Touch engages visual spatial contextual processing

Visual perception depends strongly on spatial context. A classic example is the tilt illusion where the perceived orientation of a central stimulus differs from its physical orientation when surrounded by tilted spatial contexts. Here we show that such contextual modulation of orientation perception exhibits trait-like interindividual diversity that correlates with interindividual differences in effective connectivity within human primary visual cortex. We found that the degree to which spatial contexts induced illusory orientation perception, namely, the magnitude of the tilt illusion, varied across healthy human adults in a trait-like fashion independent of stimulus size or contrast. Parallel to contextual modulation of orientation perception, the presence of spatial contexts affected effective connectivity within human primary visual cortex between peripheral and foveal representations that responded to spatial context and central stimulus, respectively. Importantly, this effective connectivity from peripheral to foveal primary visual cortex correlated with interindividual differences in the magnitude of the tilt illusion. Moreover, this correlation with illusion perception was observed for effective connectivity under tilted contextual stimulation but not for that under iso-oriented contextual stimulation, suggesting that it reflected the impact of orientation-dependent intra-areal connections. Our findings revealed an interindividual correlation between intra-areal connectivity within primary visual cortex and contextual influence on orientation perception. This neurophysiological-perceptual link provides empirical evidence for theoretical proposals that intra-areal connections in early visual cortices are involved in contextual modulation of visual perception.

Neural responses to visual stimuli are modulated by spatial and temporal context. For example, in primary visual cortex (V1), responses to an oriented target stimulus will be suppressed when embedded within an oriented surround stimulus. This suppression is orientation-specific, with the largest suppression observed when stimuli in the neuron's classical receptive field and surround are of similar orientation. In human psychological experiments, the tilt illusion and tilt aftereffect demonstrate an effect of context on perceived orientation of a target stimulus. Similar to the neurophysiological data, the strength of these effects is modulated by the orientation difference between the target stimulus and context. It has been hypothesized that the neural mechanism underlying both the tilt illusion and tilt aftereffect involves orientation-tuned inhibition in V1. However, to date there is no direct evidence linking human perception of these illusions with measurements of inhibition from human visual cortex. Here, we measured context-induced suppression of neural responses in human visual cortex using functional magnetic resonance imaging (fMRI). In the same participants, we also measured magnitudes of their tilt illusion and tilt aftereffect. Our data revealed a significant relationship between the magnitude of neural suppression in V1 and size of the tilt illusion and tilt aftereffect. That is, participants who showed stronger blood oxygenation level dependent (BOLD) suppression in V1 also perceived stronger shifts in illusory tilt. This agreement between perception and neural responses in human V1 suggests a shared inhibitory mechanism that mediates both spatial and temporal effects of context in human perception.

We studied a novel illusion of tilt inside checkerboards due to the role of contrast polarity in contour integration. The preference for binding of oriented contours having same contrast polarity, over binding of opposite polarity ones (CP rule), has been used to explain several visual illusions. In three experiments we investigated how the binding effect is influenced by luminance contrast value, relatability of contour elements, and distance among them. Experiment 1 showed that the effect was indeed present only when the CP rule was satisfied, and found it to be stronger when the luminance contrast values of the elements are more similar. In experiment 2 the illusion was reported only with relatable edges, and its strength was modulated by the degree of relatability. The CP-rule effectiveness, thus, seems to depend on good continuation. The intensity of contrast polarity signals propagating from an oriented contour might be the less intense, the more its direction deviates from linearity. In experiment 3 we estimated the distance threshold and found it to be smaller than the one found for other illusions, arising with collinear fragments. This seems to show that the reach of the contrast polarity signal inside the association field of a contour unit is shorter along non-collinear orientations than along collinear ones.

Social behaviour of domestic dogs (Canis familiaris) in a public off-leash dog park

The processing and perception of visual stimuli are greatly dependent on the context in which those stimuli are presented. While this is not always (and indeed is probably not supposed to be) evident when viewing real-world scenes, the abundance of contextual effects is revealed for example by the vast number of different visual illusions. Context can profoundly change the way the visual system processes single visual stimuli. In contrast masking, surround suppression, and crowding, distracting stimuli impair the observer's ability to detect, identify, and make other judgements about visual stimuli. These perceptual phenomena presumably reflect the operation of neural mechanisms that adjust the operating range of the visual system according to the prevailing conditions, or act to reduce responses to redundant stimulus features. This work first investigates the relationship between masking, which is caused by stimuli that are spatially superimposed on a target stimulus, and surround suppression, which is caused by spatially displaced stimuli. This was done using a temporal masking paradigm and measuring the time-courses of masking and surround suppression. The results reveal how the effects of these suppressive interactions are delicately dependent on stimulus timing and suggest that surround suppression acts extremely fast, having an effect on the early part of the neural response. Finally, contextual effects such as surround suppression and crowding are often considered to be automatic processes that occur over fixed areas in the visual field. The final part of this work shows how changing the spatial layout, and consequently the perceptual organization, of the stimuli can dramatically reduce surround suppression and crowding effects, even in conditions where the current models would predict strong effects. Surround suppression and crowding seem to operate only within perceptually homogeneous areas, while stimuli that are perceptually separate, the ones that stand out, are not affected.

Visual illusions occur around us all the time, which present in nature and appear when you least expect it. It is well known that visual illusions can have a dramatic effect upon our visual perception of an object 's size and position. However, whether visual illusions have a similar influence on visual guided action or not, it remains the subject of much debate. The purpose of this study is to explore whether the visual information used to identify and categorize an object would be similar to the visual information used to plan and control visually guided movements directed toward that object. The outcome of this study will be helpful for designers to understand our visual information system and apply that knowledge to the design practice. In order to achieve the purpose of this study mentioned above, three visual illusions as the experiment's apparatus are applied to examine the relative effect of visual illusions on both the visual perceived center of an object and the position of a grasp on that object when a balanced lift is required. The results of the experiment show that (1) Illusions influence both the perceived and the grasped estimates of the center position, but the grasp center is more veridical; (2) Judd-illusion, one of the three visual illusions, has a bigger degree of effect than two other illusions on both the perceived and the grasped estimates of the center position; (3) By providing the participants with a mean to guide their visual perception of these illusions, the errors from the estimation of the center position can be significantly reduced.

Introduction: The present study sets out to determine which sensory system mostly influences self-motion perception when visual and vestibular cues are in conflict. We paired caloric vestibular stimulation that signaled motion in either the clockwise or counter-clockwise direction with a visual display that indicated self-rotation in either the same or opposite directions.Methods: In Experiment 1 (E1), caloric vestibular stimulation was used to produce vestibular circular vection. In Experiment 2 (E2), a virtual optokinetic drum was used to produce visual circular vection in a VR headset. Vection speed, direction, and duration were recorded using a potentiometer knob the participant controlled in E1 and E2. In Experiment 3 (E3), visual and vestibular stimuli were matched to be at approximately equal speeds across visual and vestibular modalities for each participant setting up Experiment 4 (E4). In E4, participants observed a moving visual pattern in a virtual reality (VR) headset while receiving caloric vestibular stimulation. Participants rotated the potentiometer knob while attending to visual–vestibular stimuli presentations to indicate their perceived circular vection. E4 had two conditions: 1) A congruent condition where calorics and visual display indicated circular vection in the same direction; 2) an incongruent condition where calorics and visual display indicated circular vection in opposite directions.Results and discussion: There were equal reports of knob rotation in the direction consistent with the visual and vestibular self-rotation direction in the incongruent condition of E4 across trials. There were no significant differences in knob rotation speed and duration in both conditions. These results demonstrate that the brain appears to weigh visual and vestibular cues equally during a visual–vestibular conflict of approximately equal speeds. These results are most consistent with the optimal cue integration hypothesis.

Sensory substitution as an artificially acquired synaesthesia

The responses of neurons in the visual pathway depend on the context in which a stimulus is presented. Responses to predictable stimuli are usually suppressed, highlighting responses to unexpected stimuli that might be important for behavior. Here, we established how context modulates the response of neurons in the superior colliculus (SC), a region important in orienting toward or away from visual stimuli. We made extracellular recordings from single units in the superficial layers of SC in awake mice. We found strong suppression of visual response by spatial context (surround suppression) and temporal context (adaptation). Neurons showing stronger surround suppression also showed stronger adaptation effects. In neurons where it was present, surround suppression was dynamic and was reduced by adaptation. Adaptation's effects further revealed two components to surround suppression: one component that was weakly tuned for orientation and adaptable, and another component that was more strongly tuned but less adaptable. The selectivity of the tuned component was flexible, such that suppression was stronger when the stimulus over the surround matched that over the receptive field. Our results therefore reveal strong interactions between spatial and temporal context in regulating the flow of signals through mouse SC, and suggest the presence of a subpopulation of neurons that might signal novelty in either space or time.

Optical illusions have long been used in behavioural studies to investigate the perceptual mechanisms underlying vision in animals. So far, three studies have focused on ungulates, providing evidence that they may be susceptible to some optical illusions, in a way similar to humans. Here, we used two food-choice tasks to study susceptibility to the Müller-Lyer and Delboeuf illusions in 17 captive individuals belonging to four ungulate species (Lama guanicoe, Lama glama, Ovis aries, Capra hircus). At the group level, there was a significant preference for the longer/larger food over the shorter/smaller one in control trials. Additionally, the whole group significantly preferred the food stick between two inward arrowheads over an identical one between two outward arrowheads in experimental trials of the Müller-Lyer task, and also preferred the food on the smaller circle over an identical one on the larger circle in the experimental trials of the Delboeuf task. Group-level analyses further showed no significant differences across species, although at the individual level we found significant variation in performance. Our findings suggest that, in line with our predictions, ungulates are overall susceptible to the Müller-Lyer and the Delboeuf illusions, and indicate that the perceptual mechanisms underlying size estimation in artiodactyls might be similar to those of other species, including humans.

Atypical excitation–inhibition balance in autism captured by the gamma response to contextual modulation☆

Female mate choice by chemical signals in a semi-terrestrial crab

Perceptual illusions refer to systematically oriented errors in the perception of figures or scenes, and these errors are observed in almost all people. For centuries, they have been called ‘opto-geometric illusions’ because it was thought that they concerned only visual perception. Although visual errors are relatively rare, comments and questions about visual illusions are found as early as in the Greek and Roman literature. In scientific psychology, the theoretical and practical problems raised by these deformations have been intensively studied since the end of the 19th Century, and the elements of the figure inducing each error are now identified. However, there is no general theory explaining all the visual illusions. Instead, each figure must be analysed in order to determine the specific processes leading to the error. KeywordsVisual IllusionPerceptual ErrorHaptic PerceptionExploratory MovementPonzo IllusionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The goal of the present study was to develop and empirically evaluate three countermeasures to tactile change blindness (where a tactile signal is missed in the presence of a tactile transient). Each of these countermeasures relates to a different cognitive step involved in successful change detection. To date, change blindness has been studied primarily in vision, but there is limited empirical evidence that the tactile modality may also be subject to this phenomenon. Change blindness raises concerns regarding the robustness of tactile and multimodal interfaces. Three countermeasures to tactile change blindness were evaluated in the context of a highly demanding monitoring task. One countermeasure was proactive (alerting the participant to a possible change before it occurred) whereas the other two were adaptive (triggered after the change upon an observed miss). Performance and subjective data were collected. Compared to the baseline condition, all countermeasures improved intramodal tactile change detection. Adaptive measures resulted in the highest detection rates, specifically when signal gradation was employed (i.e., when the intensity of the tactile signal was increased after a miss was observed). Adaptive displays can be used to counter the effects of change blindness and ensure that tactile information is reliably detected. Increasing the tactile intensity after a missed change appears most promising and was the preferred countermeasure. The findings from this study can inform the design of interfaces employing the tactile modality to support monitoring and attention management in data-rich domains.

Bodily self-awareness relies on a constant integration of visual, tactile, proprioceptive, and motor signals. In the 'rubber hand illusion' (RHI), conflicting visuo-tactile stimuli lead to changes in self-awareness. It remains unclear whether other, somatic signals could compensate for the alterations in self-awareness caused by visual information about the body. Here, we used the RHI in combination with robot-mediated self-touch to systematically investigate the role of tactile, proprioceptive and motor signals in maintaining and restoring bodily self-awareness. Participants moved the handle of a leader robot with their right hand and simultaneously received corresponding tactile feedback on their left hand from a follower robot. This self-touch stimulation was performed either before or after the induction of a classical RHI. Across three experiments, active self-touch delivered after-but not before-the RHI, significantly reduced the proprioceptive drift caused by RHI, supporting a restorative role of active self-touch on bodily self-awareness. The effect was not present during involuntary self-touch. Unimodal control conditions confirmed that both tactile and motor components of self-touch were necessary to restore bodily self-awareness. We hypothesize that active self-touch transiently boosts the precision of proprioceptive representation of the touched body part, thus counteracting the visual capture effects that underlie the RHI.