Many investigations of the detection threshold of the human visual system have been conducted, and a few recognition threshold studies can be found, however no identification threshold data are available. This paper documents research on the observer\u27s identification threshold for an alphanumeric resolution test object presented at various average luminance levels, contrasts, and contrast polarities. These factors affected the identification threshold in a similar way to the effects they exert on the observer\u27s detection and recognition thresholds; the test object contrast being the most significant factor. Direct numerical comparisons between the various thresholds were not possible due to the large inherent differences between the test object visual task complexities found in the many threshold investigations
