ACTIVITAS NERVOSA SUPERIOR Activitas Nervosa Superior 2013, 55, No. 1-2 IDEAS & PERSPECTIVES THEORETICAL IMPLICATIONS ON VISUAL (COLOR) REPRESENTATION AND CYTOCHROME OXIDASE BLOBS (cid:2)(cid:2) István Bókkon and Ram L.P. Vimal Vision Research Institute, Lowell, MA, USA Abstract The rich concentration of mitochondrial cytochrome oxidase (CO) blobs in the V1 (striate) primate visual cortex has never been explained. Although the distribution of CO blobs provided a persuasive example of columnar structure in the V1, there are contradictions about the existence of hypercolumns. Since photoreceptors and other retinal cells process and convey basically external visible photonic signals, it suggests that one of the most important tasks of early visual areas is to represent these external visible color photonic signals during visual perception. This representation may occur essentially in CO-rich blobs of the V1. Here we suggest that the representation of external visible photon signals (i.e. visual representation) can be the most energetic allocation process in the brain, which is reasonably performed by the highest density neuronal V1 areas and mitochondrial-rich cytochrome oxidases. It is also raised that the functional unit for phosphene induction can be linked to small clusters of CO –rich blobs in V1. We present some implications about distinction between the physics of visible photons/light and its subjective experiences. We also discuss that amodal and modal visual completions are possible due to the visual perception induced visualization when the brain tries to interpret the unseen parts of objects or represent features of perceived objects that are not actually visible. It is raised that continuously produced intrinsic bioluminescent photons from retinal lipid peroxidation may have functional role in initial development of retinogeniculate pathways as well as initial appearance topographic organizations of V1 before birth. Finally, the metaphysical framework is the extended version of dual-aspect monism (DAMv) that has the least number of problems compared to all other frameworks and hence it is better than the materialism that is currently dominant in science. Key words: Color representation; Visible electromagnetic photons; Amodal and modal visual completions; CO- rich blobs in V1; Phosphenes; Metaphysics; Materialism; Dual-aspect monism; Visual channels 1. INTRODUCTION The attributes of visible electromagnetic photons, such as wavelength and intensity, are physics, but both exogenous (stimulus/ light dependent) and/ or endogenous (such as phosphenes) colors are subjective experiences related to its attributes hue, saturation, and brightness (Vimal, Pokorny, & Smith, 1987). When we talk about our visual perception, in reality, we talk about the perception/ detection of external electromagnetic visible photons. Although external visible photon signals that are conveyed to V1 can be modulated by other (cid:2)Correspondence to: Istvan Bokkon: [email protected]; url: http://bokkon-brain-imagery.5mp.eu Received January 17, 2013; accepted February5, 2013; Act Nerv Super (Praha) 55(1-2), 15-37. 15 Activitas Nervosa Superior 2013, 55, No. 1-2 sensory modalities during multisensory integration (Calvert, Spence, & Stein, 2004), it is hardly questionable that photoreceptors and other retinal cells process and convey principally external visible photonic information to Lateral geniculate nucleus (LGN) and then to V1 (primary visual cortex) and other visual areas. It suggests that one of the most important tasks of early V1 area is to represent these detected external photonic signals. Although vision science makes difference between achromatic and chromatic vision, however, both are subjective color experiences produced by mixed visible (color) photon signals in the human eye ranging from about 400 to 700 nm. Explicitly, in the following sections, we point out that the representation of external visible photon signals (i.e. visual representation) might be one the most energetic allocation processes in the brain, which is reasonably performed by highest density neuronal V1 areas with mitochondrial-rich cytochrome oxidase (CO) areas, which send signals to visual V4/ V8/ VO color-related-neural-network. It is also raised that small clusters (3-4 blobs/ mm2) of CO blobs might work as functional units for conscious phosphene perception. In addition, we present some implications about distinction between the physics of visible photons/ light and its subjective experiences since the latter is the mental aspect of color-related-neural- network-state; its inseparable physical aspect is the V4/ V8/ VO color-related-neural-network and its activities. We also argue that amodal and modal visual completions are possible due to the visual perception induced visual imagery when higher level regions in the brain tries to interpret the unseen parts of objects or represent features of perceived objects that are not actually visible. Then, it is raised that retinal bioluminescent biophotons originated from natural retinal lipid peroxidation might have important role in the development structural organization of visual system before birth. Since we try to elucidate subject experiences related to color, we must clearly disclose our metaphysics. So, finally, the metaphysical framework is the extended version of dual-aspect monism that has the least number of problems. This is called the DAMv framework: the Dual-Aspect Monism with dual-mode and varying degrees of the dominance of aspects depending on the levels of entities, where each entity has inseparable mental and physical aspects (Vimal, 2008, 2010a, 2012; Bruzzo & Vimal, 2007). This is better than the dominant view, materialism, in science. 2. HYPERCOLUMN IDEA The cortical column notion as a functional unit for monkey somatosensory cortex was first suggested by Mountcastle and co-workers (Mountcastle, 1957; Powell & Mountcastle, 1959). Soon after ocular dominance column (eye-selective cells) concept was proposed by Hubel and Wiesel (1962) based on recordings from cells in primary visual cortex of anesthetized cats and monkeys (Hubel & Wiesel, 1962, 1974, 1977). Hubel and Wiesel also proposed that the columns can be assembled into larger units (i.e. hypercolumns constructed by adjacent ocular dominance columns) that include representation of all functions (all orientations and both eyes) within each area of retinotopic space (Hubel & Wiesel, 1974, 1977). The proposed width of a hypercolumn is 1–2 mm. A hypercolumn contains a cluster of neurons that respond to the same retinal location, but with different orientation preferences (Horton & Adams, 2005(cid:3) Lu & Roe, 2008). That is, hypercolumns contains three subsystems as ocular-dominance columns, iso-orientation domains, and blobs. The ocular-dominance column is the segregation of inputs from the right and the left eye. These segregated inputs form the ocular-dominance columns, which run almost parallel to one another in slabs. In the iso-orientation domains (or orientation- preference bands), each domain containing cells respond best to a given stimulus orientation. The same hypercolumn also includes the representation of all orientations. The third subsystem includes neurons that are selective for other attributes of the visual stimulus, such as color and spatial frequency. Thus, a hypercolumn contains the representations of all attributes of a stimulus within each area of retinotopic space (receptive field). These neuronal cells are placed in the mitochondrial cytochrome oxidase-rich blobs. 16 Activitas Nervosa Superior 2013, 55, No. 1-2 Although hypercolumn idea suggested by Hubel and Wiesel can be an attractive notion, to date, there are disagreements about the existence of hypercolumns. The visual cortex (like other parts of the cortex) is a continuous sheet and we cannot find a structure that corresponds to the borders between the hypercolumns. Hubel mentions in his Nobel Prize Lecture that the hypercolumns borders are arbitrary, but it didn’t seem to worry him. In a recent review by Lund et al. (2003) states that there is no fixed boundary to such hypercolumns as there is a continuous change in property and mean visual field position across the cortex. In addition, as per (Horton & Adams, 2005), “Although the column has been offered as the fundamental unit of the cortex, it has not earned this lofty designation. After half a century, it is still unclear what precisely is meant by the term. It does not correspond to any single structure within the cortex. It has been impossible to find a canonical microcircuit that corresponds to the cortical column”. 3. MITOCHONDRIAL CYTOCHROME OXIDASE-RICH BLOBS AND COLOR REPRESENTATION In primates, the major pathway serving visual perception runs from the retina via the lateral geniculate nucleus (LGN) to V1, V2, to extra striate areas and distribution to higher cortical regions. From V1, most signals are conveyed to the V2 area before distribution to higher cortical areas. During visual perception and imagery, the high activity of cytochrome oxidase (CO) is associated with high mitochondrial activity. CO is the last enzyme in the mitochondrial electron transport chain. The strict coupling between neuronal activity and oxidative energy metabolism is the basis for the use of CO as an endogenous metabolic marker for neurons (Wong-Riley, 1989). Because CO staining intensity correlates with neuronal functional activity, when we talk about CO activity we also talk about mitochondrial activity. Namely, CO activity can have direct link with mitochondrial activity, distributions, and processes (as in neuronal activity) (Bókkon & Vimal, 2010). Although the distribution of mitochondrial CO provided a persuasive example of columnar structure in the V1, there are contradictions about the existence of hypercolumns. In addition, a nonlinear distribution of mitochondrial-rich CO blobs, with increased enzyme activity, can be identified in the V1. These blobs can also be revealed by diverse labeling techniques such as increased expression of N-methyl-D-aspartate (NMDA) or (cid:1)-amino-5- hydroxy-3-methyl-4-isoxazole propionic acid (AMPA) receptors, and increased activity glutamate or ATPase, among others (Carder & Hendry, 1994; Carder, 1997; Wong-Riley, Anderson, Liebl, & Huang, 1998). Besides, CO blobs appear to be common to all primates (Preuss & Kaas, 1996). In addition, blobs and interblob are found not only in trichromatic or dichromatic primates but also in nocturnal primates with single functional type of cone within the retina (Wikler & Rakic, 1990). The functional CO blobs in the supragranular layers extend to layer 6, with the exception of layer 4C (Takahata, Higo, Kaas, & Yamamori, 2009). Neurons in the V1 blobs have low orientation selectivity but respond to color and have higher firing rates compared to surrounding regions (interblobs) (Lu & Roe, 2008; Economides, Sincich, Adams, & Horton, 2011). In V1, layers 2 and 3 are composed of CO-dense blobs and surrounding regions (interblobs) (Xiao & Felleman, 2004). V2 is composed of alternating thin and thick CO-rich stripes and the pale interstripe regions between them. According to Sincich et al. (2007), different CO compartments in V1 and V2 are connected in parallel and the projection from V1 CO blobs to V2 CO thin stripes is responsible for color. In addition, V1 and V2 can represent all the principal submodalities of vision such as color, form, motion, and depth (Bartels & Zeki, 1998). In the latest experiments by Economides, Sincich, Adams, and Horton, published in Nature Neuroscience (2011), confirmed previously presented notion by Sincich and Horton 17 Activitas Nervosa Superior 2013, 55, No. 1-2 (2005) that the visual attributes of color, form, and motion are not really segregated in V1. According to Economides et al. (2011), V1 contains local cluster of neurons jointly sensitive to orientation and color, perhaps corresponding to cytochrome oxidase blobs. Economides et al. (2011) also mention: “The abundant concentration of cytochrome oxidase in patches or blobs of primate striate cortex has never been explained”. It is lesser-known that the highest density of neurons in neocortex (number of neurons per degree of visual angle) (Rockel, Hoirns, & Powell, 1980; O’Kusky & Colonnier, 1982) devoted to representing the visual field are found in V1. However, it is hardly accidental that the highest mitochondrial (energetic) activity can be achieved in V1 with mitochondrial CO-rich regions in the brain. Namely, V1 has the highest energy allocation for the visual representation and imagery in the brain, and mitochondrial-rich CO blobs may represent monocular sites of color processing. All things that exist in the nature and universe have (dynamic) form (Pereira, 2012). If the (dynamic) form is the quintessence of our world it may support that visual information via reflected visible photons (400-700 nm) from objects/ forms might play the key role in visual perception/ representation and imagery. Edwald Hering (a German physiologist (1834-1918) who proposed opponent color theory in 1892) noted in the last century that colors are always spatial. “Our visual world consists solely of differently formed colors […] seen objects, are nothing other than colors of different kinds and forms” (Hering, 1874). 4. V1 MAY GUARANTEE THE FINEST AND DETAILED VISUAL REPRESENTATION During critical period, both visual stimulation and intact visual regions are necessary for normal development of visual functions and imagery. Although there are contradictions about if mental images and perceived stimuli are represented similarly as well as if V1 is activated during visual imagery, recent experiments support that V1 can be activated during these states in healthy subjects (Chen et al., 1998; Borst & Kosslyn, 2008; Klein et al., 2004; Cichy, Heinzle, & Haynes, 2012). Our presented notions in this paper are related to intact V1 of healthy persons and not to the exceptional subjects with diverse V1 damages, lesions, and malfunctions. Nevertheless, in exceptional V1 cases (damages, lesions), for example, as it was revealed in blindsight phenomenon, there are further possible mechanisms bypassing or helping V1 such as compensation, neural reorganization, preserved “islands” in V1 (geniculostriate visual pathway), projections to the superior colliculus and pulvinar that can provide indirect visual input to the extrastriate areas (retinotectal visual pathway) (Fendrich, Wessinger, & Gazzaniga, 1992; Ptito & Leh, 2007), and at present still unknown V1 bypassing visual networks. Recently, Boyer et al. (2005) demonstrated that TMS induces blindsight in a normal population via an alternate geniculoextrastriate visual pathway that bypasses V1, which can process orientation and color without conscious awareness. According to Ganis et al. (2003), “Many sorts of deficits in imagery follow brain damage, but the relation between the site of damage and the type of deficit is not simple or straightforward. The dissociations in performance after brain damage provide hints regarding the processing system underlying imagery, but difficulties in interpretation urge caution in mapping these findings to theoretic models. Neuroimaging techniques, such as PET and fMRI, open a window into the working brain and offer valuable information not easily accessible through the study of patients, who, as noted, may have deficits beyond those observable and may rely on compensation and neural reorganization”. Lately, Ffytche and Zeki (2012) reported visual awareness in blind fields of three patients with hemianopic field defects. Authors concluded that “the primary visual cortex or back- projections to it are not necessary for visual awareness”, however, they also acknowledged that the blind field experiences of all three subjects were degraded and crude. If V1 striate cortex can be totally damaged, the processes that would take place there would then take place in the next available V2 visual area. The V2 areas are also well 18 Activitas Nervosa Superior 2013, 55, No. 1-2 retinotopically organized (Cavusoglu, Bartels, Yesilyurt, & Uludağ, 2012) and preserve the local spatial geometry of the retina (similarly to V1), so patterns of activation in V2 can depict shape (Kosslyn, 1994). There are numerous further visual areas beyond V1 and V2 in what is known as the prestriate cortex, and they have larger receptive fields and cruder topographic organizations. V1 and V2 have comparable surface areas in the brain (Sincich, Jocson, & Horton, 2007). A map of V2 approximates a mirror image of the V1 (Zeki, 1977). V1 sends most of its cortical output to V2 and in return receives a strong feedback projection. There are approximately 11,000 feedback neurons in V2 and 14,000 feedforward neurons in V1 (Rockland, 1997). There are especially rapid feedforward and feedback processes between V1 and V2 with conduction velocities around 3.5 m/ s (Girard, Hupé, & Bullier, 2001). According to Sincich and Horton’s (2005), “…along with physiological and imaging studies, now make it likely that the visual attributes of color, form, and motion are not neatly segregated by V1 into different stripe compartments in V2. Instead, there are just two main streams, originating from cytochrome oxidase patches and interpatches, that project to V2”. It suggests that V2 could represent the principal submodalities of vision such as colour, form, motion and depth. Thus, when V1 can be damaged, V2 may be available to take up V1 roles and produce similar effective visual imagery than V1 should do. According to latest transcranial magnetic stimulation (TMS) experiments (Salminen- Vaparanta et al., 2012) human visual awareness cannot be generated without an intact V2. It may support our above mentioned notion that when striate cortex is damaged, V2 may be able to take up V1 roles and produce similar effective visual imagery than V1 should do. It is also possible that intact V1 may guarantee the finest visual perception and visual imagery, but it is difficult to observe due to the subjective reports of visual experiments and to the significant individual structural variability between normal visual systems of subjects. For example, the mean V1 surface area is 2643 mm2 in human, but the surface range is between 1986–3477 mm2 (Adams, Sincich, & Horton, 2007). Is it possible that the size of V1 (i.e. the number and size of functional cells in V1) area can have some influence on the visual perception and imagination? According to Cattaneo, Bona, and Silvanto (2012), it is possible that fine details of imagery for which the small receptive fields of V1 are suited requires the primary visual cortex, although when fine details are not necessary, extrastriate regions are enough for imagery. It is a simple but important question, would size of mitochondria population be correlated with reports of phosphenes and imagery and vividness and individual differences in these phenomena? This would be an important experiment to do in the future. Energetic processes can have essential role of V1 representation mechanisms. Recent experiments suggest (Basole, White, & Fitzpatrick, 2003(cid:3) Basole, Kreft-Kerekes, White, & Fitzpatrick, 2006) that population activity ((i.e. combinations of different stimulus features such as orientation, direction, spatial frequency) in V1 can be better revealed by a single map of spatiotemporal energy rather than multiple maps of different stimulus features. Recently, we pointed out that spatiotemporal mitochondrial networks and processes can also reflect represented information within neurons during sensory experiences (Bókkon & Vimal, 2010). Namely, while the brain processes information from different perceptions, the energetic mechanisms (dynamic mitochondria networks and processes activated neurons) have to reflect the perceived information processes because the energy demand of neuronal electrical activity is realized fundamentally by mitochondrial processes. Since sensory information processes are directly linked to mitochondrial energetic processes, it means that information that comes from the different perceptions have to be represented not only by structural processes (such as neural networks) and neuronal electrical activity, but also by spatiotemporal energetic processes of mitochondrial networks within neurons. 19 Activitas Nervosa Superior 2013, 55, No. 1-2 5. CLUSTERS OF CO-RICH BLOBS AS POSSIBLE FUNCTIONAL UNITS FOR CONSCIOUS PHOSPHENE PERCEPTION Phosphene light perceptions can be produced in the visual hemifield contra-lateral to the stimulated cortical hemisphere and reflect the retinotopic organization of the visual cortex (Brindley & Lewin, 1968). TMS induced phosphenes can be perceived regardless of whether subjects' eyes are opened or closed. In addition, phosphenes are only perceived by blind patients that have prior visual experience, suggesting that early visual stimulus is essential to maintain any level of residual visual function (Merabet, Theoret, & Pascual-Leone, 2003). Visual imagery can lower phosphene threshold (PT) (Sparing et al., 2002) suggesting that visual imagery and intrinsic phosphene perception can be in direct functional relationship. The characteristics of phosphenes are related to the function and receptive field organization of the stimulated neurons. Phosphenes induced in V1, V2, and V3 visual areas usually are stationary small blob-like forms (wedges, crescents, ellipses) (Kammer, 1999). Induced phosphenes in V4 and V5/ MT+ visual regions usually are larger and present a ruder retinotopic structure, and even adopt qualities such as color, motion or texture (Marg & Rudiak, 1994; Cowey & Walsh, 2000). The CO blobs form nonlinear repeating functional units in V1. According to Tehovnik and Slocum, (2007), “The functional unit for phosphene induction in V1 is most likely the hypercolumn, which is about 1 x 0.7 mm of tissue composed of layers spanning some 2 mm of tissue from the surface of cortex.” The sizes of CO blobs in monkeys are about 514 (cid:4)m in the neonate enucleated and 560 (cid:4)m in normal animals (Kuljis & Rakic, 1990; Kennedy, Dehay, & Horsburgh, 1990). Kuljis and Rakic (1990) found that the center-to-center spacing of blobs is 590 (cid:4)m in normal and 598 (cid:4)m in strabismic macaques. In addition, the mean density of blobs was 3.67 blobs/ mm2 in normal and 3.45 blobs/ mm2 in strabismic macaques. Besides, CO blobs can develop in the absence of external visual cues from photoreceptors, and the CO layout of the visual cortex is not modifiable by visual experiences (Kuljis & Rakic, 1990). If we compare Tehovnik and Slocum suggestion that the functional unit for phosphene induction is about 1 x 0.7 mm of tissue with (Kennedy, Dehay, & Horsburgh, 1990; Kuljis & Rakic, 1990) experimental results that the size of blobs 514-560 (cid:4)m or 590 - 598 (cid:4)m in animals, it may suggest that is more reasonable if the functional unit for phosphene induction can be linked to small clusters (3-4 blobs/ mm2) of CO blobs and not definitely to the doubtful and unproved hypercolumns structure. One may argue that why conscious phosphene perception should be linked to small clusters of CO blobs, because phosphenes can be elicited not only in CO-rich V1 area but also in V2, V3, V4, V5/ MT+, intraparietal sulcus (IPS) regions among them. First, the existence of hypercolumns is doubtful while repeating nonlinear units CO blobs in V1 has been presented by many experiments (Lu & Roe, 2008, Nakagama & Tanaka, 2004(cid:3) Murphy et al, 1998). Second, recent experiments (Fried et al., 2011; Taylor, Walsh, & Eimer, 2010) suggest that all phosphenes (that can be induced in various regions (such as V2, V3 V4 or V5/ MT+, IPS among others) are due to the induced activity of local circuits (local processes contributing to phosphene generation are independent) but feed-forward visual input from excited local circuits to V1 areas are necessary to phosphene awareness. In addition, since we can interpret the form, color and movement of induced phosphenes, it suggests that not only feed-forward visual input from excited local circuits to V1 are necessary to phosphene awareness but also feed back signals from higher level association areas. Since, as was mentioned, V1 has the highest energy allocation for the visual representation and imagery; it suggests that V1 mitochondrial CO-rich blobs can have especially high role in the energy allocation for the visual representation and imagery. According to Taylor, Walsh and Eimer (2010), „While the ‘‘early’’ hypothesis suggests that phosphene related potentials after occipital TMS are functionally analogous to motor-evoked potentials following M1 (primary motor cortex) TMS, the ‘‘late’’ hypothesis claims that conscious phosphene perception and its associated phosphene-related potentials are similar 20 Activitas Nervosa Superior 2013, 55, No. 1-2 to the conscious perception of external visual stimuli and its electrophysiological correlates”. It suggests that the processing of phosphene perception is very similar to model of the reverse hierarchy vision (Ahissar & Hochstein, 1997; Hochstein & Ahissar, 2002). According to reverse hierarchy hypothesis (Hochstein & Ahissar, 2002), …„our initial conscious percept—vision at a glance—matches a high-level, generalized, categorical scene interpretation, identifying “forest before trees.” For later vision with scrutiny, reverse hierarchy routines focus attention to specific, active, low-level units, incorporating into conscious perception detailed information available there. Reverse Hierarchy Theory dissociates between early explicit perception and implicit low-level vision, explaining a variety of phenomena”. However, this hypothesis can support that visual apperception has the highest energy allocation as we also elucidated in our previously paper (Bókkon & Vimal, 2010). This extra energy allocation of explicit perception might serve the detailed (holistic (Hochstein et al., 2004) representation of detected visual information in V1 (determines whether that information reaches awareness (Silvanto, Cowey, Lavie, & Walsh, 2005). One of the most important questions in neuroscience is “The Binding Problem”. Namely, how encoded items can be combined for coherent perception, decision, and action by distinct brain regions. During object perception, separated visual features must be correctly integrated. According to feature integration assumption (Treisman, 1996), visual stimulation activates feature detectors in striate and extrastriate regions that link automatically to the object nodes in the temporal lobe. Latest studies support that reentrant processing between higher areas and early (V1) visual cortex is critical factor for visual binding and necessary for conscious (and unconscious) visual perception (Koivisto, Mäntylä, & Silvanto, 2010; Koivisto & Silvanto, 2012). It may also support the notion that early (V1) visual cortex is critical for conscious visual perception as well as for conscious phosphene perception. 6. PSYCHOPHYSICS AND NEUROPHYSIOLOGY OF COLOR VISION Trichomats have 3 psychophysical visual channels (Kaiser & Boynton, 1996): Luminance/ Achromatic channel, Red-Green color channel, and Yellow-Blue color channel. Achromatic and chromatic perceptions and representations are processed by the luminance/ achromatic channel and the two chromatic channels (Red-Green color channel, and Yellow-Blue color channel), respectively. Each has a number of tuned mechanisms in orientation (Vimal, 1997), spatial frequency (Vimal, 1998a, 1998b, 2002b), temporal frequency (Metha & Mullen, 1996, 1997; Vimal, Pandey & McCagg, 1995), and spectral/ color tuning (De Valois & Jacobs, 1984; Engel, Zhang, & Wandell, 1997). As per (Vimal, 2011a), “A psychophysical entity is an abstract mathematical construct derived by modeling the experimental data related to psychophysics and neurophysiology. For example, there are 3 psychophysical visual (cardinal (Krauskopf, Williams, & Heeley, 1982)) channels (such as the Red-Green, the Yellow-Blue, and the achromatic or luminance channels) derived from psychophysical and physiological data (Hurvich & Jameson, 1957; Kaiser & Boynton 1996; Krauskopf, Williams, & Heeley, 1982). [...] The genuine first-person measurements lead to the subjective experience of color qualia such as redness to greenness (see also (Dennett, 2003)). The third-person measurements will reveal the physical attributes such as neural activities in related neural-network that includes visual red-green (R-G) color area ‘V4/ V8/ VO’. In addition, the experience of hue, saturation and brightness (first-person data) (Vimal et al, 1987) correlates with the activity of its neural-network and the properties of associated color stimuli (third-person data) (Bartels & Zeki, 2000; Hadjikhani et al, 1998; Kaiser & Boynton, 1996; Krauskopf et al, 1982; Tootell, Tsao, & Vanduffel, 2003; Vimal, 1998b, 2002b; Wandell, 1999). This psychophysical entity (such as the R-G channel) provides a link between first- person data (phenomenal or mental aspect, such as redness to greenness) and third-person data (physical aspect, such as ‘V4/ V8/ VO R-G color neural-network’). Subjective experiences (SEs) redness to greenness and ‘V4/ V8/ VO R-G color neural-network’ are causally related via the Red-Green channel. That is, active ‘V4/ V8/ VO R-G color neural-network’ causes SEs redness 21 Activitas Nervosa Superior 2013, 55, No. 1-2 to greenness upon the presentation of equiluminant red-green patterns via the spatial frequency (SF) tuned mechanisms of the Red-Green channel (Vimal, 1998b, 2002b); these are external stimulus driven SEs. Subjective experience of color can also occur by internal activation, such as electrical stimulation, transcranial magnetic stimulation (TMS), and ‘meditation-induced cortical phosphenes with eyes closed’ (Vimal & Pandey-Vimal, 2007). […] The color-contrast-constancy is partly achieved at high contrasts and the information processing at suprathreshold levels is different from that at the threshold levels (Vimal, 2000). Color and luminance SF discrimination thresholds have a different SF dependence; while color appears to perform better than luminance vision at low SFs, this effect is lost or even reversed at high SFs; color and form interact, but color and motion are largely segregated (i.e. they weakly interact) (Vimal, 2002a).” 7. COLOR AS SUBJECTIVE VISUAL EXPERIENCE It is well-known that humans have three different types of cones in their eyes that perceive the blue, green, and red visible photons reflecting from objects. Human cones pigments have spectral peaks of about 445 nm, 535 nm, and 570 nm (Hunt, Carvalho, Cowing, & Davies, 2009). The color vision of dogs is dichromatic and they have only two types of light-catching cone photoreceptor pigments. These two types of pigments have spectral peaks of about 429 nm and 555 nm (Neitz, Geist, & Jacobs, 1989). Dogs cannot see red, orange or green colors but red, orange and green appear as yellow or blue to them. Namely, dogs can see yellow, blue, and grey colors. Several types of birds have a fourth type of retinal cone photoreceptor cells (tetrachromatic UV (Ultraviolet), 300 nm), so their vision is more refined as compared to human color vision. When we can see a red apple at the same time, dogs can see this apple with yellow-like color. So the question can emerge, this apple in Figure 1 is red or yellow-like. A dog’s subjective visual experience can be that this apple is yellow-like but a human’s subjective visual experience is red. The correct definition could be that this apple under normal photopic circumstances for people with intact vision makes a red visual sense. So a color is not a physical feature of an given object but a subjective visual experience that is depend on the long wavelength sensitive (LWS or red) cone, middle wavelength sensitive (MWS or green) cone, and short wavelength sensitive (SWS or blue) cone/ photoreceptor and visual processes and also on the context of apple. Figure 1. A red apple. When we can see a red apple at the same time, dogs can see this apple with yellow-like color. (See the related thoughts in the text.) 8. ACHROMATIC AND CHROMATIC VISION Electromagnetic light waves (photons) visible to the human eye range from about 400 to 700 nm. Attributes of visible photons/ light, such as wavelength and intensity, are physics; but 22 Activitas Nervosa Superior 2013, 55, No. 1-2 color and its attributes (such as hue, saturation, and brightness (Vimal et al, 1987)) are subjective experiences, which are the mental aspect of color-related-neural-network-state (Vimal, 2008, 2010a, 2012). A hue is a pure color, i.e. one with no black or white in it. In our previous paper (Bókkon et al, 2011), we elaborated that the white light (visible electromagnetic photons) is a mixture of all colors. Black or white, it's not an all or nothing case in everyday life. White objects are white because the most of the light that falls on them is reflected by the material. Black objects absorb light of all frequencies but a little light (electromagnetic photons) is reflected from them. Thus, black is also a mixture of all colors! White and black have the same hue and saturation, and the lightness is all that is different. The sensation of black is not the same as absence of light is one of the central tenets of Hering’s teaching (Hering, 1874). A B Figure 2. The same photo by colors (A) and by black (grey) and white (B). When you can see the photo in Figure 2a under photopic level, you say that is a color photo that is your subjective experience (SE) about this photo due to the reflected mixture of visible “color” photons (mixture of electromagnetic photons visible to the human eye range from about 400 to 700 nm wavelength). When you can see the same photo in Figure 2b under photopic level, you say that is a black and white photo. However, this is also your subjective experience about this photo but your blackness and whiteness subjective experiences about the photo of Figure 2b are also due to the reflected mixture of visible “color” photons (mixture of electromagnetic photons visible to the human eye range from about 400 to 700 nm wavelengths). In the human retina there are rods and three types of cones photoreceptors, each of which absorbs different range wavelengths (Figure 3) of external visible electromagnetic photons (Brown & Wald, 1964). 23 Activitas Nervosa Superior 2013, 55, No. 1-2 Figure 3. Photon absorption curve for R: rod is shown by black dotted curves., L: long wavelength sensitive cone by red curve, M: middle wavelength sensitive cone by green curve, and S: short wavelength sensitive cone by blue curve. We can read essentially in the most of scientific literatures that rods do not discern colors like cones do (i.e., rod vision is achromatic night vision), although they are highly sensitive to light, and usually the photon absorption curve for rod is shown by black dotted curves., long wavelength sensitive cone by red curve, middle wavelength sensitive cone by green curve, and short wavelength sensitive cone by blue curve (see in Figure 3). However, rod photoreceptors convey electromagnetic visible photonic signals in the human eye ranging from about 400 to 700 nm wavelength; similarly for cones with limited range. Cones are for color vision, nevertheless, rods also absorb similar color photons as cones do, and they also could contribute to subjective color perception (Stabell & Stabell, 1994; Cao, Pokorny, Smith, & Zele, 2008) to certain extent, but not like day color vision via 3 cones. In other words, but rods convey electromagnetic visible color mixed photonic signals in the human eye ranging from about 400 to 700 nm these produce subjective black and white experience in the brain. Although vision science makes practical difference between achromatic and chromatic vision, both are subjective experiences are produced by mixed visible color photon signals in the human eye ranging from about 400 to 700 nm. 9. MODAL AND AMODAL VISUAL COMPLETION Although recent experiments provided evidence that visual, auditory, and somatosensory integrations take place parallel at numerous levels along brain pathways (Giard & Peronnet, 1999; Macaluso, Frith, & Driver, 2000; Calvert, Spence. & Stein, 2004) and in our everyday perception most objects and events can be seen, heard, and touched, i.e. these are primarily intermodal perception, i.e. information from events or objects available to multiple senses simultaneously, for the understanding of our thoughts presented here we focus to visual perception per se. A major challenge of vision research is to make it clear how the visual system can complete missing structures during visual perception. In our everyday awareness of the surrounding world in almost all cases of visual perception include one or more amodal parts. In amodal completion, there is a completion of an object that is not completely visible because it is covered (occluded, hidden) by something else (Kanizsa & Gerbino, 1982). In modal completion phenomenon a shape can be perceived that is occluding other shapes even when the shape itself is not drawn (Figure 4). For example the triangle that appears to be occluding three disks in the Kanizsa triangle. According to (Nanay, 2007), “amodal perception relies heavily on our background knowledge of how the occluded parts of the object (may) look. If I have never seen a cat, I will have difficulties attributing properties to its tail behind the fence”. Nanay states that 24