusion). He therefore concluded that it is most likely that the two phenomena are not directly related. Another feature of the combined effect theory, as found by Anstis, is the shortening of the background's decay time with the reduction of light intensity, as well as the same effect for the spot's decay time, though with different time constants. This also served as proof that the two are not directly related. Furthermore, as the light intensity was reduced, the intensity of the complementary hue of the background (SC) grew. This is another contradiction to the Ferre and Rand theory, because if the process was only SC  AI, the result should have been an increase in the intensity of the Afterimage as well as the Simultaneous Contrast, when reducing the light intensity, which is not the actual result. Other features that were monitored by the different researchers, were time constants of the appearance of the full illusion, after removing the original image. They were color dependant – SC appeared before AI for red background, while AI appeared first for blue-green background. Furthermore, this order could be reversed, depending on the light intensity. To conclude this summary, the present common belief is that the full illusion is caused by some combination of Simultaneous Contrast and Afterimages. Nevertheless, it remains a phenomenon that is not well-explained, as some logical faults can be found in all previous publications, since they did not take into account the possibility of a completely different mechanism that is not directly related to neither AI nor SC. These faults will be shown in the next paragraph. We believe this mechanism is related to the newly branded terms of Time and Space Edges. In this paper, it is argued that the full Visionary Illusion described above is in fact a result of a mechanism not yet referred to in up-to-date literature and is not related directly to Afterimages or Simultaneous Contrast, as is the common perception at the present time, but rather this mechanism is based on Time and Space Edges. This will be proven by showing a non-linear relationship between the full illusion strength and each of the mentioned effects. 2. Methods: In this research, I am making use of the ViSaGe Visual Stimulus Generator (VSG), by Cambridge Research Systems (CRS), including the CRS Matlab toolbox. The VSG system is located in room 108 in the Interdisciplinary Building at Tel-Aviv University, and includes the generator, which is connected to a high-resolution Mitsubishi screen on one side and to the computer, via the VSG board. The first stage of the project was to plan a series of experiments to find a non-linear relationship between SC and the strength of the illusion (described further on in this part of the paper). The same goal was set for AfterImages. Using the CRS Matlab toolbox, I designed a set of experiments to be taken by several human subjects, in an isolated environment. The experiments are completely automatic and are based on feedback which is given directly by the test taker (using a specially assembled Response Box with several buttons), while the test operator is not in the room. The two main experiments, plus an extra one, are hereby described: a. The "SC against total illusion" relationship experiment: The strength of the SC effect was controlled by changing the size of the colored ring surrounding the neutral spot. For each ring size, which refers to a specific strength of SC effect, a "strength of total illusion" value is given by the test taker. This value is determined using the input given by the test taker, using the response box: For a certain SC-effect value, the test taker decides whether to add a correcting hue to the perceived spot, or to subtract it. The strength of the total illusion is determined, for each ring size, by the amount of hue correction needed to cancel out the illusion. If the resulting graph will reach a plateau that is not zero at the lower values of ring size, this will serve as proof that eliminating SC is not enough to completely cancel the total illusion. Anstis' logical mistake, we believe, is that he concluded that since the total illusion's strength diminished with the reduction of the SC effect, the first must rely on the latter completely. He failed to consider the existence of the total illusion even without the SC effect, as shown at the low end of the X-axis in Figure 5: b. The "AI against total illusion" relationship experiment: A similar experiment was designed for determining the relationship between AfterImage effect strength and the total illusion strength. The strength of the AI was set by using different flickering durations, where a short flicker duration (~0.1 seconds) of the colored ring around the neutral spot is equivalent to a weak AI effect, and a long flicker of the ring (up to 4 seconds) is equivalent to strong AI. The total illusion strength is determined in the exact same way as in the previous experiment. In this experiment we expect to see similar results as the previous SC test, e.g. a non-zero plateau at the left part of the horizontal axis. This time, this result will serve as proof that eliminating AI is not enough to completely cancel the total illusion. Even though proving a non-linear relationship between either AI or SC and the strength of the illusion would be logically sufficient to prove a third mechanism is involved, we figured it would be more elegant to show it for both. Furthermore, since our hypothesis concerns Time and Space Edges, I planned a third experiment aimed at showing a linear relationship between the length of the border of the spot and the strength of the illusion. This third experiment is not officially part of this project, therefore it will be executed only if time allows, though an explanation of the rationale will be brought in the next few lines. c. The "border length against total illusion" relationship experiment: In this experiment, the program asks the test taker to correct the hues as usual, but this time the generated spot has varying border lengths, determined by a circular sine wave of varying amplitude. The expected result is a linear relationship between the length of the border and the strength of the total illusion. Preliminary iso-brightness/equiluminance experiment: All the above experiments have a preliminary stage during which the subject must determine iso-brightness levels for the different colors being used. Iso-brightness is defined as the luminance level of the chromatic light as perceived by the eye and has a different value for each human subject, and for each color. This is the reason these values must be determined before each session, in order to create an environment that is as equal and objective as possible, for every human subject. The iso-brightness/equiluminance is determined by using the Minimum Motion Technique designed by Anstis and Cavanagh[14]. In brief, I designed a preliminary experiment, during which the subject looks at a repeating sequence of 4 frames, at a high frequency. The first and third frames are made of vertical stripes of the two specific colors to be matched (e.g. green and red) that switch between them (at half a spatial phase). The second and fourth frames are made of vertical stripes of a color which is the mixture of the two colors to be matched (see Figure 6) – dark yellow and light yellow if green and red are to be compared in frames 1 and 3. The test taker then has to determine whether the lines appear to be drifting left or right and correct them accordingly, using the mentioned Response Box. According to Anstis and Cavanagh, once the green and magenta have equal brightness value for that specific human subject, they will stop "drifting". The series of experiments sets iso-brightness/equiluminance levels for several colors by comparing them all in turn to the same color (grey in this case): green-gray are matched, then magenta-gray are matched, the cyan-gray etc. At the end of the sequence of experiments, any one of these colors can be chosen for the main experiment. 3. First Results: I have started to perform the first experiments recently, in order to test-drive the program and system. I performed the full set of experiments on myself as the subject. These are not objective results and will not be included in the final results reported, of course, but they serve as a general direction marker. The results were encouraging (detailed in the next paragraph). The whole experiment cycle takes about 75 minutes to complete, and shortening it may be considered in order to improve levels of mental concentration. This may be done by reducing the number of colors tested with each subject, but it also means using more subjects. After completing the cycle of Minimum Motion experiments and setting iso-brightness/equiluminance levels to all the colors, I chose magenta and green for the main experiment. As described earlier, the two colors with the adjusted levels of luminance flickered at different ring widths (experiment a) and at different temporal frequencies (experiment b). Experiment c was not performed yet. The results of experiment a are shown in Figure 7. Similar results were achieved in experiment b. 4. Discussion about the First Results: Even though it is too early for a comprehensive discussion of the results, an encouraging direction can be declared: The graph in Figure 7 resembles the ideal graph shown earlier in Figure 5: the strength of the illusion is linear only in the middle part of the graph, while at the lower ring-width values (=lower SC levels), its values reach a non-zero plateau. Similar results were obtained for the AI effect. This indicates that a different mechanism, other than SC and AI exists that controls the full illusion. 5. Bibliography: [1] Anstis S., Rogers B. and Henry J. (1977); "Interactions between Simultaneous Contrast and colored Afterimages"; Vision Research, Vol. 18, 899-911. [2] King. W. L. and Wertheimer M. (1963); "Induced colors and colors produced by chromatic illumination may have similar physiological bases"; Perceptual Motor Skills, Vol. 17,379-382. [3] Ferree C. E. and Rand G. (1934); "Contrast induced by color so far removed into the peripheral field as to be below the threshold of sensation"; Journal of General Psychology, Vol. 11, 193-197. [4] Ferree C. E. and Rand G. (1933); "Color contrast of the second order"; Journal of General Psychology, Vol. 9, 450-452. [5] Ferree C. E. and Rand G. (1932); "A method of greatly increasing sensitivity to color contrast"; Journal of General Psychology, Vol. 7, 466-472. [6] http://illusioncontest.neuralcorrelate.com/2009/color-dove-illusion/ [7] Spitzer, H. and Barkan, Y. (2005); "Computational adaptation model and its predictions for color induction of first and second orders"; Vision Research, Vol. 45, Issue 27, 3323-3342. [8] Shapiro, A. G. (2008); "Separating color from color contrast"; Journal of Vision, 8(1):8, 1-18, http://journalofvision.org/8/1/8/, doi:10.1167/8.1.8. [9] Shapiro, A. G., Charles, J. P., & Shear-Heyman, M. (2005); "Visual illusions based on single-field contrast asynchronies"; Journal of Vision, 5(10):2, 764-782; http://journalofvision.org/5/10/2/, doi:10.1167/5.10.2. [10] Wandell, B. A. (1995); "Foundations of Vision"; Sinauer associates Inc., Sunderland, Massachusetts. [11] Sejnowski, T. J., Churchland, P. S. (1992); "The Computational Brain"; The MIT press, Cambridge, Massachusetts. [12] Nichols, J. G., Martin, A. R., Wallace, B. G. (1992); "From Neuron to Brain"; Sinauer associates Inc., Sunderland, Massachusetts. [13] Berns, R. S. (2000); "Billmayer and Saltzman's Principals of Color Technology"; John Wiley & Sons, New York. [14] Anstis, S. M., & Cavanagh, P. (1983); "A Minimum Motion Technique for Judging Equiluminance"; In J. D. Mollon & L. T. Sharpe (editors.) Colour vision: Psychophysics and physiology. London: Academic Press, 66-77. Visual Temporal and Spatial Edges: The Perception Illusion Stav Davis Department of Bio-Medical Engineering, Faculty of Engineering, Tel-Aviv University Academic Supervisors: Dr. Hedva Spitzer, Mr. Yuval Barkan Abstract: This research project refers to a vision related phenomenon, which involves the perception of a colored field under temporal and spatial conditions that were not previously known. The significance of the phenomenon is in the creation of a new definition of both temporal and spatial edges, which percolate into the field. In order to convey the present hypothesis, as it is agreed upon in up-to-date literature, two well known phenomena in the field of vision must be introduced: Afterimages and Simultaneous Contrasts. After defining them along with the relationships between them, it is possible to phrase the new hypothesis brought here, which contradicts the old one, and prove it to be true. It is argued here that the full Visionary Illusion is in fact a result of a mechanism not yet referred to in up-to-date literature and is not related directly to Afterimages or Simultaneous Contrast, as is the common perception at the present time, but rather this mechanism is based on Time and Space Edges. This will be proven by showing a non-linear relationship between the full illusion strength and each of the mentioned effects, using the ViSaGe system by Cambridge Research Systems, together with the CRS Matlab toolbox to plan and execute the experiments. 1. Background: This research project refers to a vision related phenomenon, which involves the perception of a colored field under temporal and spatial conditions that were not previously known. The significance of the phenomenon is in the creation of a new definition of both temporal and spatial edges, which percolate into the field. In order to convey the present hypothesis, as it is agreed upon in up-to-date literature, two well known phenomena in the field of vision must be introduced: Afterimages and Simultaneous Contrasts. After they will both be defined, together with the relationships between them, it will be possible to phrase the new hypothesis brought here, which contradicts the old one, and prove it to be true. An afterimage is the illusion of a complementary hue, created as a result of the adaptation of the human eye to a colored stimulus. For example, a magenta colored spot on a gray (neutral, a-chromatic) background will produce a green afterimage of the spot, seen against a neutral test field (Figure 1). The time-decay graph of the afterimages (after the primary image is replaced by the secondary image) is an exponential decay curve, with decay constants ranging from 24-54 seconds, in an experiment conducted by Anstis et al[1]. Simultaneous Contrast can be described as a colored background, which induces the complementary hue within the spot it surrounds. An example is shown in Figure 2. A relevant feature of Simultaneous Contrast, was shown by King and Wertheimer [2]: It is possible to compensate for the illusion of color within the spot, by changing the actual hue of the spot, i.e. adding magenta colored light to the neutral achromatic gray, will cancel the green effect, making the perceived spot neutral. This is an important observation, since it shows that physical colors and induced colors can be mixed efficiently.