Search results

Two experiments are reported that demonstrate that visual search for a signal from a number of potential signal sources in a sustained monitoring task is dependent upon previous visual-load history. It is shown that both temporal and spatial variations in load produce performance decrements, and occasionally increments, that cannot be predicted from static-load experiments. These data are not consistent with previous attempts to explain performance changes associated with workload history. An interpretation is offered in terms of the persistence of information-processing strategies across changing task conditions.

The impact of metrication of roadside speed signs upon vehicle speeds was investigated for four different road types using concealed roadside radar. The study was conducted one year after metrication to determine whether there were any long-term changes in traffic patterns in addition to the short-term influences reported previously. There was no evidence for any tendency for drivers to increase traveled speed on roads for which metrication resulted in an increase in the speed limit. Analysis of accident statistics for the month following metrication revealed no significant increase in accident rate over that projected from nine-year accident trends. It is concluded that highway metrication does not present the safety hazard suggested by critics of the metrication program.

A roadside survey of vehicle velocities was carried out by radar on a four lane, median divided highway with a 50 mile-per-hour (80 km/h) legal speed limit. Northbound traffic on the highway had been previously exposed to expressway conditions with vehicle speeds in excess of 96 km/h, whereas southbound traffic had been previously exposed to an urban highway with speeds of about 64 km/h. Northbound traffic velocities exceeded those of southbound traffic by an average of 6.9 km/h, which, it is argued, is the result of drivers of northbound vehicles being exposed to conditions under which velocity adaptation occurs. An analysis of the data by vehicle category indicates that while large cars are driven significantly faster than small cars under all conditions, the magnitude of the velocity adaptation effect is greater for drivers of small cars.

The effect of prolonged cathode ray tube (CRT) work on the afferent visual neural and focusing system of the human eye was examined by visually evoked potentials (VEPs) and laser optometer techniques, respectively. These measures were compared with parallel measurements of search performance. Ten volunteers performed three 4-hr sessions of a search/decision task on a high-resolution-red/ green/blue (RGB) monitor. Stimuli were numbers and symbols presented in a blue/black, red/black, or red/green foreground/background combination. Results showed minimal changes in the neural and focusing responses to each foreground/background combination over time on task. Weak correlations were found between neural-optical and search performance measurements. These data suggest that the use of chromatic stimuli in the color combinations examined do not have a detrimental effect on visual performancé.

Visual search and decision-making performance together with subjective fatigue were investigated over a 4-hr time block as a function of display foreground and background chromaticity using colors matched for brightness. Although some small differences in performance related to chromaticity were observed, these were not exacerbated over time. On the basis of the performance data obtained and the subjective reports, there was no support for the general recommendation to avoid the use of red and blue stimuli, either alone or in combination, in CRT displays.

When a visual detection task is performed with distant targets in the absence of adequate accommodative cues, a performance loss is obtained which has been attributed to empty field myopia. It is shown that in a visual search situation an accommodative aid located at optical infinity improves detection by approximately 30% over empty field performance. It is further demonstrated that such an aid may overcome the conflicting accommodative cues provided by proximal contours defining the search area, i.e., a situation that is analogous to the detection of distant targets by observers searching through aircraft cabin windows.