49 research outputs found
The mechanisms of feature inheritance as predicted by a systems-level model of visual attention and decision making
Feature inheritance provides evidence that properties of an invisible target
stimulus can be attached to a following mask. We apply a systemslevel model of
attention and decision making to explore the influence of memory and feedback
connections in feature inheritance. We find that the presence of feedback loops
alone is sufficient to account for feature inheritance. Although our simulations
do not cover all experimental variations and focus only on the general
principle, our result appears of specific interest since the model was designed
for a completely different purpose than to explain feature inheritance. We
suggest that feedback is an important property in visual perception and provide
a description of its mechanism and its role in perception
A hierarchical system for a distributed representation of the peripersonal space of a humanoid robot
Reaching a target object in an unknown and unstructured environment is easily performed by human beings. However, designing a humanoid robot that executes the same task requires the implementation of complex abilities, such as identifying the target in the visual field, estimating its spatial location, and precisely driving the motors of the arm to reach it. While research usually tackles the development of such abilities singularly, in this work we integrate a number of computational models into a unified framework, and demonstrate in a humanoid torso the feasibility of an integrated working representation of its peripersonal space. To achieve this goal, we propose a cognitive architecture that connects several models inspired by neural circuits of the visual, frontal and posterior parietal cortices of the brain. The outcome of the integration process is a system that allows the robot to create its internal model and its representation of the surrounding space by interacting with the environment directly, through a mutual adaptation of perception and action. The robot is eventually capable of executing a set of tasks, such as recognizing, gazing and reaching target objects, which can work separately or cooperate for supporting more structured and effective behaviors
Mislocalization of Visual Stimuli: Independent Effects of Static and Dynamic Attention
Shifts of visual attention cause systematic distortions of the perceived locations of visual objects around the focus of attention. In the attention repulsion effect, the perceived location of a visual target is shifted away from an attention-attracting cue when the cue is presented before the target. Recently it has been found that, if the visual cue is presented after the target, the perceived location of the target shifts toward the location of the following cue. One unanswered question is whether a single mechanism underlies both attentional repulsion and attraction effects. We presented participants with two disks at diagonal locations as visual cues and two vertical lines as targets. Participants were asked to perform a forced-choice task to judge targets' positions. The present study examined whether the magnitude of the repulsion effect and the attraction effect would differ (Experiment 1), whether the two effects would interact (Experiment 2), and whether the location or the dynamic shift of attentional focus would determine the distortions effects (Experiment 3). The results showed that the effect size of the attraction effect was slightly larger than the repulsion effect and the preceding and following cues have independent influences on the perceived positions. The repulsion effect was caused by the location of attnetion and the attraction effect was due to the dynamic shift of attentional focus, suggesting that the underlying mechanisms for the retrospective attraction effect might be different from those for the repulsion effect
Temporal processes in prime–mask interaction: Assessing perceptual consequences of masked information
Visual backward masking is frequently used to study the temporal dynamics of
visual perception. These dynamics may include the temporal features of conscious
percepts, as suggested, for instance, by the asynchronous–updating model (Neumann, 1982) and perceptual–retouch
theory ((Bachmann, 1994). These models
predict that the perceptual latency of a visual backward mask is shorter than
that of a like reference stimulus that was not preceded by a masked stimulus.
The prediction has been confirmed by studies using temporal–order judgments: For
certain asynchronies between mask and reference stimulus, temporal–order
reversals are quite frequent (e.g. Scharlau,
& Neumann, 2003a). However, it may be argued that these
reversals were due to a response bias in favour of the mask rather than true
temporal-perceptual effects. I introduce two measures for assessing latency
effects that (1) are not prone to such a response bias, (2) allow to quantify
the latency gain, and (3) extend the perceptual evidence from order reversals to
duration/interval perception, that is, demonstrate that the perceived interval
between a mask and a reference stimulus may be shortened as well as prolonged by
the presence of a masked stimulus. Consequences for theories of visual masking
such as asynchronous–updating, perceptual–retouch, and reentrant models are
discussed
Neuro-cognitive mechanisms of conscious and unconscious visual perception: From a plethora of phenomena to general principles
Psychological and neuroscience approaches have promoted much progress in
elucidating the cognitive and neural mechanisms that underlie phenomenal visual
awareness during the last decades. In this article, we provide an overview of
the latest research investigating important phenomena in conscious and
unconscious vision. We identify general principles to characterize conscious and
unconscious visual perception, which may serve as important building blocks for
a unified model to explain the plethora of findings. We argue that in particular
the integration of principles from both conscious and unconscious vision is
advantageous and provides critical constraints for developing adequate
theoretical models. Based on the principles identified in our review, we outline
essential components of a unified model of conscious and unconscious visual
perception. We propose that awareness refers to consolidated
visual representations, which are accessible to the entire brain and therefore
globally available. However, visual awareness not only depends
on consolidation within the visual system, but is additionally the result of a
post-sensory gating process, which is mediated by higher-level cognitive control
mechanisms. We further propose that amplification of visual representations by
attentional sensitization is not exclusive to the domain of conscious
perception, but also applies to visual stimuli, which remain unconscious.
Conscious and unconscious processing modes are highly interdependent with
influences in both directions. We therefore argue that exactly this
interdependence renders a unified model of conscious and unconscious visual
perception valuable. Computational modeling jointly with focused experimental
research could lead to a better understanding of the plethora of empirical
phenomena in consciousness research
Influence of Low-Level Stimulus Features, Task Dependent Factors, and Spatial Biases on Overt Visual Attention
Visual attention is thought to be driven by the interplay between low-level visual features and task dependent information content of local image regions, as well as by spatial viewing biases. Though dependent on experimental paradigms and model assumptions, this idea has given rise to varying claims that either bottom-up or top-down mechanisms dominate visual attention. To contribute toward a resolution of this discussion, here we quantify the influence of these factors and their relative importance in a set of classification tasks. Our stimuli consist of individual image patches (bubbles). For each bubble we derive three measures: a measure of salience based on low-level stimulus features, a measure of salience based on the task dependent information content derived from our subjects' classification responses and a measure of salience based on spatial viewing biases. Furthermore, we measure the empirical salience of each bubble based on our subjects' measured eye gazes thus characterizing the overt visual attention each bubble receives. A multivariate linear model relates the three salience measures to overt visual attention. It reveals that all three salience measures contribute significantly. The effect of spatial viewing biases is highest and rather constant in different tasks. The contribution of task dependent information is a close runner-up. Specifically, in a standardized task of judging facial expressions it scores highly. The contribution of low-level features is, on average, somewhat lower. However, in a prototypical search task, without an available template, it makes a strong contribution on par with the two other measures. Finally, the contributions of the three factors are only slightly redundant, and the semi-partial correlation coefficients are only slightly lower than the coefficients for full correlations. These data provide evidence that all three measures make significant and independent contributions and that none can be neglected in a model of human overt visual attention
Testing a dynamic field account of interactions between spatial attention and spatial working memory
Studies examining the relationship between spatial attention and spatial working memory (SWM) have shown that discrimination responses are faster for targets appearing at locations that are being maintained in SWM, and that location memory is impaired when attention is withdrawn during the delay. These observations support the proposal that sustained attention is required for successful retention in SWM: if attention is withdrawn, memory representations are likely to fail, increasing errors. In the present study, this proposal is reexamined in light of a neural process model of SWM. On the basis of the model’s functioning, we propose an alternative explanation for the observed decline in SWM performance when a secondary task is performed during retention: SWM representations drift systematically toward the location of targets appearing during the delay. To test this explanation, participants completed a color-discrimination task during the delay interval of a spatial recall task. In the critical shifting attention condition, the color stimulus could appear either toward or away from the memorized location relative to a midline reference axis. We hypothesized that if shifting attention during the delay leads to the failure of SWM representations, there should be an increase in the variance of recall errors but no change in directional error, regardless of the direction of the shift. Conversely, if shifting attention induces drift of SWM representations—as predicted by the model—there should be systematic changes in the pattern of spatial recall errors depending on the direction of the shift. Results were consistent with the latter possibility—recall errors were biased toward the location of discrimination targets appearing during the delay
Incremental grouping of image elements in vision
One important task for the visual system is to group image elements that belong to an object and to segregate them from other objects and the background. We here present an incremental grouping theory (IGT) that addresses the role of object-based attention in perceptual grouping at a psychological level and, at the same time, outlines the mechanisms for grouping at the neurophysiological level. The IGT proposes that there are two processes for perceptual grouping. The first process is base grouping and relies on neurons that are tuned to feature conjunctions. Base grouping is fast and occurs in parallel across the visual scene, but not all possible feature conjunctions can be coded as base groupings. If there are no neurons tuned to the relevant feature conjunctions, a second process called incremental grouping comes into play. Incremental grouping is a time-consuming and capacity-limited process that requires the gradual spread of enhanced neuronal activity across the representation of an object in the visual cortex. The spread of enhanced neuronal activity corresponds to the labeling of image elements with object-based attention
25th Annual Computational Neuroscience Meeting: CNS-2016
Abstracts of the 25th Annual Computational Neuroscience
Meeting: CNS-2016
Seogwipo City, Jeju-do, South Korea. 2–7 July 201
25th annual computational neuroscience meeting: CNS-2016
The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong