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The role of feedback in visual masking and visual processing.

Macknik SL, Martinez-Conde S - Adv Cogn Psychol (2008)

Bottom Line: We propose a feedforward model of visual masking, and provide a hypothesis to explain the role of feedback in visual masking and visual processing in general.We review the anato-my and physiology of feedback mechanisms, and propose that the massive ratio of feedback versus feedforward connections in the visual system may be explained solely by the critical need for top-down attentional modulation.Finally, we propose a new set of neurophysiological standards needed to establish whether any given neuron or brain circuit may be the neural substrate of awareness.

View Article: PubMed Central - PubMed

Affiliation: Barrow Neurological Institute, Phoenix, USA.

ABSTRACT
This paper reviews the potential role of feedback in visual masking, for and against. Our analysis reveals constraints for feedback mecha- nisms that limit their potential role in visual masking, and in all other general brain functions. We propose a feedforward model of visual masking, and provide a hypothesis to explain the role of feedback in visual masking and visual processing in general. We review the anato-my and physiology of feedback mechanisms, and propose that the massive ratio of feedback versus feedforward connections in the visual system may be explained solely by the critical need for top-down attentional modulation. We discuss the merits of visual masking as a tool to discover the neural correlates of consciousness, especially as compared to other popular illusions, such as binocular rivalry. Finally, we propose a new set of neurophysiological standards needed to establish whether any given neuron or brain circuit may be the neural substrate of awareness.

No MeSH data available.


Related in: MedlinePlus

Localization of visibility-correlated responses to the occipital lobe.								(A) An individual brain model from all perspectives,							including both hemispheres flat-mapped, overlaid with the functional							activation from 17 subjects. The green shaded areas are those portions							of the brain that did not show significant activation to Target Only							stimuli. The blue voxels exhibited significant target activation (Target							Only activation > Mask Only activation). Yellow voxels represent a							significant difference between Control (target and mask both presented,							with target-visible) and SWI (target and mask both presented, with							target-invisible) conditions, indicating potentially effective visual							masking, and thus a correlation with perceived visibility.								(B) Response time-course plots from Control versus SWI							conditions in the occipital cortex. (C) Response							time-course plots from Control versus SWI conditions in non-occipital							cortex. (D) Response time-course plots from the							non-illusory conditions (Target Only and Mask Only combined) in							occipital versus non-occipital cortex. This analysis controls for the							possibility that occipital visual circuits have a higher degree of blood							flow than non-occipital circuits. On the contrary, occipital BOLD signal							to non-illusory stimuli is relatively low, as compared to non-occipital							BOLD signal. Error bars in panels B, C, and D represent SEM between							subjects. Reprinted from Tse, et al. (2005).
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Figure 12: Localization of visibility-correlated responses to the occipital lobe. (A) An individual brain model from all perspectives, including both hemispheres flat-mapped, overlaid with the functional activation from 17 subjects. The green shaded areas are those portions of the brain that did not show significant activation to Target Only stimuli. The blue voxels exhibited significant target activation (Target Only activation > Mask Only activation). Yellow voxels represent a significant difference between Control (target and mask both presented, with target-visible) and SWI (target and mask both presented, with target-invisible) conditions, indicating potentially effective visual masking, and thus a correlation with perceived visibility. (B) Response time-course plots from Control versus SWI conditions in the occipital cortex. (C) Response time-course plots from Control versus SWI conditions in non-occipital cortex. (D) Response time-course plots from the non-illusory conditions (Target Only and Mask Only combined) in occipital versus non-occipital cortex. This analysis controls for the possibility that occipital visual circuits have a higher degree of blood flow than non-occipital circuits. On the contrary, occipital BOLD signal to non-illusory stimuli is relatively low, as compared to non-occipital BOLD signal. Error bars in panels B, C, and D represent SEM between subjects. Reprinted from Tse, et al. (2005).

Mentions: Having determined the lower boundary in the visual hierarchy for the visibility of simple targets, we set out to determine the upper boundary. To do this, we isolated the parts of the brain that both showed an increase in BOLD signal when the visible stimuli from the non-illusory conditions (Target Only and Mask Only) were displayed, as well as a decrease in BOLD signal when the same targets were rendered less visible by visual masking. Surprisingly, only areas within the occipital lobe showed differential activation between visible and invisible targets (Figure 12).


The role of feedback in visual masking and visual processing.

Macknik SL, Martinez-Conde S - Adv Cogn Psychol (2008)

Localization of visibility-correlated responses to the occipital lobe.								(A) An individual brain model from all perspectives,							including both hemispheres flat-mapped, overlaid with the functional							activation from 17 subjects. The green shaded areas are those portions							of the brain that did not show significant activation to Target Only							stimuli. The blue voxels exhibited significant target activation (Target							Only activation > Mask Only activation). Yellow voxels represent a							significant difference between Control (target and mask both presented,							with target-visible) and SWI (target and mask both presented, with							target-invisible) conditions, indicating potentially effective visual							masking, and thus a correlation with perceived visibility.								(B) Response time-course plots from Control versus SWI							conditions in the occipital cortex. (C) Response							time-course plots from Control versus SWI conditions in non-occipital							cortex. (D) Response time-course plots from the							non-illusory conditions (Target Only and Mask Only combined) in							occipital versus non-occipital cortex. This analysis controls for the							possibility that occipital visual circuits have a higher degree of blood							flow than non-occipital circuits. On the contrary, occipital BOLD signal							to non-illusory stimuli is relatively low, as compared to non-occipital							BOLD signal. Error bars in panels B, C, and D represent SEM between							subjects. Reprinted from Tse, et al. (2005).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2864985&req=5

Figure 12: Localization of visibility-correlated responses to the occipital lobe. (A) An individual brain model from all perspectives, including both hemispheres flat-mapped, overlaid with the functional activation from 17 subjects. The green shaded areas are those portions of the brain that did not show significant activation to Target Only stimuli. The blue voxels exhibited significant target activation (Target Only activation > Mask Only activation). Yellow voxels represent a significant difference between Control (target and mask both presented, with target-visible) and SWI (target and mask both presented, with target-invisible) conditions, indicating potentially effective visual masking, and thus a correlation with perceived visibility. (B) Response time-course plots from Control versus SWI conditions in the occipital cortex. (C) Response time-course plots from Control versus SWI conditions in non-occipital cortex. (D) Response time-course plots from the non-illusory conditions (Target Only and Mask Only combined) in occipital versus non-occipital cortex. This analysis controls for the possibility that occipital visual circuits have a higher degree of blood flow than non-occipital circuits. On the contrary, occipital BOLD signal to non-illusory stimuli is relatively low, as compared to non-occipital BOLD signal. Error bars in panels B, C, and D represent SEM between subjects. Reprinted from Tse, et al. (2005).
Mentions: Having determined the lower boundary in the visual hierarchy for the visibility of simple targets, we set out to determine the upper boundary. To do this, we isolated the parts of the brain that both showed an increase in BOLD signal when the visible stimuli from the non-illusory conditions (Target Only and Mask Only) were displayed, as well as a decrease in BOLD signal when the same targets were rendered less visible by visual masking. Surprisingly, only areas within the occipital lobe showed differential activation between visible and invisible targets (Figure 12).

Bottom Line: We propose a feedforward model of visual masking, and provide a hypothesis to explain the role of feedback in visual masking and visual processing in general.We review the anato-my and physiology of feedback mechanisms, and propose that the massive ratio of feedback versus feedforward connections in the visual system may be explained solely by the critical need for top-down attentional modulation.Finally, we propose a new set of neurophysiological standards needed to establish whether any given neuron or brain circuit may be the neural substrate of awareness.

View Article: PubMed Central - PubMed

Affiliation: Barrow Neurological Institute, Phoenix, USA.

ABSTRACT
This paper reviews the potential role of feedback in visual masking, for and against. Our analysis reveals constraints for feedback mecha- nisms that limit their potential role in visual masking, and in all other general brain functions. We propose a feedforward model of visual masking, and provide a hypothesis to explain the role of feedback in visual masking and visual processing in general. We review the anato-my and physiology of feedback mechanisms, and propose that the massive ratio of feedback versus feedforward connections in the visual system may be explained solely by the critical need for top-down attentional modulation. We discuss the merits of visual masking as a tool to discover the neural correlates of consciousness, especially as compared to other popular illusions, such as binocular rivalry. Finally, we propose a new set of neurophysiological standards needed to establish whether any given neuron or brain circuit may be the neural substrate of awareness.

No MeSH data available.


Related in: MedlinePlus