Detection of blurred cracks: a step towards an empirical vision standard

There are no government mandated vision standards for aviation maintenance inspectors. Empirically derived vision standards for other occupations cannot be extended to this very different occupation. One important maintenance task is the detection of metal fatigue cracks. To assess the effects of lowered visual capacity on this visual detection task, we measured detection performance by aircraft maintenance inspectors as a function of image blur. The data are used to estimate the effect of blur-induced acuity decline on crack detection probability, and provides empirical support for the construction of a taskrelevant visual acuity standard. INTRODUCTION It is difficult, if not impossible, to eliminate human error in the process of inspection. Interventions must be developed to reduce these errors and make the process more error-tolerant. Since visual inspection represents a large part of aviation maintenance inspection, one mitigation strategy is to define vision standards for this vision-intensive, safety-critical occupation. A fine-tuned ability to localize, detect, discriminate, and identify job-relevant stimuli can bring cost savings and safety benefits to industry. In 2001, an FAA Advisory Circular (AC No: 65-31) recommended examination guidelines for the vision of non-destructive inspection (NDI) personnel. It was suggested that near and far vision in at least one eye must be 20/25 and 20/50, respectively. Both near and far requirements could be met with corrected or uncorrected vision. This FAA recommendation was based on acuity standards defined in other NDI/NDT occupations. No current general standard exists in the aviation industry for the visual qualifications of aircraft maintenance inspectors. Some maintenance facilities use the visual acuity and color vision standards suggested in the FAA Advisory Circular, while other facilities have defined their own vision requirements. This illustrates the need for a uniform and universally accepted set of vision standards that would apply to all aircraft non-destructive inspection and testing (NDI/NDT) personnel. There are several broad steps that should be taken toward setting an objective and empirically-based occupational vision requirement. The first step is a thorough vision task analysis. In the current context, the FAA commissioned CAMI to perform this analysis focusing on the role of visual processes. Next, to see if a rigorously defined standard can be borrowed from a similar occupation, a review of the literature should be undertaken. Beard et al. (2002) compiled a review of a text and WEB-based search for occupational vision requirements, knowledge gained from site visits to major aircraft maintenance facilities, relevant information from technical, mechanical, and inspection textbooks, the FAA maintenance human factors web-site, and the human vision literature. Beard et al. (2002) found no studies that allow generalization of standards to aircraft maintenance inspection. It is unknown how similar tasks must be to validly borrow standards from another occupation without being subject to compromise. What is needed is a rapid, empirically-based methodology for defining occupational vision standards. If the standard cannot be legitimately borrowed from a previous standard, an objective research methodology should be followed. In their review of the vision standards literature, Beard et al. (2002) identified four occupations that had empirically derived standards. These empirical methodologies ranged from mathematically measuring the size and working distance of the critical visual details (Sheedy, 1980) 1[1] http://hfskyway.faa.gov to psychophysical measurements with blurring lenses placed in front of the eye on a single task (Good & Augsburger, 1987; Good et al., 1996) or multiple tasks (Padgett, 1989). Here we present a strategy for defining a visual acuity standard that permits increased experimental control by blurring the image before presenting it to the observer, within a computer program. In this way what is done to the signal is exactly known. The primary objective of this research is to aid in the development of recommendations for visual acuity requirements for aviation inspection personnel. Specifically we determine that visual acuity deficits reduce critical task performance and show in graphical form the relationship between acuity decline and performance.