Coherence and the judgment of spatial displacements in retinitis pigmentosa

An EZ-Diffusion Model Analysis of Attentional Ability in Patients With Retinal Pigmentosa

Retinitis pigmentosa (RP) is characterized by visual acuity decrease and visual field loss. However, the impact of visual field loss on the cognitive performance of RP patients remains unknown. In the present study, in order to understand whether and how RP affects spatial processing and attentional function, one spatial processing task and three attentional tasks were conducted on RP patients and healthy controls. In addition, an EZ-diffusion model was performed for further data analysis with four parameters, mean decision time, non-decision time, drift rate, and boundary separation. It was found that in the spatial processing task, compared with the control group, the RP group exhibited a slower response speed in large and medium visual eccentricities, and slower drift rate for the large stimulus, which is strongly verified by the significant linear correlation between the visual field eccentricity with both reaction time (p = 0.047) and non-decision time (p = 0.043) in RP patients. In the attentional orienting task and the attentional switching task, RP exerted a reduction of speed and an increase of non-decision time on every condition, with a decrease of drift rate in the orienting task and boundary separation in the switching task. In addition, the switching cost for large stimulus was observed in the control group but not in the RP group. The stop-signal task demonstrated similar inhibition function between the two groups. These findings implied that RP exerted the impairment of spatial cognition correlated with the visual field eccentricity, mainly in the peripheral visual field. Moreover, specific to the peripheral visual field, RP patients had deficits in the attentional orienting and flexibility but not in the attentional inhibition.

The Effects of Optical Blur on Motion and Texture Perception

PURPOSE

The purpose of this study is to determine how decreased visual acuity affects performance on tasks of motion and texture perception.

METHODS

Positive diopter lenses were used to match three subjects at five levels of decimal visual acuity (DVA) ranging from an uncorrected DVA of 1.6 to the lowest DVA of 0.2. Performance thresholds were determined at each acuity level for five different psychophysical tasks. The tasks assessed the perception of motion-defined form, global motion, maximum motion displacement (Dmax), texture-defined form, and global texture.

RESULTS

Reducing visual acuity decreased performance on the tasks of motion-defined form identification, texture-defined form identification, and global texture integration. Performance on the Dmax task improved with a reduction in visual acuity. Performance on the global motion task was unaffected by changes in visual acuity.

CONCLUSIONS

Visual acuity should be considered when interpreting the results of developmental or clinical studies of motion and texture perception. The only exception to this is global motion perception, at least when DVA is better than 0.2. The effect of blur on tasks of motion and texture perception may reflect the extent to which high spatial frequency information is required for performance on these tasks.