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

Matthew L Patten,Andrew E Welchman,Natasha M Maurits

doi:10.1371/journal.pone.0140696

Matthew L Patten, Andrew E Welchman + Show 1 more

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https://doi.org/10.1371/journal.pone.0140696

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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.

Highlights

The successful use of visual information relies on the brain’s ability to extract meaningful targets from cluttered backgrounds
Error of mean classifier performance when data labels had been permuted). This created a scaled version of the behavioral results and allowed us to compare the simultaneously recorded fMRI activity and behavioral performance. We present these fMR-metric functions for regions of interest (ROIs) with above chance performance in Fig 5 and performed a goodness-of-fit test to quantify the fit of the fMRI classification accuracies to the values on the scaled fMR-metric function (Table 1). fMRI responses in V2 as well as intermediate dorsal (V3A, V7) and early parietal (VIPS, parieto-occipital IPS (POIPS)) visual areas could be decoded in a manner that was similar to the behavioral performance
Our results suggest a close association between fMRI activity and human depth discrimination in the later regions of the dorsal pathway (V7, ventral IPS (VIPS) and POIPS) for the signal-in-noise task, and in early parietal regions VIPS and POIPS for the feature difference task

Summary

Introduction

The successful use of visual information relies on the brain’s ability to extract meaningful targets from cluttered backgrounds This skill depends on (i) detecting and segmenting visual elements into coherent targets, and (ii) discriminating the diagnostic features of different target objects. A hiker on an arid trail would want to (i) break the camouflage of a snake from surrounding rocks and (ii) determine whether it is a rattlesnake or harmless gopher snake. These processes are central to everyday visual function, yet the neural architecture that supports them is not fully understood. 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

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