Random Dot Patterns Research Articles

Effect of attention on human direction-discrimination thresholds at iso-eccentric locations in the visual field: A registered report protocol.

Human visual perceptual performance is strongly dependent on a given stimulus' distance from the line of sight, i.e. its eccentricity. In addition, multiple studies have shown a dependence on a stimulus' angular position relative to the fovea. In humans, the resulting spatial profile of perceptual performance (the "performance field") typically shows better performance near the lower vertical meridian, compared to the upper vertical meridian, and better performance near the horizontal meridian compared to the vertical meridian. Predominantly, these variations have been interpreted as sensory inhomogeneities. But it has also been shown that they are modulated by the allocation of spatial attention, either homogeneously elevating performance or compensating for the sensory inhomogeneities. Here, we propose a study protocol for pre-registration to investigate such interactions between sensory and attentional effects. First, we will determine performance fields for time-dependent, dynamic stimuli, namely the direction discrimination of moving random dot patterns. Then, we will establish whether directing focal attention to a particular stimulus location differentially improves thresholds compared to a distributed attention condition.

On Human-like Biases in Convolutional Neural Networks for the Perception of Slant from Texture

Depth estimation is fundamental to 3D perception, and humans are known to have biased estimates of depth. This study investigates whether convolutional neural networks (CNNs) can be biased when predicting the sign of curvature and depth of surfaces of textured surfaces under different viewing conditions (field of view) and surface parameters (slant and texture irregularity). This hypothesis is drawn from the idea that texture gradients described by local neighborhoods—a cue identified in human vision literature—are also representable within convolutional neural networks. To this end, we trained both unsupervised and supervised CNN models on the renderings of slanted surfaces with random Polka dot patterns and analyzed their internal latent representations. The results show that the unsupervised models have similar prediction biases as humans across all experiments, while supervised CNN models do not exhibit similar biases. The latent spaces of the unsupervised models can be linearly separated into axes representing field of view and optical slant. For supervised models, this ability varies substantially with model architecture and the kind of supervision (continuous slant vs. sign of slant). Even though this study says nothing of any shared mechanism, these findings suggest that unsupervised CNN models can share similar predictions to the human visual system. Code: github.com/brownvc/Slant-CNN-Biases.

Reduced visual context effects in global motion processing in depression.

Research supports abnormal inhibitory visual motion processing in adults with remitted and current depression, but all studies to date have used paradigms with simple grating stimuli. Global motion processing, where multiple motion signals must be integrated, has not been explored in depression, nor have inhibitory processes within that domain. Depressed participants (n = 46) and healthy controls (n = 28) completed a direction discrimination task featuring a random dot pattern stimulus. Various signal (rightward or leftward dots) to noise (dots with randomly assigned directions) ratios modulated task difficulty. Metrics of global center surround suppression and facilitation were calculated. Accuracy in the baseline condition (i.e., no surrounding annulus) was not significantly different between depressed and healthy participants. Global center surround suppression and facilitation were not significantly different between healthy and depressed participants overall. When limiting the sample to unmedicated individuals, depressed participants (n = 27) showed a reduced global center surround suppression effect compared to controls, and there was no difference in global center surround facilitation. While global motion processing is intact in depression, abnormal center surround suppression effects in depression do extend to global motion stimuli. These alterations may be mitigated by the psychotropic medications taken by some subjects in our depressed sample. Future studies should explore the mechanisms underlying these effects.

Elimination of Apparent Image on Single-Pixel-Imaging by Use of High-Frame-Rate Display With Latent Random Dot Patterns

Elimination of Apparent Image on Single-Pixel-Imaging by Use of High-Frame-Rate Display With Latent Random Dot Patterns

Disentangling Object Category Representations Driven by Dynamic and Static Visual Input.

Humans can label and categorize objects in a visual scene with high accuracy and speed, a capacity well characterized with studies using static images. However, motion is another cue that could be used by the visual system to classify objects. To determine how motion-defined object category information is processed by the brain in the absence of luminance-defined form information, we created a novel stimulus set of "object kinematograms" to isolate motion-defined signals from other sources of visual information. Object kinematograms were generated by extracting motion information from videos of 6 object categories and applying the motion to limited-lifetime random dot patterns. Using functional magnetic resonance imaging (fMRI) (n = 15, 40% women), we investigated whether category information from the object kinematograms could be decoded within the occipitotemporal and parietal cortex and evaluated whether the information overlapped with category responses to static images from the original videos. We decoded object category for both stimulus formats in all higher-order regions of interest (ROIs). More posterior occipitotemporal and ventral regions showed higher accuracy in the static condition, while more anterior occipitotemporal and dorsal regions showed higher accuracy in the dynamic condition. Further, decoding across the two stimulus formats was possible in all regions. These results demonstrate that motion cues can elicit widespread and robust category responses on par with those elicited by static luminance cues, even in ventral regions of visual cortex that have traditionally been associated with primarily image-defined form processing.SIGNIFICANCE STATEMENT Much research on visual object recognition has focused on recognizing objects in static images. However, motion is a rich source of information that humans might also use to categorize objects. Here, we present the first study to compare neural representations of several animate and inanimate objects when category information is presented in two formats: static cues or isolated dynamic motion cues. Our study shows that, while higher-order brain regions differentially process object categories depending on format, they also contain robust, abstract category representations that generalize across format. These results expand our previous understanding of motion-derived animate and inanimate object category processing and provide useful tools for future research on object category processing driven by multiple sources of visual information.

Perceptual Grouping of Random Dot Patterns in the Presence of a Tilting Frame.

The objective of this study was to investigate the effect of tilting a frame on the perceptual organization in random dot patterns. Ten random patterns of nine dots were generated. For each pattern, a square frame was tilted at seven angles around the dots. Ten observers were asked to indicate the groups of dots in each stimulus. Each stimulus was seen 4 times by each observer which enabled us to study within-subject consistencies provided grouping reports. Within- and between-subject consistencies were computed to study if the responses provided by participants were consistent and thus reliable. The dominant group was defined as the most repeated group in all 40 reports (10 participants, 4 repetitions) obtained for each stimulus. We studied how tilting a frame affected the dominant group in each dot pattern. Perceptual grouping was not affected by tilting the frame. Based on a qualitative inspection, we remark that fundamental principles, for example, proximity, good continuation, and closure, respectively, in the order of strength, may remain the main drivers of the grouping behavior, irrespective of differences in the number of dots in each group, and the frame orientation. The numerosity condition did not affect our results. Similar trends were observed in patterns of 9 and 18 dots patterns.

Use of the reflective background oriented schlieren technique to measure free surface deformations in a thin liquid layer non-uniformly heated from below

To measure liquid film surface deformations, we use the Background Oriented Schlieren (BOS) technique with a reflective optical scheme, which includes a random dot pattern located above the liquid surface, and a camera that captures its reflection from the liquid interface. The substrate was covered with a special black coating to minimize stray light reflection, which allowed to provide clear visualization of the dot pattern reflected from the free surface even for very thin liquid films. Local slopes of the film surface cause the dot displacement on the pattern image relative to the pattern image captured in the absence of any free-surface deformations. Hence, the topography of the liquid film surface is encoded by the apparent displacement of the dot pattern. Using the cross correlation image processing, the displacement vector field was determined, which was then substituted in Poisson equation to reconstruct the free-surface profile of the liquid film. The main advantages of this technique are: applicability for liquids with surface temperature inhomogeneities, experimental simplicity, sensitivity and applicability for both transparent and opaque liquids. Using the reflective BOS technique and using substrate with black coating we measure the free-surface deformation field of a thin layer of silicone oil non-uniformly heated from below. Despite the fact that thermocapillary shear stresses tend to decrease the thickness of the liquid layer in hotter regions, in the experiment, a convex deformation of the liquid film surface was observed above the heater for a few seconds immediately after the start of heating. This phenomenon is explained by the expansion of the liquid induced by the heating, due to the dependence of the liquid density on temperature. The measurement results are compared with those obtained in a single point using the confocal sensor. A good agreement is achieved.

Sensory computations in the cuneate nucleus of macaques

Tactile nerve fibers fall into a few classes that can be readily distinguished based on their spatiotemporal response properties. Because nerve fibers reflect local skin deformations, they individually carry ambiguous signals about object features. In contrast, cortical neurons exhibit heterogeneous response properties that reflect computations applied to convergent input from multiple classes of afferents, which confer to them a selectivity for behaviorally relevant features of objects. The conventional view is that these complex response properties arise within the cortex itself, implying that sensory signals are not processed to any significant extent in the two intervening structures-the cuneate nucleus (CN) and the thalamus. To test this hypothesis, we recorded the responses evoked in the CN to a battery of stimuli that have been extensively used to characterize tactile coding in both the periphery and cortex, including skin indentations, vibrations, random dot patterns, and scanned edges. We found that CN responses are more similar to their cortical counterparts than they are to their inputs: CN neurons receive input from multiple classes of nerve fibers, they have spatially complex receptive fields, and they exhibit selectivity for object features. Contrary to consensus, then, the CN plays a key role in processing tactile information.

Preattentive processing of visually guided self-motion in humans and monkeys.

The visually-based control of self-motion is a challenging task, requiring - if needed - immediate adjustments to keep on track. Accordingly, it would appear advantageous if the processing of self-motion direction (heading) was predictive, thereby accelerating the encoding of unexpected changes, and un-impaired by attentional load. We tested this hypothesis by recording EEG in humans and macaque monkeys with similar experimental protocols. Subjects viewed a random dot pattern simulating self-motion across a ground plane in an oddball EEG paradigm. Standard and deviant trials differed only in their simulated heading direction (forward-left vs. forward-right). Event-related potentials (ERPs) were compared in order to test for the occurrence of a visual mismatch negativity (vMMN), a component that reflects preattentive and likely also predictive processing of sensory stimuli. Analysis of the ERPs revealed signatures of a prediction mismatch for deviant stimuli in both humans and monkeys. In humans, a MMN was observed starting 110 ms after self-motion onset. In monkeys, peak response amplitudes following deviant stimuli were enhanced compared to the standard already 100 ms after self-motion onset. We consider our results strong evidence for a preattentive processing of visual self-motion information in humans and monkeys, allowing for ultrafast adjustments of their heading direction.

Estimation of the degree of autism spectrum disorder by the slow phase of optokinetic nystagmus in typical adults

Atypical eye movement patterns demonstrated by individuals with autism spectrum disorder (ASD) have the potential to serve as biomarkers for ASD diagnosis. However, instead of estimating individual differences in the degree of ASD from those patterns, many researchers have compared ASD groups with typical development groups. This study investigates the relationship between the Autism-spectrum Quotient (AQ) scores in typical adults, which can evaluate the degree of the traits associated with ASD, as well as the properties of optokinetic nystagmus (OKN), including the gain of the slow phase, the peak velocity and duration of the fast phase, the frequency, and the mean eye position of OKN. A random dot pattern that moved in one direction was presented on the display, and the participants' eye movements were measured. The results showed a negative correlation between subjects' AQ scores and the gain of slow-phase OKN. In addition, the correlations between subjects' AQ scores and the properties of OKN fast phase were not significant. These results indicate that the gain of slow-phase OKN could be a biomarker that estimates individual differences in the degree of ASD, reflected in our findings which considered AQ scores in typical adults.

Visual motion integration of bidirectional transparent motion in mouse opto-locomotor reflexes

Visual motion perception depends on readout of direction selective sensors. We investigated in mice whether the response to bidirectional transparent motion, activating oppositely tuned sensors, reflects integration (averaging) or winner-take-all (mutual inhibition) mechanisms. We measured whole body opto-locomotor reflexes (OLRs) to bidirectional oppositely moving random dot patterns (leftward and rightward) and compared the response to predictions based on responses to unidirectional motion (leftward or rightward). In addition, responses were compared to stimulation with stationary patterns. When comparing OLRs to bidirectional and unidirectional conditions, we found that the OLR to bidirectional motion best fits an averaging model. These results reflect integration mechanisms in neural responses to contradicting sensory evidence as has been documented for other sensory and motor domains.

Pupil response is modulated with optokinetic nystagmus in transparent motion.

When two visual patterns moving in opposite directions are superimposed on the same depth plane, they appear to have two transparent surfaces moving independently (transparent motion). Additionally, the direction of the slow phase of optokinetic nystagmus (OKN) corresponds to the direction of motion that dominates the perceptual appearance. This study examines whether pupil changes correspond to the luminance of the dominated objects related to the transition of the slow-phase direction in OKN following objects. Stimuli consisted of two random dot patterns of different luminance that moved in opposite directions. The results showed that pupil size changed in accordance with the luminance of the pattern in the slow phase of OKN immediately after OKN transition. This suggests that pupil size is modulated with OKN in transparent motion.

Stereomotion Processing in the Nonhuman Primate Brain.

The cortical areas that process disparity-defined motion-in-depth (i.e., cyclopean stereomotion [CSM]) were characterized with functional magnetic resonance imaging (fMRI) in two awake, behaving macaques. The experimental protocol was similar to previous human neuroimaging studies. We contrasted the responses to dynamic random-dot patterns that continuously changed their binocular disparity over time with those to a control condition that shared the same properties, except that the temporal frames were shuffled. A whole-brain voxel-wise analysis revealed that in all four cortical hemispheres, three areas showed consistent sensitivity to CSM. Two of them were localized respectively in the lower bank of the superior temporal sulcus (CSMSTS) and on the neighboring infero-temporal gyrus (CSMITG). The third area was situated in the posterior parietal cortex (CSMPPC). Additional regions of interest-based analyses within retinotopic areas defined in both animals indicated weaker but significant responses to CSM within the MT cluster (most notably in areas MSTv and FST). Altogether, our results are in agreement with previous findings in both human and macaque and suggest that the cortical areas that process CSM are relatively well preserved between the two primate species.

Opto-locomotor reflexes of mice to reverse-phi stimuli.

In a reverse-phi stimulus, the contrast luminance of moving dots is reversed each displacement step. Under those conditions, the direction of the moving dots is perceived in the direction opposite of the displacement direction of the dots. In this study, we investigate if mice respond oppositely to phi and reverse-phi stimuli. Mice ran head-fixed on a Styrofoam ball floating on pressurized air at the center of a large dome. We projected random dot patterns that were displaced rightward or leftward, using either a phi or a reverse-phi stimulus. For phi stimuli, changes in direction caused the mice to reflexively compensate and adjust their running direction in the direction of the displaced pattern. We show that for reverse-phi stimuli mice compensate in the direction opposite to the displacement direction of the dots, in accordance with the perceived direction of displacement in humans for reverse-phi stimuli.

Extraction of Moving Areas in Random-Dot Animation with Parallel Computation

The observation of random-dot animations requires the motion detection techniques of moving objects from the background, allowing the boundary of the moving areas to be perceived despite that each frame consists of random-dot patterns with no boundaries. The present study aims to extract the moving parts as well as its moving direction on the random-dot animations based on the local parallel computation of the pixel level. Assuming motion is captured in high frame rate, the variable range of an optical flow is restricted within a finite discretized area of pixels. Then, the system is constructed to select the suitable optical flow among the finite possibilities according to the reaction-diffusion equation dynamics, computed in a distributed manner. This process is one of the regularization methods and is described as the minimization process of the potential functional. Using the computation result of the previous frames, we attempted to reduce the computational iterations and to detect the plural objects moving at different speeds. These effects are demonstrated by computer simulations using actual random-dot animations.

Analysis and reduction of spurious displacements in high-framing-rate background-oriented Schlieren

Spurious displacements (SDs) associated with high-framing-rate background-oriented Schlieren (BOS) measurements were investigated experimentally in this study. To obtain the SDs, a multiple-pass cross-correlation algorithm was applied to reference/data images on a background printed with random dot pattern. Four sets of image pairs were dedicatedly selected to characterize the SDs. To isolate the SDs unique to the high-framing-rate BOS, measures were taken to minimize the contributions from other sources. Results showed that the SDs distinctive in high-framing-rate BOS measurements can be categorized according to their characteristic time: spatially uniform and fast oscillating SD (F-SD) that could be resolved during one recording event and non-uniform slowly varied SD (S-SD) that only become identifiable after several minutes time intervals between the two subsequent recordings. The proper boundary conditions (BCs) were proposed for solving the Poisson equation of the displacement fields contaminated by the SDs. A method allowing in-situ mitigation of both SDs was also proposed by introducing one additional light path into the BOS setup. Experiments on quasi-two-dimensional helium jets were conducted with and without acoustic excitations. The results confirmed the effectiveness of the proposed method to remove the SDs in both steady and unsteady flows.

Analysis and optimization of the Glass pattern realized by a microlens array.

It is well known that the superposition of two identical random dot patterns may give rise to a particular form of moiré effect known as a Glass pattern. By integrating a microlens array and a micropattern array and applying a small geometrical transformation, it is possible to show the parallactic or the orthoparallactic motion effect when varying the viewing angle. In this paper, we study the effect of the structural parameters of a Glass pattern optical system on its image quality. The position of each elemental pattern in the micropattern array is derived based on a revised model that considers the finite observation distance. The image quality is evaluated by the ray analysis on the observation plane and the reconstructed image plane. Rays from different pixels of the micropattern array are evaluated by the spot size. The depth of the Glass pattern in image space is also analyzed. In addition, a Glass pattern optical system is simulated and optimized by ZEMAX software. An optimal result is obtained that validates the theoretical analysis. Our study can find potential application for designing Glass pattern optical systems or optimization of those imaging systems based on microlens arrays.

Visual objects interact differently during encoding and memory maintenance.

The storage mechanisms of working memory are the matter of an ongoing debate. The sensory recruitment hypothesis states that memory maintenance and perceptual encoding rely on the same neural substrate. This suggests that the same cortical mechanisms that shape object perception also apply to maintained memory content. We tested this prediction using the Direction Illusion, i.e., the mutual repulsion of two concurrently visible motion directions. Participants memorized the directions of two random dot patterns for later recall. In Experiments 1 and 2, we varied the temporal separation of spatially distinct stimuli to manipulate perceptual concurrency, while keeping concurrency within working memory constant. We observed mutual motion repulsion only under simultaneous stimulus presentation, but proactive repulsion and retroactive attraction under immediate stimulus succession. At inter-stimulus intervals of 0.5 and 2 s, however, proactive repulsion vanished, while the retroactive attraction remained. In Experiment 3, we presented both stimuli at the same spatial position and observed a reappearance of the repulsion effect. Our results indicate that the repulsive mechanisms that shape object perception across space fade during the transition from a perceptual representation to a consolidated memory content. This suggests differences in the underlying structure of perceptual and mnemonic representations. The persistence of local interactions, however, indicates different mechanisms of spatially global and local feature interactions.

Encoding- and decision-related brain activity during a motion judgment task

We have previously used steady-state VEPs to show that responses in visual cortex are strongly suppressed when motion stimuli produce inter-ocular velocity differences (Kohler et al., 2018), regardless of whether these differences give rise to movement in depth (MID). Here we used an event-related VEP design to explore how activity evoked by lateral movement and MID unfolds over time. Participants (n=20) viewed stereoscopically presented random-dot patterns in which a central region moved in one of four directions. Dots underwent single-shot apparent motion on every trial: in-phase motion between the two eyes produced lateral movement (left/right), while anti-phase motion gave rise to MID (towards/away). Participants indicated movement direction as quickly and accurately as possible using the keyboard arrow keys. For lateral movement, accuracy was at ceiling and reaction time (RT) was ~800ms, while MID produced lower accuracies (~80%) and longer RTs (~1000ms). We used reliable components analysis to extract maximally correlated signal components from the EEG data (Dmochowski et al., 2012). A medio-frontal component appeared to capture decision-related activity, exhibiting a ramp-like shape that was shallower for MID, consistent with a longer integration period leading to slower RTs. An additional component, centered over occipital cortex, appeared to primarily capture encoding-related activity. Lateral movement and MID produced indistinguishable positive peaks at ~70ms, but diverged at later negative (~180ms) and positive (~350ms) peaks. MID responses were enhanced (more negative) around the negative peak (100–200ms) and suppressed (less positive) leading up to the second positive peak (250–350ms). This late-onset suppression is consistent with the finding that suppression depends on second-order processes, including extraction of relative motion and relative disparity (Kohler et al., 2018). The current results provide a time-resolved electrophysiological analogue to psychophysical data showing that temporal integration underlying decision making is near-perfect for lateral motion, but sub-optimal for MID (Katz et al., 2015).

Monkey EEG links neuronal color and motion information across species and scales.

It remains challenging to relate EEG and MEG to underlying circuit processes and comparable experiments on both spatial scales are rare. To close this gap between invasive and non-invasive electrophysiology we developed and recorded human-comparable EEG in macaque monkeys during visual stimulation with colored dynamic random dot patterns. Furthermore, we performed simultaneous microelectrode recordings from 6 areas of macaque cortex and human MEG. Motion direction and color information were accessible in all signals. Tuning of the non-invasive signals was similar to V4 and IT, but not to dorsal and frontal areas. Thus, MEG and EEG were dominated by early visual and ventral stream sources. Source level analysis revealed corresponding information and latency gradients across cortex. We show how information-based methods and monkey EEG can identify analogous properties of visual processing in signals spanning spatial scales from single units to MEG - a valuable framework for relating human and animal studies.