In daily reality, people often pay attention to several objects that change positions while being observed. In the laboratory, this process is investigated by a phenomenon known as multiple object tracking (MOT) which is a task that evaluates attentive tracking performance. Recent findings suggest that the attentional set for multiple moving objects whose depth changes in three dimensions from one plane to another is influenced by the initial configuration of the objects. When tracking objects, it is difficult for people to expand their attentional set to multiple-depth planes once attention has been focused on a single plane. However, less is known about people contracting their attentional set from multiple-depth planes to a single-depth plane. In two experiments, we examined tracking accuracy when four targets or four distractors, which were initially distributed on two planes, come together on one of the planes during an MOT task. The results from this study suggest that people have difficulty changing the depth range of their attention during attentive tracking, and attentive tracking performance depends on the initial attentional set based on the configuration prior to attentive tracking.

Recent advances in 3-D technologies draw an interest on the just noticeable difference in depth (JNDD) that describes a perceptual threshold of depth differences. In this letter, we address a new application of the JNDD to the depth image enhancement. In the proposed algorithm, a depth image is first segmented into multiple layers and then the depth range of the layer is expanded if the depth difference between adjacent layers is smaller than the JNDD. Therefore, viewers can effectively perceive the depth differences between layers and thus the human depth perception can be improved. The proposed algorithm can be applied to any depth-based 3-D display applications.

In this paper, we introduce a new method for depth perception from a 2D natural scene using scale variation of patterns. As the surface from a 2D scene gets farther away from us, the texture appears finer and smoother. Texture gradient is one of the monocular depth cues which can be represented by gradual scale variations of textured patterns. To extract feature vectors from textured patterns, higher order local autocorrelation functions are utilized at each scale step. The hierarchical linear discriminant analysis is employed to classify the scale rate of the feature vector which can be divided into subspaces by recursively grouping the overlapped classes. In the experiment, relative depth perception of 2D natural scenes is performed on the proposed method and it is expected to play an important role in natural scene analysis.

We are developing a simple three-dimensional (3-D) display method that uses only two transparent images using luminance division displays without any extra equipment. This method can be applied to not only electronic displays but also the printed sheets. The method utilizes a 3-D visual illusion in which two ordinary images with many edges can be perceived as an apparent 3-D image with continuous depth between the two image planes, when two identical images are overlapped from the midpoint of the observer's eyes and their optical-density ratio is changed according to the desired image depths. We can use transparent printed sheets or transparent liquid crystal displays to display two overlapping transparent images using this 3-D display method. Subjective test results show that the perceived depths changed continuously as the optical-density ratio changed. Deviations of the perceived depths from the average for each observer were sufficiently small. The depths perceived by all six observers coincided well.

We propose a novel three-dimensional (3-D) display using only two 2-D images displayed at different depths. It is based on a new perceptual phenomenon induced by the human binocular visual system and enables an observer using no extra equipment to perceive an apparent 3-D image of continuous depth when the luminance is divided between the 2-D images according to the 3-D image depth. Our prototype direct-vision 3-D display using this mechanism can easily produce moving 3-D color images by using conventional 2-D color displays.

To clarify the stereopsis disturbance in patients with Alzheimer's disease (AD), we analyzed binocular eye movement when subjects shifted their gaze between targets at different depths. Subjects are patients with Alzheimer's disease, Mluti-infarct dementia (MID), or Olivopontocerebellar atrophy (OPCA), and healthy controls. Targets are arranged in two ways: along the median plane and asymmetrically crossing the median plane, at distances from the eyes of 1000 mm and 300 mm. When the targets are switched at the onset of a beep, the subjects shifted their gaze to the lit target. The experiment is conducted in a dimly lit room whose structure is capable of providing good binocular cues for depth. In AD subjects, especially in the subjects whose symptoms are moderate (advanced stage), vergence is limited and the change in the convergence angle is small, unstable, and non-uniform. These results are different from those of other patients (MID) and OPCA) or healthy controls and suggest a disturbance of stereopsis in the parietal lobe where AD patients typically have dysfunctions.