Enhanced human contrast sensitivity with increased stimulation of melanopsin in intrinsically photosensitive retinal ganglion cells.

The intrinsically photosensitive retinal ganglion cells (ipRGCs) are known to serve non-image-forming functions, such as photoentrainment of the circadian rhythm and pupillary light reflex. However, how they affect human spatial vision is largely unknown. The spatial contrast sensitivity function (CSF), which measures contrast sensitivity as a function of spatial frequency, was used in the current study to investigate the function of ipRGCs in pattern vision. To compare the effects of different background lights on the CSF, we utilized the silent substitution technique. We manipulated the stimulation level of melanopsin (i.e., the visual pigment of ipRGCs) from the background light while keeping the cone stimulations constant, or vice versa. We conducted four experiments to measure the CSFs at various spatial frequencies, eccentricities, and levels of background luminance. Results showed that melanopsin stimulation from the background light enhances spatial contrast sensitivity across different eccentricities and luminance levels. Our finding that melanopsin contributes to CSF, combined with the receptive field analysis, suggests a role for the magnocellular pathway and challenges the conventional view that ipRGCs are primarily responsible for non-visual functions.

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.

The modulation of background color on perceiving audiovisual simultaneity.

Perceiving simultaneity is critical in integrating visual and auditory signals that give rise to a unified perception. We examined whether background color modulates people's perception of audiovisual simultaneity. Two hypotheses were proposed and examined: (1) the red-impairment hypothesis: visual processing speed deteriorates when viewing a red background because the magnocellular system is inhibited by red light; and (2) the blue-enhancement hypothesis: the detection of both visual and auditory signals is enhanced when viewing a blue background because it stimulates the blue-light sensitive intrinsically photosensitive retinal ganglion cells (ipRGCs), which trigger a higher alert state. Participants were exposed to different backgrounds while performing an audiovisual simultaneity judgment (SJ) task: a flash and a beep were presented at pre-designated stimulus onset asynchronies (SOAs) and participants judged whether or not the two stimuli were presented simultaneously. Experiment 1 demonstrated a shift of the point of subjective simultaneity (PSS) toward the visual-leading condition in the red compared to the blue background when the flash was presented in the periphery. In Experiment 2, the stimulation of ipRGCs was specifically manipulated to test the blue-enhancement hypothesis. The results showed no support for this hypothesis, perhaps due to top-down cortical modulations. Taken together, the shift of PSS toward the visual-leading condition in the red background was attributed to impaired visual processing speed with respect to auditory processing speed, caused by the inhibition of the magnocellular system under red light.

An intrinsic algorithm for viewing angle tolerance of object discrimination in human subjects.

Prevailing theories suggest that view-invariant object recognition is accomplished via spatiotemporal correlations of multiple views that bind different views to the same object. However, it is unknown how the exposure to multiple views without association affects view-invariant recognition generating. Behavioural studies have shown that monkeys acquired view-invariant object recognition capability in a range of the viewing angles of 30° to 60° after experiencing discrimination of similar objects at each of several viewing angles without associating different views, but the monkeys could not discriminate novel objects from similar distractors when the viewing angle changed. In the present study the development of the view invariance was tested in the human subjects and compared with the results of the monkeys previously reported. The view-invariant object recognition capability of human subjects was tested using either familiar objects that the subjects experienced in a preparatory object discrimination task at the same viewpoints or novel objects that the subjects had never experienced. In the viewing angle range of 30°, human subjects showed significant object discrimination capability across views, with no need for prior experience of the objects. Prior discrimination experience within the same viewpoints endowed the human subjects with broadening of the viewing angle tuning, because an object discrimination test immediately after the prior discrimination experience at a single view showed wider viewing angle tuning than a test without prior experience. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

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.

Subjective time expansion with increased stimulation of intrinsically photosensitive retinal ganglion cells.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) contain photoreceptors that are especially sensitive to blue light. Nevertheless, how blue light and ipRGCs affect time perception remains unsolved. We used the oddball paradigm and manipulated the background light to examine whether and how blue light and ipRGCs affect perceived duration. In the oddball paradigm, participants were asked to judge the duration of the target (oddball), compared to that of the standard, with a two alternative-forced-choice procedure. When the background light was controlled to be either blue or red in Experiment 1, results showed that blue light led to longer subjective duration compared to red light. Experiment 2 further clarified the contribution of the ipRGCs. A set of multi-primary projector system that could manipulate the ipRGC stimulation were used, while the color and luminance of the background lights were kept constant throughout. Results showed that increased stimulation of ipRGCs under metameric background expanded subjective time. These results suggest that ipRGC stimulation increases arousal/attention so as to expand subjective duration.

Crossmodal association of auditory and visual material properties in infants.

The human perceptual system enables us to extract visual properties of an object's material from auditory information. In monkeys, the neural basis underlying such multisensory association develops through experience of exposure to a material; material information could be processed in the posterior inferior temporal cortex, progressively from the high-order visual areas. In humans, however, the development of this neural representation remains poorly understood. Here, we demonstrated for the first time the presence of a mapping of the auditory material property with visual material ("Metal" and "Wood") in the right temporal region in preverbal 4- to 8-month-old infants, using near-infrared spectroscopy (NIRS). Furthermore, we found that infants acquired the audio-visual mapping for a property of the "Metal" material later than for the "Wood" material, since infants form the visual property of "Metal" material after approximately 6 months of age. These findings indicate that multisensory processing of material information induces the activation of brain areas related to sound symbolism. Our findings also indicate that the material's familiarity might facilitate the development of multisensory processing during the first year of life.

Three-quarter view preference for three-dimensional objects in 8-month-old infants.

This study examined infants' visual perception of three-dimensional common objects. It has been reported that human adults perceive object images in a view-dependent manner: three-quarter views are often preferred to other views, and the sensitivity to object orientation is lower for three-quarter views than for other views. We tested whether such characteristics were observed in 6- to 8-month-old infants by measuring their preferential looking behavior. In Experiment 1 we examined 190- to 240-day-olds' sensitivity to orientation change and in Experiment 2 we examined these infants' preferential looking for the three-quarter view. The 240-day-old infants showed a pattern of results similar to adults for some objects, while the 190-day-old infants did not. The 240-day-old infants' perception of object view is (partly) similar to that of adults. These results suggest that human visual perception of three-dimensional objects develops at 6 to 8 months of age.

Tolerance of geometric distortions in infant's face recognition.

The aim of the current study is to reveal the effect of global linear transformations (shearing, horizontal stretching, and vertical stretching) on the recognition of familiar faces (e.g., a mother's face) in 6- to 7-month-old infants. In this experiment, we applied the global linear transformations to both the infants' own mother's face and to a stranger's face, and we tested infants' preference between these faces. We found that only 7-month-old infants maintained preference for their own mother's face during the presentation of vertical stretching, while the preference for the mother's face disappeared during the presentation of shearing or horizontal stretching. These findings suggest that 7-month-old infants might not recognize faces based on calculating the absolute distance between facial features, and that the vertical dimension of facial features might be more related to infants' face recognition rather than the horizontal dimension.

The effect of gaze direction on three-dimensional face recognition in infants.

Eye gaze is an important tool for social contact. In this study, we investigated whether direct gaze facilitates the recognition of three-dimensional face images in infants. We presented artificially produced face images in rotation to 6-8 month-old infants. The eye gaze of the face images was either direct or averted. Sixty-one sequential images of each face were created by rotating the vertical axis of the face from frontal view to ± 30°. The recognition performances of the infants were then compared between faces with direct gaze and faces with averted gaze. Infants showed evidence that they were able to discriminate the novel from familiarized face by 8 months of age and only when gaze is direct. These results suggest that gaze direction may affect three-dimensional face recognition in infants.

The effect of gaze direction on three-dimensional face recognition in infant brain activity.

In three-dimensional face recognition studies, it is well known that viewing rotating faces enhance face recognition. For infants, our previous study indicated that 8-month-old infants showed recognition of three-dimensional rotating faces with a direct gaze, and they did not learn with an averted gaze. This suggests that gaze direction may affect three-dimensional face recognition in infants. In this experiment, we used near-infrared spectroscopy to measure infants' hemodynamic responses to averted gaze and direct gaze. We hypothesized that infants would show different neural activity for averted and direct gazes. The responses were compared with the baseline activation during the presentation of non-face objects. We found that the concentration of oxyhemoglobin increased in the temporal cortex on both sides only during the presentation of averted gaze compared with that of the baseline period. This is the first study to show that infants' brain activity in three-dimensional face processing is different between averted gaze and direct gaze.

Infant learning ability for recognizing artificially produced three-dimensional faces and objects.

This study investigated infants' ability to learn artificially produced three-dimensional faces and non-face objects by using the three-dimensional graphic software. We created three-dimensional faces and non-face objects that contained no texture or fixed light source and used a familiarization-novelty preference procedure to familiarize infants with multiple views of a face or a shoe (non-face object). We set two familiarization presentations: one of sequentially rotating images of a single object (rotating presentation) and another of 6 different static view images (static presentation). After familiarization, we checked infants' recognition of the learning objects between these conditions. In Experiment 1, we examined the infants' ability to learn face and non-face objects in static and rotating presentations. Results showed that 6- to 8-month-old infants could learn the non-face objects in both presentations, while they could not learn the faces in the rotating presentation. In Experiments 2 and 3, we modified the rotating presentation for face learning. In Experiment 2, we used three-quarter views at test. In Experiment 3, we set a slower speed rotation. However, the infants still could not learn the faces. These results showed that infants' ability to learn faces differs from their ability to learn non-face objects.

View-invariant object recognition ability develops after discrimination, not mere exposure, at several viewing angles.

One usually fails to recognize an unfamiliar object across changes in viewing angle when it has to be discriminated from similar distractor objects. Previous work has demonstrated that after long-term experience in discriminating among a set of objects seen from the same viewing angle, immediate recognition of the objects across 30-60 degrees changes in viewing angle becomes possible. The capability for view-invariant object recognition should develop during the within-viewing-angle discrimination, which includes two kinds of experience: seeing individual views and discriminating among the objects. The aim of the present study was to determine the relative contribution of each factor to the development of view-invariant object recognition capability. Monkeys were first extensively trained in a task that required view-invariant object recognition (Object task) with several sets of objects. The animals were then exposed to a new set of objects over 26 days in one of two preparatory tasks: one in which each object view was seen individually, and a second that required discrimination among the objects at each of four viewing angles. After the preparatory period, we measured the monkeys' ability to recognize the objects across changes in viewing angle, by introducing the object set to the Object task. Results indicated significant view-invariant recognition after the second but not first preparatory task. These results suggest that discrimination of objects from distractors at each of several viewing angles is required for the development of view-invariant recognition of the objects when the distractors are similar to the objects.

Prior experience of rotation is not required for recognizing objects seen from different angles.

An object viewed from different angles can be recognized and distinguished from similar distractors after the viewer has had experience watching it rotate. It has been assumed that as an observer watches the rotation, separate representations of individual views become associated with one another. However, we show here that once monkeys learned to discriminate individual views of objects, they were able to recognize objects across rotations up to 60 degrees , even though there had been no opportunity to learn the association between different views. Our results suggest that object recognition across small or medium changes in viewing angle depends on features common to similar views of objects.