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Primary Visual Cortex as a Saliency Map: A Parameter-Free Prediction and Its Test by Behavioral Data.

Zhaoping L, Zhe L - PLoS Comput. Biol. (2015)

Bottom Line: This hypothesis has so far provided only qualitative predictions and their confirmations.A requirement for this successful prediction is a data-motivated assumption that V1 lacks neurons tuned simultaneously to color, orientation, and motion direction of visual inputs.Since evidence suggests that extrastriate cortices do have such neurons, we discuss the possibility that the extrastriate cortices play no role in guiding exogenous attention so that they can be devoted to other functions like visual decoding and endogenous attention.

View Article: PubMed Central - PubMed

Affiliation: University College London, London, United Kingdom.

ABSTRACT
It has been hypothesized that neural activities in the primary visual cortex (V1) represent a saliency map of the visual field to exogenously guide attention. This hypothesis has so far provided only qualitative predictions and their confirmations. We report this hypothesis' first quantitative prediction, derived without free parameters, and its confirmation by human behavioral data. The hypothesis provides a direct link between V1 neural responses to a visual location and the saliency of that location to guide attention exogenously. In a visual input containing many bars, one of them saliently different from all the other bars which are identical to each other, saliency at the singleton's location can be measured by the shortness of the reaction time in a visual search for singletons. The hypothesis predicts quantitatively the whole distribution of the reaction times to find a singleton unique in color, orientation, and motion direction from the reaction times to find other types of singletons. The prediction matches human reaction time data. A requirement for this successful prediction is a data-motivated assumption that V1 lacks neurons tuned simultaneously to color, orientation, and motion direction of visual inputs. Since evidence suggests that extrastriate cortices do have such neurons, we discuss the possibility that the extrastriate cortices play no role in guiding exogenous attention so that they can be devoted to other functions like visual decoding and endogenous attention.

No MeSH data available.


Related in: MedlinePlus

V1 saliency hypothesis states that the bottom-up saliency of a location is represented by the maximum V1 response to this location.In this schematic, V1 is simplified to contain only two kinds of neurons, one tuned to color (their responses are visualized by the purple dots) and the other tuned to orientation (black dots). Each input bar evokes responses in a cell tuned to its color and another cell tuned to its orientation (indicated for two input bars by linking each bar to its two evoked responses by dotted lines), and the receptive fields of these two cells cover the same bar location even though (for better visualization) the dots representing these cells are not overlapping in the cortical map. Iso-feature suppression makes nearby V1 neurons tuned to similar features (e.g., similar color or similar orientation) suppress each other. The orientation singleton in this image evokes the highest V1 response to this image because the orientation-tuned neuron responding to it escapes iso-orientation suppression. The color tuned neuron tuned and responding to the singleton’s color is under iso-color suppression. The saliency map is likely read out by the superior colliculus to execute gaze shifts to salient locations [9].
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pcbi.1004375.g001: V1 saliency hypothesis states that the bottom-up saliency of a location is represented by the maximum V1 response to this location.In this schematic, V1 is simplified to contain only two kinds of neurons, one tuned to color (their responses are visualized by the purple dots) and the other tuned to orientation (black dots). Each input bar evokes responses in a cell tuned to its color and another cell tuned to its orientation (indicated for two input bars by linking each bar to its two evoked responses by dotted lines), and the receptive fields of these two cells cover the same bar location even though (for better visualization) the dots representing these cells are not overlapping in the cortical map. Iso-feature suppression makes nearby V1 neurons tuned to similar features (e.g., similar color or similar orientation) suppress each other. The orientation singleton in this image evokes the highest V1 response to this image because the orientation-tuned neuron responding to it escapes iso-orientation suppression. The color tuned neuron tuned and responding to the singleton’s color is under iso-color suppression. The saliency map is likely read out by the superior colliculus to execute gaze shifts to salient locations [9].

Mentions: It was proposed a decade ago [7, 8] that V1 computes a saliency map, such that the saliency of a location is represented by the maximum response from V1 neurons to this location relative to the maximum responses to the other locations. It is only the V1 response vigor that matters for saliency, and not the preferred features of the responding neurons. For example, the image in Fig 1 contains many colored bars, each activates some V1 neurons tuned to its color and/or orientation. The maximum response to each bar signals the saliency of its location regardless of whether the V1 neuron giving this response is tuned to the color or orientation (or both color and orientation) of the bar. In another example, Fig 2A and 2B contain an orientation and color singleton, respectively, in the same background of uniformly feature bars. If the two images evoke the same background V1 responses to all the background locations, then the two singletons are equally salient if they evoke the same level of maximum response even if the maximum response is evoked in an orientation-tuned cell in one image and a color-tuned cell in the other; conversely, if the two singletons differ by their respective maximally evoked responses, then the singleton evoking the higher response is more salient regardless of the preferred features of the responding neurons.


Primary Visual Cortex as a Saliency Map: A Parameter-Free Prediction and Its Test by Behavioral Data.

Zhaoping L, Zhe L - PLoS Comput. Biol. (2015)

V1 saliency hypothesis states that the bottom-up saliency of a location is represented by the maximum V1 response to this location.In this schematic, V1 is simplified to contain only two kinds of neurons, one tuned to color (their responses are visualized by the purple dots) and the other tuned to orientation (black dots). Each input bar evokes responses in a cell tuned to its color and another cell tuned to its orientation (indicated for two input bars by linking each bar to its two evoked responses by dotted lines), and the receptive fields of these two cells cover the same bar location even though (for better visualization) the dots representing these cells are not overlapping in the cortical map. Iso-feature suppression makes nearby V1 neurons tuned to similar features (e.g., similar color or similar orientation) suppress each other. The orientation singleton in this image evokes the highest V1 response to this image because the orientation-tuned neuron responding to it escapes iso-orientation suppression. The color tuned neuron tuned and responding to the singleton’s color is under iso-color suppression. The saliency map is likely read out by the superior colliculus to execute gaze shifts to salient locations [9].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595278&req=5

pcbi.1004375.g001: V1 saliency hypothesis states that the bottom-up saliency of a location is represented by the maximum V1 response to this location.In this schematic, V1 is simplified to contain only two kinds of neurons, one tuned to color (their responses are visualized by the purple dots) and the other tuned to orientation (black dots). Each input bar evokes responses in a cell tuned to its color and another cell tuned to its orientation (indicated for two input bars by linking each bar to its two evoked responses by dotted lines), and the receptive fields of these two cells cover the same bar location even though (for better visualization) the dots representing these cells are not overlapping in the cortical map. Iso-feature suppression makes nearby V1 neurons tuned to similar features (e.g., similar color or similar orientation) suppress each other. The orientation singleton in this image evokes the highest V1 response to this image because the orientation-tuned neuron responding to it escapes iso-orientation suppression. The color tuned neuron tuned and responding to the singleton’s color is under iso-color suppression. The saliency map is likely read out by the superior colliculus to execute gaze shifts to salient locations [9].
Mentions: It was proposed a decade ago [7, 8] that V1 computes a saliency map, such that the saliency of a location is represented by the maximum response from V1 neurons to this location relative to the maximum responses to the other locations. It is only the V1 response vigor that matters for saliency, and not the preferred features of the responding neurons. For example, the image in Fig 1 contains many colored bars, each activates some V1 neurons tuned to its color and/or orientation. The maximum response to each bar signals the saliency of its location regardless of whether the V1 neuron giving this response is tuned to the color or orientation (or both color and orientation) of the bar. In another example, Fig 2A and 2B contain an orientation and color singleton, respectively, in the same background of uniformly feature bars. If the two images evoke the same background V1 responses to all the background locations, then the two singletons are equally salient if they evoke the same level of maximum response even if the maximum response is evoked in an orientation-tuned cell in one image and a color-tuned cell in the other; conversely, if the two singletons differ by their respective maximally evoked responses, then the singleton evoking the higher response is more salient regardless of the preferred features of the responding neurons.

Bottom Line: This hypothesis has so far provided only qualitative predictions and their confirmations.A requirement for this successful prediction is a data-motivated assumption that V1 lacks neurons tuned simultaneously to color, orientation, and motion direction of visual inputs.Since evidence suggests that extrastriate cortices do have such neurons, we discuss the possibility that the extrastriate cortices play no role in guiding exogenous attention so that they can be devoted to other functions like visual decoding and endogenous attention.

View Article: PubMed Central - PubMed

Affiliation: University College London, London, United Kingdom.

ABSTRACT
It has been hypothesized that neural activities in the primary visual cortex (V1) represent a saliency map of the visual field to exogenously guide attention. This hypothesis has so far provided only qualitative predictions and their confirmations. We report this hypothesis' first quantitative prediction, derived without free parameters, and its confirmation by human behavioral data. The hypothesis provides a direct link between V1 neural responses to a visual location and the saliency of that location to guide attention exogenously. In a visual input containing many bars, one of them saliently different from all the other bars which are identical to each other, saliency at the singleton's location can be measured by the shortness of the reaction time in a visual search for singletons. The hypothesis predicts quantitatively the whole distribution of the reaction times to find a singleton unique in color, orientation, and motion direction from the reaction times to find other types of singletons. The prediction matches human reaction time data. A requirement for this successful prediction is a data-motivated assumption that V1 lacks neurons tuned simultaneously to color, orientation, and motion direction of visual inputs. Since evidence suggests that extrastriate cortices do have such neurons, we discuss the possibility that the extrastriate cortices play no role in guiding exogenous attention so that they can be devoted to other functions like visual decoding and endogenous attention.

No MeSH data available.


Related in: MedlinePlus