[Perception of nail-hammering actions and tool features from a dynamic point-light display].

Twenty participants observed and interpreted 16 nail-hammering movies, each of which was composed of motion of four point-lights that were attached to an actor's hand, elbow, and shoulder and the hammer head. Each participant judged the length and the weight of hammers, the sizes of the nails, and the degree of hammering skill, and rated the actor's motion in terms of briskness, lightness, regularity, smoothness, quickness, stability, complexity, and politeness. The results showed the following perceptual characteristics. A higher angular velocity of the hammer at the hand contributed to the perception of the hammering action as more skillful and brisk, whereas an increase in linear velocity of the point at the shoulder was judged as less skilled. The judgment of nail size was positively correlated with the linear velocity of the points at the hand. The judgment of hammer weight was negatively correlated with the linear velocity of the points at the hammer. The different roles that linear and angular velocities of light points play in biological motion perception were discussed.

[Visual illusion of a vertical gradient: A pitched visual environment and a pitched floor].

We investgated visual illusions of a vertical gradient by using minitures of a road in three experiments. The independent variables were the pitched visual pattern around the road and the pitched floor on which the observer stood. The dependent variable was the angle of the road that the observer adjusted to appear to be level in depth. In Experiment 1, the experimental room was pitched independently of the pitched floor on which the observer stood. Pitching the room was found to be effective for the illusion, but pitching the floor was not. In Experiment 2, the horizontally striped pattern of the sidewalls was.pitched in the range of +/- 30 degrees and the height of the sidewalls was also varied. The illusion was found to be maximal for patterns pitched at +/- 10 degrees, but the sidewall height did not influence the illusion. In Experiment 3, six visual patterns that were produced by combining horizontal and vertical stripes were pitched at +/- 10 degrees. The results showed that the lattice pattern was the most effective, and the horizontal stripe was more effective than the vertical, in contributing to the illusion.

[The study of skewed staircase illusion].

When we look at a flight of level stairs where its longitudinal section obliquely intersected the direction of treads, we perceive the stairs to be tilted laterally. We call this phenomenon a "skewed staircase illusion (SSI)." To investigate features of the SSI, using miniatures of skewed stairs or of laterally sloped planes, we measured their apparent lateral tilts. Main findings were: 1) the stairs were perceived to be less tilted than the laterally sloped planes, 2) the stairs of 32 steps were perceived to be more tilted than those of five steps, 3) the stairs were perceived to be more tilted when we looked them down from the top than when we looked them up from the base, and 4) the apparent tilt of the skewed stairs or laterally sloped planes had a positive correlation with cross-component of slope. We proposed that the SSI is affected by an apparent plane generated by perceptual connection of the treads of stairs.

[Comprehension of emotions accompanied by everyday actions: comparison of biological-motion pictures with real-person pictures].

Forty participants viewed and interpreted videotapes that were composed of displays representing different human actions (e.g., running and washing hands) and emotions (pleasant, neutral, and unpleasant). Half the videotapes were usual movies of real persons and the other videotapes were biological motions as produced by 22 light points on a human body in otherwise total darkness. In each display, an expert or a novice played a series of large or small body actions under each emotion. We found that (1) pleasant-unpleasant feeling was well discriminated in the real-person displays and in the biological motion display of large body actions, but it was less discriminated in the biological-motion displays of small body actions, (2) actions by experts were rated to be pleasant, and (3) actions were successfully identified for the real displays of large actions by experts, but they were poorly identified for the biological-motion displays of small body actions by novices. These results suggested that the observers correctly judged the emotion of players that was represented through suitable actions.