Use of a visuospatial cue to focus attention at areas of residual vision amplifies long-term neuronal plasticity. The authors propose that top-down signals preactivate partially damaged areas of V1, thus linking visual and attentional neuronal networks, with the effect of permanently increasing conscious visual perception.

This study investigated the neural substrates of preserved visual functioning in a patient with homonymous hemianopsia and Riddoch syndrome after a posterior cerebral artery stroke affecting the primary visual cortex (area V1). The limited visual abilities of this patient included above-chance verbal reports of movement and color change as well as discrimination of movement direction in the hemianopic field. Functional magnetic resonance imaging showed that motion and color-change stimuli presented to the hemianopic field produced activation in several extrastriate areas of the lesioned hemisphere that were defined using retinotopic mapping. Magnetoencephalographic recordings indicated that evoked activity occurred earlier in the higher-tier visual areas V4/V8 and V5 than in the lower-tier areas V2/V3 adjacent to the lesion. In addition, the functional magnetic resonance imaging analysis showed an increased functional connectivity between areas V4/V8 and V5 of the lesioned hemisphere in comparison with the same areas in the intact hemisphere during the presentation of color changes. These results suggest that visual perception after the V1 lesion in Riddoch syndrome is mediated by subcortical pathways that bypass V1 and project first to higher-tier visual areas V5 and V4/V8 and subsequently to lower-tier areas V2/V3.

Spatial cueing of transient attention has recently been shown to reduce temporal sensitivity. We investigated how the size of the sustained attentional focus influences double-pulse resolution (DPR) thresholds mapped across the visual field in a sample of 95 healthy subjects using a 9-fold interleaved adaptive algorithm (YAAP). Peripheral DPR thresholds increased for measurements between 2.5 degrees and 20 degrees eccentricity. Additionally, central DPR thresholds increased at a similar rate when measured with increasingly larger stimulus displays for peripheral measurements. This latter effect suggests that temporal resolution decreases with a larger sustained attention focus and cannot be explained by retinal characteristics only.

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