Hybrid correlator employing a chirp-encoded binary phase-only filter.

A novel correlator architecture is described that is similar to the VanderLugt correlator (VLC) but differs because the input Fourier transform (FT) is performed electronically rather than optically. We present results in which the FT's are reduced to binary phase-only filters (BPOF's); the required multiplication of the input and the reference FT's (performed optically in the VLC) is performed electronically simply by use of a single XOR logic gate. The problematic zero order and symmetric correlation peak are shown to be removed by use of a chirp-encoded BPOF.

Weighted optical diffraction gratings.

This paper describes the behavior of optical diffraction gratings which have been weighted in various ways analogous to those used in surface acoustic wave devices. It is shown experimentally and theoretically that a wide variety of 2-D responses can be achieved by these means. In this study we have chosen to concentrate on quasirectangular responses, and we describe the factors that limit the performance achievable in practice. Some possible applications of these techniques in the spatial, temporal, and spectral domains are mentioned.

Effects of approach lighting and variation in visible runway length on perception of approach angle in simulated night landings.

Previous experiments in this laboratory have demonstrated illusions due to variations in both length and width of runways in nighttime "black hole" approaches. Even though approach lighting is not designed to provide vertical guidance, it is possible that cues from approach lights could interact with cues from runway lighting to reduce illusions due to variation in runway size. Two experiments were conducted to evaluate the effect of approach lighting on perception of approach angle in simulated night approaches. In the first experiment, 40 pilots made simulated visual approaches to a 150- by 6,000-ft runway (45.7-1829 m) with and without a 3,000-ft approach (914 m) light system (ALSF-2). Pilots controlled a moving runway model to produce a constant "normal" angle of approach over the distance range of 23,000 ft (7010 m) to 8,000 ft (2438 m) from threshold. In the second experiment, 24 pilots made simulated approaches to a 150- by 6,000-ft runway which was either fully visible or which had lights of the upwind half occluded. In addition, a 1,400-ft (427 m) abbreviated approach light system (SSALS) was used at three intensities. Decreasing the visible length of the runway by occulting lights of the far half increased mean generated approach angles from 2.2 degrees to 2.7 degrees in agreement with results of a previous experiment involving similar lengths of runways. Neither the presence of equal intensity approach lights nor uncomfortable glare from approach lights 20 times brighter than runway lights had an effect of practical significance on responses. These findings reinforce previous experimental demonstrations of the importance of runway size cues related to varying runway length, and also show that potential size cues provided by approach lights do not prevent illusions due to variations in runway size.

Effect of different runway sizes on pilot performance during simulated night landing approaches.

Both anecdotal reports from pilots and theories of visual cues would predict lower approaches to narrow or long runways than to wide and short runways. Similar, practice approaches made by pilots to a particular width of runway should lead to an increase in subsequent approach angles flown to wider runways and a decrease in approach angles flown to narrower runways. Two experiments with instrument-rated pilots made quantitative tests and these predictions. In Experiment I, three pilots flew simulated approaches and landings in a fixed-base simulator with a computer-generated image visual display. Practice approaches were flown with an 8,000-ft long runway that was either 75, 150, or 300 ft wide; test approaches were to runways with widths or 75, 100, 150, 200, and 300 ft. In Experiment II, 40 pilots controlled the slant of a moving model runway during simulated night visual approaches. Five different models simulated runways from 100 to 300 ft wide and 3,000 to 9,000 ft long. As predicted, training on a wide runway in Experiment I lowered approach angle in approaches to narrower runways; a narrow practice runway also raised approach angles to wider runways. The magnitude of these practice effects increased as distance from runway threshold decreased. There was also a general tendency for approach angles to decrease as runway width decreased. The latter effect was corroborated in Experiment II; in addition, generated approach angles decreased with increasing runway length. Giving half the pilots information about runway size prior to each approach had no effect on responses. These findings add to the quantitative evidence of danger in night visual approaches due to visual illusions and large variability in the visual perception of approach angle.

Pilot performance during simulated approaches and landings made with various computer-generated visual glidepath indicators.

Two simulator experiments were conducted to quantify the effectiveness, in terms of pilot performance, of four different visual glidepath indicator systems (the 2-bar VASI, 3-bar VASI, T-VASIS, and PAPI) in the severely reduced nighttime visual environment often referred to as the "black hole." Performance in Experiment I was best with the T-VASIS and decreased with the 3-bar BASI, PAPI, and 2-bar VASI, in that order; but differences between the T-VASIS, 3-bar VASI, and Papi were not statistically significant. Approaches flown withou the ground-vased glidepath indicators tended to be low and extremely variable. Observing behavior was compared in approaches with the T-VASIS and 2-bar VASI. Observing response frequency increased as distance from runway threshold decreased and was significantly higher with the T-VASIS. Differences in performanange provided by a given system and to the rate of observing the indicator during approaches.

Some behavioral effects of pesticides: The interaction of mevinphos and atropine in pigeons.

The interaction of the organophosphate mevinphos and atropine was examined in two pigeons performing in a variable interval schedule of reinforcement. When administered separately, both atropine and mevinphos produced a dose-related decrement in responding. The combined exposure to these drugs produced a performance decrement greater than that caused by exposure to each component drug alone. These findings suggest that prophylactic use of atropine may increase the detrimental behavioral effects of organophosphate exposure and that the atropine exposure alone may produce serious behavioral deficits.

Interaction between marihuana and altitude on a complex behavioral task in baboons.

Marihuana, or its principal active ingredient, delta-9-tetra-hydrocannabinal (delta9-THC), impairs performance on complex behavioral tasks in animals and man. Although there exists some evidence that altitude-induced hypoxia potentiates the physiological effects of marihuana, the interaction between altitude and marihuana on behavioral tasks has not been established. In the absence of evidence that use of marihuana is less frequent among members of the aviation community than among the general population, it was necessary to evaluate the effects on performance of any interaction between hypoxia and marihuana. Two baboons were trained to perform on a delayed matching-to-sample task at ground level and altitudes of 2438 and 3658 m (8000 and 12000 ft). The animals were orally administered doses of delta9-THC, ranging from 0.25 to 2.0 mg/kg, 2 h prior to experimental sessions at each altitude. No effects on accuracy of matching performance were observed for any of the drug doses or altitudes used. Amount of work output, as measured by number of trials completed and speed of responding, was not affected by delta9-THC at ground level but was markedly reduced by the higher drug doses at the 2438- and 3658-m altitudes. This interaction suggests that the behavioral impairment produced by marihuana can be potentiated by hypoxia.

The effects of mevinphos on appetitive operant behavior in the gerbil.

The need for study of the effects on performance of non-lethal organophosphate insecticide exposure is founded on many reports of behavioral difficulties in aerial applicators following exposure. In this study, a different pair of gerbils served in each of the following schedules of reinforcement: FR 25, FR 75, DRL 12-sec, DRL 20-sec, and VI 1-min. Baseline performance in these tasks tended to be comparable to that of more common laboratory species, but was more variable in the case of the VI 1-min task. Mevinphos doses of 0.20 mg/kg and above produced observable somatic signs of poisoning and also produced dose-related decrements in performance in FR and VI tasks. Performance in the DRL schedule was affected only at a dose of 0.30 mg/kg. No performance deficits or overt somatic signs of poisoning were present at mevinphos doses of 0.10 mg/kg or lower. These results do not agree with those of an earlier study which decrements in VI performance of pigeons and squirrel monkeys appeared at low mevinphos doses which did not produce overt somatic signs of poisoning. The possibility of variations in mevinphos effect as a function of species and task was discussed.