Bottom-up Visual Information Research Articles

Targeted rhythmic visual stimulation at individual participants’ intrinsic alpha frequency causes selective increase of occipitoparietal BOLD-fMRI and EEG functional connectivity

Neural oscillations in distinct frequency bands are ubiquitous in the brain and play a role in many cognitive processes. The "communication by coherence" hypothesis, poses that the synchronization through phase coupling of frequency-specific neural oscillations regulate information flow across distribute brain regions. Specifically, the posterior alpha frequency band (7-12Hz) is thought to gate bottom-up visual information flow by inhibition during visual processing. Evidence shows that increased alpha phase coherency positively correlates with functional connectivity in resting state connectivity networks, supporting alpha mediates neural communication through coherency. However, these findings have mainly been derived from spontaneous changes in the ongoing alpha rhythm. In this study, we experimentally modulate the alpha rhythm by targeting individuals' intrinsic alpha frequency with sustained rhythmic light to investigate alpha-mediated synchronous cortical activity in both EEG and fMRI. We hypothesize increased alpha coherency and fMRI connectivity should arise from modulation of the intrinsic alpha frequency (IAF) as opposed to control frequencies in the alpha range. Sustained rhythmic and arrhythmic stimulation at the IAF and at neighboring frequencies within the alpha band range (7-12Hz) was implemented and assessed in a separate EEG and fMRI study. We observed increased cortical alpha phase coherency in the visual cortex during rhythmic stimulation at the IAF as in comparison to rhythmic stimulation of control frequencies. In the fMRI, we found increased functional connectivity for stimulation at the IAF in visual and parietal areas as compared to other rhythmic control frequencies by correlating time courses from a set of regions of interest for the different stimulation conditions and applying network-based statistics. This suggests that rhythmic stimulation at the IAF frequency induces a higher degree of synchronicity of neural activity across the occipital and parietal cortex, which supports the role of the alpha oscillation in gating information flow during visual processing.

LAG-1: A dynamic, integrative model of learning, attention, and gaze.

It is clear that learning and attention interact, but it is an ongoing challenge to integrate their psychological and neurophysiological descriptions. Here we introduce LAG-1, a dynamic neural field model of learning, attention and gaze, that we fit to human learning and eye-movement data from two category learning experiments. LAG-1 comprises three control systems: one for visuospatial attention, one for saccadic timing and control, and one for category learning. The model is able to extract a kind of information gain from pairwise differences in simple associations between visual features and categories. Providing this gain as a reentrant signal with bottom-up visual information, and in top-down spatial priority, appropriately influences the initiation of saccades. LAG-1 provides a moment-by-moment simulation of the interactions of learning and gaze, and thus simultaneously produces phenomena on many timescales, from the duration of saccades and gaze fixations, to the response times for trials, to the slow optimization of attention toward task relevant information across a whole experiment. With only three free parameters (learning rate, trial impatience, and fixation impatience) LAG-1 produces qualitatively correct fits for learning, behavioural timing and eye movement measures, and also for previously unmodelled empirical phenomena (e.g., fixation orders showing stimulus-specific attention, and decreasing fixation counts during feedback). Because LAG-1 is built to capture attention and gaze generally, we demonstrate how it can be applied to other phenomena of visual cognition such as the free viewing of visual stimuli, visual search, and covert attention.

Comparison of pop-out responses to luminance and motion contrasting stimuli of tectal neurons in pigeons

The emergence of visual saliency has been widely studied in the primary visual cortex and the superior colliculus (SC) in mammals. There are fewer studies on the pop-out response to motion direction contrasting stimuli taken in the optic tectum (OT, homologous to mammalian SC), and these are mainly of owls and fish. To our knowledge the influence of spatial luminance has not been reported. In this study, we have recorded multi-units in pigeon OT and analyzed the tectal response to spatial luminance contrasting, motion direction contrasting, and contrasting stimuli from both feature dimensions. The comparison results showed that 1) the tectal response would pop-out in either motion direction or spatial luminance contrasting conditions. 2) The modulation from motion direction contrasting was independent of the temporal luminance variation of the visual stimuli. 3) When both spatial luminance and motion direction were salient, the response of tectal neurons was modulated more intensely by motion direction than by spatial luminance. The phenomenon was consistent with the innate instinct of avians in their natural environment. This study will help to deepen the understanding of mechanisms involved in bottom-up visual information processing and selective attention in the avian.

B or 13? Unconscious Top-Down Contextual Effects at the Categorical but Not the Lexical Level

Contextual effects require integration of top-down predictions and bottom-up visual information. Given the widely assumed link between integration and consciousness, we asked whether contextual effects require consciousness. In two experiments (total N = 60), an ambiguous stimulus (which could be read as either B or 13) was presented alongside masked numbers (12 and 14) or letters (A and C). Context biased stimulus classification when it was consciously and unconsciously perceived. However, unconsciously perceived contexts evoked smaller effects. This finding was replicated and generalized into another language in a further experiment (N = 46) using a different set of stimuli, strengthening the claim that symbolic contextual effects can occur without awareness. Moreover, four experiments (total N = 160) suggested that these unconscious effects might be limited to the categorical level (numbers context vs. letters context) and do not extend to the lexical level (words context vs. nonwords context). Taken together, our results suggest that although consciousness may not be necessary for effects that require simple integration or none at all, it is nevertheless required for integration over larger semantic windows.

Oscillatory networks of high-level mental alignment: A perspective-taking MEG study

Mentally imagining another's perspective is a high-level social process, reliant on manipulating internal representations of the self in an embodied manner. Recently Wang et al. (2016) showed that theta-band (3–7 Hz) brain oscillations within the right temporo-parietal junction (rTPJ) and brain regions coding for motor/body schema contribute to the process of perspective-taking. Using a similar paradigm, we set out to unravel the extended functional brain network in detail. Increasing the angle between self and other perspective was accompanied by longer reaction times and increases in theta power within rTPJ, right lateral prefrontal cortex (PFC) and right anterior cingulate cortex (ACC). Using Granger-causality, we showed that lateral PFC and ACC exert top-down influence over rTPJ, indicative of executive control processes required for managing conflicts between self and other perspectives. Finally, we quantified patterns of whole-brain phase coupling in relation to the rTPJ. Results suggest that rTPJ increases its theta-band phase synchrony with brain regions involved in mentalizing and regions coding for motor/body schema; whilst decreasing synchrony to visual regions. Implications for neurocognitive models are discussed, and it is proposed that rTPJ acts as a ‘hub’ to route bottom-up visual information to internal representations of the self during perspective-taking, co-ordinated by theta-band oscillations.

Decoding of top-down cognitive processing for SSVEP-controlled BMI.

We present a fast and accurate non-invasive brain-machine interface (BMI) based on demodulating steady-state visual evoked potentials (SSVEPs) in electroencephalography (EEG). Our study reports an SSVEP-BMI that, for the first time, decodes primarily based on top-down and not bottom-up visual information processing. The experimental setup presents a grid-shaped flickering line array that the participants observe while intentionally attending to a subset of flickering lines representing the shape of a letter. While the flickering pixels stimulate the participant’s visual cortex uniformly with equal probability, the participant’s intention groups the strokes and thus perceives a ‘letter Gestalt’. We observed decoding accuracy of 35.81% (up to 65.83%) with a regularized linear discriminant analysis; on average 2.05-fold, and up to 3.77-fold greater than chance levels in multi-class classification. Compared to the EEG signals, an electrooculogram (EOG) did not significantly contribute to decoding accuracies. Further analysis reveals that the top-down SSVEP paradigm shows the most focalised activation pattern around occipital visual areas; Granger causality analysis consistently revealed prefrontal top-down control over early visual processing. Taken together, the present paradigm provides the first neurophysiological evidence for the top-down SSVEP BMI paradigm, which potentially enables multi-class intentional control of EEG-BMIs without using gaze-shifting.

Anticipatory eye fixations reveal tool knowledge for tool interaction.

Action-oriented eye-tracking studies have shown that eye fixations reveal much about current behavioral intentions. The eyes typically fixate those positions of a tool or an object where the fingers will be placed next, or those positions in a scene, where obstacles need to be avoided to successfully reach or transport a tool or object. Here, we asked to what extent eye fixations can also reveal active cognitive inference processes, which are expected to integrate bottom-up visual information with internal knowledge for planning suitable object interactions task-dependently. In accordance to the available literature, we expected that task-relevant knowledge will include sensorimotor, semantic, and mechanical aspects. To investigate if and in which way this internal knowledge influences eye fixation behavior while planning an object interaction, we presented pictures of familiar and unfamiliar tools and instructed participants to either pantomime 'lifting' or 'using' the respective tool. When confronted with unfamiliar tools, participants fixated the tool's effector part closer and longer in comparison with familiar tools. This difference was particularly prominent during 'using' trials when compared with 'lifting' trials. We suggest that this difference indicates that the brain actively extracts mechanical information about the unknown tool in order to infer its appropriate usage. Moreover, the successive fixations over a trial indicate that a dynamic, task-oriented, active cognitive process unfolds, which integrates available tool knowledge with visually gathered information to plan and determine the currently intended tool interaction.

There's Waldo! A Normalization Model of Visual Search Predicts Single-Trial Human Fixations in an Object Search Task

When searching for an object in a scene, how does the brain decide where to look next? Visual search theories suggest the existence of a global "priority map" that integrates bottom-up visual information with top-down, target-specific signals. We propose a mechanistic model of visual search that is consistent with recent neurophysiological evidence, can localize targets in cluttered images, and predicts single-trial behavior in a search task. This model posits that a high-level retinotopic area selective for shape features receives global, target-specific modulation and implements local normalization through divisive inhibition. The normalization step is critical to prevent highly salient bottom-up features from monopolizing attention. The resulting activity pattern constitues a priority map that tracks the correlation between local input and target features. The maximum of this priority map is selected as the locus of attention. The visual input is then spatially enhanced around the selected location, allowing object-selective visual areas to determine whether the target is present at this location. This model can localize objects both in array images and when objects are pasted in natural scenes. The model can also predict single-trial human fixations, including those in error and target-absent trials, in a search task involving complex objects.

Monkey pulvinar neurons fire differentially to snake postures.

There is growing evidence from both behavioral and neurophysiological approaches that primates are able to rapidly discriminate visually between snakes and innocuous stimuli. Recent behavioral evidence suggests that primates are also able to discriminate the level of threat posed by snakes, by responding more intensely to a snake model poised to strike than to snake models in coiled or sinusoidal postures (Etting and Isbell 2014). In the present study, we examine the potential for an underlying neurological basis for this ability. Previous research indicated that the pulvinar is highly sensitive to snake images. We thus recorded pulvinar neurons in Japanese macaques (Macaca fuscata) while they viewed photos of snakes in striking and non-striking postures in a delayed non-matching to sample (DNMS) task. Of 821 neurons recorded, 78 visually responsive neurons were tested with the all snake images. We found that pulvinar neurons in the medial and dorsolateral pulvinar responded more strongly to snakes in threat displays poised to strike than snakes in non-threat-displaying postures with no significant difference in response latencies. A multidimensional scaling analysis of the 78 visually responsive neurons indicated that threat-displaying and non-threat-displaying snakes were separated into two different clusters in the first epoch of 50 ms after stimulus onset, suggesting bottom-up visual information processing. These results indicate that pulvinar neurons in primates discriminate between poised to strike from those in non-threat-displaying postures. This neuronal ability likely facilitates behavioral discrimination and has clear adaptive value. Our results are thus consistent with the Snake Detection Theory, which posits that snakes were instrumental in the evolution of primate visual systems.

The neural basis of stereotypic impact on multiple social categorization

Perceivers extract multiple social dimensions from another's face (e.g., race, emotion), and these dimensions can become linked due to stereotypes (e.g., Black individuals→angry). The current research examined the neural basis of detecting and resolving conflicts between top-down stereotypes and bottom-up visual information in person perception. Participants viewed faces congruent and incongruent with stereotypes, via variations in race and emotion, while neural activity was measured using fMRI. Hand movements en route to race/emotion responses were recorded using mouse-tracking to behaviorally index individual differences in stereotypical associations during categorization. The medial prefrontal cortex (mPFC) and anterior cingulate cortex (ACC) showed stronger activation to faces that violated stereotypical expectancies at the intersection of multiple social categories (i.e., race and emotion). These regions were highly sensitive to the degree of incongruency, exhibiting linearly increasing responses as race and emotion became stereotypically more incongruent. Further, the ACC exhibited greater functional connectivity with the lateral fusiform cortex, a region implicated in face processing, when viewing stereotypically incongruent (relative to congruent) targets. Finally, participants with stronger behavioral tendencies to link race and emotion stereotypically during categorization showed greater dorsolateral prefrontal cortex activation to stereotypically incongruent targets. Together, the findings provide insight into how conflicting stereotypes at the nexus of multiple social dimensions are resolved at the neural level to accurately perceive other people.

Embodied attention and word learning by toddlers

Many theories of early word learning begin with the uncertainty inherent to learning a word from its co-occurrence with a visual scene. However, the relevant visual scene for infant word learning is neither from the adult theorist’s view nor the mature partner’s view, but is rather from the learner’s personal view. Here we show that when 18-month old infants interacted with objects in play with their parents, they created moments in which a single object was visually dominant. If parents named the object during these moments of bottom-up selectivity, later forced-choice tests showed that infants learned the name, but did not when naming occurred during a less visually selective moment. The momentary visual input for parents and toddlers was captured via head cameras placed low on each participant’s forehead as parents played with and named objects for their infant. Frame-by-frame analyses of the head camera images at and around naming moments were conducted to determine the visual properties at input that were associated with learning. The analyses indicated that learning occurred when bottom-up visual information was clean and uncluttered. The sensory-motor behaviors of infants and parents were also analyzed to determine how their actions on the objects may have created these optimal visual moments for learning. The results are discussed with respect to early word learning, embodied attention, and the social role of parents in early word learning.

The Research of Bottom-Up and Top-Down Combination Visual Attention Calculative Method

A new bottom-up and top-down combination visual attention calculative method is proposed in paper. The method proposed is focus on the improvement of top-down guidance. The total visual attention process is divided into the process of bottom-up visual information extraction and top-down visual attention guiding. The construction and calculate method of visual attention guiding layer is presented in paper, it can automatic calculate the key feature of the target based on current task condition, and guide the process of bottom-up visual information extraction.

Top-down and bottom-up visual information processing of non-social stimuli in high-functioning autism spectrum disorder

Individuals with high-functioning autism spectrum disorder (HF-ASD) often show superior performance in simple visual tasks, despite difficulties in the perception of socially important information such as facial expression. The neural basis of visual perception abnormalities associated with HF-ASD is currently unclear. We sought to elucidate the functioning of bottom-up and top-down visual information processing in HF-ASD using event-related potentials (ERPs). Eleven adults with HF-ASD and 11 age-matched normal controls (NC) participated in this study. Visual ERPs were recorded using 128-channel EEG. The P1 and P300 were recorded in response to target stimuli. Visual mismatch negativity (vMMN) potentials were obtained by subtracting responses to standard from those to deviant stimuli. Behaviorally, individuals with HF-ASD showed faster target detection than NCs. However, vMMN amplitude and latency were the same between the two groups. In contrast, P1 and P300 amplitudes were significantly decreased in HF-ASD compared with NCs. In addition, P300 latency was significantly delayed in HF-ASD. Individuals with HF-ASD exhibit altered visual information processing. Intact bottom-up attention (vMMN) may contribute to their superior simple visual task performance in spite of abnormal low-level (P1) and top-down (P300) visual information processing.

Phase synchronization of oscillatory brain activity and the matching of top-down and bottom up visual information

When information which is stored in memory is compared to new visual information there has to be a matching between provided top-down memory information and bottom-up sensory processing. The neural correlates of such memory matching are not yet completely clear. There is evidence that top-down processing and central executive functions of working memory are associated with distributed fronto-parietal interaction at theta frequency (around 5 Hz) in the human electroencephalogram (EEG). On the other hand gamma oscillations (beyond 30 Hz) were shown to be involved in bottom-up visual information processing. Here, data from an experiment in which subjects had to hold ‘templates’ of visual targets in memory and match them with incoming visual information will be reported. It will be shown that distributed interregional phase coherence at theta frequency is increased during time intervals in which top-down memory information had to be provided by a working memory system. This top-down memory content was then matched at posterior parietal brain sites with incoming visual information indicated by increased cross-frequency phase synchronization between theta and gamma oscillations. This correlate of memory matching was most pronounced in a time interval between 100 and 200 ms after presentation of visual information. Furthermore, it will be shown that phase synchronization between theta and gamma oscillations as brain correlate of memory matching was amplified by visual attention. As a conclusion of the study it can be stated that interregional and cross-frequency phase synchronization in the human EEG are informative about the interplay of top-down and bottom-up processing. They seem to reflect the interaction of distributed and local cortical networks and therefore may play an important role in most higher cognitive functions.

Neural substrates of visual percepts, imagery, and hallucinations

Recent neural models clarify many properties of mental imagery as part of the process whereby bottom-up visual information is influenced by top-down expectations, and how these expectations control visual attention. Volitional signals can transform modulatory top-down signals into supra-threshold imagery. Visual hallucinations can occur when the normal control of these volitional signals is lost.