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.

The zooming-speed illusion: A meta illusion?

A movie taken from the front window of a running train, with zooming in and out, has been popularly acknowledged as a perceptual illusion such that the train motion is perceived as much slower when zoomed in. This is, however, not a real illusion because the image speed varies as a function of the focal length of the lens. This could be a meta-illusion, that is, an illusory sense of illusion, that might reflect a lack of understanding of how zooming changes the geometrical structure of the image.

Illu-Shoal Choice: An Exploration of Different Means for Enrichment of Captive Zebrafish.

Fish of any variety are nowadays being kept captive for several purposes, from recreational to alimentary to research. It is possible that we humans often underestimate or misunderstand the basic, natural needs of the species we use for our purposes. Sociality is likely to play an extensive and fundamental role in the quality of life of animals such as zebrafish. This study aimed to develop a dummy conspecific that included depth and motion illusions in order to assess whether these stimuli could represent a valid alternative to a conspecific in triggering shoaling behaviour in a well-known model in genetics and neuroscience, the zebrafish (Dario rerio). We thus replaced the natural livery of a zebrafish shape with three visual illusions: the Ouchi-Spillmann illusion, which generates an effect of local tilting motion; and another two which should create pictorial cues of tridimensionality. Via a binary shoal choice test, we assessed the time spent close to each of the three artificial dummies compared to neutral control stimuli such as grey ellipses. We found no preference for the illusory patterns, suggesting that the illusion was not perceived or, alternatively, that the perception of the illusion was not enough to elicit recognition of the dummy as conspecific and subsequent social behaviours.

Simple Assumptions to Improve Markov Illuminance and Reflectance.

Murray recently introduced a novel computational lightness model, Markov illuminance and reflectance (MIR). MIR is a promising new approach that simulates human lightness processing using a conditional random field (CRF) where natural-scene statistics of reflectance and illumination are implemented. Although MIR can account for various lightness illusions and phenomena, it has limitations, such as the inability to predict reverse-contrast phenomena. In this study, we improved MIR performance by modifying its inference process, the prior on X-junctions, and that on general illumination changes. Our modified model improved predictions for Checkerboard assimilation, the simplified Checkershadow and its control figure, the influence of luminance noise, and White's effect and its several variants. In particular, White's effect is a partial reverse contrast that is challenging for computational models, so this improvement is a significant advance for the MIR framework. This study showed the high extensibility and potential of MIR, which shows the promise for further sophistication.

The Eye Pupil Adjusts to Illusorily Expanding Holes.

Some static patterns evoke the perception of an illusory expanding central region or "hole." We asked observers to rate the magnitudes of illusory motion or expansion of black holes, and these predicted the degree of dilation of the pupil, measured with an eye tracker. In contrast, when the "holes" were colored (including white), i.e., emitted light, these patterns constricted the pupils, but the subjective expansions were also weaker compared with the black holes. The change rates of pupil diameters were significantly related to the illusory motion phenomenology only with the black holes. These findings can be accounted for within a perceiving-the-present account of visual illusions, where both the illusory motion and the pupillary adjustments represent compensatory mechanisms to the perception of the next moment, based on shared experiences with the ecological regularities of light.

Motion illusion-like patterns extracted from photo and art images using predictive deep neural networks.

In our previous study, we successfully reproduced the illusory motion perceived in the rotating snakes illusion using deep neural networks incorporating predictive coding theory. In the present study, we further examined the properties of the network using a set of 1500 images, including ordinary static images of paintings and photographs and images of various types of motion illusions. Results showed that the networks clearly classified a group of illusory images and others and reproduced illusory motions against various types of illusions similar to human perception. Notably, the networks occasionally detected anomalous motion vectors, even in ordinally static images where humans were unable to perceive any illusory motion. Additionally, illusion-like designs with repeating patterns were generated using areas where anomalous vectors were detected, and psychophysical experiments were conducted, in which illusory motion perception in the generated designs was detected. The observed inaccuracy of the networks will provide useful information for further understanding information processing associated with human vision.

Cross-modal size-contrast illusion: Acoustic increases in intensity and bandwidth modulate haptic representation of object size.

Changes in the retinal size of stationary objects provide a cue to the observer's motion in the environment: Increases indicate the observer's forward motion, and decreases backward motion. In this study, a series of images each comprising a pair of pine-tree figures were translated into auditory modality using sensory substitution software. Resulting auditory stimuli were presented in an ascending sequence (i.e. increasing in intensity and bandwidth compatible with forward motion), descending sequence (i.e. decreasing in intensity and bandwidth compatible with backward motion), or in a scrambled order. During the presentation of stimuli, blindfolded participants estimated the lengths of wooden sticks by haptics. Results showed that those exposed to the stimuli compatible with forward motion underestimated the lengths of the sticks. This consistent underestimation may share some aspects with visual size-contrast effects such as the Ebbinghaus illusion. In contrast, participants in the other two conditions did not show such magnitude of error in size estimation; which is consistent with the "adaptive perceptual bias" towards acoustic increases in intensity and bandwidth. In sum, we report a novel cross-modal size-contrast illusion, which reveals that auditory motion cues compatible with listeners' forward motion modulate haptic representations of object size.

Reversed Phi and the "Phenomenal Phenomena" Revisited.

Reversed apparent motion (or reversed phi) can be seen during a continuous dissolve between a positive and a spatially shifted negative version of the same image. Similar reversed effects can be seen in stereo when positive and spatially shifted negative images are presented separately to the two eyes or in a Vernier alignment task when the two images are juxtaposed one above the other. Gregory and Heard reported similar effects that they called "phenomenal phenomena." Here, we investigate the similarities between these different effects and put forward a simple, spatial-smoothing explanation that can account for both the direction and magnitude of the reversed effects in the motion, stereo and Vernier domains. In addition, we consider whether the striking motion effects seen when viewing Kitaoka's colour-dependent Fraser-Wilcox figures are related to the reversed phi illusion, given the similarity of the luminance profiles.

Blindness to Curvature and Blindness to Illusory Curvature.

We compare two versions of two known phenomena, the Curvature blindness and the Kite mesh illusions, to highlight how similar manipulations lead to blindness to curvature and blindness to illusory curvature, respectively. The critical factor is a change in luminance polarity; this factor interferes with the computation of curvature along the contour, for both real and illusory curvature.

Illusory Motion Reproduced by Deep Neural Networks Trained for Prediction.

The cerebral cortex predicts visual motion to adapt human behavior to surrounding objects moving in real time. Although the underlying mechanisms are still unknown, predictive coding is one of the leading theories. Predictive coding assumes that the brain's internal models (which are acquired through learning) predict the visual world at all times and that errors between the prediction and the actual sensory input further refine the internal models. In the past year, deep neural networks based on predictive coding were reported for a video prediction machine called PredNet. If the theory substantially reproduces the visual information processing of the cerebral cortex, then PredNet can be expected to represent the human visual perception of motion. In this study, PredNet was trained with natural scene videos of the self-motion of the viewer, and the motion prediction ability of the obtained computer model was verified using unlearned videos. We found that the computer model accurately predicted the magnitude and direction of motion of a rotating propeller in unlearned videos. Surprisingly, it also represented the rotational motion for illusion images that were not moving physically, much like human visual perception. While the trained network accurately reproduced the direction of illusory rotation, it did not detect motion components in negative control pictures wherein people do not perceive illusory motion. This research supports the exciting idea that the mechanism assumed by the predictive coding theory is one of basis of motion illusion generation. Using sensory illusions as indicators of human perception, deep neural networks are expected to contribute significantly to the development of brain research.

Kitaoka's Tomato: Two Simple Explanations Based on Information in the Stimulus.

Kitaoka's Tomato is a color illusion in which a semitransparent blue-green field is placed on top of a red object (a tomato). The tomato appears red even though the pixels would appear green if viewed in isolation. We show that this phenomenon can be explained by a high-pass filter and by histogram equalization. The results suggest that this illusion does not require complex inferences about color constancy; rather, the tomato's red is available in the physical stimulus at the appropriate spatial scale and dynamic range.

The "Spinner" Illusion: More Dots, More Speed?

The perceived speed of a ring of equally spaced dots moving around a circular path appears faster as the number of dots increases (Ho & Anstis, 2013, Best Illusion of the Year contest). We measured this "spinner" effect with radial sinusoidal gratings, using a 2AFC procedure where participants selected the faster one between two briefly presented gratings of different spatial frequencies (SFs) rotating at various angular speeds. Compared with the reference stimulus with 4 c/rev (0.64 c/rad), participants consistently overestimated the angular speed for test stimuli of higher radial SFs but underestimated that for a test stimulus of lower radial SFs. The spinner effect increased in magnitude but saturated rapidly as the test radial SF increased. Similar effects were observed with translating linear sinusoidal gratings of different SFs. Our results support the idea that human speed perception is biased by temporal frequency, which physically goes up as SF increases when the speed is held constant. Hence, the more dots or lines, the greater the perceived speed when they are moving coherently in a defined area.

Second-Order Footsteps Illusions.

In the "footsteps illusion", light and dark squares travel at constant speed across black and white stripes. The squares appear to move faster and slower as their contrast against the stripes varies. We now demonstrate some second-order footsteps illusions, in which all edges are defined by colors or textures-even though luminance-based neural motion detectors are blind to such edges.

Color-dependent motion illusions in stationary images and their phenomenal dimorphism.

The color-dependent motion illusion in stationary images--a special type of the Fraser-Wilcox illusion--is introduced and discussed. The direction of illusory motion changes depending on whether the image is of high or low luminance and whether the room is bright or dark. This dimorphism of illusion was confirmed by surveys. It is suggested that two different spatial arrangements of color can produce the motion illusion. One is a spatial arrangement where long- and short-wavelength color regions sandwich a darker strip; the other is where the same color regions sandwich a brighter strip.

Infants see illusory motion in static figures.

We investigated illusory motion perception in 6-to-8-month-old infants using a static figure which produces strong illusory motion. In experiment 1 we prepared a control figure, which was physically similar to the illusory motion figure but which did not produce illusory motion. We presented the illusory figure and the control figure side-by-side, and measured infants' looking time at the target illusory figure. Results showed that the infants' looking time at the illusory figure was significantly longer than that for the control. In experiment 2 we made another set of stimuli consisting of the same local pattern used in experiment 1, but which did not produce illusory motion. The results showed that no preferences were observed in experiment 2. These results suggest that 6-to-8-month-old infants perceive illusory motion in static figures.

Vection induced by illusory motion in a stationary image.

Ilusory self-motion (vection) can be induced by large areas of visual motion stimulation. Here we demonstrate for the first time that illusory expansion can induce vection in the absence of any physical display motion.

Anomalous motion illusion contributes to visual preference.

This study investigated the relationship between the magnitude of illusory motion in the variants of the "Rotating Snakes" pattern and the visual preference among such patterns. In Experiment 1 we manipulated the outer contour and the internal geometrical structure of the figure to test for corresponding modulations in the perceived illusion magnitude. The strength of illusory motion was estimated by the method of adjustment where the speed of a standard moving figure was matched to the speed of the perceived illusory motion in test figures. We observed modulation of the perceived strength of illusory motion congruent with our geometrical manipulations. In Experiment 2, we directly compared the magnitude of the perceived illusory motion and the preference for these patterns by a method of paired comparison. Images differing in illusion magnitude showed corresponding differences in the reported preference for these patterns. In addition, further analysis revealed that the geometry and lower level image characteristics also substantially contributed to the observed preference ratings. Together these results support the idea that presence of illusory effect and geometrical characteristics determine affective preference for images, as they may be regarded as more interesting, surprising, or fascinating.

Evidence for a size underestimation of upright faces.

We quantitatively examined the difference in perceived size between upright and inverted faces using the method of constant stimuli. The stimuli included eight face images modified from two cartoon faces produced by Kitaoka (2007, http://www.psy.ritsumei.ac.jp/-akitaoka/kao-e.html and 2008, Cognitive Psychology 5 177-185) and six photographic faces, including a photographic face used by Thompson (2010, http://illusionncontest.neuralcorrelate.com/2010/the-fat-face-thin-fft-ilusion/). Experiment 1 showed that an upright face and outline were perceived to be significantly smaller than an inverted face and outline, respectively. Moreover, the amount of the size underestimation in the face stimulus condition was significantly larger than that in the outline stimulus condition. Experiment 2 showed that an upright face was perceived to be significantly smaller than 90 degrees and 270 degrees rotated faces, whereas an inverted face was not perceived to be significantly larger than a 90 degrees or 270 degrees rotated face. Experiment 3 showed that upright faces were perceived to be significantly smaller than upright and inverted outlines, whereas inverted faces were not perceived to be significantly larger than upright or inverted outlines. Experiments 4 and 5 showed that upright photographic faces were also perceived to be significantly smaller than inverted photographic faces. These results provide quantitative evidence for a size underestimation of upright faces.

Aesthetic valence of visual illusions.

Visual illusions constitute an interesting perceptual phenomenon, but they also have an aesthetic and affective dimension. We hypothesized that the illusive nature itself causes the increased aesthetic and affective valence of illusions compared with their non-illusory counterparts. We created pairs of stimuli. One qualified as a standard visual illusion whereas the other one did not, although they were matched in as many perceptual dimensions as possible. The phenomenal quality of being an illusion had significant effects on "Aesthetic Experience" (fascinating, irresistible, exceptional, etc), "Evaluation" (pleasant, cheerful, clear, bright, etc), "Arousal" (interesting, imaginative, complex, diverse, etc), and "Regularity" (balanced, coherent, clear, realistic, etc). A subsequent multiple regression analysis suggested that Arousal was a better predictor of Aesthetic Experience than Evaluation. The findings of this study demonstrate that illusion is a phenomenal quality of the percept which has measurable aesthetic and affective valence.

Neural correlates of induced motion perception in the human brain.

A physically stationary stimulus surrounded by a moving stimulus appears to move in the opposite direction. There are similarities between the characteristics of this phenomenon of induced motion and surround suppression of directionally selective neurons in the brain. Here, functional magnetic resonance imaging was used to investigate the link between the subjective perception of induced motion and cortical activity. The visual stimuli consisted of a central drifting sinusoid surrounded by a moving random-dot pattern. The change in cortical activity in response to changes in speed and direction of the central stimulus was measured. The human cortical area hMT+ showed the greatest activation when the central stimulus moved at a fast speed in the direction opposite to that of the surround. More importantly, the activity in this area was the lowest when the central stimulus moved in the same direction as the surround and at a speed such that the central stimulus appeared to be stationary. The results indicate that the activity in hMT+ is related to perceived speed modulated by induced motion rather than to physical speed or a kinetic boundary. Early visual areas (V1, V2, V3, and V3A) showed a similar pattern; however, the relationship to perceived speed was not as clear as that in hMT+. These results suggest that hMT+ may be a neural correlate of induced motion perception and play an important role in contrasting motion signals in relation to their surrounding context and adaptively modulating our motion perception depending on the spatial context.