The behavioral and neural effects of long–term deprivation

Abstract

Abstract: : Purpose:Recent ophthalmic advances offer a unique opportunity to examine visual plasticity. We characterized visual processing in a patient (MM) whose sight was restored by stem cell and corneal replacement after suffering severe visual deprivation (light perception) between the ages of 3 and 43.Methods: Over the last few years we have measured the neural and behavioral effects of deprivation in MM using a conjunction of psychophysics and functional magnetic resonance imaging (fMRI).Results:Deprivation resulted in a behavioral and neural shift in spatial frequency tuning towards low spatial frequencies: MM's resolution limit, measured using psychophysics, fMRI and visual evoked potentials was 1cpd (20/600–20/800). These losses were probably central to the retina: his optical quality was 20/40 or better, his retina showed no visible indications of degeneration, and electroretinogram responses were normal. We also measured MM’s performance in higher level vision tasks. He showed behavioral impairments in 3D shape perception (including interpreting transparency, shading and perspective cues) as well as object and face recognition. MM performed at 25% correct on an object recognition task and 61% and 70% correct in face expression and gender identification tasks. Control observers, using stimuli blurred to match MMs neural resolution losses, performed at 100% in both tasks. In contrast, MM's performance on color and motion tasks was relatively normal. Consistent with this behavioral data, fMRI activity in MM’s motion processing areas was as great and covered as large an area as control observers, while responses to retinotopic stimuli in V1/2 were weak and these areas appear smaller than normal. Face and object stimuli did not produce activity in areas near fusiform and lingual gyri associated with face and object processing.Conclusions: Long–term interruptions in visual experience have complex and interesting effects on visual processing that differ between both visual functions and visual areas. This research will provide sight recovery patients with better information as to what sort of sight they should expect postoperatively, and thus allow for better risk–benefit estimates.

Keywords: amblyopia • plasticity • visual cortex