Spatial judgments with monoscopic and stereoscopic presentation of perspective displays.

Spatial judgments with monoscopic and stereoscopic presentation of perspective displays were investigated in the present study. The stimulus configuration emulated a visual scene consisting of a volume of airspace above a ground reference plane. Two target symbols were situated at various positions in the space, and observers were instructed to identify the relative depth or altitude of the two symbols. Three viewing orientations (15, 45, or 90 deg elevation angle) were implemented in the perspective projection. In the monoscopic view, depth cues in size, brightness, occlusion, and linear perspective were provided in the format. In the stereoscopic view, binocular disparity was added along the line of sight from the center of projection to reinforce the relative depth in the visual scene. Results revealed that spatial judgments were affected by manipulation of the relative spatial positions of the two target symbols and by the interaction between relative position and viewing orientation. The addition of binocular disparity improved judgments of three-dimensional spatial relationships, and the enhancement was greater when monocular depth cues were less effective and/or ambiguous in recovering the three-dimensional spatial characteristics.

Visibility of transmissive liquid crystal displays under dynamic lighting conditions.

Liquid crystal displays maintain superior contrast under bright sunlight conditions compared with cathode-ray tube displays. This attribute, along with reduced weight, volume, and power requirements, make liquid crystal displays especially desirable for use in vehicular applications. The present experiment was designed to determine the luminance requirements for transmissive liquid crystal displays viewed under a wide range of lighting conditions typical of many vehicular environments. Both the ambient illumination incident on the display surface and the forward-field-of-view adaptation luminance were parametrically manipulated. The visual task involved speeded spatial discrimination responses for detection of the gap in a modified Landolt-C acuity target. The results indicate that under the worst lighting conditions tested, a display luminance of approximately 180 cd/m2 yielded asymptotic spatial discrimination performance. The results have been incorporated into a predictive visual performance model for spatial discrimination tasks, which describes the present data well and represents a first step toward a device-independent model of display visibility.

Limits of fusion and depth judgment in stereoscopic color displays.

The effective use of stereoscopic display systems is dependent, in part, on reliable data describing binocular fusion limits and the accuracy of depth discrimination for such visual display devices. These issues were addressed in three experiments, as were the effects of interocular cross talk. Results showed that limits of fusion were approximately 27.0 min arc for crossed disparity and 24.0 min arc for uncrossed disparity. Subjects were extremely accurate in distinguishing the relative distance among four groups of stimuli, were able to identify a pair of stimuli colocated at the same depth plane within each group, and were fairly accurate in scaling stimuli along the depth dimension. The mean error in using disparity as a depth cue was approximately 2.2 min arc. Interocular cross talk had little effect on fusion limits for 200-ms stimulus presentations but significantly affected fusion for longer (2 s) presentations that enabled vergence responses to be executed. Depth discrimination performance was essentially unaffected by interocular cross talk; however, cross talk significantly influenced subjective ratings of image quality and visual comfort.

Preconditioning and excitability of the human orbicularis oculi reflex as a function of state.

Reflex excitability and unstimulated activity of orbicularis oculi were found to vary as a function of state but the effects of weak conditioning stimuli, preceding reflex stimulation by 30--210 msec, were independent of state. Electromyographic activity was recorded from 23 young adults: 12 subjects with eyes closed during quiet wakefulness, 3 subjects during all-night sleep, 8 subjects during an afternoon nap. Stimulation with a 50 msec, 105 dB(A) white noise burst elicited a reflex response in 92% of waking trials and 87% of trials during REM sleep, but responses occurred in only 54% of trials during NREM sleep. Further, response latency was longer and magnitude less during the NREM state. Despite the differences in reflex excitability associated with state, state did not affect the modifications of reflex activity produced by a 20 msec, 70 dB(A) conditioning tone. At all lead intervals, reflex magnitude was reduced by the weak prestimulation even though, at the shortest interval, reflex activity was initiated more rapidly. The discordant changes in reflex size and latency have been seen in previous waking studies and appear to be mediated by different mechanisms. The persistence of both effects during sleep suggests that neither effect depends on high-level central processes.

The stability of the sigma sleep spindle.

The present study closely examined the distribution of sigma sleep spindle activity or six normal human males who slept undisturbed for approximately 8 h/night for 3 consecutive nights. Sigma spindle activity was monitored by an automatic spindle detector system which performed at 92.5% accuracy when judged against established visual criteria. Individuals differed markedly in total sigma spindle production across nights, but the failure to detect significant differences among nights and the large intra-class correlation suggests noteworthy inter-night stability of the sigma spindle.