704 research outputs found
Time-course of early visual extrastriate activity in a blindsight patient using event related potentials. Abstract
Trans-saccadic priming in hemianopia: sighted-field sensitivity is boosted by a blind-field prime
We experience visual stability despite shifts of the visual array across the retina produced by eye movements.
A process known as remapping is thought to keep track of the spatial locations of objects as they
move on the retina. We explored remapping in damaged visual cortex by presenting a stimulus in the
blind field of two patients with hemianopia. When they executed a saccadic eye movement that would
bring the stimulated location into the sighted field, reported awareness of the stimulus increased, even
though the stimulus was removed before the saccade began and so never actually fell in the sighted
field. Moreover, when a location was primed by a blind-field stimulus and then brought into the sighted
field by a saccade, detection sensitivity for near-threshold targets appearing at this location increased
dramatically. The results demonstrate that brain areas supporting conscious vision are not necessary
for remapping, and suggest visual stability is maintained for salient objects even when they are not
consciously perceived
Seeing without Seeing? Degraded Conscious Vision in a Blindsight Patient
Blindsight patients, whose primary visual cortex is lesioned, exhibit preserved ability to discriminate visual stimuli presented in their âblindâ field, yet report no visual awareness hereof. Blindsight is generally studied in experimental investigations of single patients, as very few patients have been given this âdiagnosisâ. In our single case study of patient GR, we ask whether blindsight is best described as unconscious vision, or rather as conscious, yet severely degraded vision. In experiment 1 and 2, we successfully replicate the typical findings of previous studies on blindsight. The third experiment, however, suggests that GR's ability to discriminate amongst visual stimuli does not reflect unconscious vision, but rather degraded, yet conscious vision. As our finding results from using a method for obtaining subjective reports that has not previously used in blindsight studies (but validated in studies of healthy subjects and other patients with brain injury), our results call for a reconsideration of blindsight, and, arguably also of many previous studies of unconscious perception in healthy subjects
Personhood, consciousness, and god : how to be a proper pantheist
Š Springer Nature B.V. 2018In this paper I develop a theory of personhood which leaves open the possibility of construing the universe as a person. If successful, it removes one bar to endorsing pantheism. I do this by examining a rising school of thought on personhood, on which persons, or selves, are understood as identical to episodes of consciousness. Through a critique of this experiential approach to personhood, I develop a theory of self as constituted of qualitative mental contents, but where these contents are also capable of unconscious existence. On this theory, though we can be conscious of our selves, consciousness turns out to be inessential to personhood. This move, I then argue, provides resources for responding to the pantheistâs problem of Godâs person.Peer reviewedFinal Accepted Versio
Concepts of visual consciousness and their measurement.
Although visual consciousness can be manipulated easily (e.g., by visual
masking), it is unresolved whether it can be assessed accurately with behavioral
measures such as discrimination ability and self-report. Older theories of
visual consciousness postulated a sensory threshold and distinguished between
subjective and objective thresholds. In contrast, newer theories distinguish
among three aspects: phenomenal, access, and reflexive consciousness. This
review shows that discrimination ability and self-report differ in their
sensitivity to these aspects. Therefore, both need to be assessed in the study
of visual consciousness
Action Without Awareness: Reaching to an Object You Do Not Remember Seeing
BACKGROUND: Previous work by our group has shown that the scaling of reach trajectories to target size is independent of obligatory awareness of that target property and that "action without awareness" can persist for up to 2000 ms of visual delay. In the present investigation we sought to determine if the ability to scale reaching trajectories to target size following a delay is related to the pre-computing of movement parameters during initial stimulus presentation or the maintenance of a sensory (i.e., visual) representation for on-demand response parameterization. METHODOLOGY/PRINCIPAL FINDINGS: Participants completed immediate or delayed (i.e., 2000 ms) perceptual reports and reaching responses to different sized targets under non-masked and masked target conditions. For the reaching task, the limb associated with a trial (i.e., left or right) was not specified until the time of response cuing: a manipulation that prevented participants from pre-computing the effector-related parameters of their response. In terms of the immediate and delayed perceptual tasks, target size was accurately reported during non-masked trials; however, for masked trials only a chance level of accuracy was observed. For the immediate and delayed reaching tasks, movement time as well as other temporal kinematic measures (e.g., times to peak acceleration, velocity and deceleration) increased in relation to decreasing target size across non-masked and masked trials. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that speed-accuracy relations were observed regardless of whether participants were aware (i.e., non-masked trials) or unaware (i.e., masked trials) of target size. Moreover, the equivalent scaling of immediate and delayed reaches during masked trials indicates that a persistent sensory-based representation supports the unconscious and metrical scaling of memory-guided reaching
Visual masking and the dynamics of human perception, cognition, and consciousness A century of progress, a contemporary synthesis, and future directions
The 1990s, the âdecade of the brain,â witnessed major advances in the study of
visual perception, cognition, and consciousness. Impressive techniques in
neurophysiology, neuroanatomy, neuropsychology, electrophysiology, psychophysics
and brain-imaging were developed to address how the nervous system transforms
and represents visual inputs. Many of these advances have dealt with the
steady-state properties of processing. To complement this âsteady-state
approach,â more recent research emphasized the importance of dynamic aspects of
visual processing. Visual masking has been a paradigm of choice for more than a
century when it comes to the study of dynamic vision. A recent workshop
(http://lpsy.epfl.ch/VMworkshop/), held in Delmenhorst, Germany,
brought together an international group of researchers to present
state-of-the-art research on dynamic visual processing with a focus on visual
masking. This special issue presents peer-reviewed contributions by the workshop
participants and provides a contemporary synthesis of how visual masking can
inform the dynamics of human perception, cognition, and consciousness
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