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At least 181 records · Page 10Linked to original sources
PubMed2003

Vision for spatial perception and vision for action: a dissociation between the left-right and near-far dimensions.

Neuropsychological and psychophysical studies have suggested that two distinct visual sub-systems are responsible for perception and action. One of the main psychophysical arguments for this is based on visual illusion such as the Induced Roelofs Effect (IRE), where the location of a visual target presented with an off-centre frame is misperceived when evaluated verbally, but not with a reaching response. This dissociated effect suggests the existence of two independent representations of visual space devoted, respectively, to categorisation and to egocentric localisation of reachable objects. These "cognitive" and "sensorimotor" representations have been assumed to be produced through specific anatomical pathways stemming from the primary visual cortex (respectively, the ventral and dorsal streams). To account for the dissociation found with the IRE, it has been suggested that only the cognitive system is sensitive to contextual information. However this view has been challenged by recent psychophysical studies demonstrating the influence of environmental cues on distance perception and the guiding of movement. In the present study, the IRE is re-evaluated but the near-far and right-left dimensions were dissociated. In agreement with previous findings, our results showed that the IRE in the right-left dimension gives rise to a perceptual misperception of target position with no effect on motor performance. Conversely, when the IRE was induced in the near-far dimension a misperception of the target position affected both perceptual and motor responses. This dissociation indicates that the spatial constraints of the task, and not only the nature of the response, interfere with sensitivity to contextual information leading to visual illusions. It is thus likely that the action system (imputed to the dorsal stream) can be sensitive to contextual information, at least when depth processing is emphasised.

Adult↗
PubMed2002

Near death experiences in cardiac arrest: visions of a dying brain or visions of a new science of consciousness.

Very little is known about the dying process and in particular the state of the human mind at the end of life. Cardiac arrest is the final step in the dying process irrespective of cause, and is also the closest physiological model of the dying process. Recent studies in cardiac arrest survivors have indicated that although the majority of cardiac arrest survivors have no memory recall from the event, nevertheless approximately 10% develop memories that are consistent with typical near death experiences. These include an ability to 'see' and recall specific detailed descriptions of the resuscitation, as verified by resuscitation staff. Many studies in humans and animals have indicated that brain function ceases during cardiac arrest, thus raising the question of how such lucid, well-structured thought processes with reasoning and memory formation can occur at such a time. This has led to much interest as regards the potential implications for the study of consciousness and its relationship with the brain, which still remains an enigma. In this article, we will review published research examining brain physiology and function during cardiac arrest as well as its potential relationship with near death experiences during this time. Finally, we will explore the contribution that near death experiences during cardiac arrest may make to the wider understanding of human consciousness.

Attitude to Death↗
PubMed1998

Guidelines for calibration of stimulus and recording parameters used in clinical electrophysiology of vision. Calibration Standard Committee of the International Society for Clinical Electrophysiology of Vision (ISCEV).

In order to perform a technically adequate clinical electrophysiological procedure it is necessary to calibrate the stimulating and recording equipment. Published standards for the electroretinogram (ERG), electro-oculogram (EOG), visual evoked potential (VEP), and guidelines for the Pattern ERG (PERG) specify stimulus and recording parameters. Yet, most commercial instruments do not provide the means for calibration of these parameters. The goal of this document is to provide guidelines for proper calibration of stimulus and recording equipment. The need for such guidelines is clear on both clinical and scientific grounds. Stimulus and amplifier characteristics have substantial effects on the peak latency and amplitude measurements that are commonly used in clinical electrophysiology. Many review articles on clinical electrophysiology emphasize the need for establishing norms for each laboratory as a function of age and gender rather than relying on published norms. However, if stimulus and recording parameters are not calibrated periodically, then these norms may actually be misleading due to changes in stimulus or recording conditions induced by aging of equipment or inadvertent change in settings. This document is divided into two major sections. The first is concerned with calibration of the visual stimulus. It begins with background technical information on the physics of light and its measurement. This is followed by protocols for measurement of the luminous intensity of flash stimuli and the mean luminance, contrast, and visual angle of pattern stimuli. The second section is concerned with calibration of electrophysiologic recording systems. It begins with a description of the characteristics of bioelectrical signals and their measurement. This is followed by protocols for measurement of electrode impedance and amplifier calibration. Although this document was prepared as guidelines for clinical electrophysiological testing, it should be noted that the techniques described are more generally applicable to studies which are dependent upon accurate measurement of luminance or electrophysiological signals.

Electrooculography↗
PubMed1991

[Is vision measurement by vision tables accurate?].

We observed that often visual tables are different, so that one patient can be shown to have different visual acuities. We show the more important characteristics that a standardized visual table should have.

Amblyopia↗
PubMed1981

Don Juan and the vision of Vision.

Castaneda's well-known sequence of Don Juan books is used as a paradigmatic example of the relativist position. Central to Don Juan's teaching is the problem of perception: the main task, he constantly reiterates, is simply to 'see', to recognise that the commonsense world we customarily perceive is nothing more than a cultural construct. To combat this thoroughgoing relativism a case study is taken from the early history of visual science. In classical antiquity several fundamentally different 'views' (to use Don Juan's term) of how we see contended for approval. It was only at the beginning of the seventeenth century that the 'modern' interpretation was selected. This interpretation was selected, ultimately, because it 'worked'. Reference is made to both Wittgenstein and Marx to support this appeal to praxis. It is argued that through an intricate, complex, and ill-understood process of popularisation our self-image is ultimately grounded in the theories of natural science; and these, in turn, are ultimately grounded in our action in the world of things.

Greece↗