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fMRI Activity in Posterior Parietal Cortex Relates to the Perceptual Use of Binocular Disparity for Both Signal-In-Noise and Feature Difference Tasks.

Patten ML, Welchman AE - PLoS ONE (2015)

Bottom Line: Binocular disparity is known to facilitate this process, and it is an open question how activity in different parts of the visual cortex relates to these fundamental visual abilities.To look for similarities between perceptual judgments and brain activity, we constructed 'fMR-metric' functions that described decoding performance as a function of signal magnitude.This highlights common stages of processing during perceptual performance on these tasks.

View Article: PubMed Central - PubMed

Affiliation: School of Psychology, University of Birmingham, Edgbaston, United Kingdom, B15 2TT; School of Psychology, UNSW Australia, Sydney, NSW, Australia.

ABSTRACT
Visually guided action and interaction depends on the brain's ability to (a) extract and (b) discriminate meaningful targets from complex retinal inputs. Binocular disparity is known to facilitate this process, and it is an open question how activity in different parts of the visual cortex relates to these fundamental visual abilities. Here we examined fMRI responses related to performance on two different tasks (signal-in-noise "coarse" and feature difference "fine" tasks) that have been widely used in previous work, and are believed to differentially target the visual processes of signal extraction and feature discrimination. We used multi-voxel pattern analysis to decode depth positions (near vs. far) from the fMRI activity evoked while participants were engaged in these tasks. To look for similarities between perceptual judgments and brain activity, we constructed 'fMR-metric' functions that described decoding performance as a function of signal magnitude. Thereafter we compared fMR-metric and psychometric functions, and report an association between judged depth and fMRI responses in the posterior parietal cortex during performance on both tasks. This highlights common stages of processing during perceptual performance on these tasks.

No MeSH data available.


Stimuli and design of signal-in-noise and feature difference tasks.(A) A representation of stimuli in the signal-in-noise task viewed from above, and an illustrative red-green stereogram of the stimulus. Only a certain percentage of dots are located at the correct depth plane; the remainder are given random disparities. In the left image, blue dots represent ‘signal’ dots that were located at the target disparity, green dots represent distracting ‘noise’ dots, and black dots represent the surrounding pedestal disparity, located at the plane of fixation (horizontal line). In the experiment, all dots were black or white. (B) A representation of stimuli in the feature difference task viewed from above, and an illustrative stereogram of the stimulus. The pedestal was always located at a crossed disparity and the central test plane was titrated around this. Although all dots are given a crossed disparity, there is a central patch of dots that have a smaller disparity and appear behind the surrounding dots; therefore this stimulus is classified as ‘far’. (C) The procedure for a typical trial. The first black bar indicates stimulus onset and duration, the second black bar indicates presentation of the response cue.
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pone.0140696.g001: Stimuli and design of signal-in-noise and feature difference tasks.(A) A representation of stimuli in the signal-in-noise task viewed from above, and an illustrative red-green stereogram of the stimulus. Only a certain percentage of dots are located at the correct depth plane; the remainder are given random disparities. In the left image, blue dots represent ‘signal’ dots that were located at the target disparity, green dots represent distracting ‘noise’ dots, and black dots represent the surrounding pedestal disparity, located at the plane of fixation (horizontal line). In the experiment, all dots were black or white. (B) A representation of stimuli in the feature difference task viewed from above, and an illustrative stereogram of the stimulus. The pedestal was always located at a crossed disparity and the central test plane was titrated around this. Although all dots are given a crossed disparity, there is a central patch of dots that have a smaller disparity and appear behind the surrounding dots; therefore this stimulus is classified as ‘far’. (C) The procedure for a typical trial. The first black bar indicates stimulus onset and duration, the second black bar indicates presentation of the response cue.

Mentions: It is believed that binocular disparity between the two eyes plays a significant role in both breaking camouflage to segment objects, and providing fine structural shape information that differentiates objects. Studies of disparity processing in the primate brain have examined the processes of segmentation and discrimination by contrasting performance on two different types of task. In particular, signal-in-noise (or “coarse”) tasks ask an observer to detect a disparity-defined target plane hidden in a cloud of random dots that mask the target, while feature difference (or “fine”) tasks require an observer to judge small differences between the depth of a target and its local neighborhood (Fig 1).


fMRI Activity in Posterior Parietal Cortex Relates to the Perceptual Use of Binocular Disparity for Both Signal-In-Noise and Feature Difference Tasks.

Patten ML, Welchman AE - PLoS ONE (2015)

Stimuli and design of signal-in-noise and feature difference tasks.(A) A representation of stimuli in the signal-in-noise task viewed from above, and an illustrative red-green stereogram of the stimulus. Only a certain percentage of dots are located at the correct depth plane; the remainder are given random disparities. In the left image, blue dots represent ‘signal’ dots that were located at the target disparity, green dots represent distracting ‘noise’ dots, and black dots represent the surrounding pedestal disparity, located at the plane of fixation (horizontal line). In the experiment, all dots were black or white. (B) A representation of stimuli in the feature difference task viewed from above, and an illustrative stereogram of the stimulus. The pedestal was always located at a crossed disparity and the central test plane was titrated around this. Although all dots are given a crossed disparity, there is a central patch of dots that have a smaller disparity and appear behind the surrounding dots; therefore this stimulus is classified as ‘far’. (C) The procedure for a typical trial. The first black bar indicates stimulus onset and duration, the second black bar indicates presentation of the response cue.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4631361&req=5

pone.0140696.g001: Stimuli and design of signal-in-noise and feature difference tasks.(A) A representation of stimuli in the signal-in-noise task viewed from above, and an illustrative red-green stereogram of the stimulus. Only a certain percentage of dots are located at the correct depth plane; the remainder are given random disparities. In the left image, blue dots represent ‘signal’ dots that were located at the target disparity, green dots represent distracting ‘noise’ dots, and black dots represent the surrounding pedestal disparity, located at the plane of fixation (horizontal line). In the experiment, all dots were black or white. (B) A representation of stimuli in the feature difference task viewed from above, and an illustrative stereogram of the stimulus. The pedestal was always located at a crossed disparity and the central test plane was titrated around this. Although all dots are given a crossed disparity, there is a central patch of dots that have a smaller disparity and appear behind the surrounding dots; therefore this stimulus is classified as ‘far’. (C) The procedure for a typical trial. The first black bar indicates stimulus onset and duration, the second black bar indicates presentation of the response cue.
Mentions: It is believed that binocular disparity between the two eyes plays a significant role in both breaking camouflage to segment objects, and providing fine structural shape information that differentiates objects. Studies of disparity processing in the primate brain have examined the processes of segmentation and discrimination by contrasting performance on two different types of task. In particular, signal-in-noise (or “coarse”) tasks ask an observer to detect a disparity-defined target plane hidden in a cloud of random dots that mask the target, while feature difference (or “fine”) tasks require an observer to judge small differences between the depth of a target and its local neighborhood (Fig 1).

Bottom Line: Binocular disparity is known to facilitate this process, and it is an open question how activity in different parts of the visual cortex relates to these fundamental visual abilities.To look for similarities between perceptual judgments and brain activity, we constructed 'fMR-metric' functions that described decoding performance as a function of signal magnitude.This highlights common stages of processing during perceptual performance on these tasks.

View Article: PubMed Central - PubMed

Affiliation: School of Psychology, University of Birmingham, Edgbaston, United Kingdom, B15 2TT; School of Psychology, UNSW Australia, Sydney, NSW, Australia.

ABSTRACT
Visually guided action and interaction depends on the brain's ability to (a) extract and (b) discriminate meaningful targets from complex retinal inputs. Binocular disparity is known to facilitate this process, and it is an open question how activity in different parts of the visual cortex relates to these fundamental visual abilities. Here we examined fMRI responses related to performance on two different tasks (signal-in-noise "coarse" and feature difference "fine" tasks) that have been widely used in previous work, and are believed to differentially target the visual processes of signal extraction and feature discrimination. We used multi-voxel pattern analysis to decode depth positions (near vs. far) from the fMRI activity evoked while participants were engaged in these tasks. To look for similarities between perceptual judgments and brain activity, we constructed 'fMR-metric' functions that described decoding performance as a function of signal magnitude. Thereafter we compared fMR-metric and psychometric functions, and report an association between judged depth and fMRI responses in the posterior parietal cortex during performance on both tasks. This highlights common stages of processing during perceptual performance on these tasks.

No MeSH data available.