Critical Bandwidth for Image Identification in AMD, Young and Aged Normal Controls and in Normal Periphery

Abstract

Abstract: : Purpose: To test the influence of natural context on the spatial frequency bandwidth requirements for identifying images in persons with Age Related Macular Degeneration (AMD) and in young and aged normal controls. Methods: Fifteen patients with AMD, 13 normal young and 20 aged controls were tested monocularly. Each observer was presented with 20 images: 10 of objects in a natural context, and 10 pre–processed to darken selectively the background. For each image, a series of 9 progressively low–pass (Gaussian) filtered images was generated, starting with 4 c/image and incremented by half–octave steps. Each series, with the full–bandwidth image was presented in an ascending method of limits. The bandwidth at which 50% of the images were recognized was defined as the critical bandwidth (cb). In a second experiment, 10 young observers were tested similarly, comparing central and peripheral viewing (4.5 deg) for 150 ms presentation. Results: In the first experiment, both controls and patients displayed a lower cb with a darkened background (p < 0.05). In addition, patients were able to identify significantly more images at full bandwidth when the background was darkened (p < 0.05). In the second experiment, isolated objects were recognized at lower cb but without a significant eccentricity effect. Conclusions: The results support previous findings that segmented objects are easier to identify by AMD patients. In addition, we were not able to mimick the AMD results by testing normal peripheral vision. Globally, similar results were obtained in normal central vision.

Keywords: low vision • age-related macular degeneration • pattern vision