Pupillary fluctuation amplitude preceding target presentation is linked to the variable foreperiod effect on reaction time in Psychomotor Vigilance Tasks.

Understanding temporally attention fluctuations can benefit scientific knowledge and real-life applications. Temporal attention studies have typically used the reaction time (RT), which can be measured only after a target presentation, as an index of attention level. We have proposed the Micro-Pupillary Unrest Index (M-PUI) based on pupillary fluctuation amplitude to estimate RT before the target presentation. However, the kind of temporal attention effects that the M-PUI reflects remains unclear. We examined if the M-PUI shows two types of temporal attention effects initially reported for RTs in the variable foreperiod tasks: the variable foreperiod effect (FP effect) and the sequential effect (SE effect). The FP effect refers to a decrease in the RT due to an increase in the foreperiod of the current trial, whereas the SE effect refers to an increase in the RT in the early part of the foreperiod of the current trial due to an increase in the foreperiod of the previous trial. We used a simple reaction task with the medium-term variable foreperiods (Psychomotor Vigilance Task) and found that the M-PUI primarily reflects the FP effect. Inter-individual analyses showed that the FP effect on the M-PUI, unlike other eye movement indices, is correlated with the FP effect on RT. These results suggest that the M-PUI is a potentially powerful tool for investigating temporal attention fluctuations for a partly unpredictable target.

The structure of the superior and inferior parietal lobes predicts inter-individual suitability for virtual reality.

The global virtual reality (VR) market is significantly expanding and being challenged with an increased demand owing to COVID-19. Unfortunately, VR is not useful for everyone due to large interindividual variability existing in VR suitability. To understand the neurobiological basis of this variability, we obtained neural structural and functional data from the participants using 3T magnetic resonance imaging. The participants completed one of two tasks (sports training or cognitive task) using VR, which differed in the time scale (months/minutes) and domain (motor learning/attention task). Behavioral results showed that some participants improved their motor skills in the real world after 1-month training in the virtual space or obtained high scores in the 3D attention task (high suitability for VR), whereas others did not (low suitability for VR). Brain structure analysis revealed that the structural properties of the superior and inferior parietal lobes contain information that can predict an individual's suitability for VR.

Pupillary fluctuation amplitude before target presentation reflects short-term vigilance level in Psychomotor Vigilance Tasks.

Our daily activities require vigilance. Therefore, it is useful to externally monitor and predict our vigilance level using a straightforward method. It is known that the vigilance level is linked to pupillary fluctuations via Locus Coeruleus and Norepinephrine (LC-NE) system. However, previous methods of estimating long-term vigilance require monitoring pupillary fluctuations at rest over a long period. We developed a method of predicting the short-term vigilance level by monitoring pupillary fluctuation for a shorter period consisting of several seconds. The LC activity also fluctuates at a timescale of seconds. Therefore, we hypothesized that the short-term vigilance level could be estimated using pupillary fluctuations in a short period and quantified their amplitude as the Micro-Pupillary Unrest Index (M-PUI). We found an intra-individual trial-by-trial positive correlation between Reaction Time (RT) reflecting the short-term vigilance level and M-PUI in the period immediately before the target onset in a Psychomotor Vigilance Task (PVT). This relationship was most evident when the fluctuation was smoothed by a Hanning window of approximately 50 to 100 ms (including cases of down-sampled data at 100 and 50 Hz), and M-PUI was calculated in the period up to one or two seconds before the target onset. These results suggest that M-PUI can monitor and predict fluctuating levels of vigilance. M-PUI is also useful for examining pupillary fluctuations in a short period for elucidating the psychophysiological mechanisms of short-term vigilance.

"Textual Prosody" Can Change Impressions of Reading in People With Normal Hearing and Hearing Loss.

Recently, dynamic text presentation, such as scrolling text, has been widely used. Texts are often presented at constant timing and speed in conventional dynamic text presentation. However, dynamic text presentation enables visually presented texts to indicate timing information, such as prosody, and the texts might influence the impression of reading. In this paper, we examined this possibility by focusing on the temporal features of digital text in which texts are represented sequentially and with varying speed, duration, and timing. We call this "textual prosody." We used three types of textual prosody: "Recorded," "Shuffled," and "Constant." Recorded prosody is the reproduction of a reader's reading with pauses and varying speed that simulates talking. Shuffled prosody randomly shuffles the time course of speed and pauses in the recorded type. Constant prosody has a constant presentation speed and provides no timing information. Experiment 1 examined the effect of textual prosody on people with normal hearing. Participants read dynamic text with textual prosody silently and rated their impressions of texts. The results showed that readers with normal hearing preferred recorded textual prosody and constant prosody at the optimum speed (6 letters/second). Recorded prosody was also preferred at a low presentation speed. Experiment 2 examined the characteristics of textual prosody using an articulatory suppression paradigm. The results showed that some textual prosody was stored in the articulatory loop despite it being presented visually. In Experiment 3, we examined the effect of textual prosody with readers with hearing loss. The results demonstrated that readers with hearing loss had positive impressions at relatively low presentation speeds when the recorded prosody was presented. The results of this study indicate that the temporal structure is processed regardless of whether the input is visual or auditory. Moreover, these results suggest that textual prosody can enrich reading not only in people with normal hearing but also in those with hearing loss, regardless of acoustic experiences.

Reading Traits for Dynamically Presented Texts: Comparison of the Optimum Reading Rates of Dynamic Text Presentation and the Reading Rates of Static Text Presentation.

With the growth in digital display technologies, dynamic text presentation is used widely in every day life, such as in electric advertisements and tickers on TV programs. Unlike static text reading, little is known about the basic characteristics underlying reading dynamically presented texts. Two experiments were performed to investigate this. Experiment 1 examined the optimum rate of dynamic text presentation in terms of a readability and favorability. This experiment demonstrated that, when the rate of text presentation was changed, there was an optimum presentation rate (around 6 letters/s in our condition) regardless of difficulty level. This indicates that the presentation rate of dynamic texts can affect the impression of reading. In Experiment 2, to elucidate the traits underlying dynamic text reading, we measured the reading speeds of silent and trace reading among the same participants and compared them with the optimum presentation rate obtained in Experiment 1. The results showed that the optimum rate was slower than with silent reading and faster than with trace reading, and, interestingly, the individual optimum rates of dynamic text presentation were correlated with the speeds of both silent and trace reading. In other words, the readers who preferred a fast rate in dynamic text presentation would also have a high reading speed for silent and trace reading.

Perceptual transparency from image deformation.

Human vision has a remarkable ability to perceive two layers at the same retinal locations, a transparent layer in front of a background surface. Critical image cues to perceptual transparency, studied extensively in the past, are changes in luminance or color that could be caused by light absorptions and reflections by the front layer, but such image changes may not be clearly visible when the front layer consists of a pure transparent material such as water. Our daily experiences with transparent materials of this kind suggest that an alternative potential cue of visual transparency is image deformations of a background pattern caused by light refraction. Although previous studies have indicated that these image deformations, at least static ones, play little role in perceptual transparency, here we show that dynamic image deformations of the background pattern, which could be produced by light refraction on a moving liquid's surface, can produce a vivid impression of a transparent liquid layer without the aid of any other visual cues as to the presence of a transparent layer. Furthermore, a transparent liquid layer perceptually emerges even from a randomly generated dynamic image deformation as long as it is similar to real liquid deformations in its spatiotemporal frequency profile. Our findings indicate that the brain can perceptually infer the presence of "invisible" transparent liquids by analyzing the spatiotemporal structure of dynamic image deformation, for which it uses a relatively simple computation that does not require high-level knowledge about the detailed physics of liquid deformation.

Seeing liquids from visual motion.

Most research on human visual recognition focuses on solid objects, whose identity is defined primarily by shape. In daily life, however, we often encounter materials that have no specific form, including liquids whose shape changes dynamically over time. Here we show that human observers can recognize liquids and their viscosities solely from image motion information. Using a two-dimensional array of noise patches, we presented observers with motion vector fields derived from diverse computer rendered scenes of liquid flow. Our observers perceived liquid-like materials in the noise-based motion fields, and could judge the simulated viscosity with surprising accuracy, given total absence of non-motion information including form. We find that the critical feature for apparent liquid viscosity is local motion speed, whereas for the impression of liquidness, image statistics related to spatial smoothness-including the mean discrete Laplacian of motion vectors-is important. Our results show the brain exploits a wide range of motion statistics to identify non-solid materials.

A temporal window for estimating surface brightness in the Craik-O'Brien-Cornsweet effect.

The central edge of an opposing pair of luminance gradients (COC edge) makes adjoining regions with identical luminance appear to be different. This brightness illusion, called the Craik-O'Brien-Cornsweet effect (COCe), can be explained by low-level spatial filtering mechanisms (Dakin and Bex, 2003). Also, the COCe is greatly reduced when the stimulus lacks a frame element surrounding the COC edge (Purves et al., 1999). This indicates that the COCe can be modulated by extra contextual cues that are related to ideas about lighting priors. In this study, we examined whether processing for contextual modulation could be independent of the main COCe processing mediated by the filtering mechanism. We displayed the COC edge and frame element at physically different times. Then, while varying the onset asynchrony between them and changing the luminance contrast of the frame element, we measured the size of the COCe. We found that the COCe was observed in the temporal range of around 600-800 ms centered at the 0 ms (from around -400 to 400 ms in stimulus onset asynchrony), which was much larger than the range of typical visual persistency. More importantly, this temporal range did not change significantly regardless of differences in the luminance contrast of the frame element (5-100%), in the durations of COC edge and/or the frame element (50 or 200 ms), in the display condition (interocular or binocular), and in the type of lines constituting the frame element (solid or illusory lines). Results suggest that the visual system can bind the COC edge and frame element with a temporal window of ~1 s to estimate surface brightness. Information from the basic filtering mechanism and information of contextual cue are separately processed and are linked afterwards.

Rapid encoding of relationships between spatially remote motion signals.

For visual processing, the temporal correlation of remote local motion signals is a strong cue to detect meaningful large-scale structures in the retinal image, because related points are likely to move together regardless of their spatial separation. While the processing of multi-element motion patterns involved in biological motion and optic flow has been studied intensively, the encoding of simpler pairwise relationships between remote motion signals remains poorly understood. We investigated this process by measuring the temporal rate limit for perceiving the relationship of two motion directions presented at the same time at different spatial locations. Compared to luminance or orientation, motion comparison was more rapid. Performance remained very high even when interstimulus separation was increased up to 100°. Motion comparison also remained rapid regardless of whether the two motion directions were similar to or different from each other. The exception was a dramatic slowing when the elements formed an orthogonal "T," in which two motions do not perceptually group together. Motion presented at task-irrelevant positions did not reduce performance, suggesting that the rapid motion comparison could not be ascribed to global optic flow processing. Our findings reveal the existence and unique nature of specialized processing that encodes long-range relationships between motion signals for quick appreciation of global dynamic scene structure.

Temporal characteristics of depth perception from motion parallax.

Temporal characteristics of depth perception from motion parallax were examined by modulating parallax intermittently while observers moved their head side to side. In Experiment 1, parallax of a fixed value was introduced only for the central 1/6 to 5/6 portion of each component head movement. It was found that the perceived depth was proportional to the temporal average of parallax-specified depth. In addition, observers did not notice any abrupt temporal change of depth. In Experiment 2, parallax was increased or decreased once per trial either at the center or the end of one of the component head movements, and observers judged the direction of depth change. Again, observers did not notice any abrupt change of depth. The percentage of correct responses was almost constant for large change amplitudes. Reaction times to the change were over 1 s even for the largest changes, and it increased for smaller change amplitudes. These results indicate that the mechanism for depth from parallax has a configuration similar to that proposed for structure from motion, and that it involves a temporal integration process with a relatively long time-constant.

Human neural responses involved in spatial pooling of locally ambiguous motion signals.

Early visual motion signals are local and one-dimensional (1-D). For specification of global two-dimensional (2-D) motion vectors, the visual system should appropriately integrate these signals across orientation and space. Previous neurophysiological studies have suggested that this integration process consists of two computational steps (estimation of local 2-D motion vectors, followed by their spatial pooling), both being identified in the area MT. Psychophysical findings, however, suggest that under certain stimulus conditions, the human visual system can also compute mathematically correct global motion vectors from direct pooling of spatially distributed 1-D motion signals. To study the neural mechanisms responsible for this novel 1-D motion pooling, we conducted human magnetoencephalography (MEG) and functional MRI experiments using a global motion stimulus comprising multiple moving Gabors (global-Gabor motion). In the first experiment, we measured MEG and blood oxygen level-dependent responses while changing motion coherence of global-Gabor motion. In the second experiment, we investigated cortical responses correlated with direction-selective adaptation to the global 2-D motion, not to local 1-D motions. We found that human MT complex (hMT+) responses show both coherence dependency and direction selectivity to global motion based on 1-D pooling. The results provide the first evidence that hMT+ is the locus of 1-D motion pooling, as well as that of conventional 2-D motion pooling.

Awareness of Central Luminance Edge is Crucial for the Craik-O'Brien-Cornsweet Effect.

The Craik-O'Brien-Cornsweet (COC) effect demonstrates that perceived lightness depends not only on the retinal input at corresponding visual areas but also on distal retinal inputs. In the COC effect, the central edge of an opposing pair of luminance gradients (COC edge) makes adjoining regions with identical luminance appear to be different. To investigate the underlying mechanisms of the effect, we examined whether the subjective awareness of the COC edge is necessary for the generation of the effect. We manipulated the visibility of the COC edge using visual backward masking and continuous flash suppression while monitoring subjective reports regarding online percepts and aftereffects of adaptation. Psychophysical results showed that the online percept of the COC effect nearly vanishes in conditions where the COC edge is rendered invisible. On the other hand, the results of adaptation experiments showed that the COC edge is still processed at the early stage even under the perceptual suppression. These results suggest that processing of the COC edge at the early stage is not sufficient for generating the COC effect, and that subjective awareness of the COC edge is necessary.

Spatial pooling of one-dimensional second-order motion signals.

We can detect visual movements not only from luminance motion signals (first-order motion) but also from non-luminance motion signals (second-order motion). It has been established for first-order motions that the visual system pools local one-dimensional motion signals across space and orientation to solve the aperture problem and to estimate two-dimensional object motion. In this study, we investigated (i) whether local one-dimensional second-order motion signals are also pooled across space and orientation into a global 2D motion, and if so, (ii) whether the second-order motion signals are pooled independently of, or in cooperation with, first-order motion signals. We measured the direction-discrimination performance and the rating of a global circular translation of four oscillating bars, each defined either by luminance or by a non-luminance attribute, such as flicker and binocular depth. The results showed evidence of motion pooling both when the stimulus consisted only of second-order bars and when it consisted of first-order and second-order bars. We observed global motion pooling across first-order motion and second-order motions even when the first-order motion was not accompanied by trackable position changes. These results suggest the presence of a universal pooling system for first- and second-order one-dimensional motion signals.

Conditional spatial-frequency selective pooling of one-dimensional motion signals into global two-dimensional motion.

This study examined spatial-frequency effects on a motion-pooling process in which spatially distributed local one-dimensional motion signals are integrated into the perception of global two-dimensional motion. Motion pooling over two- to three-octave frequency differences was found to be nearly impossible when all Gabor elements had circular envelopes, but possible when the width of high-frequency elements was reduced, and the stimulus as a whole formed a closed contour configuration. These results are consistent with a view that motion pooling is controlled by form information, and that spatial-frequency difference is one, but not an absolute, form cue of segmentation.

Spatial spread of interocular suppression is guided by stimulus configuration.

When the two eyes view dissimilar monocular stimuli, the resulting interocular suppression can spread beyond the region of explicit stimulus conflict: portions of one rival target will disappear even though there is no competing stimulation at the corresponding location in the other eye's view. In a series of experiments we examined whether this spread of suppression is spatially isotropic or governed by the configuration of the stimulus a portion of which is subject to suppression. Observers reported the incidence of stimulus disappearance at different locations along or nearby the contours of a large figure, part of which was suppressed by presentation of a continuous flash-suppression stimulus to a restricted region of the other eye. For all observers, suppression spread over several degrees along the contours of the figure, but tended not to spread to locations nearby but disconnected from the figure. Suppression spread effectively over a smoothly curved contour, and it spread around a sharp corner defined by two abutting contours, albeit less effectively. Suppression tended not to spread to features within the interior of a figure (a face), even if those features formed an integral part of the figure. A gap within a spatially extended stimulus arrested the spread of suppression, unless that gap appeared to arise from occlusion. Spread of suppression was unrelated to sensory eye dominance and was found with a more conventional binocular rivalry configuration, too. These findings implicate the involvement of neural circuitry in which inhibition propagates along paths of excitation beyond spatial regions of explicit interocular conflict.

Adaptation to invisible motion results in low-level but not high-level aftereffects.

After prolonged exposure to moving stimuli, illusory motion is perceived in stimuli that do not contain consistent motion, a phenomenon termed the motion aftereffect (MAE). In this study, we tested MAEs under binocular suppression that renders the motion adaptor invisible for the entire adaptation period. We developed a variant of the continuous flash suppression method to reliably suppress target motion stimuli for durations longer than several tens of seconds. Here, we ask whether motion systems are functional in the absence of perception by measuring the MAE, a question difficult to address using binocular rivalry that accompanies a switch of percept between visible and invisible. Results show that both the MAEs with static and dynamic tests are attenuated with an invisible adaptor when the adaptor and the test stimulus are presented to the same eye. In contrast, when the test pattern was presented to the other eye, the dynamic MAE was observed in invisible adaptor conditions. These results indicate that low-level adaptation survives under total binocular suppression, a finding predicted by previous studies. In contrast, disappearance of interocular transfer in the dynamic MAE suggests that a high-level motion detector does not operate when the motion adaptor is rendered invisible.

Voluntary action influences visual competition.

Converging lines of evidence point to a strong link between action and perception. In this study, we show that this linkage plays a role in controlling the dynamics of binocular rivalry, in which two stimuli compete for perceptual awareness. Observers dichoptically viewed two dynamic rival stimuli while moving a computer mouse with one hand. When the motion of one rival stimulus was consistent with observers' own hand movements, dominance durations of that stimulus were extended and, remarkably, suppression durations of that stimulus were abbreviated. Additional measurements revealed that this change in rivalry dynamics was not attributable to observers' knowledge about the condition under test. Thus, self-generated actions can influence the resolution of perceptual conflict, even when the object being controlled falls outside of visual awareness.

Reversed Café Wall illusion with missing fundamental gratings.

The direction of Café Wall illusion was measured for ordinary Café Wall figures comprised of blocks with a square wave profile and for those with a missing fundamental (MF) profile. For the MF version, it was found that the illusion direction alternates according to the patterns' main component frequency when the shift between adjacent rows was systematically varied. The direction of illusion for the MF version was opposite to that for the original version when the phase shifts of adjacent rows were between 60 and 120degrees of the original grating. The results indicate that the illusion depends on the physical component rather than the appearance of the pattern. The possibility of the Café Wall illusion being mediated by low-level luminance mechanisms each tuned to a different spatial frequency is discussed based on the results.

Reversed-phi perception with motion-defined motion stimuli.

Perception of reversed-phi with motion-defined motion (MDM) stimuli was examined while varying various parameters including eccentricity. For peripheral viewing, reversed-phi was observed at all displacements between 30 degrees and 135 degrees. The perception most prominent at 90 degrees, but was disrupted by dichoptic presentation. These results suggest operations of an energy-based motion system similar to the first-order motion system for luminance motion, which most likely resides at a relatively early level (cf. [Vision Res. 33 (1993) 533]). For central viewing, reversed motion was observed only for larger displacements. The perceived motion at smaller displacements was predominantly in the forward direction. Transition between the two modes occurred around 90 degrees displacement. In addition, this motion perception was not disrupted by dichoptic presentation. This indicated the operation of a polarity independent matching-based motion system residing at a higher-level. Thus, the results indicate the involvement of at least two separate mechanisms for MDM detection, and that there is a dominance shift between the two systems according to the eccentricity.