Influence of colour vision on attention to, and impression of, complex aesthetic images.

Humans exhibit colour vision variations due to genetic polymorphisms, with trichromacy being the most common, while some people are classified as dichromats. Whether genetic differences in colour vision affect the way of viewing complex images remains unknown. Here, we investigated how people with different colour vision focused their gaze on aesthetic paintings by eye-tracking while freely viewing digital rendering of paintings and assessed individual impressions through a decomposition analysis of adjective ratings for the images. Gaze-concentrated areas among trichromats were more highly correlated than those among dichromats. However, compared with the brief dichromatic experience with the simulated images, there was little effect of innate colour vision differences on impressions. These results indicate that chromatic information is instructive as a cue for guiding attention, whereas the impression of each person is generated according to their own sensory experience and normalized through one's own colour space.

Effects of luminance contrast, averaged luminance and spatial frequency on vection.

Changing the speed, size and material properties of optic flow can significantly alter the experience of vection (i.e. visually induced illusions of self-motion). Until now, there has not been a systematic investigation of the effects of luminance contrast, averaged luminance and stimulus spatial frequency on vection. This study examined the vection induced by horizontally oriented gratings that continuously drifted downwards at either 20° or 60°/s. Each of the visual motion stimuli tested had one of: (a) six different levels of luminance contrast; (b) four different levels of averaged luminance; and (c) four different spatial frequencies. Our experiments showed that vection could be significantly altered by manipulating each of these visual properties. Vection strength increased with the grating's luminance contrast (in Experiment 1), its averaged luminance (in Experiment 2), and its spatial frequency (in Experiment 3). Importantly, interactions between these three factors were also found for the vection induced in Experiment 4. While simulations showed that these vection results could have been caused by effects on stimulus motion energy, differences in perceived grating visibility, brightness or speed may have also contributed to our findings.

Hot Wind to the Body Can Facilitate Vection Only When Participants Walk Through a Fire Corridor Virtually.

Vection has been reported to be enhanced by wind, as long as the wind is a normal temperature and not hot. However, here we report that a hot wind can facilitate vection, as long as it is natural and consistent with the visual stimulus. We created a fire-corridor stimulus that was consistent with a hot wind and a control stimulus composed of cubes, which were irrelevant to a hot wind. We compared the vection strength induced by a fire-corridor (fire condition) visual stimulus with that induced by geometric cubes (no-fire condition) visual stimulus. There were three wind type conditions: a normal temperature wind, hot wind, and no wind. The results showed that a normal temperature wind facilitated vection and that a hot wind (but not a normal wind) highly enhanced vection when a fire-corridor stimulus was presented. These results suggest that vection is highly affected and modulated by high-level cognitive processes.

Visualization by P-flow: gradient- and feature-based optical flow and vector fields extracted from image analysis.

We proposed a method for extracting the optical flow suitable for visualization, pseudo-flow (P-flow), from a natural movie [Exp. Brain Res.237, 3321 (2019)EXBRAP0014-481910.1007/s00221-019-05674-0]. The P-flow algorithm comprises two stages: (1) extraction of a local motion vector field from two successive frames and (2) tracking of vectors between two successive frame pairs. In this study, we show that while P-flow takes a feature (vector) tracking approach, it is also classified as a gradient-based approach that satisfies the brightness constancy constraint. We also incorporate interpolation and a corner detector to address the shortcomings associated with the two approaches.

Material surface properties modulate vection strength.

Realistic appearance and complexity in the visual field are known to affect the strength of vection (visually induced self-motion perception). Although surface properties of materials are, therefore, expected to be visual features that influence vection, to date, the results have been mixed. Here, we used computer graphics to simulate self-motion through rendered 3D tunnels constructed from nine different materials (bark, ceramic, fabric, fur, glass, leather, metal, stone, and wood). There are three ways in which the new stimuli are changed from those found in previous studies: (1) as they move, their appearances interactively change with the 3D structures of the simulated world, as do all the lighting effects and 3D geometric appearances, (2) they are colored, (3) and their components covered a large portion of the visual field. The entire inner surface of each tunnel was composed from one of the nine materials, and optic flow was evoked when an observer virtually moved through the tunnel. Bark, fabric, leather, stone, and wood effectively induced strong vection, whereas, ceramic, glass, fur, and metal did not. Regression analyses suggested that low-level image features such as the lighting and amplitude of spatial frequency were the main factors that modulated vection strength. Additionally, subjective impressions of the nine surface materials showed that the perceived depth, smoothness, and rigidity were related to the perceived vection strength. Overall, our results indicate that surface properties of materials do indeed modulate vection strength.

Vection induced by low-level motion extracted from complex animation films.

This study examined the contributions of low-, mid- and high-level visual motion information to vection. We compared the vection experiences induced by hand-drawn and computer-generated animation clips to those induced by versions of these movies that contained only their pure optic flow. While the original movies were found to induce longer and stronger vection experiences than the pure optic flow, vection onsets were not significantly altered by removing the mid- and high-level information. We conclude that low-level visual motion information appears to be important for vection induction, whereas mid- and higher-level display information appears to be important for sustaining and strengthening this vection after its initial induction.

Inhibition of vection by grasping an object.

The present study investigated whether vection could be modified by an object grasping movement. Twenty-five university students were asked to do one of the following four types of left-hand movements while they were viewing a radial optic flow: (1) grasping the hand-gripper strongly; (2) holding the hand-gripper; (3) clenching fist strongly; and (4) open hand without having anything in their left hands (normal hand condition). The participants' tasks were to keep pressing a button with their right hands while they were perceiving vection. After each trial, they estimated the subjective strength of vection on a 101-point scale. The result showed that the vection was inhibited by strongly grasping the hand-gripper task more than by the other hand movements. Vection could be weakened by the object grasping movement. It might be suggested that vection could be inhibited by the presence of an object being grasped and also by the grasping movement itself. We speculated that the mechanism underlying this inhibition might be related to cognitive pressure, attentional load, power and muscle tonus, and multisensory and proprioception interactions.

Smoothness of stimulus motion can affect vection strength.

We examined the effect of the smoothness of motion on vection strength. The smoothness of stimulus motion was modulated by varying the number of frames comprising the movement. In this study, a horizontal grating translated through 360° of phase in 1 s divided into steps of 3, 4, 6, 12, 20, 30, or 60 frames. We hypothesized that smoother motion should induce stronger vection because the smoother stimulus is more natural and contains more motion energy. We examined this effect of frame number on vection for both downward (Experiment 1) and expanding (Experiment 2) optical flow. The results clearly showed that vection strength increased with increasing frame rate, however, the rates of increase in the vection strength with frame rate are not constant, but rapidly increase in the low frame-rate range and appear to asymptote in the high range. The strength estimates saturated at lower frame rates for expanding flow than for downward flow. This might be related to the fact that to process expanding flow it is necessary to integrate motion signals across the visual field. We conclude that the smoothness of the motion stimulus highly affects vection induction.

Default perception of high-speed motion.

When human observers are exposed to even slight motion signals followed by brief visual transients--stimuli containing no detectable coherent motion signals--they perceive large and salient illusory jumps. This visually striking effect, which we call "high phi," challenges well-entrenched assumptions about the perception of motion, namely the minimal-motion principle and the breakdown of coherent motion perception with steps above an upper limit called dmax. Our experiments with transients, such as texture randomization or contrast reversal, show that the magnitude of the jump depends on spatial frequency and transient duration--but not on the speed of the inducing motion signals--and the direction of the jump depends on the duration of the inducer. Jump magnitude is robust across jump directions and different types of transient. In addition, when a texture is actually displaced by a large step beyond the upper step size limit of dmax, a breakdown of coherent motion perception is expected; however, in the presence of an inducer, observers again perceive coherent displacements at or just above dmax. In summary, across a large variety of stimuli, we find that when incoherent motion noise is preceded by a small bias, instead of perceiving little or no motion--as suggested by the minimal-motion principle--observers perceive jumps whose amplitude closely follows their own dmax limits.

Walking without optic flow reduces subsequent vection.

This experiment investigated the effect of walking without optic flow on subsequent vection induction and strength. Two groups of participants walked for 5 min (either wearing Ganzfeld goggles or with normal vision) prior to exposure to a vection-inducing stimulus. We then measured the onset latency and strength of vection induced by a radially expanding pattern of optic flow. The results showed that walking without optic flow transiently yielded later vection onsets and reduced vection strength. We propose that walking without optic flow triggered a sensory readjustment, which reduced the ability of optic flow to induce self-motion perception.

Spontaneous postural sway predicts the strength of smooth vection.

This study asked whether individual differences in the influence of vision on postural stability could be used to predict the strength of subsequently induced visual illusions of self-motion (vection). In the experiment, we first measured spontaneous postural sway while subjects stood erect for 60 s with their eyes both open and both closed. We then showed our subjects two types of self-motion display: radially expanding optic flow (simulating constant velocity forwards self-motion) and vertically oscillating radially expanding optic flow (simulating constant velocity forwards self-motion combined with vertical head oscillation). As expected, subjects swayed more with their eyes closed (compared to open) and experienced more compelling illusions of self-motion with vertically oscillating (as opposed to smooth) radial flow. The extent to which participants relied on vision for postural stability-measured as the ratio of sway with eyes closed compared to that with eyes open-was found to predict vection strength. However, this was only the case for displays representing smooth self-motion. It seems that for oscillating displays, other factors, such as visual-vestibular interactions, may be more important.

Illusory self-motion (vection) may be inhibited by hypobaric hypoxia.

INTRODUCTION: Previous reports have shown that higher altitudes can alter human perception. We add further evidence to this claim, describing a new finding in which higher altitudes inhibit the perception of illusory self-motion, i.e., vection. METHOD: We compared vection strength under both normal and high altitude (hypobaric hypoxia) conditions. In the high altitude condition, atmospheric pressure in the climatic chamber was decreased to 13,123 ft (4000 m; 492 ft/150 m x min(-1)) for 28 min and then maintained at the 13,123-ft (4000-m) level for 30 min by a preprogrammed operation. Vection was induced by an optic flow stimulus. RESULTS: Significant differences were observed between the normal and high altitude conditions for all three of the vection strength measurements (latency, duration, and magnitude). Vection was decreased by 14.6%, and Spo2 was decreased by 16.7% in the hypoxia condition. CONCLUSION: Vection was inhibited in the high altitude condition. Applications of this finding include informing aircraft pilots of this effect of self-motion perception inhibition at higher altitudes to promote safer flying.

Illusory motion and vection induced by a printed static image under flickering ambient light at rates up to 100†Hz.

Visual motion signals can produce self-motion perception known as vection in observers. Vection can be generated by illusory motions in the form of global expantion in still images as well as by visual motion signals. The perception of vection can be enhanced by flickering images at a rate of 5 Hz. This study examined the illusory motion and vection induced by a printed static image under flickering ambient light at rates up to 100 Hz. The perception of illusory motion and vection were enhanced by flickering ambient lights at 50, 75, and 100 Hz. The enhancement effect was higher for the flicker rates expected to be detectable by humans. The findings of this study suggest that alternating bright and dark signals to the cone receptors and primary visual cortex trigger perceptions of illusory motions.

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).

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.

The Effects of Bilateral and Ipsilateral Auditory Stimuli on the Subcomponents of Visual Attention.

Attention contains three functional network subcomponents of alerting, orienting, and executive control. The attention network test (ANT) is usually used to measure the efficiency of three attention subcomponents. Previous researches have focused on examining the unimodal attention with visual or auditory ANT paradigms. However, it is still unclear how an auditory stimulus influences the visual attention networks. This study investigated the effects of bilateral auditory stimuli (Experiment 1) and ipsilateral auditory stimulus (Experiment 2) on the visual attention subcomponents. We employed an ANT paradigm and manipulated the target modality types, including visual and audiovisual modalities. The participants were instructed to distinguish the direction of the central arrow surrounded by distractor arrows. In Experiment 1, we found that the simultaneous bilateral auditory stimuli reduced the efficiency of visual alerting and orienting, but had no significant effect on the efficiency of visual executive control. In Experiment 2, the ipsilateral auditory stimulus reduced the efficiency of visual executive control, but had no significant effect on the efficiency of visual alerting and orienting. We also observed a reduced relative multisensory response enhancement (rMRE) effect in cue condition relative to no cue condition (Experiment 1), and an increased rMRE effect in congruent condition compared with incongruent condition (Experiment 2). These results firstly provide evidence for the alerting, orienting and executive control effects in audiovisual condition. And the bilateral and ipsilateral auditory stimuli have different effects on the subcomponents of visual attention.

The Effect of Optical Flow Motion Direction on Vection Strength.

In some phenomena of visual perception, the motion direction of visual stimuli can affect perception. In particular, asymmetries between oblique directions and cardinal (horizontal and vertical) directions have been reported and are known as oblique effects (e.g., contrast sensitivity and motion threshold). In this study, we investigated how vection strength depends on motion direction. Participants observed random-dot optical flow in a circular field and rated the perceived vection strength. Dot movement was systematically controlled using the following angles: 0° (up), 30°, 45°, 60°, 90°, 120°, 135°, 150°, and 180° (down). We found that vection strength depended on motion direction and was weaker in the oblique directions than cardinal directions. Thus, the effect of motion direction on vection strength was variable, as seen in the shape of the oblique effect.

Differences in Three Vection Indices (Latency, Duration, and Magnitude) Induced by "Camera-Moving" and "Object-Moving" in a Virtual Computer Graphics World, Despite Similarity in the Retinal Images.

To create a self-motion (vection) situation in three-dimensional computer graphics (CG), there are mainly two ways: moving a camera toward an object ("camera moving") or by moving the object and its surrounding environment toward the camera ("object moving"). As both methods vary considerably in the amount of computer calculations involved in generating CG, knowing how each method affects self-motion perception should be important to CG-creators and psychologists. Here, we simulated self-motion in a virtual three-dimensional CG-world, without stereoscopic disparity, which correctly reflected the lighting and glare. Self-motion was induced by "camera moving" or by "object moving," which in the present experiments was done by moving a tunnel surrounding the camera toward the camera. This produced two retinal images that were virtually identical in Experiment 1 and very similar in Experiments 2 and 3. The stimuli were presented on a large plasma display to 15 naive participants and induced substantial vection. Three experiments comparing vection strength between the two methods found weak but significant differences. The results suggest that when creating CG visual experiences, "camera-moving" induces stronger vection.

Positional and directional preponderances in vection.

We examined the biases in vection strength caused by motion direction (temporonasal vs. nasotemporal motion) and position of stimulus presentation (nasal and temporal semi-retinas) to investigate a subcortical contribution to vection. These biases have been identified for optokinetic nystagmus (OKN) and are acknowledged as evidence for a subcortical origin of OKN. In experiments, subjects monocularly observed hemi-field motion stimuli and made magnitude estimations. The results indicated significant directional and positional biases when luminance modulated gratings were used as stimuli. Vection was stronger with nasotemporal motions and nasal retina presentations, but there were no interactions between the two factors. However, these biases disappeared for second-order motion stimuli (contrast modulation), which are presumably processed by the cortex. In addition, when subjects were asked to make subjective ratings of motion impression, there was no significant difference in subjective strength between the stimuli that induced the strongest vection and weakest vection. These results, together, suggest the involvement of the subcortical pathway in vection induction.

Development of Asymmetric Vection for Radial Expansion or Contraction Motion: Comparison Between School-Age Children and Adults.

Vection is illusory self-motion elicited by visual stimuli and is more easily induced by radial contraction than expansion flow in adults. The asymmetric feature of vection was reexamined with 18 younger (age: 6-8 years) and 19 older children (age: 9-11 years) and 20 adults. In each experimental trial, participants observed either radial expansion or contraction flow; the latency, cumulative duration, and saturation of vection were measured. The results indicated that the latency for contraction was significantly shorter than that for expansion in all age-groups. In addition, the latency and saturation were significantly shorter and greater, respectively, in the younger or older children compared with the adults, regardless of the flow pattern. These results indicate that the asymmetry in vection for expansion or contraction flow emerges by school age, and that school-age children experience significantly more rapid and stronger vection than adults.