Nikos K. Logothetis University of Manchester, Manchester, UK In binocular rivalry, the visual percept alternates stochastically between two dichoptically presented stimuli. It is established that both processes related to the eye of origin and binocular, stimulus-related processes account for these fluctuations in conscious perception. Here we studied how their relative contributions vary over time. We applied brief disruptions to rivalry displays, concurrent with an optional eye swap, at varying time intervals after one stimulus became visible (dominant). We found (...) that early in a dominance phase the dominant eye determined the percept by stabilizing its own contribution (regardless of the stimulus), with an additional yet weaker stabilizing contribution of the stimulus (regardless of the eye). Their stabilizing contributions declined in parallel with time so that late in a dominance phase the stimulus (and in some cases also the eye-based) contribution turned negative, favoring a perceptual (or ocular) switch. Our findings show that depending on the time, first processes related to the eye of origin and then those related to the stimulus can have a greater net influence on the stability of the conscious percept. Their co-varying change may be due to feedback from image- to eyeof-origin representations. (shrink)

In addressing thescientific study of consciousness, Crick and Koch state, It is probable that at any moment some active neuronal processes in your head correlate with consciousness, while others do not: what is the difference between them? (1998, p. 97). Evidence from electrophysiological and brain-imaging studies of binocular rivalry supports the premise of this statement and answers to some extent, the question posed. I discuss these recent developments and outline the rationale and experimental evidence for the interhemispheric switch hypothesis (...) of perceptual rivalry. According to this model, the perceptual alternations of rivalry reflect hemispheric alternations, suggesting that visual consciousness of rivalling stimuli may be unihemispheric at any one time (Miller et al., 2000). However, in this paper, I suggest that interhemispheric switching could involve alternating unihemispheric attentional selection of neuronal processes for access to visual consciousness. On this view, visual consciousness during rivalry could be bi hemispheric because the processes constitutive of attentional selection may be distinct from those constitutive of visual consciousness. This is a special case of the important distinction between the neuronal correlates and constitution of visual consciousness. (shrink)

According to the prevalent 'sum view' of stuffs, each portion of stuff is a mereological sum of its subportions. The purpose of this paper is to re-examine the sum view in the light of a modal temporal mereology which distinguishes between different varieties of summation relations. While admitting David Barnett's recent counter-example to the sum view, we show that there is nonetheless an important sense in which all portions of stuff are sums of their subportions. We use our (...) class='Hi'>summation relations to develop, as an alternative to the sum view, an analysis of stuffs that distinguisher between the ways in which different sorts of stuffs are sums of their subportions. (shrink)

We investigated binocular rivalry in the twocerebral hemispheres of callosotomized(split-brain) observers. We found that rivalryoccurs for complex stimuli in split-brainobservers, and that it is similar in the twohemispheres. This poses difficulties for twotheories of rivalry: (1) that rivalry occursbecause of switching of activity between thetwo hemispheres, and (2) that rivalry iscontrolled by a structure in the rightfrontoparietal cortex. Instead, similar rivalryfrom the two hemispheres is consistent with atheory that its mechanism is low in the visualsystem, at which each hemisphere (...) conducts asimilar analysis of its half of visual space. (shrink)

Among psychologists and vision scientists,binocular rivalry has enjoyed sustainedinterest for decades dating back to the 19thcentury. In recent years, however, rivalry''saudience has expanded to includeneuroscientists who envision rivalry as a tool for exploring the neural concomitants ofconscious visual awareness and perceptualorganization. For rivalry''s potential to berealized, workers using this tool need toknow details of this fascinating phenomenon,and providing those details is the purpose ofthis article. After placing rivalry in ahistorical context, I summarize major findingsconcerning the spatial characteristics and thetemporal (...) dynamics of rivalry, discuss two majortheoretical accounts of rivalry ( eye vs stimulus rivalry) and speculate on possibleneural concomitants of binocular rivalry. (shrink)

The encounter between Christian culture and religion in Minahasa has attracted attention because it reflects various resonances and fluctuations. Furthermore, culture contains strong social and religious values, and both aspects are scrambling to confirm the identity of each other’s traditions. Therefore, this study aims to find the Minahasa cultural religiosity value that can be an object for conversation with Christianity. By using a descriptive qualitative approach and interviews with several sources, the cultural values were adopted and communicated with Christianity through (...) Stephen Bevans’s contextual approach. Hence, the awareness of the supernatural, belief in life before and after death and the celebration of foso rummages reflect the religiosity value that can be discussed with Christianity.Contribution: Through the examination of religiosity in Minahasa, its expressions and values, the study provides alternative contribution to Christian missiology. The result shares rich insight that leads to a specific meeting point for contextual study. Minahasan cultures and Christianity could engage in harmony. (shrink)

Physiological studies of binocular rivalry have provided important clues to the relationship between neural activity in the brain and visual awareness.However, uncertainty about these insights has been raised by a recent study showing that the events underlying binocular rivalry occur earlier in the visual pathway than was previously thought.

In addressing the scientific study of consciousness, Crick and Koch state, “It is prob- able that at any moment some active neuronal processes in your head correlate with consciousness, while others do not: what is the difference between them?” (1998, p. 97). Evidence from electro- physiological and brain-imaging studies of binocular rivalry supports the premise of this statement and answers to some extent, the question posed. I discuss these recent developments and outline the rationale and experimental evidence for the (...) interhemispheric switch hypothesis of perceptual rivalry. According to this model, the perceptual alternations of rivalry reflect hemispheric alterna- tions, suggesting that visual consciousness of rivalling stimuli may be unihemispheric at any one time (Miller et al., 2000). However, in this paper, I suggest that interhemispheric switching could involve alternating unihemispheric attentional selection of neuronal processes for access to visual consciousness. On this view, visual consciousness during rivalry could be bihemispheric because the processes constitutive of attentional selection may be distinct from those constitutive of visual consciousness. This is a special case of the important distinction between the neuronal correlates and constitution of visual consciousness. (shrink)

The relationship between brain activity and conscious visual experience is central to our understanding of the neural mechanisms underlying perception. Binocular rivalry, where monocular stimuli compete for perceptual dominance, has been previously used to dissociate the constant stimulus from the varying percept. We report here fMRI results from humans experiencing binocular rivalry under a dichoptic stimulation paradigm that consisted of two drifting random dot patterns with different motion coherence. Each pattern had also a different color, which both enhanced (...) rivalry and was used for reporting which of the two patterns was visible at each time. As the perception of the subjects alternated between coherent motion and motion noise, we examined the effect that these alternations had on the strength of the MR signal throughout the brain. Our results demonstrate that motion perception is able to modulate the activity of several of the visual areas which are known to be involved in motion processing. More specifically, in addition to area V5 which showed the strongest modulation, a higher activity during the perception of motion than during the perception of noise was also clearly observed in areas V3A and LOC, and less so in area V3. In previous studies, these areas had been selectively activated by motion stimuli but whether their activity reflects motion perception or not remained unclear; here we show that they are involved in motion perception as well. The present findings therefore suggest a lack of a clear distinction between ?processing? versus ?perceptual? areas in the brain, but rather that the areas involved in the processing of a specific visual attribute are also part of the neuronal network that is collectively responsible for its perceptual representation. (shrink)

Results from three experiments using spatial forced-choice techniques show that an illusory contour improves the detectability of a spatially superimposed, 1pixel-thin subthreshold line of either contrast polarity. Furthermore, the subthreshold line is found to enhance the visibility of an illusory contour bridging the gap between the two colinear edges of physically defined boundaries. Stimuli which do not induce illusory contours, but reduce uncertainty about the spatial position of the line, give rise to a slight detection facilitation, but the threshold of (...) 75% correct responses is not attained. The data indicate that superimposing illusory contours and 1pixel thin subthreshold lines produces interactions which are similar to classic subthreshold summation. This provides psychophysical evidence for the functional equivalence of illusory and real lines, as suggested by neurophysiological data from single-cell recordings in V1 and V2 of cats and primates. (shrink)

Kepler’s 1604 Optics proposed among many other things a new way of locating the place of the image under reflection or refraction. He rejected the “perspectivist” method that had been used through antiquity and the Middle Ages, whereby the image was located on the perpendicular between the object and the mirror. Kepler faulted the method for requiring a metaphysical commitment to the action of final causes in optics: the notion that the image was at that place because it was best (...) or appropriate for it to be there, and for no other discernible reason. Kepler’s new theory relied on binocular vision and depth perception to determine the location of the image. No final causes were required, and he showed that the image would in general not be found on the cathetus. According to modern scholarship, Kepler’s theory was part of his revolutionary transformation of the science of optics, and his abandonment of perspectivist optics; as a consequence, the theory of binocular vision is also thought to be original with him. This article demonstrates that the very same theory of binocular image location was set out by Giovanni Battista Benedetti some twenty years earlier, and his writings on this subject may have been Kepler’s unacknowledged source for his own theory. Furthermore, another mathematician, Simon Stevin, developed much the same theory at the same time as Kepler and, it seems, independently of either Benedetti or Kepler. The discovery of these other binocular theories, especially Benedetti’s, requires us to recognize that Kepler’s revolution emerged out of a wider dissatisfaction with the foundations of perspectivist optics, which other lesser-known opticians resolved in much the same way that Kepler did. (shrink)

In this paper, I consider two sorts of objections to summative theories of value. The first objection concerns “indeterminate” value. The second concerns the importance of variety. I argue that both objections pose serious problems for the summative approach. I also argue that if we accept certain plausible views about the value of variety, we should reject certain forms of argument concerning what sorts of states have intrinsic value.

Cognitive functions like perception, memory, language, or consciousness are based on highly parallel and distributed information processing by the brain. One of the major unresolved questions is how information can be integrated and how coherent representational states can be established in the distributed neuronal systems subserving these functions. It has been suggested that this so-called ''binding problem'' may be solved in the temporal domain. The hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into (...) cell assemblies and that this process may underlie the selection of perceptually and behaviorally relevant information. As we intend to show here, this temporal binding hypothesis has implications for the search of the neural correlate of consciousness. We review experimental results, mainly obtained in the visual system, which support the notion of temporal binding. In particular, we discuss recent experiments on the neural mechanisms of binocular rivalry which suggest that appropriate synchronization among cortical neurons may be one of the necessary conditions for the buildup of perceptual states and awareness of sensory stimuli. (shrink)