Elsevier

NeuroImage

Volume 199, 1 October 2019, Pages 245-260
NeuroImage

Population receptive field estimates for motion-defined stimuli

https://doi.org/10.1016/j.neuroimage.2019.05.068Get rights and content
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Abstract

The processing of motion changes throughout the visual hierarchy, from spatially restricted ‘local motion’ in early visual cortex to more complex large-field ‘global motion’ at later stages. Here we used functional magnetic resonance imaging (fMRI) to examine spatially selective responses in these areas related to the processing of random-dot stimuli defined by differences in motion. We used population receptive field (pRF) analyses to map retinotopic cortex using bar stimuli comprising coherently moving dots. In the first experiment, we used three separate background conditions: no background dots (dot-defined bar-only), dots moving coherently in the opposite direction to the bar (kinetic boundary) and dots moving incoherently in random directions (global motion). Clear retinotopic maps were obtained for the bar-only and kinetic-boundary conditions across visual areas V1–V3 and in higher dorsal areas. For the global-motion condition, retinotopic maps were much weaker in early areas and became clear only in higher areas, consistent with the emergence of global-motion processing throughout the visual hierarchy. However, in a second experiment we demonstrate that this pattern is not specific to motion-defined stimuli, with very similar results for a transparent-motion stimulus and a bar defined by a static low-level property (dot size) that should have driven responses particularly in V1. We further exclude explanations based on stimulus visibility by demonstrating that the observed differences in pRF properties do not follow the ability of observers to localise or attend to these bar elements. Rather, our findings indicate that dorsal extrastriate retinotopic maps may primarily be determined by the visibility of the neural responses to the bar relative to the background response (i.e. neural signal-to-noise ratios) and suggests that claims about stimulus selectivity from pRF experiments must be interpreted with caution.

Keywords

Vision
Motion
Population receptive field analysis

Cited by (0)

1

Present address: Centre for Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, UK, TR10 9FE

2

Present address: School of Psychology, The University of Queensland, St Lucia QLD 4072, Australia.

3

Present address: School of Optometry and Vision Science, University of Auckland, 85 Park Road, Auckland, New Zealand.