In psychophysical experiments, the use of a psychophysical procedure of brightness/darkness cancellation shed light on interactions between spatial arrangement and figure–ground contrast in the perceptual filling in of achromatic and colored surfaces.Achromatic and chromatic Kanizsa squares with varying contrast, contrast polarity, and inducer spacingwere used to test how these factors interact in the perceptual filling in of surface brightness or darkness. The results suggest that the neuronal processing of surfaces with apparent contrast, leading to figure–ground segregation (...) (i.e., perceptual organization), is governed by mechanisms that integrate both luminance contrast and spatial information carried by the inducing stimuli, while discarding information on contrast polarity or color. The findings are discussed in relation to earlier observations on brightness assimilation and contrast. They support theories of nonantagonistic neural mechanisms suppressing local contrast or color signs in brightnessbased figure–ground percepts. Such mechanismsmight be necessary to cancel potentially conflicting polarities in geometricallycomplex visual stimuli so that perceptual filling in resulting in the most plausible representation of figure and ground can be achieved. (shrink)

Can psychology explain the qualitative content of experience? A persistent philosophical objection to that discipline is that it cannot. Qualitative states or 'qualia' are argued to have characteristics which cannot be explained in terms of their relationships to other psychological states, stimuli, and behavior. Since psychology is confined to descriptions of such relationships, it seems that psychology cannot explain qualia. A paradigm case of qualia is provided by simultaneous color contrast effects, in which a neutral grey patch is (...) made to look reddish by being enclosed in a green surround. If the qualia based objections are sound, psychology ought not to be able to explain simultaneous color contrast; but psychology at least seems to be able quite successfully to explain those effects. This paper analyzes the logic of psychological explanations of simultaneous color contrast effects, and the import of various qualia based objections to those explanations. I argue that the qualia objections do not demonstrate any explanatory inadequacy in existing psychological explanations of 'looks'. Psychology succeeds in explaining at least some qualia. In a more positive vein, I argue that once the structure of such explanations is sufficiently understood, a place can be found for qualia within the emerging scientific account of color perception. The resulting account can deal with many of the traditional perplexities over qualia. (shrink)

Inter-species variation in colour perception poses a serious problem for the view that colours are mind-independent properties. Given that colour perception varies so drastically across species, which species perceives colours as they really are? In this paper, I argue that all do. Specifically, I argue that members of different species perceive properties that are determinates of different, mutually compatible, determinables. This is an instance of a general selectionist strategy for dealing with cases of perceptual variation. According to selectionist (...) views, objects simultaneously instantiate a plurality of colours, all of them genuinely mind-independent, and subjects select from amongst this plurality which colours they perceive. I contrast selectionist views with relationalist views that deny the mind-independence of colour, and consider some general objections to this strategy. (shrink)

We show that true colors as defined by Chevreul (1839) produce unsuspected simultaneous brightness induction effects on their immediate grey backgrounds when these are placed on a darker (black) general background surrounding two spatially separated configurations. Assimilation and apparent contrast may occur in one and the same stimulus display. We examined the possible link between these effects and the perceived depth of the color patterns which induce them as a function of their luminance contrast. Patterns of square-shaped (...) inducers of a single color (red, green, blue, yellow, or grey) were placed on background fields of a lighter and a darker grey, presented on a darker screen. Inducers were always darker on one side of the display and brighter on the other in a given trial. The intensity of the grey backgrounds varied between trials only. This permitted generating four inducer luminance contrasts, presented in random order, for each color. Background fields were either spatially separated or consisted of a single grey field on the black screen. Experiments were run under three environmental conditions: dark-adaptation, daylight, and rod-saturation after exposure to bright light. In a first task, we measured probabilities of contrast, assimilation, and no effect in a three-alternative forced-choice procedure (background appears brighter on the ‘left’, on the ‘right’ or the ‘same’). Visual adaptation and inducer contrast had no significant influence on the induction effects produced by colored inducers. Achromatic inducers produced significantly stronger contrast effects after dark-adaptation, and significantly stronger assimilation in daylight conditions. Grouping two backgrounds into a single one was found to significantly decrease probabilities of apparent contrast. Under the same conditions, we measured probabilities of the inducers to be perceived as nearer to the observer inducers. These, as predicted by Chevreul’s law of contrast, were determined by the luminance contrast of the inducers only, with significantly higher probabilities of brighter inducers to be seen as nearer, and a marked asymmetry between effects produced by inducers of opposite sign. Implications of these findings for theories which attempt to link simultaneous induction effects to the relative depth of object surfaces in the visual field are discussed. (shrink)

There have been a number of criticisms, based on visual processes, of the Australian view that colour is an objective property of the world. These criticisms have led to subjective theories about colour. These visual processes (metamers, retinex theory, opponent processes, simultaneous contrast, colour constancy, subjective colours) have been examined and it is suggested that they do not carry their supposed critical weight against an objective theory. In particular, it is argued that metamers don’t occur (...) in nature and primate colour vision evolved without metamers. Thus normal colour vision occurs without the problem of metamers. This argument, in conjunction with evidence against the critical roles of opponent processes and retinex theory in colour vision, is taken to suggest that colour can be given a photon energy/wavelengthrealism explanation. This proposal allows an account of the many microstructural bases of colour generation put forward by Nassau (1983). It is argued that neither disjunctive realism or reflectance realism are adequate objective explanations of colour. (shrink)

Chromatic induction is a major contextual effect of color appearance. Patterned backgrounds are known to induce strong chromatic induction effects. However, it has not been clarified whether the spatial extent of the chromatic surrounding induces a chromatic contrast or assimilation effects. In this study, we examined the influence of the width of a center line and its flanking white contour on the color appearance when the line was surrounded by chromatic backgrounds. A strong color shift was observed when the (...) center line was flanked by white contours with the L/M- and S-cone chromatic backgrounds. There was a difference between the optimal widths of the center line and the contour for the shift in color appearance for the L/M-cone chromaticity and the S-cone chromaticity. The optimal width of the center line for the L/M-cone was finer than the resolution-limit width of the chromatic contrast sensitivity and coarser than that of the luminance contrast sensitivity. Thus, the color appearance of the center line could be obtained by integrating broad chromatic information and fine luminance details. Due to blurring and chromatic aberrations, the simulated artifact was large for the darker center line and S-cone background, thus suggesting that the artifact could explain the luminance dependency of the induction along the S-cone chromaticity. Moreover, the findings of this study reveal that the dominant factor of the color shift is neural instead of optical. (shrink)

Spatial facilitation has been observed with luminance-defined, achromatic stimuli on achromatic backgrounds as well as with targets and inducers defined by colour contrast. This paper reviews psychophysical results from detection experiments with human observers showing the conditions under which spatially separated contour inducers facilitate the detection of simultaneously presented target stimuli. The findings point towards two types of spatial mechanisms: (i) Short-range mechanisms that are sensitive to narrowly spaced stimuli of small size and, at distinct target locations, selective (...) to the contrast polarity of targets and inducers. (ii) Long-range mechanisms that are triggered by longer stimuli, generate facilitation across wider spatial gaps between targets and inducers, and are insensitive to their contrast polarity. Spatial facilitation with chromatic stimuli requires a longer inducer exposure than spatial facilitation with achromatic stimuli, which is already fully effective at inducer exposures of 30 ms. This difference in temporal dynamics indicates some functional segregation between mechanisms for colour and luminance contrast in the perception of space. (shrink)

Intrapersonal variation due to color contrast effects has been used to argue against the following intuitive propositions about the colors: No object can be more than one determinable or determinate color of the same grade all over at the same time ; external objects are actually colored ; and the colors of objects are mind-independent. In this article, I provide a defense of Incompatibility, Realism, and Objectivism from intrapersonal variation arguments that rely on color contrast effects. I provide (...) a novel, ecumenical response to such arguments according to which typical variants are right, and which respects Incompatibility, Realism, and Objectivism, using the thesis that the colors of objects depend on the colors of objects in their surrounds. (shrink)

The purpose of the present study was two-fold. First we examined whether visible motion appearance was altered by the spatial interaction between invisible and visible motion. We addressed this issue by means of simultaneous motion contrast, in which a horizontal test grating with a counterphase luminance modulation was seen to have the opposite motion direction to a peripheral inducer grating with unidirectional upward or downward motion. Using a mirror stereoscope, observers viewed the inducer and test gratings with one (...) eye, and continuous flashes of colorful squares forming an annulus shape with the other eye. The continuous flashes rendered the inducer subjectively invisible. The observers’ task was to report whether the test grating moved upward or downward. Consequently, simultaneous motion contrast was observed even when the inducer was invisible . Second, we examined whether the observers could correctly respond to the direction of invisible motion: It was impossible. (shrink)

This dissertation studies how Aristotle understands and justifies his Rhetorical Art. It proceeds by explicating the Art in its intellectual context. Rhetoric emerges as a dynamic investigation of human affairs working through the "given" in speech and thought to a plausible account, while giving consideration to the opinions and characters of both speaker and audience within the horizon of a particular occasion. The basic dynamic determines a structure which is comparable to Socrates' requirements in the Phaedrus. That this is the (...) structure and dynamic is supported by considering the fundamentally contingent nature of human experience, understanding the inference types , common sense principles and starting points by which such experience is explicated, and placing such experience in three mutually exclusive genres. Aristotle's art is essentially the resulting plausible account while actual composition is supplementary. ;Aristotle limits the art by reference to dialectic and ethical life. When it is seen that Aristotle's Organon is not a science of logic and the Posterior Analytics is a rarely applicable mode of presentation, the point of dialectic becomes accessible. It too involves strenuous grappling with speech and thought, but its highest purpose lies in peirastic. Peirastic and sophistry are uses of dialectic which have a contrasting moral color. Peirastic aims at the discovery of ignorance and, at the same time, the difference between accident and essence and knowledge and opinion: Being educated is essentially knowing what one does not know. ;What Socrates only alludes to as political art, Aristotle attempts to expound as praxis perfected into phronesis. Even Aristotle does no more than suggest the nature of phronesis negatively as simultaneously a seeking, a finding and an act which is both self-determination and self-knowledge, and none of these separately; it is profoundly disruptive of existing opinion and most clearly to be seen in the rejection of the laws and rules upon which, as deliberation, it is dependent. The Art differs from Gorgias' rhetoric in its emphasis on the plausible and in its subordination to an ethical self-determination that gains the weight of experience appropriated by intelligence and virtue. (shrink)

The vivid, dramatic images of distant stars and galaxies taken by the Hubble Space Telescope have come to define how we visualize the cosmos. In their immediacy and vibrancy, photographs from the Hubble show what future generations of space travelers might see should they venture beyond our solar system. But their brilliant hues and precise details are not simply products of the telescope's unprecedented orbital location and technologically advanced optical system. Rather, they result from a series of deliberate decisions made (...) by the astronomers who convert raw data from the Hubble into spectacular pictures by assigning colors, adjusting contrast, and actively composing the images, balancing the desire for an aesthetically pleasing representation with the need for a scientifically valid one. In Picturing the Cosmos, Elizabeth A. Kessler examines the Hubble's deep space images, highlighting the remarkable resemblance they bear to nineteenth-century paintings and photographs of the American West and their invocation of the visual language of the sublime. Drawing on art history and the history of science, as well as interviews with astronomers who work on the Hubble Heritage Project, Kessler traces the ways that the sublime, with its inherent tension between reason and imagination, not only forms the appearance of the images, but also operates on other levels. The sublime informs the dual expression—numeric and pictorial—of digital data and underpins the relevance of the frontier for a new era of exploration performed by our instruments rather than our bodies. Through their engagement with the sublime the Hubble images are a complex act of translation that encourages an experience of the universe as simultaneously beyond humanity's grasp and within the reach of our knowledge. Strikingly illustrated with full-color images, this book reveals the scientific, aesthetic, and cultural significance of the Hubble pictures, offering a nuanced understanding of how they shape our ideas—and dreams—about the cosmos and our places within it. (shrink)

Charles Mills makes visible in the world of mainstream philosophy some of the crucial issues of the black experience. Ralph Ellison's metaphor of black invisibility has special relevance to philosophy, whose demographic and conceptual "whiteness" has long been a source of wonder and complaint to racial minorities. Mills points out the absence of any philosophical narrative theorizing and detailing race's centrality to the recent history of the West, such as feminists have articulated for gender domination. European expansionism in its various (...) forms, Mills contends, generates a social ontology of race that warrants philosophical attention. Through expropriation, settlement, slavery, and colonialism, race comes into existence as simultaneously real and unreal: ontological without being biological, metaphysical without being physical, existential without being essential, shaping one's being without being in one's shape. His essays explore the contrasting sums of a white and black modernity, examine standpoint epistemology and the metaphysics of racial identity, look at black-Jewish relations and racial conspiracy theories, map the workings of a white-supremacist polity and the contours of a racist moral consciousness, and analyze the presuppositions of Frederick Douglass's famous July 4 prognosis for black political inclusion. Collectively they demonstrate what exciting new philosophical terrain can be opened up once the color line in western philosophy is made visible and addressed. (shrink)

Located in Kleinbasel close to the Rhine, the Kaskadenkondensator is a place of mediation and experimental, research-and process-based art production with a focus on performance and performative expression. The gallery, founded in 1994, and located on the third floor of the former Sudhaus Warteck Brewery (hence cascade condenser), seeks to develop interactions between artists, theorists and audiences. Eight, maybe, nine or ten 40 litre bags of potting compost lie strewn about the floor of a high-ceilinged white washed hall. Dumped, split (...) open, the soil mixed with iridescent specks of green, blue and red glitter. On the walls hang large black and white photographic images—negative and positive prints barely clean, hardly sharp, scavenged from the world and presented half processed. On a third wall, hangs a framed golden and charcoal surface. Finally, a huge stain of black dye runs down a wall that descends into a sunken quarter of the Kaskadenkondensator gallery space. The results of a collaboration between Oliver Minder and Walter Derungs reflect on themes addressed in the recent Aesthetics in the 21st Century conference held by the department of English, University of Basel. In particular, the joint show questions how an aesthetic experience may be other than a human-world interaction, hinting at the withdrawal and veiling that objects perform, while demanding that different works engage with each other and play out this game under the non-supervisory eyes of a human audience. Things here are becoming—sometimes it’s a movement towards a more complete ontic whole in a projection of finality, other times it’s a dispersal, an atrophy to rather disarrayed entities. Yet, in the moment and place in which the objects are, we take them as here and now. Let’s get to the material of the stuff that Minder and Derungs have assembled. Oliver Minder employs organic materials—potting earth, cuttlefish ink secretion, rice, and insects; yet his works hardly seem natural in the sense of a harmonic relation between material and the form they are constrained into, the objects they are compelled to occupy. For the substrates on, through, or within which these natural materials are mediated are harshly inorganic substances—Plexiglas, safety glass, acrylic resin, boat varnish, spray paint. Minder, thus, generates a conflict within the materiality of his work between two polar opposites—from the human perspective—in the contiguity of materials engaging with each other in a thrown together formation that nonetheless appears to keep the materials and the objects they make in happy accidental relation to each other. Let me expand a little: on the one hand, the things Minder makes query our belief in substance as belonging in a particular domain, an environment suited to precisely that stuff. We are focused on thinking categorically where things belong, both in terms of natural place and natural relations they might extend to each other. Hence, we are driven to think of environment and order. On the other hand, while extracting things from their conventional place and arranging them within awkward constellations that we as observers feel isn’t quite right, Minder manages to persuade the viewer that the materials are nonetheless “doing alright.” So, simultaneous to our awareness of the appropriateness of the world according to our global notions of accord and uniformity, we are forced to accept the local discrepancies of disassociation, inappropriateness and misplacement. The tension between these two vectors generates a vacillation that intensifies Minder’s work. In the Kaskadenkondensator works, then, it is vital to first consider the material of Minder’s works: potting compost—what is it doing here in the first place?—seems to enjoy being “polluted” by sparkly glitter. Glitter has a long history, used in cosmetics by the Egyptians, and in cave paintings, too, earlier made of beetle shells and mica, nowadays glitter is made of plastic cut to minute sizes down to 50 microns. So what’s the point here? Well shiny bits of dust-like material are actually generated from ultra-thin plastic sheets and are normally cut into shapes that fit contiguously on a two-dimensional surface: squares, triangles, hexagons etc. What then appears to be totally random, chaotic decoration, is actually an array of extremely regular identifiable objects. 1 Of course scale has a role to play here. The minuteness of the dimensions means the regularity is beyond our recognition—all we see are the twinkling surfaces of the multi-coloured grains of plastic. In contrast, potting compost, which appears to be unary in its dull unresponsive lumpen disposition, is in fact an amalgam of a variety of organic and inorganic materials: peat, bark, mushroom compost, and sand and perlite, and should perhaps be more proactively exciting to the viewer because of this complexity. Yes; we can (if we care to) identify different textures, different sizes in the mixture of the medium, but I claim that we tend to treat this organic/inorganic assemblage as just a simple substance. Further and crucially important to our consideration here is that the medium is partially contained, but also partially spilling from the split plastic bags in which it is sold in garden centres. That the compost spills out gives it a movement suggesting life; that the bags are cast here and there in a random fashion by Oliver Minder, lying like discarded carcasses, hacked torsos, dismembered bodies, suggests a horrific murder scene, a Tatort. 2 The glitter flourishes in the medium, lies happy and decorative; that is simply what it does, how it is—always already broken, made-for-scattering, designed to be incomplete; the taken-to-be-natural compost, in contrast, cannot rest content but is forced to speak to us metaphorically in its abject overflowing of violence and rupture. While Oliver Minder’s elements in the installation direct our attention to material, Walter Derungs’ works raise questions around seeing and making in photography. There is a simultaneous flicker between the materials and their use in the production of a sense making representation, on the one hand, and on the other the very notion of what is worthy of picturing, framing, representing on the other. Derungs' images are of non-places. Ranging from archaic decaying monster buildings, buildings that have gone far beyond the ravages of a time that we can safely associate with the genteel preservation of a Bernd and Hill Belcher post-industrial decline, to the background “noise” of an urban world that is falling apart, and to which we most of the time seem to pay little attention, and habitually just pass by. In this respect, their non-ness differs somewhat from the conventional association of the term with Marc Augé 3 , where emphasis is on the specifics (if we do care to examine them for their non-placedness) of the spatial or place containment in which movement between multimodal coordinates occurs in supermodern late capitalist post-urban spaces. In other words, we might be in an Augéian non-place and (not) experience—be impervious to—that environment, or we might in Derungs’ manner look out from such a position at the “scenery” around us. I claim scenery, as this is what Derungs seems to do with his partial photography—construct a very purposefully articulated, symmetric, flat world of image. Mostly depopulated, his images construct a space in which the direction of time is uncertain: are these partial structures falling apart, or perhaps terminated in a never-to-be-completed state, or are they a few steps from final completion? Temporal and spatial dimensions figure large in Derungs’ image-making: his world, and perhaps this is in fact the only way for it to be registered photographically, is already image before it is photographed. A key combination of images in this show is a matrix of six black and white negative prints measuring 300 x 215 cm that form the image of a semi-derelict (or is it yet incomplete) church, and adjacent on a perpendicular wall, a single black and white positive print 150 x 250 cm of two bricked-up windows of a late-Victorian industrial building. What are we led to believe that we see here? In the negative print, the conditions of perception 4 are sufficiently reproduced for us to recognise the structure of the building, to distinguish ground and form, to relate some partial elements of narrative, and to recognize symbols such as the alter cross and figure of Christ, a looming crane, a traffic cone, and banks of tiered seating. We piece the image together both from the individual forms which we recognize despite the tonal reversal, and we piece the six prints together as a whole, the matrix of lines between them emphasizing our purview onto the world. While we recognise the forms at work in the image and might possibly relate the negative reversals to other figurations such as Vera Lutter’s camera obscura exposures, we cannot but avoid seeing the partialness of the image in the sponge marks of the developer that was spread by hand across the prints. 5 Derungs’ thus intervenes with our usual conception of photography as the mimetic realist vehicle sine qua non , by exposing the viewer to tonal reversal and incomplete or over developed areas of the print. We thus confront both the idiom of such image making and its raw (chemical) materiality at once in the simultaneity of the recognition of what the image pictures and the recognition that it is in the act of picturing. The church image, taken from the series “BW Negativs 2011,” thus orients us towards how we see things in the world via photographs. The single image of the bricked-up wall presents us with a completely different visuality that relates to a faciality 6 which we cannot easily escape from. We look, or rather try to look with no success, through the face of the windows, through the classic Albertian screen 7 which has already been given to us in the church matrix beside. Yet although we should be able to make more of these concealed windows because they are a positive print, because they are complete, because they approach us on a more realistic scale, reproduced at life size, we cannot. The objects pictured here withdraw from us; furthermore, they merely mock our blindness at not seeing how we look. Blocked up with quite a hint of paned glass behind, one window is blanked out with a white blind, the other simply blankly dark. The apertures look like eyes with teeth in them, or a Dogon mask, or even Man Ray’s Noire et Blanche (1926) if we want to get really perverse. The height of elegant modernist chauvinist beauty thrown against the vacuity of post-industrial decline. Derungs thus catapults us consciously into a world enfolded with and through images, but in such a way that the images themselves become objects that stand resistant to us, impervious to our gaze, indifferent. We—and indeed they—do not attempt to reach out to a real that is beyond, rather the images play in a world that is just theirs, and we can only enter that world if we too submit to their regime: tonal reversal, segmented, partial, inadequate, still, wrenched out of time. In contemplation, in the flood of the image “falling” off the wall, we too become image-object. Perhaps enough has now been said about the works, yet enough can never really be said, we know the image will always exceed the word—let’s accelerate the critique: Derungs’ work continues in a second space partially partitioned from this first room. Opposing three more “BW Negativs” which figure yet more quotidian aspects of the world is Minder’s gold spray paint and cuttlefish secretion mix: things that just shouldn’t work together do in the dialogue between stuff that Derungs and Minder have constructed. Minder makes things; Derungs makes images; together they make objects which inhabit their own world which we can approach and sensually engage with and come to grips with only on those objects’ own terms. This is best summarised by a final work made by Oliver Minder which on a third wall faces these two semi-partitioned spaces. A deep black stain about 100 X 200 cm with streak marks running down a further 2 metres hovers positioned to observe the whole work, and also to be part of this installation, too. This liminal flat suzerain lies in/out of the whole work. The stain of cuttlefish secretion resonates with Derungs’ sponge strokes on the church image; it mirrors the iris of an all-seeing eye; it combines material in situ with the situation itself. Where Minder’s other works have material and medium or substrate upon which the material is exercised, this single black hole is image which sucks everything up into itself. It draws the viewer, who must otherwise look away attentively at the floor work, and imagine horror, or smile at the ironic play of glitter. Look away at the image constructions that suggest how it is we too look to our world. See the play of thing and image in a third area. Or, finally return to the base of the pyramid that triangulates, to realise the stuff-image that unlocks it all for us. Black on white, organic on inorganic, material to substrate, that which in the falling out of one on the other, in its running down the wall simply gives form to both content and expression in one direction, and content and expression to form in another. NOTES In fact, glitter is used as associative forensic evidence: the 20,000 or so varieties are all uniquely identifiable. Joel Sternfeld, Tatorte: Bilder gegen das Vergessen (München: Schirmer/Mosel, 1996). Marc Augé, Non­places: Introduction to an Anthropology of Supermodernity trans. John Howe (London: Verso, 2006). An echo of the uneven paint strokes of light­sensitive chemicals in the paper preparations made by Henry Talbot some 170 years ago in the first sun drawings that also often pictured architectural forms. It was Talbot’s surprising discovery that where a weaker chemical solution was more thinly spread, greater light sensitivity was actualized, yet this virtual image had then to be chemically developed in a second step. Thus, Derungs unevenly finished spongings suggestively trace back to this originary technology (although his sweeps are the stains of uneven development and not those of the initial preparation of light–sensitive material). Umberto Eco, “Critique of the Image” in “Articulations of Cinematic Code” Cinematics 1, 1970. Gilles Deleuze and Felix Guattari, A Thousand Plateaus: Capitalism and Schizophrenia trans. Brian Massumi (Minneapolis: University of Minnesota Press, 2007). Geoffrey Batchen, Burning With Desire: the Conception of Photography (Cambridge, Mass: MIT Press, 1999). (shrink)

Can qualia be analyzed by theories that contain only non-qualitative terms? A host of philosophers including Block, Levine, Nagel, and Jackson have argued that, in principle, they cannot. And yet psychophysicists have advanced explanations that seem to account for sensory appearances in terms of the operations of nervous systems. Here are some examples: Mach bands, the assimilation effect, and the Hermann grid illusion all have to do with the look of things, and all are routinely thought to be a consequence (...) of the structure of visual receptive fields. Simultaneous contrast and auditory tuning—both perceptual effects—are lateral inhibition phenomena. That television sets with only three phosphor colors can replicate natural scenes with thousands of distinguishable colors is due to our eyes having just three photopigments. The difference between a three-type receptoral configuration and an array of thousands of receptors with distinct responses accounts for the fact that hues form a closed loop in color space, whereas there are no closed pitch loops in auditory space. (shrink)

Poorly saturated colors are closer to a pure grey than strongly saturated ones and, therefore, appear less “colorful”. Color saturation is effectively manipulated in the visual arts for balancing conflicting sensations and moods and for inducing the perception of relative distance in the pictorial plane. While perceptual science has proven quite clearly that the luminance contrast of any hue acts as a self-sufficient cue to relative depth in visual images, the role of color saturation in such figure-ground organization has (...) remained unclear. We presented configurations of colored inducers on grey ‘test’ backgrounds to human observers. Luminance and saturation of the inducers was uniform on each trial, but varied across trials. We ran two separate experimental tasks. In the relative background brightness task, perceptual judgments indicated whether the apparent brightness of the grey test background contrasted with, assimilated to, or appeared equal (no effect) to that of a comparison background with the same luminance contrast. Contrast polarity and its interaction with color saturation affected response proportions for contrast, assimilation and no effect. In the figure-ground task, perceptual judgments indicated whether the inducers appeared to lie in front of, behind, or in the same depth with the background. Strongly saturated inducers produced significantly larger proportions of foreground effects indicating that these inducers stand out as figure against the background. Weakly saturated inducers produced significantly larger proportions of background effects, indicating that these inducers are perceived as lying behind the backgrounds. We infer that color saturation modulates figure-ground organization, both directly by determining relative inducer depth, and indirectly, and in interaction with contrast polarity, by affecting apparent background brightness. The results point towards a hitherto undocumented functional role of color saturation in the genesis of form, and in particular figure-ground percepts in the absence of chromatostereopsis. (shrink)

Luminance and color are strong and self-sufficient cues to pictorial depth in visual scenes and images. The present study investigates the conditions Under which luminance or color either strengthens or overrides geometric depth cues. We investigated how luminance contrasts associated with color contrast interact with relative height in the visual field, partial occlusion, and interposition in determining the probability that a given figure is perceived as ‘‘nearer’’ than another. Latencies of ‘‘near’’ responses were analyzed to test for effects of (...) attentional selection. Figures in a pair were supported by luminance contrast or isoluminant color contrast and combined with one of the three geometric cues. The results of Experiment 1 show that luminance contrasts associated with hue, when it does not interact with other hues, produces the same effects as achromatic luminance contrasts: The probability of‘‘near’’ increases with luminance contrast while the latencies for ‘‘near’’ responses decrease. Partial occlusion is found to be a strong enough pictorial cue to support a weaker red luminance contrast. Interposition cues lose out against cues of spatial position and partial occlusion. The results of Experiment 2, with isoluminant displays of varying color contrast, reveal that red color contrast on a light background supported by any of the three geometric cues wins over green or white supported by any of the three geometric cues. On a dark background, red color contrast supported by the interposition cue loses out against green or white color contrast supported by partial occlusion. These findings reveal that color is not an independent depth cue, but is strongly influenced by luminance contrast and stimulus geometry. Systematically shorter response latencies for stronger ‘‘near’’ percepts demonstrate that selective visual attention reliably detects the most likely depth cue combination in a given configuration. (shrink)

Back when researchers thought about the various forms that color vision could take, the focus was primarily on the retinal mechanisms. Since that time, research on human color vision has shifted from an interest in retinal mechanisms to cortical color processing. This has allowed color research to provide insight into questions that are not limited to early vision but extend to cognition. Direct cortical connections from higher-level areas to lower-level areas have been found throughout the brain. One of the classic (...) questions in cognitive science is whether perception is influenced, and if so to what extent, by cognition and whether a clear distinction can be drawn between perception and cognition. Since perception is seen as providing justification for our beliefs about properties in the external world, these questions also have metaphysical and epistemological significance. The aim of this paper is to highlight some of the areas where research on color perception can shed new light on questions in the cognitive sciences. A further aim of the paper is to raise some questions about color research that are in dire need of further reflection and investigation. (shrink)

Colour has often been supposed to be a subjective property, a property to be analysed orretly in terms of the phenomenological aspects of human expereince. In contrast with subjectivism, an objectivist analysis of color takes color to be a property objects possess in themselves, independently of the character of human perceptual expereince. David Hilbert defends a form of objectivism that identifies color with a physical property of surfaces - their spectral reflectance. This analysis of color is shown to (...) provide a more adequate account of the features of human color vision than its subjectivist rivals. The author's account of colro also recognises that the human perceptual system provides a limited and idiosyncratic picture of the world. These limitations are shown to be consistent with a realist account of colour and to provide the necessary tools for giving an analysis of common sense knowledge of color phenomena. (shrink)

Colour vision plays a foundational explanatory role in the philosophy of colour, and serves as perennial quarry in the wider philosophy of perception. I present two contributions to our understanding of this notion. The first is to develop a constitutive approach to characterizing colour vision. This approach seeks to comprehend the nature of colour vision qua psychological kind, as contrasted with traditional experiential approaches, which prioritize descriptions of our ordinary visual experience of colour. The second (...) contribution is to argue that colour vision does not constitutively involve the ability to see colours, in a natural and categorically committed sense. I argue that two subjects exactly alike in respect of their constitutive colour vision abilities could differ in respect of whether or not they have categorical perception of colour. The argument is supported by thought experiment and dissociations observed in cognitive neuropsychology. The argument also bears connections to recent neo-Whorfian accounts of colour categorization. _1._ Introduction _2._ Colour Vision, Experience, and Natures _3._ The Central Argument _3.1._ Colour constancy and discrimination _3.2._ Dissociating colour vision and categorical perception for colour _4._ Whorf and the View from Cognitive Neuropsychology _5._ Conclusion. (shrink)

In 1993, Agostini and Proffitt showed that perceptual belongingness causes simultaneous lightness contrast to be seen in configurations in which the inducing elements are not adjacent to the target. The aim of the present research was to measure the strength of belongingness in determining the contrast phenomenon when the numbers of the inducing and induced elements and their relative positions are manipulated in Agostini-and-Proffitt-type configurations. In the first experiment, by using a forced choice paradigm, naïve observers indicated (...) which gray disks arranged to form the letter T in two rows appeared lighter/darker. In the second experiment, expert observers performed two nulling tasks: 1) the lightness of gray disk was adjusted until it was perceived equal to that of gray target aligned with white/black inducers; 2) the lightness of target organized with white/black inducers was adjusted to match the target organized with black/ white inducers. We found that also when there are few inducers, perceptual belongingness causes the contrast effect to propagate spatially on all the induced elements. Spatial position does not influence the induction effect. Low-level theories cannot account for these phenomena, but higher-level processes must be factored in to explain them. (shrink)

The quantization error in a fixed-size Self-Organizing Map (SOM) with unsupervised winner-take-all learning has previously been used successfully to detect, in minimal computation time, highly meaningful changes across images in medical time series and in time series of satellite images. Here, the functional properties of the quantization error in SOM are explored further to show that the metric is capable of reliably discriminating between the finest differences in local contrast intensities and contrast signs. While this capability of the (...) QE is akin to functional characteristics of a specific class of retinal ganglion cells (the so-called Y-cells) in the visual systems of the primate and the cat, the sensitivity of the QE surpasses the capacity limits of human visual detection. Here, the quantization error in the SOM is found to reliably signal changes in contrast or colour when contrast information is removed from or added to the image, but not when the amount and relative weight of contrast information is constant and only the local spatial position of contrast elements in the pattern changes. While the RGB Mean reflects coarser changes in colour or contrast well enough, the SOM-QE is shown to outperform the RGB Mean in the detection of single-pixel changes in images with up to five million pixels. This could have important implications in the context of unsupervised image learning and computational building block approaches to large sets of image data (big data). (shrink)