Integration of binocular disparity and monocular cues at near threshold level.

We examined the dependency of the integration of multiple depth cues upon the combined cues and upon the consistency of depth information from different cues. For each observer, depth thresholds were measured by the use of stimuli in which different depth cues (motion parallax, binocular disparity, and monocular configuration) specified the surface undulating sinusoidally with different spatial frequencies and different phases. Analysis of d(') showed that the performance was better than the prediction of probability summation only when parallax and disparity cues specified an undulation with the same spatial frequency and same phase. The probability summation model overestimated the performance for the other conditions of combination of disparity and parallax, and for all of the conditions of combination of disparity and monocular configuration. These results suggest that the improvement in depth perception caused by integration of multiple cues depends on the type of combined cues, and that the visual system possibly integrates the depth information from different cues at different stages of the visual processing.

Pupillary and cardiovascular responses to a video movie in senior human subjects.

The effects of watching video movies on autonomic functions were estimated by measuring changes in pupillary and cardiovascular parameters in 10 senior subjects. The subjects looked at a series of video images (with accompanied sounds) taken during the execution of motor vehicles. The images were rear-projected on a large screen for 15 min. Pupil diameter and parameters of the light reflex were measured by an infrared pupillometer before and after the video presentation. Their electrocardiograms (ECG) and blood pressure were measured continuously. Subjects were divided into two groups depending on their values of blood pressure and fasting plasma glucose level. Subjects in Group A had blood pressures of less than 140 mm Hg and a fasting plasma glucose level of less than 7 mmol/dl (normal group). Other subjects were included in Group B (mild hypertension or diabetes mellitus group). While changes in pupillary light reflex after video viewing were minimal in the members of Group A, amplitudes of the pupillary reflex in the members of Group B varied over a significantly wide range. By the spectral analysis of cardiovascular rhythm, %LF and %HF components of blood pressure rhythm were significantly different between the two groups before video viewing. However, the ratios of frequency components before and after video viewing were not significantly different between the two groups. Our findings suggest that pupillary light reflex was less precisely controlled in subjects with mild autonomic dysfunction after prolonged audiovisual stimulation.

Relative distance cues contribute to scaling depth from motion parallax.

The visual system scales motion parallax signals with information about absolute distance (M. E. Ono, Rivest, & H. Ono, 1986). The present study was designed to determine whether relative distance cues, which intrinsically provide information about relative distance, contribute to this scaling. In two experiments, two test stimuli, containing an equal extent of motion parallax, were presented simultaneously at a fixed viewing distance. The relative distance cues of dynamic occlusion and motion parallax in the areas surrounding the test stimuli (background motion parallax) and/or relative size were manipulated. The observers reported which of the two parallactic test stimuli appeared to have greater depth, and which appeared to be more distant. The results showed that the test stimulus specified, by the relative distance cues, as being more distant was perceived as having more depth and as being more distant. This indicates that relative distance cues contribute to scaling depth from motion parallax by modifying the information about the absolute distance of objects.