A comparison of two contrast sensitivity tests and their usefulness as a screener for aircrew

This study investigated the usefulness of two contrast sensitivity tests for aircrew selection. The first, carried out on a Nicolet CS 2000 Contrast Sensitivity System, used a two-interval forced choice methodology (2IFC) and an adaptive procedure. The second was the VISTECH VCTS 6500 Test System. The contrast sensitivity of 50 aircrew candidates and 23 subjects was measured. Two independent measures were taken on the 23 subjects to get an estimate of test-retest variability. Mean contrast sensitivity with the 2IFC methodology was significantly higher at 1.5, 3, and 6 cpd than with the VCTS 6500. The variance in the scores of the aircrew population on the VCTS 6500 was almost identical to the within-subject variance based on the test-retest data. Thus, any differences in contrast sensitivity across the aircrew population could not be picked up by the VCTS 6500. The variance in the scores of the aircrew candidates with the 2IFC method was larger than the within-subject variance, but the evidence suggested that most of this variation was due to factors other than differences in contrast sensitivity across the aircrew population. It was concluded that neither test was suitable for screening the contrast sensitivity of Canadian Forces aircrew candidates, but that both tests could be useful for testing more heterogeneous populations. Moreover, since the shape of the contrast sensitivity function varies across tests, absolute scores on different tests are not comparable.