Online research in philosophy

I defend a view of the structure of visual property-awareness by considering the phenomenon of perceptual constancy. I argue that visual property-awareness is a three-place relation between a subject, a property, and a manner of presentation. Manners of presentation mediate our visual awareness of properties without being objects of visual awareness themselves. I provide criteria of identity for manners of presentation, and I argue that our ignorance of their intrinsic nature does not compromise the viability of a theory that employs them. In closing, I argue that the proposed manners of presentation are consistent with key direct-realist claims about the structure of visual awareness.

I defend a view of the structure of visual property-awareness by considering the phenomenon of perceptual constancy. I argue that visual property-awareness is a three-place relation between a subject, a property, and a manner of presentation. Manners of presentation mediate our visual awareness of properties without being objects of visual awareness themselves. I provide criteria of identity for manners ofpresentation, and I argue that our ignorance of their intrinsic nature does not compromise the viability of a theory that employs them. In closing, I argue that the proposed manners of presentation are consistent with key direct-realist claims about the structure of visual awareness.

I set out two theses. The first is Lynn Robertson’s: (a) spatial awareness is a cause of object perception. A natural counterpoint is: (b) spatial awareness is a cause of your ability to make accurate verbal reports about a perceived object. Zenon Pylyshyn has criticized both. I argue that nonetheless, the burden of the evidence supports both (a) and (b). Finally, I argue conscious visual perception of an object has a different causal role to both: (i) non-conscious perception of the object, and (ii) experience, e.g. hallucination, that may be subjectively indiscriminable from, but is not, perception of the object.

It has been shown that visual awareness in the blind hemifield of hemianopic cats that have undergone unilateral ablations of visual cortex can be restored by sectioning the commissure of the superior colliculus or by destroying a portion of the substantia nigra contralateral to the cortical lesion (the Sprague effect). We propose that the visual awareness that is recovered is due to synchronized oscillatory activities in the superior colliculus ipsilateral to the cortical lesion. These oscillatory activities are normally partially suppressed by the inhibitory, GABAergic contralateral nigrotectal projection, and the destruction of the substantia nigra, or the sectioning of the collicular commissure, disinhibits the collicular neurons, causing an increase in the extent of oscillatory activity and/or synchronization between activities at different sites. This increase in the oscillatory and synchronized character is sufficient for the activities to give rise to visual awareness. We argue that in rodents and lower vertebrates, normal visual awareness is partly due to synchronized oscillatory activities in the optic tectum and partly due to similar activities in visual cortex. It is only in carnivores and primates that visual awareness is wholly due to cortical activities. Based on von Baerian recapitulation theory, we propose that, even in humans, there is a period in early infancy when visual awareness is partially due to activities in the superior colliculus, but that this awareness gradually disappears as the nigrotectal projection matures.

Based on theoretical considerations of Aurell (1979) and Block (1995), we argue that object recognition awareness is distinct from purely sensory awareness and that the former is mediated by neuronal activities in areas that are separate and distinct from cortical sensory areas. We propose that two of the principal functions of neuronal activities in sensory cortex, which are to provide sensory awareness and to effect the computations that are necessary for object recognition, are dissociated. We provide examples of how this dissociation might be achieved and argue that the components of the neuronal activities which carry the computations do not directly enter the awareness of the subject. The results of these computations are sparse representations (i.e., vector or distributed codes) which are activated by the presentation of particular sensory objects and are essentially engrams for the recognition of objects. These final representations occur in the highest order areas of sensory cortex; in the visual analyzer, the areas include the anterior part of the inferior temporal cortex and the perirhinal cortex. We propose, based on lesion and connectional data, that the two areas in which activities provide recognition awareness are the temporopolar cortex and the medial orbitofrontal cortex. Activities in the temporopolar cortex provide the recognition awareness of objects learned in the remote past (consolidated object recognition), and those in the medial orbitofrontal cortex provide the recognition awareness of objects learned in the recent past. The activation of the sparse representation for a particular sensory object in turn activates neurons in one or both of these regions of cortex, and it is the activities of these neurons that provide the awareness of recognition of the object in question. The neural circuitry involved in the activation of these representations is discussed.