Perceptual plasticity in the peripheral visual field of older adults
AbstractPerceptual learning is an important mechanism in the human visual system, and can lead to long-lasting improvements across a broad range of perceptual tasks. In this study we demonstrated how perceptual learning can be applied to improve word recognition in the peripheral visual field of a sample of older individuals. We have shown that improvements in thresholds can be equalised across age, simply by increasing the number of training sessions available to older observers. Based on this initial finding we further sought to establish a protocol to induce improvements in reading ability for a sample of individuals with age-related macular disease (AMD). As a prelude to this work, we investigated the effects of crowding and fixation instability on similar tasks. Having suffered damage to their central vision, our target population (individuals with AMD) must use peripheral vision for daily viewing tasks. Peripheral vision is known to be highly susceptible to crowding, the influence of which has previously been shown to strengthen with age. We investigated the relationship between age and crowding on a letter recognition task, and found that (for this task) crowding was age in-variant, implying that this key inhibitor to peripheral visual perception should not have an inordinate influence on learning in our AMD sample. Our work on fixation stability also led to promising results. We demonstrated that our proxy for fixation instability (a dynamic target or dynamic fixation point) did not adversely affect letter recognition thresholds. Fixation instability is a common issue in AMD, but our data suggests that this may not adversely affect learning on our word recognition task. The final part of this work has been the implementation of a small study in which we trained a sample of individuals with AMD on our word recognition task. Significant improvements in thresholds were observed, though these did not quite reach the level of an age-matched normally sighted sample. Nonetheless, the trajectory of the learning curve suggests that further improvements would be possible with extended training sessions. Crucially, we also observed significant transfer of learning – from the trained word recognition task to an untrained sentence reading task (the MNRead Acuity chart). This is a key aspect of the study, as we are primarily interested in developing training protocols that lead to real-world improvements in visual ability. Improvements on MNRead scores are promising, and suggest that our approach may prove to be a useful starting point in the development of a robust therapeutic protocol.
TypeThesis (University of Nottingham only)
Blighe, Alan (2014) Perceptual plasticity in the peripheral visual field of older adults. PhD thesis, University of Nottingham.