In adult humans, damage to the primary visual cortex (V1) and the associated contralateral, homonymous loss of conscious vision in both eyes (cortical blindness?CB) affects ~1% of the population >49 years of age. CB is considered to be clinically intractable and permanent, with no accepted, standardized rehabilitation strategies. A critical barrier to progress in treating CB is the assumption by many in the clinical and scientific communities that the damaged, adult visual system cannot recover functionally. However, in the last decade, work by several teams worldwide, including ours, has identified one method that can reliably recover vision in chronic CB patients: visual training to detect and discriminate single stimuli presented repeatedly, in a gaze contingent manner, at single locations in the blind field. While a definite step forward, training is difficult, requires weeks-to-months of daily computer work to elicit measurable improvements and the recovery attained is incomplete and location specific. Moreover, the factors limiting full vision restoration are only partially understood. The current proposal builds on our prior work to test specific hypotheses about the processing limitations that underlie residual visual deficits, with the goal of overcoming them. Our data suggest that the deficits observed after visual training in CB are due to abnormally high internal processing noise and broader-than-normal tuning for ?features? such as motion direction. Attention cueing either to stimulus features (feature-based attention, FBA) or visual field locations (spatial attention, SA) has been shown to enhance visual processing by decreasing internal noise and/or improving direction tuning. Spatial cueing can also enable and generalize learning across locations. Motivated by these established properties of attention, our goal here is to test the hypothesis that attention will increase the effectiveness of training for features and across locations in CB fields, restoring vision to a greater degree, faster and at multiple sites simultaneously. To this end, Aim 1 will test the hypothesis that feature-based attention during training can overcome fine discrimination deficits in CB by sharpening direction tuning and increasing the gain of spared visual circuits.
Aim 2 will test the hypothesis that spatial attention can potentiate visual recovery at multiple blind field locations simultaneously via a spatially distributed multiplicative increase in gain of the tuned population's response. If successful, our proposal will address 3 key questions in the context of CB: (1) whether normal, fine visual discriminations can ever be recovered without an intact V1; (2) what type of training can most effectively induce the necessary signal processing changes; and (3) whether recovery can be attained at multiple locations simultaneously. Comparing and contrasting different types of attention will allow us to gain insights into mechanistic changes that underlie effective vision recovery in CB. This in turn, is important both neuro-scientifically, and for devising more realistic treatment and outcome expectations for this patient population.
Our goal is to induce, magnify and accelerate vision recovery in cortical blindness (CB) using attention cues during training. The proposed stimulus and trial design will allow us to also characterize processing mechanisms that underlie training-induced plasticity in V1-damaged, adult visual systems. Expected outcomes include a better understanding of the properties and mechanisms that underlie visual recovery in CB. The impact of this project will include improved scientific knowledge, development of new methods to optimally recruit plasticity of the damaged, adult visual system, and improved technical capability and clinical practices for enhancing vision and quality of life for people suffering from CB.
|Cavanaugh, Matthew R; Huxlin, Krystel R (2017) Visual discrimination training improves Humphrey perimetry in chronic cortically induced blindness. Neurology 88:1856-1864|
|Cavanaugh, Matthew R; Barbot, Antoine; Carrasco, Marisa et al. (2017) Feature-based attention potentiates recovery of fine direction discrimination in cortically blind patients. Neuropsychologia :|