Effects of retinal image degradation on pre‐attentive visual search (PAVS) efficiency for flicker, movement and orientation stimuli

Abstract

Background: Previous research has shown that several clinical conditions cause increased pre‐attentive visual search (PAVS) times, implying reduced parallel search capabilities in glaucoma and DLB dementia. The purpose of the research reported here was to examine for the first time the resistance of PAVS to dioptric blur using targets differing from the background in terms of flicker, vertical displacement, and orientation. Resistance would enhance the applicability of PAVS as a screening method for glaucoma and other clinical conditions affecting performance of a substantial area of the retina. Method: Computer generated flicker, orientation and vertical displacement targets were used to assess PAVS efficiency. The subject's task was to locate a small single target subtending 0.92° as quickly as possible (embedded in a field of 119 distractors) on either the left‐ or right‐hand side of a computer monitor. Average PAVS response times were calculated for 40 presentations of each target type presented randomly in any one of 120 positions within ±15° of fixation. Subjects performed the test using their distance spectacles (unless emmetropic), then three tests using positive lenses simulating myopia of up to −3 D, and finally using optimum correction again. Results: anova revealed that blur of up to 3 D had no statistically significant effect on response times to the flicker target. Blur of over 2.0 D however resulted in increased response times for the displacement target, but only for eyes which were not cyclopleged. The orientation target became significantly more difficult to locate, response times becoming progressively slower with increasing levels of blur (p < 0.05%). Conclusions: The present flicker and displacement targets are relatively resistant to the effects of reduced acuity, while the orientation target is only suitable for testing subjects with good visual acuity.

Open angle glaucoma effects on preattentive visual search efficiency for flicker, motion displacement and orientation pop-out tasks

“…It is also a very rapid test taking as little as one minute per eye to perform a complete assessment using all three targets on a normal individual (under three minutes in glaucoma patients). The current test remains resistant to the potentially confounding effects of optical blur, with the exception of the high spatial frequency orientation target that is resistant to approximately 1 D of optical defocus 22. Such a rapid means of assessment, simplicity of task34 and resistance to optical blur have obvious merit for the development of a clinically viable test for glaucoma.…”

Diagnostic Sensitivity/Specificity of Preattentive Vision Tests in Glaucoma

“…The test fulfils numerous important criteria in terms of essential properties of a clinically viable test for glaucoma, including resistance to blur, 6 simplicity, high diagnostic sensitivity and specificity, as well as a ROC curve for flicker PAVS and PSI, results of normal controls vs. glaucoma subjects. ROC curve for displacement PAVS and PSI, results of normal controls vs. glaucoma subjects.…”

“…The test apparatus (computer, monitor, and test software) and testing routine have previously been described in detail elsewhere. 5,6 Subjects were informed of the nature of the task and asked for their informed consent. The research protocol followed the tenets of the Declaration of Helsinki and ethical approval was obtained from DIT Research Ethics Committee.…”