Tilt aftereffect following adaptation to translational Glass patterns

Lack of orientation specific adaptation to vertically oriented Glass patterns in human visual cortex: an fMRI adaptation investigation

The perception of coherent form configurations in natural scenes relies on the activity of early visual areas that respond to local orientation cues. Subsequently, high-level visual areas pool these local signals to construct a global representation of the initial visual input. However, it is still debated whether neurons in the early visual cortex respond also to global form features. Glass patterns (GPs) are visual stimuli employed to investigate local and global form processing and consist of randomly distributed dots pairs called dipoles arranged to form specific global configurations. In the current study, we used GPs and functional magnetic resonance imaging (fMRI) adaptation to reveal the visual areas that subserve the processing of oriented GPs. Specifically, we adapted participants to vertically oriented GP, then we presented test GPs having either the same or different orientations with respect to the adapting GP. We hypothesized that if local form features are processed exclusively by early visual areas and global form by higher-order visual areas, then the effect of visual adaptation should be more pronounced in higher tier visual areas as it requires global processing of the pattern. Contrary to this expectation, our results revealed that adaptation to GPs is robust in early visual areas (V1, V2, and V3), but not in higher tier visual areas (V3AB and V4v), suggesting that form cues in oriented GPs are primarily derived from local-processing mechanisms that originate in V1. Finally, adaptation to vertically oriented GPs causes a modification in the BOLD response within early visual areas, regardless of the relative orientations of the adapting and test stimuli, indicating a lack of orientation selectivity.

Working Memory Load Effects on the Tilt Aftereffect

Prolonged exposure to an oriented stimulus causes a subsequent test stimulus to be perceived as tilted in the opposite direction, a phenomenon referred to as the tilt aftereffect (TAE). Previous studies have demonstrated that high-level cognitive functions such as attention can modulate the TAE, which is generally well-known as a low-level perceptual process. However, it is unclear whether working memory load, another high-level cognitive function, could modulate the TAE. To address this issue, here we developed a new paradigm by combining a working memory load task with a TAE task. Participants firstly remembered a stream of digits (Experiment 1) or four color-shape conjunctions (Experiment 2) under high/low load conditions, and then recognized the probe stimuli (digits or a color-shape conjunction), which were presented at the center of an adapting grating. After the recognition task (i.e., the adaptation stage), participants performed an orientation judgment task to measure their TAEs. The result of Experiment 1, where the load stimuli were digits, showed that the magnitude of the TAEs were reduced under the condition of the high working memory load compared to that of the low working memory load. However, we failed to replicate the finding in Experiment 2, where the load stimuli were color-shape conjunctions. Together, our two experiments provided mixed evidence regarding the working memory load effects on the TAE and further replications are needed in future work.

Spatial and Temporal Selectivity of Translational Glass Patterns Assessed With the Tilt After-Effect

Glass patterns (GPs) have been widely employed to investigate the mechanisms underlying processing of global form from locally oriented cues. The current study aimed to psychophysically investigate the level at which global orientation is extracted from translational GPs using the tilt after-effect (TAE) and manipulating the spatiotemporal properties of the adapting pattern. We adapted participants to translational GPs and tested with sinewave gratings. In Experiment 1, we investigated whether orientation-selective units are sensitive to the temporal frequency of the adapting GP. We used static and dynamic translational GPs, with dynamic GPs refreshed at different temporal frequencies. In Experiment 2, we investigated the spatial frequency selectivity of orientation-selective units by manipulating the spatial frequency content of the adapting GPs. The results showed that the TAE peaked at a temporal frequency of ∼30 Hz, suggesting that orientation-selective units responding to translational GPs are sensitive to high temporal frequencies. In addition, TAE from translational GPs peaked at lower spatial frequencies than the dipoles' spatial constant. These effects are consistent with form-motion integration at low and intermediate levels of visual processing.

Interaction of surface pattern and contour shape in the tilt after effects evoked by symmetry

Integration of multiple properties of an object is a fundamental function of the visual cortex in object recognition. For instance, surface patterns and contour shapes are thought to be crucial characteristics that jointly contribute to recognition. However, the mechanisms of integration and corresponding cortical representations have not been fully clarified. We investigated the integration of surfaces and shapes by examining the tilt after effects (TAEs) evoked by the symmetry of patterns and contours. As symmetry in both pattern and contour evokes TAEs, we can directly measure the interaction between the two. The measured TAEs exhibited mutual transfer between the symmetry of the pattern (SP) and that of the contour shape (SS), i.e., adaptation by SP (SS) evoked TAEs when tested by SS (SP), suggesting the existence of an integrated representation. Next, we examined the interaction between SP and SS when both were simultaneously presented in adaptation. Congruent adaptors wherein their symmetry axes aligned evoked compressive interaction, whereas incongruent adaptors wherein the axes of SP and SS tilted to the opposite directions evoked subtractive interaction. These results suggest the existence of a cortical representation that integrates the properties of the surface and shape with suppressive interactions, which can provide crucial insights into the formation of object representation as well as the integration of visual information in the cortex.

Electrophysiological responses to regularity show specificity to global form: The case of Glass patterns

The holographic weight of evidence model (van der Helm & Leeuwenberg, J Math Psychol, 35, 1991, 151; van der Helm & Leeuwenberg, Psychol Rev, 103, 1996, 429) estimates that the perceptual goodness of moiré structures (Glass patterns), irrespective of their global form, is comparable to that of reflection symmetry. However, both behavioural and neuroscience evidences suggest that certain Glass forms (i.e. circular and radial structures) are perceptually more salient than others (i.e. translation structures) and may recruit different perceptual mechanisms. In this study, we tested whether brain responses for circular, radial and translation Glass patterns are comparable to the response for onefold bilateral reflection symmetry. We recorded an event‐related potential (ERP), called the sustained posterior negativity (SPN), which has been shown to index perceptual goodness of a range of regularities. We found that circular and radial Glass patterns generated a comparable SPN amplitude to onefold reflection symmetry (in line with the prediction of the holographic model), starting approx. 180 ms after stimulus onset. Conversely, the SPN response to translation Glass patterns had a longer latency (approx. 400 ms). These results show that Glass patterns are a special case of visual regularity, and perceptual goodness may not be fully explained by the holographic identities that constitute it. Specialised processing mechanisms might exist in the regularity‐sensitive extrastriate areas, which are tuned to global form configurations.

Limited Attention Diminishes Spatial Suppression From Large Field Glass Patterns

Glass patterns (GPs) consist of randomly distributed dot pairs (dipoles) whose orientations are determined by specific geometric transforms. We investigated the role of visuospatial attention in the processing of global form from GPs by measuring the effect of distraction on adaptation to GPs. In the nondistracted condition, observers were adapted to coherent GPs. After the adaptation period, they were presented with a test GP divided in two halves along the vertical and were required to judge which side of the test GP was more coherent. In the attention-distracted condition, a high-load rapid serial visual presentation task was performed during the adapting period. The magnitude of the form after-effect was measured using a technique that measures the coherence level at which the test GP appears random. The rationale was that if attention has a modulatory effect on the spatial summation of dipoles, in the attention-distracted condition, we should expect a weaker form after-effect. However, the results showed stronger form after-effect in the attention-distracted condition than in the nondistracted condition, suggesting that distraction during adaptation increases the strength of form adaptation. Additional experiments suggested that distraction may reduce the spatial suppression from large-scale textures, strengthening the spatial summation of local-oriented signals.

Laws of concatenated perception: Vision goes for novelty, decisions for perseverance

Every instant of perception depends on a cascade of brain processes calibrated to the history of sensory and decisional events. In the present work, we show that human visual perception is constantly shaped by two contrasting forces exerted by sensory adaptation and past decisions. In a series of experiments, we used multilevel modeling and cross-validation approaches to investigate the impact of previous stimuli and decisions on behavioral reports during adjustment and forced-choice tasks. Our results revealed that each perceptual report is permeated by opposite biases from a hierarchy of serially dependent processes: Low-level adaptation repels perception away from previous stimuli, whereas decisional traces attract perceptual reports toward the recent past. In this hierarchy of serial dependence, "continuity fields" arise from the inertia of decisional templates and not from low-level sensory processes. This finding is consistent with a Two-process model of serial dependence in which the persistence of readout weights in a decision unit compensates for sensory adaptation, leading to attractive biases in sequential perception. We propose a unified account of serial dependence in which functionally distinct mechanisms, operating at different stages, promote the differentiation and integration of visual information over time.

The interaction between orientation and motion signals in moving oriented Glass patterns

Previous psychophysical evidence suggests that motion and orientation processing systems interact asymmetrically in the human visual system, with orientation information having a stronger influence on the perceived motion direction than vice versa. To investigate the mechanisms underlying this motion-form interaction we used moving and oriented Glass patterns (GPs), which consist of randomly distributed dot pairs (dipoles) that induce the percept of an oriented texture. In Experiment 1 we varied the angle between dipole orientation and motion direction (conflict angle). In separate sessions participants either judged the orientation or motion direction of the GP. In addition, the spatiotemporal characteristics of dipole motion were manipulated as a way to limit (Experiment 1) or favor (Experiment 2) the availability of orientation signals from motion (motion streaks). The results of Experiment 1 showed that apparent GP motion direction is attracted toward dipole orientation, and apparent GP orientation is repulsed from GP motion. The results of Experiment 2 showed stronger repulsion effects when judging the GP orientation, but stronger motion streaks from the GP motion can dominate over the signals provided by conflicting dipole orientation. These results are consistent with the proposal that two separate mechanisms contribute to our perception of stimuli which contain conflicting orientation and motion information: (i) perceived GP motion is mediated by spatial motion-direction sensors, in which signals from motion sensors are combined with excitatory input from orientation-tuned sensors tuned to orientations parallel to the axis of GP motion, (ii) perceived GP orientation is mediated by orientation-tuned sensors which mutually inhibit each other. The two mechanisms are revealed by the different effects of conflict angle and dipole lifetime on perceived orientation and motion direction.

The neural basis of form and form-motion integration from static and dynamic translational Glass patterns: A rTMS investigation

A long-held view of the visual system is that form and motion are independently analysed. However, there is physiological and psychophysical evidence of early interaction in the processing of form and motion. In this study, we used a combination of Glass patterns (GPs) and repetitive Transcranial Magnetic Stimulation (rTMS) to investigate in human observers the neural mechanisms underlying form-motion integration. GPs consist of randomly distributed dot pairs (dipoles) that induce the percept of an oriented stimulus. GPs can be either static or dynamic. Dynamic GPs have both a form component (i.e., orientation) and a non-directional motion component along the orientation axis. GPs were presented in two temporal intervals and observers were asked to discriminate the temporal interval containing the most coherent GP. rTMS was delivered over early visual area (V1/V2) and over area V5/MT shortly after the presentation of the GP in each interval. The results showed that rTMS applied over early visual areas affected the perception of static GPs, but the stimulation of area V5/MT did not affect observers' performance. On the other hand, rTMS was delivered over either V1/V2 or V5/MT strongly impaired the perception of dynamic GPs. These results suggest that early visual areas seem to be involved in the processing of the spatial structure of GPs, and interfering with the extraction of the global spatial structure also affects the extraction of the motion component, possibly interfering with early form-motion integration. However, visual area V5/MT is likely to be involved only in the processing of the motion component of dynamic GPs. These results suggest that motion and form cues may interact as early as V1/V2.