An important problem for the human factors specialist involves specifying the extent to which the quality of a displayed image will affect observer performance. One approach to this problem has been to develop metrics of image quality and to correlate measured image quality with observer performance. Of the metrics that have been developed, the Modulation Transfer Factor Area (MTFA) has proven to be a useful predictor of observer performance. The MTFA metric takes into account the system's Modulation Transfer Function and observer threshold curves. Two experiments were performed to assess the effects of the quality of a televised image on eye movements and search-related dependent measures. The first experiment search task involved having subjects perform an air-to-ground search during simulated flight. The quality of the image presented was varied by either passing, low-pass filtering, or attenuating the video signal and by adding electrical white noise to the video signal. The results of this experiment indicate that (1) at the highest level of electrical noise added, the percent of correct target acquisitions was decreased moderately, (2) the larger the target, the higher the percent correct responses, (3) the low-pass filtering of the video signal led to shorter ground ranges at acquisition for the large-sized targets, and (4) that the larger the target, the longer the fixation duration. Low to moderate correlations between MTFA and performance measures generally indicated that as MTFA increases performance improves, and that as MTFA increases fixation duration decreases. The search task of the second experiment consisted of having the subjects search for a designated letter or numeral across a televised picture of randomly positioned letters and numerals. The quality of the picture was varied by either passing, low-pass filtering, high-pass filtering, or attenuating the video signal and by adding electrical white noise to the video signal. The results of this experiment indicated that (1) the high-pass filtered high noise level condition led to significantly longer search times; and (2) the fixation times associated with the high-pass filtered condition were longer than those associated with the low-pass filtered, at- tenuated, and unfiltered unattenuated conditions, and that this effect was most pronounced under high noise level conditions. Correlations between MTFA and performance measures indicated that increases in MTFA lead to decreases in search time and decreases in fixation duration.

The results of tests among fixation and saccade duration distribution across both experiments consistently showed significant individual differences and non-normality. Examination of pooled fixation duration distributions showed large dispersion differences across the static and dynamic imagery experiments. This result, and the differences of pooled fixation and saccade duration distribution ranges do not support the search model assumption of constant glimpse durations and reveal serious.flaws in the structure of search models.