Physiological Studies on Neural Mechanisms of Visual Localization and Discrimination*

Talbot, Samuel A.; Marshall, Wade H.

doi:10.1016/s0002-9394(41)91363-6

Cited by 426 publications

(167 citation statements)

References 7 publications

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“…Some have attributed the visual phenomena to primary visual cortex (32,33), because the visual image is oriented and highly retinotopic, and striate cortex is also retinotopic and selective for oriented stimuli (34)(35)(36)(37). However, human occipital cortex is comprised of multiple cortical areas, many of which (like V1) are also retinotopic (24)(25)(26)(37)(38)(39) and orientation-selective (e.g., ref.…”

Section: Discussionmentioning

confidence: 99%

Mechanisms of migraine aura revealed by functional MRI in human visual cortex

Hadjikhani

Río

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

1,312

999

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Cortical spreading depression (CSD) has been suggested to underlie migraine visual aura. However, it has been challenging to test this hypothesis in human cerebral cortex. Using high-field functional MRI with near-continuous recording during visual aura in three subjects, we observed blood oxygenation level-dependent (BOLD) signal changes that demonstrated at least eight characteristics of CSD, time-locked to percept͞onset of the aura. Initially, a focal increase in BOLD signal (possibly reflecting vasodilation), developed within extrastriate cortex (area V3A). This BOLD change progressed contiguously and slowly (3.5 ؎ 1.1 mm͞min) over occipital cortex, congruent with the retinotopy of the visual percept. Following the same retinotopic progression, the BOLD signal then diminished (possibly reflecting vasoconstriction after the initial vasodilation), as did the BOLD response to visual activation. During periods with no visual stimulation, but while the subject was experiencing scintillations, BOLD signal followed the retinotopic progression of the visual percept. These data strongly suggest that an electrophysiological event such as CSD generates the aura in human visual cortex.

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Section: Discussionmentioning

confidence: 99%

Mechanisms of migraine aura revealed by functional MRI in human visual cortex

Hadjikhani

Río

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

1,312

999

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“…This nonuniform sampling gives rise to the well known cortical magnification factor (13,14). Because the structure of V1 seems uniform with eccentricity, it can be noted that V1 carries out a wavelet transform on a distorted version of the image (strongly compressed towards the edges) and not on the image itself.…”

Section: Discussionmentioning

confidence: 99%

Preserving properties of object shape by computations in primary visual cortex

Stevens

2004

Proc. Natl. Acad. Sci. U.S.A.

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Although our visual system is extremely good at extracting objects from the visual scene, this process involves complicated computations that are thought to require image processing by many successive cortical areas. Thus, intermediate stages in object extraction should not eliminate essential properties of the objects that are still required by later stages. A particularly important characteristic of an object is its shape, and shape has the property that it is unchanged by translations, rotations, and magnifications of the image. I show that the requirement for this property of shape to be preserved in the image, as represented by the firing of neurons in the primary visual cortex (V1), is equivalent to a particular type of computation, known as a wavelet transform, determining the firing rate of V1 neurons in response to an image on the retina. Experimental data support the conclusion that the neural representation of images in V1 is described by a wavelet transform and, therefore, that the properties of shape are preserved.A well performed mechanical experiment, such as rolling balls down an inclined plane, gives the same result regardless of whether it is done in China or Italy and whether it was done yesterday or centuries ago. The remarkable thing, which was proved by Emmy Noether nearly a century ago, is that this simple observation (i.e., experimental results do not depend on the time or place at which the experiment is done) requires that energy and momentum must be conserved. This result is an example of what is called a ''symmetry argument'' because doing something, such as carrying out an experiment at a different place or time, has no effect on the result, just as rotating a 4-fold symmetric object such as a square by 90°does not change its appearance. Although arguments of this sort are very common in physics (1), they are rarely used in biology. Here, my goal is to use a symmetry argument to gain insights into how the cortex processes information. I identify abstract properties of an image that should be preserved in the cortical representation of that image (a kind of symmetry argument, because abstract image properties are preserved with cortical processing) and explore the consequences of this preservation for the types of calculations that the cortex can perform.We see the world as filled with objects, but extracting them from the complicated pattern of light and dark that is presented to the retina requires complex computations by a sequence of cortical areas. One of the most important defining characteristics of an object is its shape. Because objects are not extracted in the primary visual cortex (V1) but rather in later areas (2), the representation of an image in V1 should not eliminate the essential properties of objects needed for computations by other areas. I show that this requirement for preserving abstract shape properties (described below) in the cortical representation of images restricts the computations that V1 can carry out to a particular class known as wavelet transforms (3...

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“…As visual information enters the primary visual cortex, retinal topography is preserved: adjacent neurons process information from adjacent, and usually largely overlapping parts of the retina [54]. However, as we move further upstream in the visual processing hierarchy, things become considerably less clear.…”

Section: Remapping and Attention: Neurophysiologymentioning

confidence: 99%

Visual attention and stability

Mathôt

Theeuwes

2011

Phil. Trans. R. Soc. B

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In the present review, we address the relationship between attention and visual stability. Even though with each eye, head and body movement the retinal image changes dramatically, we perceive the world as stable and are able to perform visually guided actions. However, visual stability is not as complete as introspection would lead us to believe. We attend to only a few items at a time and stability is maintained only for those items. There appear to be two distinct mechanisms underlying visual stability. The first is a passive mechanism: the visual system assumes the world to be stable, unless there is a clear discrepancy between the pre-and post-saccadic image of the region surrounding the saccade target. This is related to the pre-saccadic shift of attention, which allows for an accurate preview of the saccade target. The second is an active mechanism: information about attended objects is remapped within retinotopic maps to compensate for eye movements. The locus of attention itself, which is also characterized by localized retinotopic activity, is remapped as well. We conclude that visual attention is crucial in our perception of a stable world.

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Physiological Studies on Neural Mechanisms of Visual Localization and Discrimination*

Cited by 426 publications

References 7 publications

Mechanisms of migraine aura revealed by functional MRI in human visual cortex

Mechanisms of migraine aura revealed by functional MRI in human visual cortex

Preserving properties of object shape by computations in primary visual cortex

Visual attention and stability

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