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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

Examples of retinotopy mapping from two subjects. (A & B) Visual							areas delineated by retinotopic mapping analysis are indicated in							different colors. Reprinted from Tse, et al. (2005).
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Figure 10: Examples of retinotopy mapping from two subjects. (A & B) Visual areas delineated by retinotopic mapping analysis are indicated in different colors. Reprinted from Tse, et al. (2005).

Mentions: We measured BOLD signal in response to monoptic and dichoptic masking within individually mapped retinotopic areas in the human brain (Figure 10). Our results showed that dichoptic masking does not correlate with visual awareness in area V1, but begins only downstream of area V2, within areas V3, V3A/B, V4 and later (Figure 11). The results agreed with previous primate electrophysiological studies using visual masking and binocular rivalry stimuli (Logothetis, Leopold, & Sheinberg, 1996; Macknik & Martinez-Conde, 2004a; Sheinberg & Logothetis, 1997), as well as with one fMRI study of binocular rivalry in humans (Moutoussis, Keliris, Kourtzi, & Logothetis, 2005). We also found that the iterative increase in lateral inhibition we previously discovered from the LGN to V1 for monoptic masking (Figure 9), continued in the extrastriate cortex for dichoptic masking (Figure 11c). This is an important fact in localizing the circuits responsible for maintaining visibility and visual awareness. For instance, if the brain areas that maintained visual awareness exhibited only weak target suppression (i.e. as in early visual areas such as the LGN and V1), then target masking would be incomplete and targets would be perceptually visible during masking. Since the perception of dichoptic masking is as strong as that of monoptic masking, and since the neural activity evoked by the target is only weakly suppressed by dichoptic masks prior to area V3, it follows that the circuits responsible for visibility must lie in V3 or later, or else targets would not be perceptually suppressed during dichoptic masking.


The role of feedback in visual masking and visual processing.

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

Examples of retinotopy mapping from two subjects. (A & B) Visual							areas delineated by retinotopic mapping analysis are indicated in							different colors. Reprinted from Tse, et al. (2005).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 10: Examples of retinotopy mapping from two subjects. (A & B) Visual areas delineated by retinotopic mapping analysis are indicated in different colors. Reprinted from Tse, et al. (2005).
Mentions: We measured BOLD signal in response to monoptic and dichoptic masking within individually mapped retinotopic areas in the human brain (Figure 10). Our results showed that dichoptic masking does not correlate with visual awareness in area V1, but begins only downstream of area V2, within areas V3, V3A/B, V4 and later (Figure 11). The results agreed with previous primate electrophysiological studies using visual masking and binocular rivalry stimuli (Logothetis, Leopold, & Sheinberg, 1996; Macknik & Martinez-Conde, 2004a; Sheinberg & Logothetis, 1997), as well as with one fMRI study of binocular rivalry in humans (Moutoussis, Keliris, Kourtzi, & Logothetis, 2005). We also found that the iterative increase in lateral inhibition we previously discovered from the LGN to V1 for monoptic masking (Figure 9), continued in the extrastriate cortex for dichoptic masking (Figure 11c). This is an important fact in localizing the circuits responsible for maintaining visibility and visual awareness. For instance, if the brain areas that maintained visual awareness exhibited only weak target suppression (i.e. as in early visual areas such as the LGN and V1), then target masking would be incomplete and targets would be perceptually visible during masking. Since the perception of dichoptic masking is as strong as that of monoptic masking, and since the neural activity evoked by the target is only weakly suppressed by dichoptic masks prior to area V3, it follows that the circuits responsible for visibility must lie in V3 or later, or else targets would not be perceptually suppressed during dichoptic masking.

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