Gunnar Jansson

Visual Perception of Bending Motion

Principles of the perception of a special kind of partially rigid motion—bending motion—are explored. The proximal stimuli consisted of an outline quadrangle with various combinations of changes of length and direction of the four sides. The result demonstrated a perceptual preference for rotary motion over bending motion, and of bending motion over two-dimensional form change (stretching). The principle of minimum object change can predict this result, implying that rotation, bending, and stretching are perceptually preferred in this order.

Perceived rotary motion from changes in a straight line

The problem dealth with was how perception of a three-dimensional space is related to the corresponding two-dimensional retinal image. The stimulation used was a straight line changing length and direction. For this stimulation a geometrical model was developed. The basic decoding principle in this model is that the changes in the two-dimensional figure will be perceived as three-dimensional motions of an object with constant shape and size. This principle was approximately verified for the majority of the data. The main deviation from the model was that there was generally less perceived depth than predicted. Also a second decoding principle was generally verified: rotary, but not translator motion is perceived from this kind of stimulation. A third unexpected decoding principle was found in the data: the line is perceived in a frontal-parallel direction when it has its maximal extention.

The detection and localization of objects by the blind with the aid of long-cane tapping sounds

The aim of the investigation was to study the usefulness of long-cane tapping sounds for echolocation by blind people. Ten long canes that differed in the spectra of their tapping sounds were selected for the experiment. The task of the three blind subjects when walking was first to detect an object and then to localize it more precisely. The following results were obtained. (1) Objects could be detected and localized with the aid of the long-cane tapping sound alone, but the task was difficult. (2) The results varied with the size of the object. (3) Differences in the spectra of tapping sounds had no behavioral effects.

Identification of real objects under conditions similar to those in haptic displays: providing spatially distributed information at the contact areas is more important than increasing the number of areas

Present day haptic displays have one or a few contact areas, the information being similar over the whole area. The aim of this investigation was to study the relative importance of increasing the number of contact areas and providing spatially distributed information at each contact area. Technical development was “simulated” in experiments with real objects where the information was constrained in ways similar to those in haptic displays. The results suggest clearly that the largest improvement can be expected if spatially distributed information is made available within each contact area. If that is made, an improvement of performance can be expected also with an increased number of contact areas. Increasing only the number of contact areas will not give the same result.

Texture perception via active touch

Abstract The importance of movement in texture perception by touch has long been appreciated, but problematic issues related to the utilization of information during active touch persist. How is the repeated demonstration of active–passive equivalence in perceptual sensitivity to felt texture to be interpreted? What does such equivalence imply about the source(s) of information used to make perceptual judgements of texture? What sort of perceptual subsystem is organized to recover texture by touch? What is the role played by the action system in this recovery? The seminal observations of David Katz and J.J. Gibson are recounted and contemporary research is described. Several unresolved issues are outlined, as are several approaches by which the availability and utilization of information within this particular perceptual-action subsystem can be empirically studied.

Can the Efficiency of a Haptic Display Be Increased by Short-Time Practice in Exploration?

The main aim was to investigate if short-term practice in exploration with a PHANToM can improve performance. A second aim was to find out if some exploration modes are more successful than other modes. Ten participants practiced exploration of nine blocks of 24 virtual objects distributed over three days. The result was that the performance for a majority improved during this practice, but that there were large individual differences. It was suggested that one of the modes has some advantage. A main conclusion is that there is a high risk that studies of displays with users without practice underestimate the usefulness of the displays.

VISIBLE DISTANCES IN SIMULATED NIGHT DRIVING CONDITIONS WITH FULL AND DIPPED HEADLIGHTS

Five experiments are reported in which visible distances on the near side of the road were measured in a situation in which two cars meet in the dark : (1)Both ears had full headlights or both had dipped symmetrical headlights. Full headlights were found to give longer visible distances during the whole meeting. (2)The same lighting conditions were compared taking signal reflectance into consideration. The higher the reflectance, the greater the difference. (3)The same lighting conditions were compared in simulated hill mooting situations. Full headlights still gave longer visible distances. (4)Symmetrical and asymmetrical dipped headlights of types common in Sweden were compared. As a source of glare in a meeting situation they were equal, although visible distance was considerably longer with the asymmetrical type. (5)Full headlights and asymmetrical dipped headlights were compared. Full headlights gave longer visible distances. These results indicate that the dipping of headlights, while cutting down t...

Exploring Tactile Maps with One or Two Fingers

Abstract Real 3D objects are typically explored with high efficiency by several fingers. The largest increase in efficiency is obtained between the use of one and two fingers. The aim of the present experiment was to investigate if the efficiency of identifying a country on a 2D tactile map can be increased by the use of two fingers exploration along opposite sides of the map compared with following along the contour. The result was that there was no significant difference between one-finger and two-finger exploration, but there were significant improvements over sessions. The difference between exploration of 2D and 3D objects is discussed.

Perceived Bending Motions from a Quadrangle Changing Form

In an earlier study by Jansson and Johansson it was found that rotation of a rigid object is perceptually preferred over bending motion, and that bending motion in turn is preferred over two-dimensional stretching. The aim of the present experiment was to study if the same preference order is retained also when the proximal stimuli are changing in a physically more complex way. The stimuli were quadrangular outline figures with two stationary and two moving corners; the figures differed in degree of phase lag between the motions of the two corners. The result was that the preference order found earlier was retained. It was also found that the relative frequency of two subcategories of bending motion, bending proper and folding, varied with phase lag. The relation of the result to a principle of minimum object change was discussed.

Perceived direction of rotary motion

The starring point for this study was the rotating trapezoidal window. The aim was to reanalyze the problem of information about direction of rotation that is available in simplified proximal stimulations and to study empirically if the Ss utilized the possibilities demonstrated in the theoretical analyses. These analyses showed that a distal poin t moving in a horizontal circular path gives different proximal stimulations when moving clockwise and counterclockwise Further, a distal vertical line moving with its midpoint in the same path has a proximal change of length with different phase relations with the horizontal back-and-forth motion for the two directions. The proximal stimulation is ambiguous, however, unless some restrictions or “decoding principles” are introduced. In the first two experiments it was shown that the Ss could not report “correct” direction of motion of the point but were able to do so about the vertical line. In a third experiment a second vertical line was introduced. This necessitates a determination of relative distance to the two lines. It was shown that the proximally shorter line was usually perceived further away than the proximally longer one. The results are discussed with reference to the trapezoidal window. and some hypotheses are stated.