Prior Exposure to Dynamic Visual Displays Reduces Vection Onset Latency.

While compelling illusions of self-motion (vection) can be induced purely by visual motion, they are rarely experienced immediately. This vection onset latency is thought to represent the time required to resolve sensory conflicts between the stationary observer's visual and nonvisual information about self-motion. In this study, we investigated whether manipulations designed to increase the weightings assigned to vision (compared to the nonvisual senses) might reduce vection onset latency. We presented two different types of visual priming displays directly before our main vection-inducing displays: (1) 'random motion' priming displays - designed to pre-activate general, as opposed to self-motion-specific, visual motion processing systems; and (2) 'dynamic no-motion' priming displays - designed to stimulate vision, but not generate conscious motion perceptions. Prior exposure to both types of priming displays was found to significantly shorten vection onset latencies for the main self-motion display. These experiments show that vection onset latencies can be reduced by pre-activating the visual system with both types of priming display. Importantly, these visual priming displays did not need to be capable of inducing vection or conscious motion perception in order to produce such benefits.

Assumed Lighting Direction in the Interpretation of Cast Shadows.

Assumed lighting direction in cast-shadow interpretation was investigated. Experiment 1 used an ambiguous object-shadow-matching task to measure bias in shadow-matching direction. The shadow-matching bias was largest when the lighting direction was on average 38.3° left from above (a median of 25.1°). Experiment 2 tested the effect of body posture (head orientation) on cast-shadow interpretation using stimuli aligned in a head-centrically vertical or horizontal orientation. The below-shadow (light-from-above) bias in the head-centric frame was robust across the sitting upright, reclining-on-the-left-side, reclining-on-the-right-side, and supine conditions. A right-shadow (light-from-left) bias in the head-centric frame was found for the sitting upright and reclining-on-the-right-side conditions. In the reclining-on-the-left-side condition, shadow biases to the gravitational below direction and head-centric right direction may have cancelled each other out. These results are consistent with findings from previous shape-from-shading studies, suggesting that the same light-source assumption is applied to shading and shadow interpretations.

Directional Bias in the Perception of Cast Shadows.

Previous studies have demonstrated that the perception of shading is based upon assumptions about lighting direction, for example, light from above. However, it is not clear whether these assumptions are used in the perception of cast shadows. Moreover, it is unclear whether a perceptual interaction exists between shading and cast shadows because until now they have been studied separately. In this study, we investigated through three experiments whether the light-from-above (or another direction) assumption is used in interpreting ambiguous cast shadows, and whether shading information influences the interpretation of cast shadows. Our results indicate the existence of the light-from-above assumption in interpreting cast shadows. Consistent shading information enhanced the interpretation, and judgments of lighting direction were also based on both cast shadow and shading information. However, the perceptual determination of shape from shading was relatively independent of the cast shadow interpretation or the lighting direction judgments of the scene.

Perceived gravitoinertial force during vection.

BACKGROUND: When we ride on a roller coaster, our experience of self-motion is accompanied by salient changes in gravitoinertial force. Here we examined whether a similar relationship exists between visually induced self-motion (vection) and perceived gravitoinertial force. METHODS: There were 15 stationary subjects, each wearing a weight jacket, who were exposed to visual displays simulating upward, backward, or no self-motion. At the end of each 30-s display exposure, subjects: 1) rated the strength of their vection experience; and 2) had the experimenter add/remove weights from their weight jackets to recreate their perceived weight during exposure to the stimulus display. RESULTS: We found that upward vection increased and downward vection decreased perceived weight. Importantly, the size of these perceived weight changes depended on the strength of the vection experience. CONCLUSIONS: We conclude that the observed strong relationship between vection and perceived weight stems from the brain's attempt to reconcile the inputs from the different self-motion senses. The current findings have important implications for all simulated self-motions either in virtual reality or in vehicle simulators (particularly fixed-base flight and driving simulators).

Evaluation of an organic light-emitting diode display for precise visual stimulation.

A new type of visual display for presentation of a visual stimulus with high quality was assessed. The characteristics of an organic light-emitting diode (OLED) display (Sony PVM-2541, 24.5 in.; Sony Corporation, Tokyo, Japan) were measured in detail from the viewpoint of its applicability to visual psychophysics. We found the new display to be superior to other display types in terms of spatial uniformity, color gamut, and contrast ratio. Changes in the intensity of luminance were sharper on the OLED display than those on a liquid crystal display. Therefore, such OLED displays could replace conventional cathode ray tube displays in vision research for high quality stimulus presentation. Benefits of using OLED displays in vision research were especially apparent in the fields of low-level vision, where precise control and description of the stimulus are needed, e.g., in mesopic or scotopic vision, color vision, and motion perception.

Effects of dynamic luminance modulation on visually induced self-motion perception: observers' perception of illumination is important in perceiving self-motion.

Coherent luminance modulation of visual objects affects visually induced perception of self-motion (vection). The perceptual mechanism underlying the effects of dynamic luminance modulation were investigated with a visual stimulus simulating an external environment illuminated by a moving spotlight (the normal spotlight condition) or an inverted luminance version of it (the inverted luminance condition). Two psychophysical experiments indicated that vection was generally weakened in the inverted luminance condition. The results cannot be fully explained by the undesirable differences of luminosity within the experimental environment, and suggest that the contrast polarity of the visual stimulus has a significant impact on vection. Furthermore, the results show that the dynamic luminance variations weaken vection in the normal spotlight condition in which the observers perceived illumination modulations. In contrast, in the inverted luminance condition, in which the observers cannot perceive the illumination manipulation, the dynamic luminance variations may not impair vection, and may even be expected to strengthen vection, even though they shared similar global and systematic luminance variation with the normal spotlight condition. These experiments suggest that the observer's perception of illumination is a key factor in considering the effects of dynamic luminance modulation of the visual stimulus.

Vection modulates emotional valence of autobiographical episodic memories.

We examined whether illusory self-motion perception ('vection') induced by viewing upward and downward grating motion stimuli can alter the emotional valence of recollected autobiographical episodic memories. We found that participants recollected positive episodes more often while perceiving upward vection. However, when we tested a small moving grating or a static grating that produced little or no vection, no modulation of emotional valence was observed. We propose that modulation of emotional valence by vection is caused by the mood congruency effect. To test this hypothesis, we examined whether vection direction affected participants' mood. Consequently, upward vection had a strongly positive effect on mood. The results indicate a close relationship between perceived self-motion direction and the emotional valence of recollected autobiographical episodic memories, and that the change in participant's mood with vection direction may underlie the modulation of the valence of recollected memories.

Vection can be induced without global-motion awareness.

A new vection illusion is reported. Vection was induced even though there was no consciously perceived global display motion corresponding to the self-motion. The resulting experience can be summarised as: "I feel that I am moving but I do not know why".

Vection can be induced in the absence of explicit motion stimuli.

The present study utilized two separate experiments to demonstrate that illusory self-motion (vection) can be induced/modulated by cognition. In the first experiment, two curved lines, which simulated road edges seen while driving at night, were employed. Although the lines induced adequate strength of forward vection, when one of the lines was horizontally reversed, vection was significantly reduced. In the second experiment, two static converging lines with moving characters, which simulated side edges of a straight road with a traffic sign, were utilized. The road sign moved only during the first 5 s. After the sign disappeared, only static lines or a blank screen were able to induce vection. These results suggested that vection was largely affected by cognitive factors and that vection could be induced by implicit motion stimuli.

Hunger enhances vertical vection.

Hunger was found to facilitate visually induced illusory upward and downward self-motions (vertical vection), but not illusory self-motion in depth (vection in depth). We propose that the origin of this hunger effect lies in the possibility that vertical self-motions (both real and illusory) are more likely to induce changes in visceral state.

Inconsistent locomotion inhibits vection.

We measured the strength of illusory self-motion perception (vection) with and without locomotion on a treadmill. The results revealed that vection was inhibited by inconsistent locomotion, but facilitated by consistent locomotion.

Halt and recovery of illusory motion perception from peripherally viewed static images.

We quantitatively investigated the halt and recovery of illusory motion perception in static images. With steady fixation, participants viewed images causing four different motion illusions. The results showed that the time courses of the Fraser-Wilcox illusion and the modified Fraser-Wilcox illusion (i.e., "Rotating Snakes") were very similar, while the Ouchi and Enigma illusions showed quite a different trend. When participants viewed images causing the Fraser-Wilcox illusion and the modified Fraser-Wilcox illusion, they typically experienced disappearance of the illusory motion within several seconds. After a variable interstimulus interval (ISI), the images were presented again in the same retinal position. The magnitude of the illusory motion from the second image presentation increased as the ISI became longer. This suggests that the same adaptation process either directly causes or attenuates both the Fraser-Wilcox illusion and the modified Fraser-Wilcox illusion.

Attentional load inhibits vection.

In this study, we examined the effects of cognitive task performance on the induction of vection. We hypothesized that, if vection requires attentional resources, performing cognitive tasks requiring attention should inhibit or weaken it. Experiment 1 tested the effects on vection of simultaneously performing a rapid serial visual presentation (RSVP) task. The results revealed that the RSVP task affected the subjective strength of vection. Experiment 2 tested the effects of a multiple-object-tracking (MOT) task on vection. Simultaneous performance of the MOT task decreased the duration and subjective strength of vection. Taken together, these findings suggest that vection induction requires attentional resources.

Consistent air flow to the face facilitates vection.

We examined whether a somatosensory cue suggesting forward self-motion facilitated vection. We provided a consistent air flow to subjects' faces by using an electric fan.Vection strength was increased when the air flow was provided.

The mental number line in depth revealed by vection.

To explore how numbers are represented in depth in our mental space, we asked participants to sequentially speak random numbers while they observed forward/backward vection. We found that participants tended to generate larger numbers when they perceived backward self-motion. The results suggest that numerical magnitudes were topographically mapped onto our mental space from front to rear in an ascending order.

Rapid learning by walking observers wearing a reversing or inverting prism.

We measured the initial rapid learning of walking observers who wore an up-down inverting or left-right reversing prism. This prism-walking version of the 'mirror-drawing' experiment revealed that the learning curve as a function of the trial number was the same as that typically acquired from a traditional mirror-drawing experiment. We suggest that the initial short-term learning process involved in prism walking is similar to that in mirror drawing and is related to the high-level decision-making process involved in visuo-motor planning of actions with feedback from transformed vision.

The 'rotating snakes' in smooth motion do not appear to rotate.

'Rotating snakes' is an illusory figure in which the 'snakes' are perceived to rotate. We report that when the image moves smoothly, the snakes do not appear to rotate, although the retinal images are continuously refreshed. Therefore, to produce the illusion, the image should remain stationary (without being refreshed) for some time on the same retinal position.

Inhibition of vection by red.

We investigated the effects of colors on vection induction. Expanding optical flows during one's forward self-motion were simulated by moving dots. The dots and the background were painted in equiluminant red and green. Experiments 1 and 2 showed that vection was weaker when the background was red than when the background was green. In addition, Experiment 3 showed that vection was weaker when the moving dots were red than when the dots were green. Experiment 4 demonstrated that red dots on a red background induced very weak vection, as compared with green dots on a green background. In Experiments 5 and 6, we showed that the present results could not be explained by a luminance artifact. Furthermore, Experiment 7 showed that a moving red grating induced weaker vection than did a green one. We concluded that a red visual stimulus inhibits vection.

Static visual components without depth modulation alter the strength of vection.

We conducted a series of psychophysical experiments to investigate the effects of static visual components on visually-induced self-motion perception ('vection'). Static gratings with various spatial frequencies were added to a moving vertical grating, presented either orthogonally or parallel to the motion of the grating. Adding a static component orthogonal to a motion component was found to facilitate vection, whereas adding a static component parallel to a motion component inhibited vection. No anisotropy was found between low and high spatial frequencies of static stimuli in the facilitation/inhibition of vection. We discuss these findings in terms of perceived motion of the visual pattern and the number of visual features in the stimulus.

Temporonasal motion projected on the nasal retina underlies expansion-contraction asymmetry in vection.

Contracting visual stimuli have been found to induce stronger vection than expanding stimuli. We sought to determine which component of motion underlies the advantage of contraction over expansion in inducing vection. Either the right or left hemi-visual field of an optic flow was presented to either the right or left eye. Our results revealed that without temporonasal motion projected on the nasal retina, vection was weak even with contracting stimuli. Conversely, vection was strong even with expanding stimuli if this type of motion was present. The advantage of contracting stimuli in inducing vection may be caused by anisotropy in processing motion on the nasal retina.