Limits...
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

Recording from a typical single neuron from monkey area V1 that was							stimulated with a target of various durations. The magnitude of the							after-discharge grows as the target duration increases. Reprinted from							Macknik & Martinez-Conde (2004a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2864985&req=5

Figure 5: Recording from a typical single neuron from monkey area V1 that was stimulated with a target of various durations. The magnitude of the after-discharge grows as the target duration increases. Reprinted from Macknik & Martinez-Conde (2004a).

Mentions: Breitmeyer and Öğmen (2006) revised the two-channel model, now called the retino-cortical dynamics (RECOD) model. One motivation for revision was provided by Super, Spekreijse, and Lamme (2001), who suggested that the late responses of V1 neurons, such as the after-discharges in Macknik and Livingstone (1998), were caused by feedback from higher visual areas, rather than from the stimulus’s termination. Breitmeyer and Öğmen (2006) thus proposed that the two channel hypothesis was essentially correct, if one considered that the fast and slow channels were not the magnocellular and parvocellular retino-geniculocortical pathways, as previously modeled, but were instead feedforward ascending input (fast channel) and feedback from higher visual areas (slow channel). In the recast two-channel model, the feedforward input from the mask would suppress the (delayed) feedback input from the target (i.e. the after-discharges), thus causing suppression of the target’s visibility. One problem with this idea, however, is that after-discharge timing varies as a function of stimulus termination time (Figure 5). This indicates that after-discharges are not caused by feedback from the stimulus’s onset. If after-discharges were caused by feedback, the areas providing the feedback would need to be able to predict the moment of termination of the stimulus. To the best of our knowledge, no study previous to Macknik and Livingstone (1998) varied the duration of both targets and masks to assess the role of after-discharges in visual masking. Thus it had not been possible to differentiate between the role of feedforward and feedback circuits in the formation of after-discharges.


The role of feedback in visual masking and visual processing.

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

Recording from a typical single neuron from monkey area V1 that was							stimulated with a target of various durations. The magnitude of the							after-discharge grows as the target duration increases. Reprinted from							Macknik & Martinez-Conde (2004a).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Recording from a typical single neuron from monkey area V1 that was stimulated with a target of various durations. The magnitude of the after-discharge grows as the target duration increases. Reprinted from Macknik & Martinez-Conde (2004a).
Mentions: Breitmeyer and Öğmen (2006) revised the two-channel model, now called the retino-cortical dynamics (RECOD) model. One motivation for revision was provided by Super, Spekreijse, and Lamme (2001), who suggested that the late responses of V1 neurons, such as the after-discharges in Macknik and Livingstone (1998), were caused by feedback from higher visual areas, rather than from the stimulus’s termination. Breitmeyer and Öğmen (2006) thus proposed that the two channel hypothesis was essentially correct, if one considered that the fast and slow channels were not the magnocellular and parvocellular retino-geniculocortical pathways, as previously modeled, but were instead feedforward ascending input (fast channel) and feedback from higher visual areas (slow channel). In the recast two-channel model, the feedforward input from the mask would suppress the (delayed) feedback input from the target (i.e. the after-discharges), thus causing suppression of the target’s visibility. One problem with this idea, however, is that after-discharge timing varies as a function of stimulus termination time (Figure 5). This indicates that after-discharges are not caused by feedback from the stimulus’s onset. If after-discharges were caused by feedback, the areas providing the feedback would need to be able to predict the moment of termination of the stimulus. To the best of our knowledge, no study previous to Macknik and Livingstone (1998) varied the duration of both targets and masks to assess the role of after-discharges in visual masking. Thus it had not been possible to differentiate between the role of feedforward and feedback circuits in the formation of after-discharges.

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