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

Psychophysical examination of dichoptic versus monoptic masking in							humans. Human psychophysical measurements of visual masking when 10 ms							duration target and 300 ms duration mask were presented to both eyes							together (monoptic masking) and to the two eyes separately (dichoptic							masking). The probability of discriminating correctly the length of two							targets is diminished, in the average responses from 7 subjects, when							targets were presented near the times of mask onset and termination.							This is true regardless of whether the target and mask were presented to							both eyes (open squares), or if the target was presented to one eye only							and the mask was presented to the other (target = left, mask = right:							closed upright triangles; target = right, mask = left: closed							upside-down triangles). Open squares signify when the target was							displayed with both shutters closed, showing that the stimuli were not							visible through the shutters. When the mask and the target were							presented simultaneously, both eyes’ shutters were necessarily open							(dichoptic presentations using shutters are impossible when both stimuli							are presented at the same time), and so between times 0-250 ms all four							conditions were equivalent. Dichoptic masking is nevertheless evident							when the target was presented before the mask’s onset (-250 to -50 ms on							the abscissa), as well as when the target was presented after the mask							had been terminated (300 ms to 500 ms on the abscissa). Reprinted from							Macknik & Martinez-Conde (2004b).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: Psychophysical examination of dichoptic versus monoptic masking in humans. Human psychophysical measurements of visual masking when 10 ms duration target and 300 ms duration mask were presented to both eyes together (monoptic masking) and to the two eyes separately (dichoptic masking). The probability of discriminating correctly the length of two targets is diminished, in the average responses from 7 subjects, when targets were presented near the times of mask onset and termination. This is true regardless of whether the target and mask were presented to both eyes (open squares), or if the target was presented to one eye only and the mask was presented to the other (target = left, mask = right: closed upright triangles; target = right, mask = left: closed upside-down triangles). Open squares signify when the target was displayed with both shutters closed, showing that the stimuli were not visible through the shutters. When the mask and the target were presented simultaneously, both eyes’ shutters were necessarily open (dichoptic presentations using shutters are impossible when both stimuli are presented at the same time), and so between times 0-250 ms all four conditions were equivalent. Dichoptic masking is nevertheless evident when the target was presented before the mask’s onset (-250 to -50 ms on the abscissa), as well as when the target was presented after the mask had been terminated (300 ms to 500 ms on the abscissa). Reprinted from Macknik & Martinez-Conde (2004b).

Mentions: The existence of “dichoptic” visual masking is one of the main reasons visual masking has been considered a cortical process (Harris & Willis, 2001; Kolers & Rosner, 1960; McFadden & Gummerman, 1973; McKee, Bravo, Smallman, & Legge, 1995; McKee, Bravo, Taylor, & Legge, 1994; Olson & Boynton, 1984; Weisstein, 1971). However, just because dichoptic masking must arise from binocular cortical circuits, does not mean that monoptic masking may not arise from monocular subcortical circuits (Macknik, 2006; Macknik & Martinez-Conde, 2004a). To be clear about the jargon: “monocular” means “with respect to a single eye”, and “monoptic” means either “monocular” or, “not different between the two eyes”. “Binocular” means “with respect to both eyes” and “dichoptic” means “different in the two eyes”. Thus, in dichoptic visual masking, the target is presented to one eye and the mask to the other eye, and the target is nevertheless suppressed. Excitatory binocular processing within the geniculocortical pathway occurs first in the primary visual cortex (Hubel, 1960; Le Gros Clark & Penman, 1934; Minkowski, 1920). Thus it has been assumed that dichoptic masking must originate from cortical circuits. The anatomical location in which dichoptic masking first begins is critical to our evaluation of most models of masking. It is also important to our understanding of LGN neurons and their relationship to the subcortical and cortical structures that feed-back onto them. In order to establish where dichoptic masking first begins, we first compared the perception of monoptic to dichoptic visual masking in humans over a wide range of timing conditions never before tested (Macknik & Martinez-Conde, 2004a), see Figure 8. We found that dichoptic masking was as robust as monoptic masking, and that it exhibited the same timing characteristics previously discovered for monoptic masking (Crawford, 1947; Macknik & Livingstone, 1998; Macknik et al., 2000).


The role of feedback in visual masking and visual processing.

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

Psychophysical examination of dichoptic versus monoptic masking in							humans. Human psychophysical measurements of visual masking when 10 ms							duration target and 300 ms duration mask were presented to both eyes							together (monoptic masking) and to the two eyes separately (dichoptic							masking). The probability of discriminating correctly the length of two							targets is diminished, in the average responses from 7 subjects, when							targets were presented near the times of mask onset and termination.							This is true regardless of whether the target and mask were presented to							both eyes (open squares), or if the target was presented to one eye only							and the mask was presented to the other (target = left, mask = right:							closed upright triangles; target = right, mask = left: closed							upside-down triangles). Open squares signify when the target was							displayed with both shutters closed, showing that the stimuli were not							visible through the shutters. When the mask and the target were							presented simultaneously, both eyes’ shutters were necessarily open							(dichoptic presentations using shutters are impossible when both stimuli							are presented at the same time), and so between times 0-250 ms all four							conditions were equivalent. Dichoptic masking is nevertheless evident							when the target was presented before the mask’s onset (-250 to -50 ms on							the abscissa), as well as when the target was presented after the mask							had been terminated (300 ms to 500 ms on the abscissa). Reprinted from							Macknik & Martinez-Conde (2004b).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: Psychophysical examination of dichoptic versus monoptic masking in humans. Human psychophysical measurements of visual masking when 10 ms duration target and 300 ms duration mask were presented to both eyes together (monoptic masking) and to the two eyes separately (dichoptic masking). The probability of discriminating correctly the length of two targets is diminished, in the average responses from 7 subjects, when targets were presented near the times of mask onset and termination. This is true regardless of whether the target and mask were presented to both eyes (open squares), or if the target was presented to one eye only and the mask was presented to the other (target = left, mask = right: closed upright triangles; target = right, mask = left: closed upside-down triangles). Open squares signify when the target was displayed with both shutters closed, showing that the stimuli were not visible through the shutters. When the mask and the target were presented simultaneously, both eyes’ shutters were necessarily open (dichoptic presentations using shutters are impossible when both stimuli are presented at the same time), and so between times 0-250 ms all four conditions were equivalent. Dichoptic masking is nevertheless evident when the target was presented before the mask’s onset (-250 to -50 ms on the abscissa), as well as when the target was presented after the mask had been terminated (300 ms to 500 ms on the abscissa). Reprinted from Macknik & Martinez-Conde (2004b).
Mentions: The existence of “dichoptic” visual masking is one of the main reasons visual masking has been considered a cortical process (Harris & Willis, 2001; Kolers & Rosner, 1960; McFadden & Gummerman, 1973; McKee, Bravo, Smallman, & Legge, 1995; McKee, Bravo, Taylor, & Legge, 1994; Olson & Boynton, 1984; Weisstein, 1971). However, just because dichoptic masking must arise from binocular cortical circuits, does not mean that monoptic masking may not arise from monocular subcortical circuits (Macknik, 2006; Macknik & Martinez-Conde, 2004a). To be clear about the jargon: “monocular” means “with respect to a single eye”, and “monoptic” means either “monocular” or, “not different between the two eyes”. “Binocular” means “with respect to both eyes” and “dichoptic” means “different in the two eyes”. Thus, in dichoptic visual masking, the target is presented to one eye and the mask to the other eye, and the target is nevertheless suppressed. Excitatory binocular processing within the geniculocortical pathway occurs first in the primary visual cortex (Hubel, 1960; Le Gros Clark & Penman, 1934; Minkowski, 1920). Thus it has been assumed that dichoptic masking must originate from cortical circuits. The anatomical location in which dichoptic masking first begins is critical to our evaluation of most models of masking. It is also important to our understanding of LGN neurons and their relationship to the subcortical and cortical structures that feed-back onto them. In order to establish where dichoptic masking first begins, we first compared the perception of monoptic to dichoptic visual masking in humans over a wide range of timing conditions never before tested (Macknik & Martinez-Conde, 2004a), see Figure 8. We found that dichoptic masking was as robust as monoptic masking, and that it exhibited the same timing characteristics previously discovered for monoptic masking (Crawford, 1947; Macknik & Livingstone, 1998; Macknik et al., 2000).

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