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Foveal pRF properties in the visual cortex depend on the extent of stimulated visual field

Gokulraj T Prabhakaran1, Joana Carvalho2, Azzurra Invernizzi2

  • 1Department of Ophthalmology, Otto-von-Guericke University, Magdeburg, Germany.

Neuroimage
|August 18, 2020
PubMed

Insights

Simulated peripheral vision loss shifts foveal (central) visual field receptive field (pRF) positions and enlarges their size. These findings in visual cortex mapping suggest caution when interpreting patient studies of visual reorganization.

Area of Science:

  • Neuroscience
  • Visual Neuroscience
  • Functional Neuroimaging

Background:

  • Alterations in functional MRI (fMRI) derived population receptive field (pRF) properties in visual cortex projection zones of retinal lesions can be mistaken for large-scale cortical reorganization.
  • It remains unclear if similar confounds exist in normal visual cortex projections, particularly for the fovea, under simulated peripheral visual field defects.

Purpose of the Study:

  • To investigate whether simulated peripheral visual field defects introduce confounds in the foveal representation within the normal visual cortex.
  • To quantify changes in pRF properties (position and size) in response to reduced peripheral stimulation in the central visual field.

Main Methods:

  • fMRI-based visual field mapping of the central visual field at 3 Tesla in eight healthy controls.
  • Comparison of pRF properties under a reference condition (14° stimulus radius) versus simulated peripheral defects (7° and 4° stimulus radii) using a peripheral gray mask.
  • Quantification of pRF shifts and size changes using conventional and advanced pRF modeling for the cortical representation of the stimulated visual field.

Main Results:

  • Foveal pRF positions (≤3°) significantly shifted towards the periphery (p<0.05, corrected) under simulated defects.
  • The largest shifts were observed in the 4° condition (V1: 0.9°, V2: 0.9°, V3: 1.0°), with notable shifts also in the 7° condition (V1: 0.5°, V2: 0.5°, V3: 0.9°).
  • An overall enlargement of pRF sizes was consistently observed across conditions with reduced peripheral stimulation.

Conclusions:

  • Foveal pRF parameters are dependent on the spatial extent of the stimulated visual field, indicating potential methodological biases or physiological mechanisms.
  • Previously reported pRF alterations in patients with actual peripheral scotomas should be interpreted with caution.
  • Adequate control conditions are necessary for accurate investigations of visual cortex reorganization in response to visual pathologies.
Keywords:
FoveaHumanRetinotopyVisual cortexVisual field defectfMRI

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